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425 V 167 1146 a FN(JEAN-YVES)28 b(GIRARD)167 1315 y FM(T)-5 b(r)l(anslate)l(d)28 b(and)g(with)g(app)l(endic)l(es)g(by)167 1450 y FN(P)-8 b(A)m(UL)29 b(T)-8 b(A)g(YLOR)167 1585 y(YVES)28 b(LAF)m(ONT)167 2889 y FL(CAMBRIDGE)g(UNIVERSITY)f(PRESS)167 3025 y(Cambridge)167 3171 y(New)g(Y)-8 b(ork)230 b(New)27 b(R)-5 b(o)g(chel)5 b(le)167 3306 y(Melb)-5 b(ourne)202 b(Sydney)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 2 1 bop 167 167 a FK(ii)167 404 y(Published)27 b(b)n(y)h(the)g(Press)f (Syndicate)h(of)g(the)f(Univ)n(ersit)n(y)g(of)h(Cam)n(bridge)167 490 y(The)f(Pitt)g(Building,)f(T)-6 b(rumpington)28 b(Street,)f(Cam)n (bridge)g(CB2)h(1RP)167 575 y(32)h(East)f(57th)g(Streey)-6 b(,)28 b(New)f(Y)-6 b(ork,)28 b(NY)f(10022,)j(USA)167 660 y(10)f(Stamford)f(Road,)h(Oakleigh,)e(Melb)r(ourne)g(3166,)j (Australia)187 826 y(c)167 828 y FJ(\015)e FK(Cam)n(bridge)f(Univ)n (ersit)n(y)g(Press,)g(1989)167 997 y(First)g(Published)g(1989)167 1082 y(Reprin)n(ted)f(with)h(minor)g(corrections)g(1990)167 1167 y(Reprin)n(ted)f(for)i(the)g(W)-6 b(eb)27 b(2003)167 1336 y(Originally)e(prin)n(ted)i(in)g(Great)h(Britain)e(at)i(the)f (Univ)n(ersit)n(y)g(Press,)g(Cam)n(bridge)167 1504 y FM(British)i(Libr)l(ary)g(Catalo)l(guing)e(in)h(Public)l(ation)f(Data)h (available)167 1673 y(Libr)l(ary)h(of)f(Congr)l(ess)g(Catalo)l(guing)g (in)f(Public)l(ation)g(Data)h(available)167 1842 y FK(ISBN)f(0)h(521)h (37181)h(3)p eop PStoPSsaved restore %%Page: (2,3) 2 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 3 2 bop 2615 167 a FK(iii)167 419 y FI(Preface)167 680 y FK(This)27 b(little)d(b)r(o)r(ok)29 b(comes)e(from)h(a)g(short)g (graduate)h(course)e(on)i(t)n(yp)r(ed)f FH(\025)p FK(-calculus)e(giv)n (en)i(at)167 765 y(the)h(Univ)n(ersit)n(\023)-33 b(e)28 b(P)n(aris)h(VI)r(I)g(in)f(the)h(autumn)h(term)e(of)i(1986{7.)43 b(It)29 b(is)g(not)h(in)n(tended)f(to)g(b)r(e)167 850 y(encyclop)r(edic)k(|)h(the)h(Ch)n(urc)n(h-Rosser)g(theorem,)h(for)f (instance,)h(is)e(not)h(pro)n(v)n(ed)g(|)g(and)167 935 y(the)27 b(selection)f(of)i(topics)f(w)n(as)i(really)d(quite)h (haphazard.)270 1061 y(Some)d(v)n(ery)h(basic)e(kno)n(wledge)i(of)f (logic)f(is)g(needed,)i(but)f(w)n(e)g(will)d(nev)n(er)j(go)g(in)n(to)g (tedious)167 1146 y(details.)65 b(Some)37 b(b)r(o)r(ok)i(in)f(pro)r(of) g(theory)-6 b(,)42 b(suc)n(h)c(as)g([)p FG(?)q FK(],)i(ma)n(y)f(b)r(e)e (useful)h(afterw)n(ards)g(to)167 1232 y(complete)26 b(the)h (information)g(on)i(those)f(p)r(oin)n(ts)g(whic)n(h)f(are)g(lac)n (king.)270 1358 y(The)41 b(notes)h(w)n(ould)g(nev)n(er)f(ha)n(v)n(e)h (reac)n(hed)f(the)g(standard)i(of)f(a)g(b)r(o)r(ok)g(without)f(the)167 1443 y(in)n(terest)26 b(tak)n(en)j(in)e(translating)h(\(and)h(in)e(man) n(y)i(cases)f(rew)n(orking\))f(them)g(b)n(y)i(Yv)n(es)f(Lafon)n(t)167 1528 y(and)c(P)n(aul)g(T)-6 b(a)n(ylor.)34 b(F)-6 b(or)24 b(instance)f(Yv)n(es)g(Lafon)n(t)i(restructured)d(c)n(hapter)h(6)h(and) g(P)n(aul)g(T)-6 b(a)n(ylor)167 1613 y(c)n(hapter)28 b(8,)g(and)h(some)e(sections)g(ha)n(v)n(e)i(b)r(een)e(dev)n(elop)r(ed)h (in)n(to)f(detailed)f(app)r(endices.)270 1739 y(The)42 b(translators)h(w)n(ould)g(lik)n(e)d(to)j(thank)g(Luk)n(e)g(Ong,)j (Christine)41 b(P)n(aulin-Mohring,)167 1824 y(Ramon)34 b(Pino,)h(Mark)f(Ry)n(an,)j(Thomas)d(Streic)n(her,)f(Bill)e(White)h (and)j(Liz)d(W)-6 b(olf)34 b(for)f(their)167 1909 y(suggestions)f(and)f (detailed)e(corrections)g(to)i(earlier)d(drafts)j(and)g(also)g(Samson)g (Abramsky)167 1995 y(for)d(his)f(encouragemen)n(t)h(throughout)i(the)d (pro)t(ject.)270 2121 y(In)h(the)g FM(r)l(eprinting)33 b FK(an)c(op)r(en)f(problem)f(on)h(page)h(140)g(has)f(b)r(een)g(resolv) n(ed.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 4 3 bop 167 874 a FF(Con)-5 b(ten)g(ts)1392 4101 y FK(iv)p eop PStoPSsaved restore %%Page: (4,5) 3 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 1 4 bop 167 877 a FF(Chapter)28 b(1)167 1173 y(Sense,)g(Denotation)f (and)h(Seman)-5 b(tics)167 1496 y FK(Theoretical)28 b(Computing)j(is)e (not)i(y)n(et)f(a)h(science.)41 b(Man)n(y)32 b(basic)e(concepts)g(ha)n (v)n(e)h(not)g(b)r(een)167 1581 y(clari\014ed,)26 b(and)j(curren)n(t)d (w)n(ork)i(in)f(the)g(area)h(ob)r(eys)g(a)g(kind)g(of)f(\\w)n(edding)h (cak)n(e")g(paradigm:)167 1666 y(for)39 b(instance)g(language)i(design) e(is)f(reminiscen)n(t)f(of)i(Ptolomeic)e(astronom)n(y)k(|)e(forev)n(er) 167 1751 y(in)33 b(need)g(of)h(further)f(corrections.)51 b(There)33 b(are,)h(ho)n(w)n(ev)n(er,)i(some)d(limited)d(topics)j(suc)n (h)g(as)167 1836 y(complexit)n(y)c(theory)i(and)g(denotational)g(seman) n(tics)e(whic)n(h)h(are)g(relativ)n(ely)e(free)i(from)g(this)167 1922 y(criticism.)270 2056 y(In)d(suc)n(h)f(a)h(situation,)f(metho)r (dological)f(remarks)h(are)g(extremely)e(imp)r(ortan)n(t,)i(since)f(w)n (e)167 2142 y(ha)n(v)n(e)k(to)f(see)f(metho)r(dology)h(as)g FM(str)l(ate)l(gy)h FK(and)g(concrete)d(results)h(as)h(of)h(a)f FM(tactic)l(al)f FK(nature.)270 2276 y(In)36 b(particular)e(what)h(w)n (e)g(are)g(in)n(terested)f(in)g(is)h(to)g(b)r(e)g(found)i(at)e(the)g (source)h(of)f(the)167 2361 y(logical)h(whirlp)r(o)r(ol)g(of)i(the)f (1900's,)42 b(illustrated)35 b(b)n(y)k(the)e(names)g(of)h(F)-6 b(rege,)40 b(L\177)-34 b(ow)n(enheim,)167 2447 y(G\177)g(odel)36 b(and)i(so)g(on.)63 b(The)37 b(reader)f(not)i(acquain)n(ted)f(with)f (the)g(history)h(of)h(logic)d(should)167 2532 y(consult)28 b([)p FG(?)p FK(].)167 2777 y FE(1.1)114 b(Sense)28 b(and)h(denotation) h(in)e(logic)167 2936 y FK(Let)i(us)i(start)f(with)f(an)h(example.)44 b(There)30 b(is)h(a)g(standard)h(pro)r(cedure)f(for)g(m)n (ultiplication,)167 3022 y(whic)n(h)j(yields)f(for)h(the)g(inputs)h(27) g(and)g(37)g(the)f(result)g(999.)56 b(What)35 b(can)g(w)n(e)e(sa)n(y)j (ab)r(out)167 3107 y(that?)270 3242 y(A)28 b(\014rst)f(attempt)g(is)g (to)h(sa)n(y)h(that)f(w)n(e)f(ha)n(v)n(e)i(an)f FM(e)l(quality)1196 3432 y FK(27)16 b FJ(\002)g FK(37)k(=)f(999)167 3622 y(This)30 b(equalit)n(y)g(mak)n(es)g(sense)h(in)f(the)g(mainstream)f (of)i(mathematics)e(b)n(y)i(sa)n(ying)h(that)e(the)167 3707 y(t)n(w)n(o)k(sides)f FM(denote)h FK(the)f(same)h(in)n(teger)1233 3682 y FD(1)1293 3707 y FK(and)h(that)52 b FJ(\002)f FK(is)33 b(a)h FM(function)g FK(in)f(the)g(Can)n(torian)167 3793 y(sense)28 b(of)g(a)g(graph.)p 167 3860 1003 3 v 246 3903 a FC(1)273 3925 y FB(By)f FA(inte)m(ger)h FB(w)n(e)g(shall,)f (throughout,)g(mean)g FA(natur)m(al)i(numb)m(er)p FB(:)34 b(0,)28 b(1,)h(2,...)1402 4101 y FK(1)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 2 5 bop 167 167 a FK(2)610 b Fz(CHAPTER)26 b(1.)63 b(SENSE,)28 b(DENOT)-6 b(A)g(TION)26 b(AND)g(SEMANTICS)270 404 y FK(This)34 b(is)f(the)h(denotational)h(asp)r(ect,)h(whic)n(h)d(is)g (undoubtedly)j(correct,)f(but)f(it)f(misses)167 490 y(the)27 b(essen)n(tial)g(p)r(oin)n(t:)270 621 y(There)35 b(is)h(a)g(\014nite)f FM(c)l(omputation)i FK(pro)r(cess)f(whic)n(h)f(sho)n(ws)i(that)f(the)f (denotations)i(are)167 706 y(equal.)76 b(It)41 b(is)g(an)h(abuse)g (\(and)h(this)d(is)h(not)h(c)n(heap)g(philosoph)n(y)g(|)f(it)g(is)f(a)i (concrete)167 791 y(question\))27 b(to)h(sa)n(y)g(that)f(27)16 b FJ(\002)f FK(37)28 b FM(e)l(quals)f FK(999,)i(since)d(if)g(the)h(t)n (w)n(o)g(things)h(w)n(e)e(ha)n(v)n(e)i(w)n(ere)e FM(the)167 876 y(same)g FK(then)f(w)n(e)g(w)n(ould)h(nev)n(er)f(feel)f(the)h(need) g(to)h(state)f(their)g(equalit)n(y)-6 b(.)34 b(Concretely)24 b(w)n(e)h(ask)167 961 y(a)31 b FM(question)p FK(,)h(27)17 b FJ(\002)f FK(37,)33 b(and)f(get)f(an)g FM(answer)p FK(,)h(999.)46 b(The)31 b(t)n(w)n(o)g(expressions)g(ha)n(v)n(e)h (di\013eren)n(t)167 1046 y FM(senses)26 b FK(and)i(w)n(e)e(m)n(ust)h FM(do)g FK(something)g(\(mak)n(e)f(a)h(pro)r(of)h(or)f(a)g (calculation,)f(or)h(at)g(least)f(lo)r(ok)167 1131 y(in)h(an)h (encyclop)r(edia\))f(to)h(sho)n(w)g(that)g(these)g(t)n(w)n(o)g FM(senses)f FK(ha)n(v)n(e)h(the)g(same)f FM(denotation)p FK(.)270 1263 y(Concerning)j FJ(\002)p FK(,)f(it)f(is)h(incorrect)f(to) h(sa)n(y)h(that)g(this)f(is)f(a)i(function)f(\(as)h(a)g(graph\))g (since)167 1348 y(the)g(computer)f(in)g(whic)n(h)h(the)f(program)i(is)e (loaded)h(has)h(no)g(ro)r(om)f(for)g(an)h(in\014nite)e(graph.)167 1433 y(Hence)34 b(w)n(e)h(ha)n(v)n(e)h(to)f(conclude)g(that)h(w)n(e)e (are)h(in)g(the)g(presence)f(of)i(a)g FM(\014nitary)f FK(dynamics)167 1518 y(related)26 b(to)i(this)f(question)h(of)h(sense.) 270 1649 y(Whereas)c(denotation)g(w)n(as)g(mo)r(delled)d(at)j(a)f(v)n (ery)h(early)f(stage,)h(sense)g(has)g(b)r(een)f(pushed)167 1734 y(to)n(w)n(ards)30 b FM(subje)l(ctivism)p FK(,)g(with)f(the)g (result)f(that)h(the)g(presen)n(t)g(mathematical)e(treatmen)n(t)i(of) 167 1819 y(sense)38 b(is)g(more)f(or)i(less)e(reduced)h(to)g FM(syntactic)g FK(manipulation.)67 b(This)38 b(is)f(not)i FM(a)f(priori)167 1905 y FK(in)f(the)h(essence)f(of)h(the)g(sub)t (ject,)i(and)f(w)n(e)e(can)h(exp)r(ect)f(in)h(the)f(next)h(decades)g (to)g(\014nd)167 1990 y(a)c(treatmen)n(t)e(of)h(computation)g(that)h(w) n(ould)f(com)n(bine)f(the)h(adv)l(an)n(tages)j(of)e(denotational)167 2075 y(seman)n(tics)j(\(mathematical)f(clarit)n(y\))h(with)g(those)i (of)f(syn)n(tax)i(\(\014nite)e(dynamics\).)67 b(This)167 2160 y(b)r(o)r(ok)33 b(clearly)c(rests)i(on)i(a)e(tradition)g(that)h (is)e(based)j(on)f(this)f(unfortunate)h(curren)n(t)f(state)167 2245 y(of)26 b(a\013airs:)35 b(in)24 b(the)i(dic)n(hotom)n(y)f(b)r(et)n (w)n(een)g FM(in\014nite,)g(static)g(denotation)h FK(and)g FM(\014nite,)f(dynamic)167 2330 y(sense)p FK(,)i(the)h(denotational)g (side)f(is)g(m)n(uc)n(h)g(more)g(dev)n(elop)r(ed)h(than)g(the)g(other.) 270 2513 y(So,)33 b(one)f(of)g(the)e(most)h(fundamen)n(tal)h (distinctions)e(in)g(logic)g(is)h(that)g(made)g(b)n(y)h(F)-6 b(rege:)167 2599 y(giv)n(en)28 b(a)g(sen)n(tence)f FH(A)p FK(,)g(there)g(are)h(t)n(w)n(o)f(w)n(a)n(ys)i(of)f(seeing)f(it:)270 2767 y FJ(\017)34 b FK(as)29 b(a)f(sequence)g(of)g FM(instructions)p FK(,)f(whic)n(h)g(determine)f(its)h FM(sense)p FK(,)g(for)h(example)f FH(A)16 b FJ(_)f FH(B)339 2852 y FK(means)28 b(\\)p FH(A)g FK(or)g FH(B)t FK(",)g FM(etc.)p FK(.)270 3000 y FJ(\017)34 b FK(as)29 b(the)e FM(ide)l(al)h(r)l(esult)34 b FK(found)29 b(b)n(y)g(these)e(op)r(erations:)36 b(this)27 b(is)g(its)g FM(denotation)p FK(.)339 3161 y(\\Denotation",)34 b(as)e(opp)r(osed)i (to)d(\\notation",)k(is)c(what)g FM(is)h(denote)l(d)p FK(,)h(and)g(not)f(what)339 3246 y FM(denotes)p FK(.)51 b(F)-6 b(or)34 b(example)e(the)g(denotation)i(of)g(a)f(logical)e(sen)n (tence)i(is)f FG(t)g FK(\(true\))h(or)g FG(f)339 3331 y FK(\(false\),)e(and)h(the)e(denotation)h(of)g FH(A)16 b FJ(_)h FH(B)34 b FK(can)d(b)r(e)f(obtained)h(from)g(the)f (denotations)339 3416 y(of)f FH(A)e FK(and)i FH(B)i FK(b)n(y)d(means)g (of)g(the)g(truth)f(table)g(for)h(disjunction.)270 3584 y(Tw)n(o)33 b(sen)n(tences)e(whic)n(h)h(ha)n(v)n(e)h(the)f(same)f (sense)h(ha)n(v)n(e)h(the)f(same)g(denotation,)i(that)f(is)167 3669 y(ob)n(vious;)d(but)f(t)n(w)n(o)f(sen)n(tences)g(with)g(the)g (same)g(denotation)h(rarely)f(ha)n(v)n(e)h(the)f(same)g(sense.)167 3754 y(F)-6 b(or)41 b(example,)j(tak)n(e)d(a)g(complicated)e (mathematical)g(equiv)l(alence)h FH(A)19 b FJ(,)g FH(B)t FK(.)75 b(The)41 b(t)n(w)n(o)167 3840 y(sen)n(tences)30 b(ha)n(v)n(e)i(the)f(same)f(denotation)i(\(they)f(are)f(true)h(at)g (the)f(same)h(time\))d(but)k(surely)167 3925 y(not)c(the)g(same)f (sense,)h(otherwise)e(what)i(is)f(the)h(p)r(oin)n(t)f(of)h(sho)n(wing)h (the)e(equiv)l(alence?)p eop PStoPSsaved restore %%Page: (6,7) 4 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 3 6 bop 167 167 a Fz(1.1.)64 b(SENSE)28 b(AND)f(DENOT)-6 b(A)g(TION)25 b(IN)i(LOGIC)1035 b FK(3)270 404 y(This)28 b(example)e(allo)n(ws)h(us)h(to)g(in)n(tro)r(duce)f(some)h(asso)r (ciations)g(of)g(ideas:)270 566 y FJ(\017)34 b FK(sense,)28 b(syn)n(tax,)i(pro)r(ofs;)270 711 y FJ(\017)k FK(denotation,)29 b(truth,)f(seman)n(tics,)f(algebraic)f(op)r(erations.)270 873 y(That)32 b(is)e(the)g(fundamen)n(tal)i(dic)n(hotom)n(y)f(in)f (logic.)44 b(Ha)n(ving)32 b(said)f(that,)h(the)e(t)n(w)n(o)i(sides)167 958 y(hardly)c(pla)n(y)g(symmetrical)d(r^)-34 b(oles!)167 1162 y Fy(1.1.1)95 b(The)27 b(algebraic)i(tradition)167 1293 y FK(This)23 b(tradition)g(\(b)r(egun)i(b)n(y)f(Bo)r(ole)f(w)n (ell)f(b)r(efore)h(the)h(time)d(of)k(F)-6 b(rege\))23 b(is)g(based)i(on)f(a)g(radical)167 1378 y(application)33 b(of)g(Oc)n(kham's)h(razor:)47 b(w)n(e)33 b(quite)f(simply)g(discard)h (the)g(sense,)i(and)g(consider)167 1463 y(only)28 b(the)f(denotation.) 36 b(The)27 b(justi\014cation)g(of)h(this)e(m)n(utilation)g(of)i(logic) e(is)h(its)f(op)r(erational)167 1549 y(side:)35 b FM(it)27 b(works!)270 1675 y FK(The)20 b(essen)n(tial)f(turning)i(p)r(oin)n(t)f (whic)n(h)g(established)f(the)h(predominance)g(of)h(this)f(tradition) 167 1760 y(w)n(as)38 b(L\177)-34 b(ow)n(enheim's)38 b(theorem)f(of)h (1916.)68 b(No)n(w)n(ada)n(ys,)43 b(one)38 b(ma)n(y)g(see)g(Mo)r(del)f (Theory)h(as)167 1845 y(the)31 b(ric)n(h)g(pa)n(y-o\013)j(from)d(this)g (epistemological)e(c)n(hoice)i(whic)n(h)g(w)n(as)h(already)g(v)n(ery)g (old.)47 b(In)167 1931 y(fact,)41 b(considering)d(logic)f(from)h(the)f (p)r(oin)n(t)i(of)f(view)f(of)i(denotation,)j FM(i.e.)c FK(the)g FM(r)l(esult)45 b FK(of)167 2016 y(op)r(erations,)33 b(w)n(e)d(disco)n(v)n(er)h(a)g(sligh)n(tly)f(p)r(eculiar)g(kind)h(of)g (algebra,)i(but)e(one)g(whic)n(h)g(allo)n(ws)167 2101 y(us)e(to)g(in)n(v)n(estigate)e(op)r(erations)i(unfamiliar)e(to)i(more) f(traditional)f(algebra.)38 b(In)29 b(particular,)167 2186 y(it)23 b(is)h(p)r(ossible)g(to)g(a)n(v)n(oid)i(the)e(limitation)d (to)k(|)f(shall)f(w)n(e)h(sa)n(y)i(|)e FM(e)l(quational)31 b FK(v)l(arieties,)24 b(and)167 2271 y(consider)33 b(general)g FM(de\014nable)k FK(structures.)52 b(Th)n(us)34 b(Mo)r(del)g(Theory)f (rejuv)n(enates)h(the)f(ideas)167 2356 y(and)c(metho)r(ds)e(of)i (algebra)f(in)f(an)h(often)g(fruitful)e(w)n(a)n(y)-6 b(.)167 2561 y Fy(1.1.2)95 b(The)27 b(syn)m(tactic)i(tradition)167 2692 y FK(On)40 b(the)f(other)h(hand,)k(it)39 b(is)g(imp)r(ossible)e (to)j(sa)n(y)h(\\forget)f(completely)e(the)h(denotation)167 2777 y(and)i(concen)n(trate)f(on)h(the)f(sense",)k(for)d(the)f(simple)e (reason)j(that)f(the)g(sense)h(con)n(tains)167 2862 y(the)34 b(denotation,)j(at)e(least)e(implicitly)-6 b(.)51 b(So)35 b(it)e(is)h(not)h(a)g(matter)e(of)i(symmetry)-6 b(.)55 b(In)34 b(fact)167 2947 y(there)d(is)h(hardly)g(an)n(y)i(uni\014ed)e (syn)n(tactic)f(p)r(oin)n(t)h(of)h(view,)f(b)r(ecause)h(w)n(e)e(ha)n(v) n(e)i(nev)n(er)f(b)r(een)167 3032 y(able)e(to)g(giv)n(e)g(an)i(op)r (erational)e(meaning)g(to)h(this)e(m)n(ysterious)h FM(sense)p FK(.)43 b(The)30 b(only)h(tangible)167 3117 y(realit)n(y)36 b(ab)r(out)i(sense)f(is)f(the)h(w)n(a)n(y)h(it)e(is)g(written,)i(the)f (formalism;)j(but)d(the)g(formalism)167 3202 y(remains)30 b(an)h(unaccommo)r(dating)h(ob)t(ject)e(of)i(study)-6 b(,)33 b(without)d(true)g(structure,)h(a)g(piece)f(of)167 3287 y FM(soft)e(c)l(amemb)l(ert)p FK(.)270 3414 y(Do)r(es)37 b(this)g(mean)f(that)i(the)e(purely)h(syn)n(tactic)f(approac)n(h)j(has) f(nothing)g(w)n(orth)n(while)167 3499 y(to)i(sa)n(y?)70 b(Surely)39 b(not,)k(and)d(the)f(famous)i(theorem)d(of)i(Gen)n(tzen)f (of)g(1934)i(sho)n(ws)g(that)167 3584 y(logic)33 b(p)r(ossesses)h(some) g(profound)h(symmetries)d(at)i(the)f(syn)n(tactical)g(lev)n(el)f (\(expressed)h(b)n(y)167 3669 y FM(cut-elimination)p FK(\).)51 b(Ho)n(w)n(ev)n(er)33 b(these)g(symmetries)e(are)i(blurred)g (b)n(y)h(the)f(imp)r(erfections)e(of)167 3754 y(syn)n(tax.)36 b(T)-6 b(o)25 b(put)f(it)g(in)f(another)i(w)n(a)n(y)-6 b(,)27 b(they)d(are)g(not)h(symmetries)d(of)j(syn)n(tax,)i(but)d(of)h (sense.)167 3840 y(F)-6 b(or)31 b(w)n(an)n(t)g(of)f(an)n(ything)i(b)r (etter,)e(w)n(e)g(m)n(ust)g(express)h(them)e(as)i(prop)r(erties)e(of)i (syn)n(tax,)i(and)167 3925 y(the)27 b(result)g(is)g(not)h(v)n(ery)g (prett)n(y)-6 b(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 4 7 bop 167 167 a FK(4)610 b Fz(CHAPTER)26 b(1.)63 b(SENSE,)28 b(DENOT)-6 b(A)g(TION)26 b(AND)g(SEMANTICS)270 404 y FK(So,)40 b(summing)c(up)h(our)h(opinion)f(ab)r(out)g(this)g (tradition,)h(it)d(is)h(alw)n(a)n(ys)i(in)e(searc)n(h)h(of)167 490 y(its)j(fundamen)n(tal)h(concepts,)k(whic)n(h)40 b(is)g(to)h(sa)n(y)-6 b(,)46 b(an)c(op)r(erational)f(distinction)e(b)r (et)n(w)n(een)167 575 y(sense)33 b(and)g(syn)n(tax.)52 b(Or)32 b(to)h(put)g(these)f(things)h(more)f(concretely)-6 b(,)33 b(it)e(aims)h(to)h(\014nd)g(deep)167 660 y(geometrical)25 b FM(invariants)34 b FK(of)28 b(syn)n(tax:)37 b(therein)26 b(is)h(to)h(b)r(e)g(found)h(the)e(sense.)270 879 y(The)g(tradition)g (called)f(\\syn)n(tactic")h(|)g(for)h(w)n(an)n(t)g(of)g(a)f(nobler)g (title)e(|)i(nev)n(er)g(reac)n(hed)167 964 y(the)35 b(lev)n(el)e(of)i (its)g(riv)l(al.)56 b(In)36 b(recen)n(t)d(y)n(ears,)38 b(during)d(whic)n(h)g(the)g(algebraic)f(tradition)g(has)167 1049 y(\015ourished,)29 b(the)e(syn)n(tactic)h(tradition)f(w)n(as)i (not)f(of)h(note)f(and)h(w)n(ould)f(without)g(doubt)h(ha)n(v)n(e)167 1134 y(disapp)r(eared)k(in)f(one)h(or)g(t)n(w)n(o)f(more)g(decades,)i (for)f(w)n(an)n(t)g(of)g(an)n(y)h(issue)e(or)h(metho)r(dology)-6 b(.)167 1219 y(The)30 b(disaster)g(w)n(as)g(a)n(v)n(erted)h(b)r(ecause) f(of)g(computer)g(science)e(|)i(that)h(great)f(manipulator)167 1304 y(of)e(syn)n(tax)h(|)f(whic)n(h)f(p)r(osed)h(it)f(some)g(v)n(ery)h (imp)r(ortan)n(t)g(theoretical)d(problems.)270 1453 y(Some)37 b(of)f(these)g(problems)g(\(suc)n(h)h(as)g(questions)f(of)h (algorithmic)d(complexit)n(y\))h(seem)167 1539 y(to)h(require)f(more)g (the)h(letter)e(than)i(the)g(spirit)e(of)j(logic.)59 b(On)36 b(the)f(other)h(hand)i(all)c(the)167 1624 y(problems)j (concerning)g(correctness)g(and)i(mo)r(dularit)n(y)e(of)h(programs)g (app)r(eal)g(in)f(a)h(deep)167 1709 y(w)n(a)n(y)c(to)g(the)f(syn)n (tactic)g(tradition,)h(to)g FM(pr)l(o)l(of)h(the)l(ory)p FK(.)53 b(W)-6 b(e)33 b(are)h(led,)g(then,)h(to)e(a)h(revision)167 1794 y(of)c(pro)r(of)h(theory)-6 b(,)31 b(from)f(the)f(fundamen)n(tal)i (theorem)d(of)j(Herbrand)f(whic)n(h)f(dates)h(bac)n(k)h(to)167 1879 y(1930.)37 b(This)27 b(revision)f(sheds)h(a)h(new)f(ligh)n(t)f(on) i(those)f(areas)h(whic)n(h)e(one)h(had)h(though)n(t)h(w)n(ere)167 1964 y(\014xed)f(forev)n(er,)g(and)h(where)e(routine)g(had)h(prev)l (ailed)f(for)h(a)g(long)g(time.)270 2113 y(In)j(the)f(exc)n(hange)i(b)r (et)n(w)n(een)e(the)g(syn)n(tactic)g(logical)f(tradition)h(and)i (computer)e(science)167 2198 y(one)37 b(can)g(w)n(ait)e(for)i(new)f (languages)i(and)g(new)e(mac)n(hines)g(on)h(the)f(computational)h (side.)167 2283 y(But)32 b(on)h(the)f(logical)f(side)g(\(whic)n(h)g(is) h(that)g(of)h(the)f(principal)f(author)i(of)g(this)e(b)r(o)r(ok\))j (one)167 2369 y(can)25 b(at)g(last)f(hop)r(e)h(to)g(dra)n(w)g(on)h(the) e(conceptual)h(basis)g(whic)n(h)e(has)j(alw)n(a)n(ys)f(b)r(een)g(so)g (cruelly)167 2454 y(ignored.)167 2716 y FE(1.2)114 b(The)28 b(t)m(w)m(o)g(seman)m(tic)g(traditions)167 2903 y Fy(1.2.1)95 b(T)-8 b(arski)167 3046 y FK(This)38 b(tradition)f(is)h(distinguished)g (b)n(y)h(an)g(extreme)d(platitude:)56 b(the)38 b(connector)h(\\)p FJ(_)p FK(")g(is)167 3131 y(translated)34 b(b)n(y)h(\\or",)i(and)e(so)g (on.)55 b(This)33 b(in)n(terpretation)g(tells)f(us)j(nothing)g (particularly)167 3216 y(remark)l(able)k(ab)r(out)h(the)g(logical)e (connectors:)59 b(its)38 b(apparen)n(t)j(lac)n(k)e(of)h(am)n(bition)f (is)f(the)167 3301 y(underlying)27 b(reason)g(for)g(its)f(op)r (erationalit)n(y)-6 b(.)35 b(W)-6 b(e)26 b(are)h(only)g(in)n(terested)e (in)h(the)g(denotation,)167 3386 y FG(t)h FK(or)h FG(f)7 b FK(,)28 b(of)h(a)f(sen)n(tence)f(\(closed)f(expression\))i(of)g(the)g (syn)n(tax.)251 3609 y(1.)35 b(F)-6 b(or)27 b(atomic)d(sen)n(tences,)i (w)n(e)g(assume)g(that)g(the)f(denotation)i(is)e(kno)n(wn;)j(for)e (example:)421 3797 y FJ(\017)35 b FK(3)16 b(+)g(2)k(=)f(5)28 b(has)h(the)e(denotation)h FG(t)p FK(.)421 3919 y FJ(\017)35 b FK(3)16 b(+)g(3)k(=)f(5)28 b(has)h(the)e(denotation)h FG(f)7 b FK(.)p eop PStoPSsaved restore %%Page: (8,9) 5 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 5 8 bop 167 167 a Fz(1.2.)64 b(THE)27 b(TW)n(O)g(SEMANTIC)g(TRADITIONS) 1071 b FK(5)251 404 y(2.)35 b(The)41 b(denotations)h(of)f(the)g (expressions)g FH(A)19 b FJ(^)g FH(B)t FK(,)45 b FH(A)19 b FJ(_)g FH(B)t FK(,)44 b FH(A)29 b FJ(\))g FH(B)45 b FK(and)d FJ(:)p FH(A)e FK(are)339 490 y(obtained)29 b(b)n(y)f(means)g (of)g(a)g(truth)g(table:)948 710 y FH(A)59 b(B)p 1169 736 3 86 v 88 w(A)16 b FJ(^)f FH(B)63 b(A)15 b FJ(_)h FH(B)63 b(A)19 b FJ(\))h FH(B)62 b FJ(:)p FH(A)p 919 738 1174 3 v 959 814 a FG(t)81 b(t)p 1169 839 3 102 v 175 w(t)213 b(t)230 b(t)185 b(f)959 899 y(f)88 b(t)p 1169 924 3 86 v 175 w(f)220 b(t)230 b(t)185 b(t)959 984 y(t)81 b(f)p 1169 1010 V 182 w(f)220 b(t)229 b(f)959 1069 y(f)88 b(f)p 1169 1095 V 182 w(f)220 b(f)237 b(t)251 1256 y FK(3.)35 b(The)27 b(denotation)g(of)g FJ(8)p FH(\030)s(:)12 b(A)25 b FK(is)h FG(t)g FK(i\013)g(for)g FM(every)32 b FH(a)27 b FK(in)f(the)g(domain)g(of)h(in)n(terpretation)2626 1231 y FD(2)2653 1256 y FK(,)339 1341 y FH(A)p FK([)p FH(a=\030)s FK(])i(is)e FG(t)p FK(.)35 b(Lik)n(ewise)26 b FJ(9)p FH(\030)s(:)12 b(A)28 b FK(is)f FG(t)g FK(i\013)g FH(A)p FK([)p FH(a=\030)s FK(])i(is)e FG(t)h FK(for)g FM(some)33 b FH(a)p FK(.)270 1503 y(Once)h(again,)k(this)c (de\014nition)g(is)g(ludicrous)g(from)h(the)f(p)r(oin)n(t)h(of)g(view)f (of)h(logic,)h(but)167 1588 y(en)n(tirely)26 b(adequate)i(for)g(its)f (purp)r(ose.)37 b(The)27 b(dev)n(elopmen)n(t)g(of)h(Mo)r(del)f(Theory)h (sho)n(ws)h(this.)167 1793 y Fy(1.2.2)95 b(Heyting)167 1924 y FK(Heyting's)27 b(idea)h(is)f(less)f(w)n(ell)g(kno)n(wn,)j(but)f (it)e(is)h(di\016cult)g(to)h(imagine)e(a)i(greater)f(disparit)n(y)167 2009 y(b)r(et)n(w)n(een)43 b(the)g(brilliance)d(of)k(the)f(original)g (idea)g(and)h(the)g(medio)r(crit)n(y)d(of)j(subsequen)n(t)167 2094 y(dev)n(elopmen)n(ts.)35 b(The)27 b(aim)g(is)g(extremely)f(am)n (bitious:)35 b(to)28 b(mo)r(del)e(not)j(the)e FM(denotation)p FK(,)h(but)167 2179 y(the)f FM(pr)l(o)l(ofs)p FK(.)270 2305 y(Instead)i(of)g(asking)g(the)f(question)g(\\when)h(is)f(a)g(sen)n (tence)g FH(A)g FM(true)5 b FK(?",)28 b(w)n(e)g(ask)h(\\what)g(is)167 2391 y(a)g FM(pr)l(o)l(of)44 b FK(of)29 b FH(A)p FK(?".)36 b(By)29 b FM(pr)l(o)l(of)44 b FK(w)n(e)28 b(understand)h(not)g(the)f (syn)n(tactic)f(formal)h(transcript,)g(but)167 2476 y(the)d(inheren)n (t)f(ob)t(ject)h(of)h(whic)n(h)e(the)h(written)f(form)h(giv)n(es)g (only)g(a)h(shado)n(wy)h(re\015ection.)33 b(W)-6 b(e)167 2561 y(tak)n(e)28 b(the)f(view)g(that)h(what)g(w)n(e)f FM(write)h FK(as)g(a)g(pro)r(of)h(is)e(merely)e(a)k(description)d(of)i (something)167 2646 y(whic)n(h)38 b(is)g FM(alr)l(e)l(ady)i FK(a)f(pro)r(cess)g(in)f(itself.)67 b(So)39 b(the)g(reply)f(to)h(our)g (extremely)e(am)n(bitious)167 2731 y(question)24 b(\(and)g(an)g(imp)r (ortan)n(t)f(one,)i(if)e(w)n(e)f(read)i(it)e(computationally\))h (cannot)h(b)r(e)g(a)g FM(formal)167 2816 y(system)p FK(.)251 3066 y(1.)35 b(F)-6 b(or)27 b(atomic)f(sen)n(tences,)g(w)n(e)g(assume)g (that)h(w)n(e)f(kno)n(w)h(in)n(trinsically)d(what)i(a)h(pro)r(of)h(is;) 339 3151 y(for)21 b(example,)g(p)r(encil)e(and)i(pap)r(er)g (calculation)f(serv)n(es)g(as)h(a)g(pro)r(of)g(of)g(\\27)5 b FJ(\002)g FK(37)22 b(=)d(999".)251 3296 y(2.)35 b(A)d(pro)r(of)h(of)f FH(A)17 b FJ(^)g FH(B)35 b FK(is)c(a)i(pair)e(\()p FH(p;)12 b(q)s FK(\))30 b(consisting)i(of)g(a)h(pro)r(of)g FH(p)e FK(of)h FH(A)g FK(and)h(a)f(pro)r(of)339 3381 y FH(q)e FK(of)e FH(B)t FK(.)251 3566 y(3.)35 b(A)28 b(pro)r(of)g(of)h FH(A)15 b FJ(_)h FH(B)31 b FK(is)c(a)h(pair)f(\()p FH(i;)12 b(p)p FK(\))27 b(with:)421 3728 y FJ(\017)35 b FH(i)19 b FK(=)g(0,)29 b(and)f FH(p)g FK(is)f(a)h(pro)r(of)g(of)g FH(A)p FK(,)g(or)p 167 3790 1003 3 v 246 3833 a FC(2)273 3854 y Fx(A)p FB([)p Fx(a=\030)s FB(])j(is)g(meta-notation)f(for)i(\\)p Fx(A)g FB(where)f(all)f(the)h(\(free\))g(o)r(ccurrences)g(of)h Fx(\030)i FB(ha)n(v)n(e)e(b)r(een)e(replaced)167 3925 y(b)n(y)e Fx(a)p FB(".)34 b(In)28 b(de\014ning)d(this)i(formally)-5 b(,)27 b(w)n(e)i(ha)n(v)n(e)f(to)g(b)r(e)f(careful)g(ab)r(out)f(b)r (ound)g(v)m(ariables.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 6 9 bop 167 167 a FK(6)610 b Fz(CHAPTER)26 b(1.)63 b(SENSE,)28 b(DENOT)-6 b(A)g(TION)26 b(AND)g(SEMANTICS)421 404 y FJ(\017)35 b FH(i)19 b FK(=)g(1,)29 b(and)f FH(p)g FK(is)f(a)h(pro)r (of)g(of)g FH(B)t FK(.)251 595 y(4.)35 b(A)26 b(pro)r(of)i(of)f FH(A)19 b FJ(\))h FH(B)30 b FK(is)c(a)g(function)h FH(f)8 b FK(,)26 b(whic)n(h)g(maps)g(eac)n(h)h(pro)r(of)g FH(p)f FK(of)h FH(A)f FK(to)g(a)h(pro)r(of)339 680 y FH(f)8 b FK(\()p FH(p)p FK(\))27 b(of)h FH(B)t FK(.)251 845 y(5.)35 b(In)25 b(general,)h(the)e(negation)i FJ(:)p FH(A)e FK(is)h(treated)f(as)i FH(A)19 b FJ(\))h(?)j FK(where)i FJ(?)e FK(is)h(a)i(sen)n(tence)e(with)339 930 y(no)29 b(p)r(ossible)e(pro)r(of.)251 1095 y(6.)35 b(A)28 b(pro)r(of)g(of)g FJ(8)p FH(\030)s(:)12 b(A)27 b FK(is)f(a)i(function)g FH(f)8 b FK(,)27 b(whic)n(h)f(maps)i(eac)n(h)g(p)r(oin)n(t)f FH(a)h FK(of)g(the)f(domain)h(of)339 1180 y(de\014nition)g(to)f(a)i (pro)r(of)f FH(f)8 b FK(\()p FH(a)p FK(\))27 b(of)h FH(A)p FK([)p FH(a=\030)s FK(].)251 1345 y(7.)35 b(A)23 b(pro)r(of)i(of)e FJ(9)p FH(\030)s(:)12 b(A)24 b FK(is)f(a)g(pair)g(\()p FH(a;)12 b(p)p FK(\))23 b(where)f FH(a)i FK(is)e(a)i(p)r(oin)n(t)g(of)f (the)g(domain)h(of)g(de\014nition)339 1430 y(and)29 b FH(p)e FK(is)g(a)h(pro)r(of)h(of)f FH(A)p FK([)p FH(a=\030)s FK(].)270 1683 y(F)-6 b(or)35 b(example,)g(the)f(sen)n(tence)f FH(A)24 b FJ(\))g FH(A)34 b FK(is)f(pro)n(v)n(ed)j(b)n(y)e(the)g(iden)n (tit)n(y)f(function,)j(whic)n(h)167 1768 y(asso)r(ciates)f(to)f(eac)n (h)h(pro)r(of)g FH(p)f FK(of)h FH(A)p FK(,)h(the)e(same)g(pro)r(of.)57 b(On)34 b(the)h(other)f(hand,)k(ho)n(w)d(can)167 1853 y(w)n(e)f(pro)n(v)n(e)i FH(A)17 b FJ(_)h(:)p FH(A)p FK(?)56 b(W)-6 b(e)34 b(ha)n(v)n(e)i(to)f(b)r(e)f(able)h(to)g(\014nd)g(either)e (a)i(pro)r(of)h(of)f FH(A)g FK(or)g(a)g(pro)r(of)167 1938 y(of)c FJ(:)p FH(A)p FK(,)g(and)g(this)f(is)g(not)h(p)r(ossible)f (in)g(general.)43 b(Heyting)30 b(seman)n(tics,)h(then,)g(corresp)r (onds)167 2024 y(to)d(another)g(logic,)f(the)g FM(intuitionistic)32 b FK(logic)26 b(of)j(Brou)n(w)n(er,)e(whic)n(h)g(w)n(e)g(shall)g(meet)f (later.)270 2175 y(Undeniably)-6 b(,)48 b(Heyting)43 b(seman)n(tics)f(is)g(v)n(ery)i(original:)66 b(it)42 b(do)r(es)i(not)g(in)n(terpret)d(the)167 2260 y(logical)28 b(op)r(erations)j(b)n(y)g(themselv)n(es,)e(but)h(b)n(y)h(abstract)f (constructions.)43 b(No)n(w)30 b(w)n(e)f(can)i(see)167 2345 y(that)39 b(these)g(constructions)f(are)h(nothing)h(but)f(t)n(yp)r (ed)g(\()p FM(i.e.)g FK(mo)r(dular\))f(programs.)70 b(But)167 2430 y(the)33 b(exp)r(erts)f(in)h(the)f(area)i(ha)n(v)n(e)g(seen)e(in)h (this)f(something)h(v)n(ery)g(di\013eren)n(t:)45 b(a)33 b(functional)167 2515 y(approac)n(h)e(to)f(mathematics.)38 b(In)30 b(other)f(w)n(ords,)h(the)f(seman)n(tics)f(of)i(pro)r(ofs)h(w)n (ould)e(express)167 2601 y(the)e(v)n(ery)h(essence)f(of)h(mathematics.) 270 2752 y(That)22 b(w)n(as)f(v)n(ery)g(fanciful:)31 b(indeed,)22 b(w)n(e)e(ha)n(v)n(e)i(on)g(the)e(one)h(hand)h(the)f(T)-6 b(arskian)22 b(tradition,)167 2837 y(whic)n(h)h(is)g(commonplace)g(but) h(honest)h(\(\\)p FJ(_)p FK(")g(means)e(\\or",)j(\\)p FJ(8)12 b FK(")24 b(means)g(\\for)h(all"\),)e(without)167 2922 y(the)37 b(least)g(pretension.)65 b(Nor)37 b(has)i(it)d (foundational)j(prosp)r(ects,)i(since)36 b(for)i(foundations,)167 3007 y(one)j(has)h(to)g(giv)n(e)e(an)i(explanation)f(in)g(terms)f(of)h (something)g(more)f(primitiv)n(e,)i(whic)n(h)167 3092 y(moreo)n(v)n(er)25 b(itself)f(needs)h(its)g(o)n(wn)h(foundation.)36 b(The)25 b(tradition)g(of)h(Heyting)f(is)g(original,)g(but)167 3177 y(fundamen)n(tally)k(has)g(the)g(same)f(problems)g(|)h(G\177)-34 b(odel's)29 b(incompleteness)d(theorem)i(assures)167 3263 y(us,)33 b(b)n(y)g(the)f(w)n(a)n(y)-6 b(,)34 b(that)e(it)e(could)i (not)g(b)r(e)g(otherwise.)47 b(If)32 b(w)n(e)f(wish)g(to)h(explain)f FH(A)h FK(b)n(y)g(the)167 3348 y(act)c(of)h(pro)n(ving)g FH(A)p FK(,)g(w)n(e)e(come)h(up)h(against)g(the)f(fact)g(that)h(the)f (de\014nition)g(of)h(a)f(pro)r(of)i(uses)167 3433 y(quan)n(ti\014ers)c (t)n(wice)d(\(for)j FJ(\))g FK(and)g FJ(8)p FK(\).)34 b(Moreo)n(v)n(er)26 b(in)e(the)h FJ(\))h FK(case,)g(one)g(cannot)g(sa)n (y)h(that)e(the)167 3518 y(domain)j(of)g(de\014nition)f(of)h FH(f)35 b FK(is)27 b(particularly)f(w)n(ell)g(understo)r(o)r(d!)270 3669 y(Since)38 b(the)h FJ(\))g FK(and)h FJ(8)e FK(cases)h(w)n(ere)f (problematic)f(\(from)h(this)g(absurd)j(foundational)167 3754 y(p)r(oin)n(t)c(of)h(view\),)h(it)d(has)j(b)r(een)e(prop)r(osed)i (to)f(add)g(to)g(clauses)f FG(??)h FK(and)g FG(??)g FK(the)g(co)r (dicil)167 3840 y(\\together)29 b(with)e(a)i(pro)r(of)h(that)e FH(f)36 b FK(has)29 b(this)f(prop)r(ert)n(y".)39 b(Of)28 b(course)g(that)h(settles)e(nothing,)167 3925 y(and)32 b(the)e(Byzan)n(tine)g(discussions)h(ab)r(out)g(the)g FM(me)l(aning)36 b FK(whic)n(h)30 b(w)n(ould)h(ha)n(v)n(e)g(to)g(b)r(e) f(giv)n(en)p eop PStoPSsaved restore %%Page: (10,11) 6 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 7 10 bop 167 167 a Fz(1.2.)64 b(THE)27 b(TW)n(O)g(SEMANTIC)g (TRADITIONS)1071 b FK(7)167 404 y(to)25 b(this)f(co)r(dicil)e(|)j (discussions)g(without)f(the)g(least)g(mathematical)f(con)n(ten)n(t)i (|)f(only)h(serv)n(e)167 490 y(to)j(discredit)e(an)i(idea)f(whic)n(h,)g (w)n(e)g(rep)r(eat,)h(is)f(one)h(of)g(the)f(cornerstones)h(of)g(Logic.) 270 616 y(W)-6 b(e)21 b(shall)e(come)h(across)h(Heyting's)g(idea)f(w)n (orking)g(in)g(the)h(Curry-Ho)n(w)n(ard)g(isomorphism.)167 701 y(It)32 b(o)r(ccurs)h(in)f(Realisabilit)n(y)e(to)r(o.)51 b(In)33 b(b)r(oth)h(these)e(cases,)j(the)d(foundational)i(pretensions) 167 786 y(ha)n(v)n(e)29 b(b)r(een)f(remo)n(v)n(ed.)37 b(This)27 b(allo)n(ws)g(us)i(to)f(mak)n(e)g(go)r(o)r(d)i(use)e(of)h(an) g(idea)e(whic)n(h)h(ma)n(y)g(ha)n(v)n(e)167 871 y(sp)r(ectacular)f (applications)g(in)g(the)h(future.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 8 11 bop 167 874 a FF(Chapter)28 b(2)167 1168 y(Natural)f(Deduction)167 1487 y FK(As)g(w)n(e)f(ha)n(v)n(e)i(said,)f(the)g(syn)n(tactic)f(p)r (oin)n(t)h(of)h(view)d(sho)n(ws)j(up)g(some)e(profound)j(symmetries)167 1573 y(of)49 b(Logic.)100 b(Gen)n(tzen's)49 b(sequen)n(t)g(calculus)f (do)r(es)h(this)g(in)f(a)h(particularly)f(satisfying)167 1658 y(manner.)g(Unfortunately)-6 b(,)33 b(the)e(computational)h (signi\014cance)f(is)g(somewhat)h(obscured)g(b)n(y)167 1743 y(syn)n(tactic)22 b(complications)f(that,)j(although)g(certainly)d (immaterial,)g(ha)n(v)n(e)i(nev)n(er)g(really)e(b)r(een)167 1828 y(o)n(v)n(ercome.)34 b(That)26 b(is)e(wh)n(y)i(w)n(e)e(presen)n(t) h(Pra)n(witz')f(natural)i(deduction)f(b)r(efore)g(w)n(e)f(deal)h(with) 167 1913 y(sequen)n(t)j(calculus.)270 2039 y(Natural)47 b(deduction)g(is)g(a)h(sligh)n(tly)d(parado)n(xical)j(system:)75 b(it)46 b(is)g(limited)e(to)j(the)167 2124 y(in)n(tuitionistic)22 b(case)k(\(in)f(the)h(classical)e(case)h(it)g(has)i(no)f(particularly)f (go)r(o)r(d)i(prop)r(erties\))e(but)167 2209 y(it)30 b(is)h(only)h(satisfactory)g(for)g(the)g(\()p FJ(^)p FH(;)12 b FJ(\))p FH(;)g FJ(8)p FK(\))30 b(fragmen)n(t)i(of)g(the)f (language:)45 b(w)n(e)31 b(shall)g(defer)167 2294 y(consideration)e(of) h FJ(_)f FK(and)h FJ(9)g FK(un)n(til)e(c)n(hapter)h FG(??)q FK(.)40 b(Y)-6 b(et)29 b(disjunction)g(and)h(existence)e(are)h(the)167 2380 y(t)n(w)n(o)f(most)f FM(typic)l(al)t(ly)35 b FK(in)n(tuitionistic) 24 b(connectors!)270 2553 y(The)35 b(basic)g(idea)g(of)g(natural)h (deduction)f(is)f(an)i(asymmetry:)50 b(a)36 b(pro)r(of)g(is)f(a)g(v)l (aguely)167 2638 y(tree-lik)n(e)g(structure)i(\(this)g(view)g(is)f (more)h(a)i(graphical)e(illusion)f(than)i(a)g(mathematical)167 2723 y(realit)n(y)-6 b(,)27 b(but)i(it)e(is)h(a)g(pleasan)n(t)h (illusion\))d(with)h(one)i(or)f(more)g(h)n(yp)r(otheses)h(\(p)r (ossibly)g(none\))167 2808 y(but)38 b(a)h(single)e(conclusion.)66 b(The)38 b(deep)g(symmetry)f(of)h(the)g(calculus)f(is)g(sho)n(wn)j(b)n (y)e(the)167 2893 y FM(intr)l(o)l(duction)47 b FK(and)42 b FM(elimination)k FK(rules)40 b(whic)n(h)g(matc)n(h)g(eac)n(h)h(other) g(exactly)-6 b(.)75 b(Observ)n(e,)167 2978 y(inciden)n(tally)-6 b(,)27 b(that)i(with)f(a)h(tree-lik)n(e)d(structure,)j(one)g(can)g(alw) n(a)n(ys)h(decide)d(uniquely)i(what)167 3063 y(w)n(as)g(the)f FM(last)35 b FK(rule)27 b(used,)i(whic)n(h)f(is)g(something)g(w)n(e)g (could)g(not)h(sa)n(y)g(if)f(there)f(w)n(ere)h(sev)n(eral)167 3149 y(conclusions.)1402 4101 y(8)p eop PStoPSsaved restore %%Page: (12,13) 7 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 9 12 bop 167 167 a Fz(2.1.)64 b(THE)27 b(CALCULUS)1745 b FK(9)167 404 y FE(2.1)114 b(The)28 b(calculus)167 564 y FK(W)-6 b(e)27 b(shall)g(use)h(the)f(notation)1396 718 y FJ(\001)1396 756 y(\001)1396 794 y(\001)1380 851 y FH(A)167 1013 y FK(to)e(designate)f(a)h FM(de)l(duction)30 b FK(of)c FH(A)p FK(,)e(that)h(is,)g(ending)g(at)g FH(A)p FK(.)34 b(The)24 b(deduction)h(will)c(b)r(e)k(written)167 1098 y(as)30 b(a)f(\014nite)g(tree,)f(and)i(in)f(particular,)g(the)f (tree)g(will)f(ha)n(v)n(e)j(lea)n(v)n(es)f(lab)r(elled)e(b)n(y)i(sen)n (tences.)167 1183 y(F)-6 b(or)28 b(these)f(sen)n(tences,)h(there)f(are) g(t)n(w)n(o)h(p)r(ossible)f(states,)h FM(de)l(ad)36 b FK(or)27 b FM(alive)p FK(.)270 1319 y(In)h(the)f(usual)h(state,)g(a)g (sen)n(tence)f(is)g(aliv)n(e,)g(that)h(is)e(to)i(sa)n(y)h(it)d(tak)n (es)j(an)f(activ)n(e)f(part)h(in)167 1404 y(the)33 b(pro)r(of:)47 b(w)n(e)32 b(sa)n(y)i(it)e(is)g(a)h FM(hyp)l(othesis)p FK(.)53 b(The)33 b(t)n(ypical)f(case)h(is)f(illustrated)f(b)n(y)i(the)g (\014rst)167 1489 y(rule)h(of)i(natural)g(deduction,)i(whic)n(h)d(allo) n(ws)g(us)h(to)f(form)h(a)g(deduction)f(consisting)h(of)g(a)167 1574 y(single)27 b(sen)n(tence:)1380 1767 y FH(A)167 1959 y FK(Here)i FH(A)h FK(is)g(b)r(oth)i(the)e(leaf)g(and)h(the)g(ro)r (ot;)h(logically)-6 b(,)30 b(w)n(e)g(deduce)g FH(A)p FK(,)h(but)g(that)g(w)n(as)g(easy)167 2044 y(b)r(ecause)d FH(A)f FK(w)n(as)h(assumed!)270 2180 y(No)n(w)c(a)g(sen)n(tence)f(at)g (a)h(leaf)f(can)h(b)r(e)f(dead,)i(when)f(it)e(no)j(longer)e(pla)n(ys)h (an)g(activ)n(e)f(part)h(in)167 2265 y(the)29 b(pro)r(of.)40 b(Dead)28 b(sen)n(tences)h(are)f(obtained)i(b)n(y)f(killing)e(liv)n(e)g (ones.)40 b(The)28 b(t)n(ypical)g(example)167 2350 y(is)f(the)g FJ(\))p FK(-in)n(tro)r(duction)h(rule:)1293 2516 y([)p FH(A)p FK(])1329 2574 y FJ(\001)1329 2612 y(\001)1329 2650 y(\001)1310 2707 y FH(B)p 1230 2752 218 4 v 1468 2768 a FJ(\)I)1230 2829 y FH(A)19 b FJ(\))h FH(B)167 2990 y FK(It)28 b(m)n(ust)h(b)r(e)f(understo)r(o)r(d)i(th)n(us:)38 b(starting)29 b(from)g(a)g(deduction)f(of)h FH(B)t FK(,)g(in)f(whic)n (h)g(w)n(e)g(c)n(ho)r(ose)167 3076 y(a)j(certain)f(n)n(um)n(b)r(er)h (of)g(o)r(ccurrences)f(of)h FH(A)g FK(as)g FM(hyp)l(otheses)h FK(\(the)f(n)n(um)n(b)r(er)f(is)h(arbitrary:)41 b(0,)167 3161 y(1,)30 b(250,)i(.)11 b(.)g(.)g(\),)31 b(w)n(e)e(form)h(a)f(new)g (deduction)h(of)g(whic)n(h)e(the)h(conclusion)h(is)e FH(A)21 b FJ(\))g FH(B)t FK(,)30 b(but)g(in)167 3246 y(whic)n(h)f(all)f(these)i(o)r(ccurrences)e(of)i FH(A)g FK(ha)n(v)n(e)g(b)r(een)g FM(dischar)l(ge)l(d)p FK(,)h FM(i.e.)f FK(killed.)39 b(There)29 b(ma)n(y)h(b)r(e)167 3331 y(other)e(o)r(ccurrences)e(of)j FH(A)e FK(whic)n(h)g(w)n(e)g(ha)n (v)n(e)i(c)n(hosen)f(not)g(to)g(disc)n(harge.)270 3467 y(This)43 b(rule)g(illustrates)e(v)n(ery)i(w)n(ell)f(the)h(illusion)e (of)j(the)f(tree-lik)n(e)e(notation:)67 b(it)43 b(is)167 3552 y(of)36 b(critical)d(imp)r(ortance)i(to)h(kno)n(w)h FM(when)j FK(a)c(h)n(yp)r(othesis)h(w)n(as)f(disc)n(harged,)j(and)e(so) f(it)f(is)167 3637 y(essen)n(tial)30 b(to)i(record)f(this.)46 b(But)31 b(if)g(w)n(e)g(do)h(this)f(in)g(the)g(example)f(ab)r(o)n(v)n (e,)k(this)d(means)h(w)n(e)167 3722 y(ha)n(v)n(e)j(to)f(link)e(the)i (crossed)g FH(A)f FK(with)g(the)g(line)f(of)i(the)g FJ(\)I)39 b FK(rule;)d(but)e(it)f(is)g(no)h(longer)g(a)167 3807 y(gen)n(uine)28 b(tree)e(w)n(e)h(are)h(considering!)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 10 13 bop 167 167 a FK(10)1139 b Fz(CHAPTER)27 b(2.)63 b(NA)-6 b(TURAL)26 b(DEDUCTION)167 404 y Fy(2.1.1)95 b(The)27 b(rules)270 537 y FJ(\017)34 b FM(Hyp)l(othesis)6 b FK(:)116 b FH(A)270 684 y FJ(\017)34 b FM(Intr)l(o)l(ductions)6 b FK(:)688 893 y FJ(\001)688 931 y(\001)688 969 y(\001)672 1026 y FH(A)889 893 y FJ(\001)889 931 y(\001)889 969 y(\001)870 1026 y FH(B)p 672 1070 255 4 v 947 1086 a FJ(^I)706 1147 y FH(A)15 b FJ(^)h FH(B)1433 869 y FK([)p FH(A)p FK(])1469 928 y FJ(\001)1469 966 y(\001)1469 1004 y(\001)1450 1061 y FH(B)p 1370 1106 218 4 v 1608 1122 a FJ(\)I)1370 1182 y FH(A)j FJ(\))h FH(B)2122 886 y FJ(\001)2122 924 y(\001)2122 962 y(\001)2106 1019 y FH(A)p 2054 1064 156 4 v 2230 1080 a FJ(8I)2054 1140 y(8)p FH(\030)s(:)12 b(A)270 1394 y FJ(\017)34 b FM(Eliminations)6 b FK(:)581 1576 y FJ(\001)581 1614 y(\001)581 1652 y(\001)498 1709 y FH(A)16 b FJ(^)f FH(B)p 498 1754 186 4 v 705 1770 a FJ(^)p FK(1)p FJ(E)565 1831 y FH(A)1072 1576 y FJ(\001)1072 1614 y(\001)1072 1652 y(\001)988 1709 y FH(A)h FJ(^)f FH(B)p 988 1754 V 1195 1770 a FJ(^)p FK(2)p FJ(E)1053 1831 y FH(B)1495 1576 y FJ(\001)1495 1614 y(\001)1495 1652 y(\001)1479 1709 y FH(A)1776 1576 y FJ(\001)1776 1614 y(\001)1776 1652 y(\001)1678 1709 y FH(A)k FJ(\))h FH(B)p 1479 1754 417 4 v 1916 1770 a FJ(\)E)1659 1831 y FH(B)2276 1567 y FJ(\001)2276 1605 y(\001)2276 1643 y(\001)2208 1701 y(8)p FH(\030)s(:)12 b(A)p 2188 1746 195 4 v 2403 1762 a FJ(8E)2188 1822 y FH(A)p FK([)p FH(a=\030)s FK(])339 2021 y(The)28 b(rule)e FJ(\))q(E)34 b FK(is)27 b(traditionally)f(called)g FM(mo)l(dus)j(p)l(onens)p FK(.)167 2232 y(Some)f(remarks:)270 2318 y(All)40 b(the)g(rules,)k (except)d FJ(\)I)5 b FK(,)45 b(preserv)n(e)c(the)g(sto)r(c)n(k)g(of)h (h)n(yp)r(otheses:)63 b(for)42 b(example,)167 2403 y(the)32 b(h)n(yp)r(otheses)i(in)d(the)h(deduction)h(ab)r(o)n(v)n(e)g(whic)n(h)f (ends)h(in)f FJ(\)E)6 b FK(,)34 b(are)e(those)h(of)g(the)f(t)n(w)n(o) 167 2489 y(immediate)25 b(sub-deductions.)270 2575 y(F)-6 b(or)28 b(w)n(ell-kno)n(wn)d(logical)h(reasons,)i(it)d(is)h(necessary)h (to)g(restrict)e FJ(8I)31 b FK(to)c(the)f(case)h(where)167 2660 y(the)j(v)l(ariable)529 2635 y FD(1)587 2660 y FH(\030)k FK(is)c(not)h(free)f(in)g(an)n(y)h(h)n(yp)r(othesis)h(\(it)d(ma)n(y)-6 b(,)32 b(on)f(the)f(other)h(hand,)i(b)r(e)d(free)167 2745 y(in)d(a)h(dead)g(leaf)5 b(\).)270 2832 y(The)47 b(fundamen)n(tal)g(symmetry)e(of)j(the)e(system)g(is)g(the)g FM(intr)l(o)l(duction/elimination)167 2917 y FK(symmetry)-6 b(,)44 b(whic)n(h)c(replaces)g(the)g FM(hyp)l(othesis/c)l(onclusion)48 b FK(symmetry)40 b(that)h(cannot)h(b)r(e)167 3002 y(implemen)n(ted)25 b(in)i(this)g(con)n(text.)167 3242 y FE(2.2)114 b(Computational)29 b(signi\014cance)167 3399 y FK(W)-6 b(e)20 b(shall)f(re-examine)f(the)h (natural)i(deduction)e(system)h(in)f(the)h(ligh)n(t)e(of)j(Heyting)e (seman)n(tics;)167 3484 y(w)n(e)32 b(shall)g(supp)r(ose)i(\014xed)f (the)f(in)n(terpretation)g(of)h(atomic)e(form)n(ulae)i(and)g(also)g (the)f(range)167 3570 y(of)d(the)f(quan)n(ti\014ers.)38 b(A)28 b(form)n(ula)g FH(A)g FK(will)e(b)r(e)i(seen)g(as)h(the)f(set)g (of)h(its)e(p)r(ossible)h(deductions;)167 3655 y(instead)g(of)g(sa)n (ying)g(\\)p FH(\016)j FK(pro)n(v)n(es)d FH(A)p FK(",)g(w)n(e)f(shall)g (sa)n(y)i(\\)p FH(\016)22 b FJ(2)e FH(A)p FK(".)p 167 3719 1003 3 v 246 3763 a FC(1)273 3784 y FB(The)28 b(v)m(ariable)e Fx(\030)31 b FB(b)r(elongs)c(to)h(the)f FA(obje)m(ct)i(language)f FB(\(it)f(ma)n(y)h(stand)g(for)g(a)g(n)n(um)n(b)r(er,)g(a)g (data-record,)167 3854 y(an)i(ev)n(en)n(t\).)43 b(W)-5 b(e)31 b(reserv)n(e)g Fx(x)p FB(,)g Fx(y)r FB(,)g Fx(z)i FB(for)e Fx(\025)p FB(-calculus)e(v)m(ariables,)h(whic)n(h)f(w)n(e)j (shall)d(in)n(tro)r(duce)g(in)g(the)h(next)167 3925 y(section.)p eop PStoPSsaved restore %%Page: (14,15) 8 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 11 14 bop 167 167 a Fz(2.2.)64 b(COMPUT)-6 b(A)g(TIONAL)26 b(SIGNIFICANCE)1093 b FK(11)270 404 y(The)33 b(rules)e(of)j(natural)f (deduction)f(then)h(app)r(ear)g(as)g(a)h(sp)r(ecial)d(w)n(a)n(y)i(of)g (constructing)167 490 y(functions:)g(a)22 b(deduction)f(of)i FH(A)e FK(on)h(the)g(h)n(yp)r(otheses)h FH(B)1630 501 y FD(1)1658 490 y FH(;)12 b(:)g(:)g(:)g(;)g(B)1865 501 y Fw(n)1920 490 y FK(can)22 b(b)r(e)f(seen)h(as)g(a)g(function)167 575 y FH(t)p FK([)p FH(x)250 586 y FD(1)278 575 y FH(;)12 b(:)g(:)g(:)g(;)g(x)472 586 y Fw(n)505 575 y FK(])25 b(whic)n(h)f(asso)r(ciates)h(to)h(elemen)n(ts)c FH(b)1466 586 y Fw(i)1506 575 y FJ(2)e FH(B)1625 586 y Fw(i)1670 575 y FK(a)25 b(result)f FH(t)p FK([)p FH(b)1996 586 y FD(1)2024 575 y FH(;)12 b(:)g(:)g(:)g(;)g(b)2208 586 y Fw(n)2241 575 y FK(])20 b FJ(2)g FH(A)p FK(.)34 b(In)25 b(fact,)167 660 y(for)31 b(this)g(corresp)r(ondence)g(to)h(b)r(e)f (exact,)h(one)g(has)g(to)f(w)n(ork)h(with)e FM(p)l(ar)l(c)l(els)i(of)g (hyp)l(otheses)6 b FK(:)167 745 y(the)30 b(same)g(form)n(ula)g FH(B)k FK(ma)n(y)d(in)f(general)g(app)r(ear)h(sev)n(eral)f(times)e (among)k(the)e(h)n(yp)r(otheses,)167 830 y(and)c(t)n(w)n(o)f(o)r (ccurrences)f(of)i FH(B)i FK(in)d(the)f(same)h(parcel)f(will)e(corresp) r(ond)k(to)f(the)g(same)f(v)l(ariable.)270 959 y(This)43 b(is)g(a)h(little)c(m)n(ysterious,)47 b(but)d(it)e(will)f(quic)n(kly)i (b)r(ecome)f(clearer)g(with)g(some)167 1044 y(examples.)167 1251 y Fy(2.2.1)95 b(In)m(terpretation)28 b(of)f(the)h(rules)251 1382 y FK(1.)35 b(A)46 b(deduction)g(consisting)f(of)i(a)f(single)f(h)n (yp)r(othesis)i FH(A)e FK(is)h(represen)n(ted)f(b)n(y)h(the)339 1468 y(expression)32 b FH(x)p FK(,)g(where)f FH(x)g FK(is)f(a)i(v)l (ariable)f(for)g(an)h(elemen)n(t)d(of)j FH(A)p FK(.)46 b(Later,)32 b(if)e(w)n(e)h(ha)n(v)n(e)339 1553 y(other)37 b(o)r(ccurrences)e(of)i FH(A)p FK(,)h(w)n(e)e(shall)g(c)n(ho)r(ose)h (the)f(same)g FH(x)p FK(,)j(or)d(another)h(v)l(ariable,)339 1638 y(dep)r(ending)h(up)r(on)h(whether)e(or)h(not)h(those)f(other)f(o) r(ccurrences)g(are)h(in)f(the)g(same)339 1723 y(parcel.)251 1869 y(2.)e(If)52 b(a)g(deduction)f(has)i(b)r(een)e(obtained)h(b)n(y)h (means)e(of)i FJ(^I)k FK(from)51 b(t)n(w)n(o)h(others)339 1954 y(corresp)r(onding)39 b(to)f FH(u)p FK([)p FH(x)993 1965 y FD(1)1021 1954 y FH(;)12 b(:)g(:)g(:)g(;)g(x)1215 1965 y Fw(n)1248 1954 y FK(])38 b(and)h FH(v)s FK([)p FH(x)1548 1965 y FD(1)1576 1954 y FH(;)12 b(:)g(:)g(:)f(;)h(x)1769 1965 y Fw(n)1803 1954 y FK(],)40 b(then)e(w)n(e)f(asso)r(ciate)h(to)g (our)339 2039 y(deduction)23 b(the)f(pair)f FJ(h)p FH(u)p FK([)p FH(x)1039 2050 y FD(1)1068 2039 y FH(;)12 b(:)g(:)g(:)g(;)g(x) 1262 2050 y Fw(n)1295 2039 y FK(])p FH(;)g(v)s FK([)p FH(x)1439 2050 y FD(1)1467 2039 y FH(;)g(:)g(:)g(:)g(;)g(x)1661 2050 y Fw(n)1694 2039 y FK(])p FJ(i)p FK(,)24 b(since)d(a)i(pro)r(of)g (of)g(a)g(conjunction)339 2124 y(is)34 b(a)h FM(p)l(air)p FK(.)57 b(W)-6 b(e)34 b(ha)n(v)n(e)h(made)f FH(u)h FK(and)g FH(v)j FK(dep)r(end)c(on)i(the)e(same)g(v)l(ariables;)k(indeed,)339 2209 y(the)f(c)n(hoice)g(of)g(v)l(ariables)g(of)h FH(u)f FK(and)i FH(v)h FK(is)c(correlated,)j(b)r(ecause)e(some)g(parcels)g(of) 339 2294 y(h)n(yp)r(otheses)29 b(will)c(b)r(e)j(iden)n(ti\014ed.)251 2440 y(3.)35 b(If)46 b(a)g(deduction)g(ends)g(in)g FJ(^)p FK(1)p FJ(E)6 b FK(,)51 b(and)c FH(t)p FK([)p FH(x)1570 2451 y FD(1)1598 2440 y FH(;)12 b(:)g(:)g(:)g(;)g(x)1792 2451 y Fw(n)1825 2440 y FK(])46 b(w)n(as)g(asso)r(ciated)g(with)f(the) 339 2525 y(immediate)f(sub-deduction,)51 b(then)46 b(w)n(e)f(shall)h (asso)r(ciate)g FH(\031)2035 2500 y FD(1)2062 2525 y FH(t)p FK([)p FH(x)2145 2536 y FD(1)2173 2525 y FH(;)12 b(:)g(:)g(:)g(;)g(x)2367 2536 y Fw(n)2400 2525 y FK(])46 b(to)h(our)339 2610 y(pro)r(of.)c(That)30 b(is)f(the)h FM(\014rst)f(pr)l(oje)l(ction)p FK(,)j(since)c FH(t)p FK(,)j(as)f(a)g(pro)r(of)h(of)f(a)g(conjunction,)h(has)339 2695 y(to)d(b)r(e)g(a)g(pair.)35 b(Lik)n(ewise,)26 b(the)h FJ(^)p FK(2)p FJ(E)35 b FK(rule)26 b(in)n(v)n(olv)n(es)i(the)f FM(se)l(c)l(ond)i(pr)l(oje)l(ction)k FH(\031)2459 2670 y FD(2)2487 2695 y FK(.)339 2853 y(Although)46 b(this)e(is)h(not)g(v)n (ery)g(formal,)k(it)44 b(will)e(b)r(e)j(necessary)h(to)f(consider)f (the)339 2939 y(fundamen)n(tal)29 b(equations:)637 3146 y FH(\031)679 3120 y FD(1)707 3146 y FJ(h)p FH(u;)12 b(v)s FJ(i)20 b FK(=)f FH(u)299 b(\031)1340 3120 y FD(2)1367 3146 y FJ(h)p FH(u;)12 b(v)s FJ(i)20 b FK(=)g FH(v)300 b FJ(h)p FH(\031)2023 3120 y FD(1)2051 3146 y FH(t;)12 b(\031)2149 3120 y FD(2)2177 3146 y FH(t)p FJ(i)20 b FK(=)f FH(t)339 3353 y FK(These)25 b(equations)h(\(and)f(the)g(similar) d(ones)k(w)n(e)e(shall)g(ha)n(v)n(e)i(o)r(ccasion)f(to)g(write)e(do)n (wn\))339 3438 y(are)28 b(the)f(essence)g(of)h(the)g(corresp)r(ondence) g(b)r(et)n(w)n(een)f(logic)f(and)j(computer)e(science.)251 3584 y(4.)35 b(If)26 b(a)g(deduction)g(ends)h(in)e FJ(\)I)5 b FK(,)27 b(let)e FH(v)j FK(b)r(e)e(the)g(term)e(asso)r(ciated)i(with)f (the)h(immediate)339 3669 y(sub-deduction;)39 b(this)33 b(immediate)f(sub-deduction)j(is)e(unam)n(biguously)j(determined)339 3754 y(at)d(the)g(lev)n(el)e(of)i(parcels)f(of)h(h)n(yp)r(otheses,)j(b) n(y)d(sa)n(ying)h(that)f(a)h(whole)e FH(A)p FK(-parcel)f(has)339 3840 y(b)r(een)h(disc)n(harged.)48 b(If)32 b FH(x)g FK(is)f(a)h(v)l (ariable)g(asso)r(ciated)g(to)g(this)f(parcel,)h(then)g(w)n(e)f(ha)n(v) n(e)339 3925 y(a)e(function)g FH(v)s FK([)p FH(x;)12 b(x)842 3936 y FD(1)870 3925 y FH(;)g(:)g(:)g(:)g(;)g(x)1064 3936 y Fw(n)1097 3925 y FK(].)38 b(W)-6 b(e)28 b(shall)g(asso)r(ciate)h (to)f(our)h(deduction)g(the)f(function)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 12 15 bop 167 167 a FK(12)1139 b Fz(CHAPTER)27 b(2.)63 b(NA)-6 b(TURAL)26 b(DEDUCTION)339 404 y FH(t)p FK([)p FH(x)422 415 y FD(1)451 404 y FH(;)12 b(:)g(:)g(:)f(;)h(x)644 415 y Fw(n)677 404 y FK(])42 b(whic)n(h)f(maps)g(eac)n(h)h(argumen)n(t) g FH(a)f FK(of)h FH(A)f FK(to)h FH(v)s FK([)p FH(a;)12 b(x)2184 415 y FD(1)2212 404 y FH(;)g(:)g(:)g(:)f(;)h(x)2405 415 y Fw(n)2439 404 y FK(].)76 b(The)339 490 y(notation)29 b(is)e FH(\025x:)12 b(v)s FK([)p FH(x;)g(x)968 501 y FD(1)996 490 y FH(;)g(:)g(:)g(:)g(;)g(x)1190 501 y Fw(n)1223 490 y FK(])28 b(in)f(whic)n(h)g FH(x)h FK(is)f(b)r(ound.)339 604 y(Observ)n(e)h(that)g FM(binding)f FK(corresp)r(onds)i(to)e FM(dischar)l(ge)p FK(.)251 748 y(5.)35 b(The)30 b(case)f(of)h(a)g (deduction)g(ending)g(with)f FJ(\)E)36 b FK(is)29 b(treated)g(b)n(y)h (considering)f(the)h(t)n(w)n(o)339 833 y(functions)40 b FH(t)p FK([)p FH(x)736 844 y FD(1)764 833 y FH(;)12 b(:)g(:)g(:)g(;)g(x)958 844 y Fw(n)991 833 y FK(])39 b(and)h FH(u)p FK([)p FH(x)1296 844 y FD(1)1325 833 y FH(;)12 b(:)g(:)g(:)f(;)h(x)1518 844 y Fw(n)1552 833 y FK(],)42 b(asso)r(ciated)d(to)h(the)f(t)n(w)n(o)g(immediate)339 918 y(sub-deductions.)i(F)-6 b(or)30 b(\014xed)g(v)l(alues)f(of)h FH(x)1485 929 y FD(1)1513 918 y FH(;)12 b(:)g(:)g(:)f(;)h(x)1706 929 y Fw(n)1740 918 y FK(,)29 b FH(t)g FK(is)f(a)i(function)f(from)g FH(A)g FK(to)g FH(B)t FK(,)339 1003 y(and)g FH(u)f FK(is)f(an)h(elemen) n(t)e(of)i FH(A)p FK(,)f(so)i FH(t)p FK(\()p FH(u)p FK(\))e(is)g(in)g FH(B)t FK(;)h(in)f(other)g(w)n(ords)1122 1206 y FH(t)p FK([)p FH(x)1205 1217 y FD(1)1233 1206 y FH(;)12 b(:)g(:)g(:)f(;)h(x) 1426 1217 y Fw(n)1460 1206 y FK(])g FH(u)p FK([)p FH(x)1588 1217 y FD(1)1616 1206 y FH(;)g(:)g(:)g(:)g(;)g(x)1810 1217 y Fw(n)1843 1206 y FK(])339 1408 y(represen)n(ts)28 b(our)g(deduction)f(in)g(the)h(sense)f(of)i(Heyting.)339 1564 y(Here)e(again,)i(w)n(e)e(ha)n(v)n(e)h(the)g(equations:)853 1760 y(\()p FH(\025x:)12 b(v)s FK(\))g FH(u)58 b FK(=)h FH(v)s FK([)p FH(u=x)p FK(])918 1845 y FH(\025x:)12 b(t)g(x)58 b FK(=)h FH(t)78 b FK(\(when)27 b FH(x)h FK(is)f(not)h(free)f(in)g FH(t)p FK(\))270 2090 y(The)38 b(rules)f(for)h FJ(8)f FK(ec)n(ho)h(those)h(for)f FJ(\))p FK(:)56 b(they)38 b(do)h(not)f(add)h(m)n(uc)n(h,)i(so)d(w)n(e)g(shall)f(in)167 2175 y(future)30 b(omit)e(them)h(from)g(our)h(discussion.)42 b(On)29 b(the)g(other)h(hand,)i(w)n(e)d(shall)f(so)r(on)j(replace)167 2260 y(the)41 b(b)r(oring)i(\014rst-order)e(quan)n(ti\014er)h(b)n(y)h (a)f(second-order)g(quan)n(ti\014er)g(with)f(more)g(no)n(v)n(el)167 2345 y(prop)r(erties.)p eop PStoPSsaved restore %%Page: (16,17) 9 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 13 16 bop 167 167 a Fz(2.2.)64 b(COMPUT)-6 b(A)g(TIONAL)26 b(SIGNIFICANCE)1093 b FK(13)167 404 y Fy(2.2.2)95 b(Iden)m (ti\014cation)28 b(of)g(deductions)167 535 y FK(Returning)h(to)h (natural)f(deduction,)h(the)f(equations)i(w)n(e)e(ha)n(v)n(e)h(written) e(lead)h(to)g(equations)167 620 y(b)r(et)n(w)n(een)e(deductions.)36 b(F)-6 b(or)28 b(example:)1039 810 y FJ(\001)1039 848 y(\001)1039 886 y(\001)1023 943 y FH(A)1240 810 y FJ(\001)1240 848 y(\001)1240 886 y(\001)1222 943 y FH(B)p 1023 988 255 4 v 1298 1003 a FJ(^I)1057 1064 y FH(A)15 b FJ(^)h FH(B)p 1057 1109 186 4 v 1264 1125 a FJ(^)p FK(1)p FJ(E)1124 1185 y FH(A)1526 926 y FK(\\equals")1934 931 y FJ(\001)1934 969 y(\001)1934 1007 y(\001)1918 1064 y FH(A)1039 1397 y FJ(\001)1039 1435 y(\001)1039 1472 y(\001)1023 1530 y FH(A)1240 1397 y FJ(\001)1240 1435 y(\001)1240 1472 y(\001)1222 1530 y FH(B)p 1023 1574 255 4 v 1298 1590 a FJ(^I)1057 1651 y FH(A)f FJ(^)h FH(B)p 1057 1696 186 4 v 1264 1712 a FJ(^)p FK(2)p FJ(E)1122 1772 y FH(B)1526 1513 y FK(\\equals")1936 1518 y FJ(\001)1936 1556 y(\001)1936 1594 y(\001)1918 1651 y FH(B)854 2175 y FJ(\001)854 2213 y(\001)854 2251 y(\001)838 2308 y FH(A)1100 1995 y FK([)p FH(A)p FK(])1136 2054 y FJ(\001)1136 2092 y(\001)1136 2130 y(\001)1117 2187 y FH(B)p 1037 2232 218 4 v 1275 2248 a FJ(\)I)1037 2308 y FH(A)j FJ(\))h FH(B)p 838 2353 417 4 v 1275 2369 a FJ(\)E)1018 2430 y FH(B)1526 2135 y FK(\\equals")1936 2053 y FJ(\001)1936 2091 y(\001)1936 2129 y(\001)1920 2186 y FH(A)1936 2227 y FJ(\001)1936 2265 y(\001)1936 2303 y(\001)1918 2360 y FH(B)167 2613 y FK(What)30 b(w)n(e)f(ha)n(v)n(e)h(written)e(is)h(clear,)f(pro)n (vided)i(that)g(w)n(e)f(observ)n(e)h(carefully)e(what)i(happ)r(ens)167 2699 y(in)35 b(the)g(last)g(case:)51 b FM(al)t(l)42 b FK(the)35 b(disc)n(harged)h(h)n(yp)r(otheses)h(are)e(replaced)g(b)n(y)h (\(copies)f(of)5 b(\))35 b(the)167 2784 y(deduction)28 b(ending)f(in)h FH(A)p FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 14 17 bop 167 874 a FF(Chapter)28 b(3)167 1168 y(The)g(Curry-Ho)-5 b(w)g(ard)28 b(Isomorphism)167 1487 y FK(W)-6 b(e)27 b(ha)n(v)n(e)i(seen)f(that)g(Heyting's)g(ideas)f(p)r(erform)g(v)n(ery)h (w)n(ell)e(in)h(the)h(framew)n(ork)f(of)i(natural)167 1573 y(deduction.)36 b(W)-6 b(e)27 b(shall)g(exploit)g(this)g(remark)h (b)n(y)g(establishing)f(a)i FM(formal)f FK(system)f(of)i(t)n(yp)r(ed) 167 1658 y(terms)39 b(for)i(discussing)g(the)f(functional)g(ob)t(jects) g(whic)n(h)g(lie)f(b)r(ehind)h(the)g(pro)r(ofs.)75 b(The)167 1743 y(signi\014cance)30 b(of)h(the)f(system)g(will)d(b)r(e)j(giv)n(en) h(b)n(y)g(means)f(of)h(the)f(functional)g(equations)i(w)n(e)167 1828 y(ha)n(v)n(e)h(written)d(do)n(wn.)50 b(In)32 b(fact,)h(these)f (equations)h(ma)n(y)f(b)r(e)g(read)g(in)g(t)n(w)n(o)g(di\013eren)n(t)f (w)n(a)n(ys,)167 1913 y(whic)n(h)c(re-iterate)e(the)j(dic)n(hotom)n(y)g (b)r(et)n(w)n(een)f(sense)g(and)i(denotation:)270 2074 y FJ(\017)34 b FK(as)41 b(the)f FM(e)l(quations)g FK(whic)n(h)f (de\014ne)h(the)g(equalit)n(y)g(of)g(terms,)i(in)e(other)g(w)n(ords)g (the)339 2159 y(equalit)n(y)27 b(of)i(denotations)f(\(the)f FM(static)h FK(viewp)r(oin)n(t\).)270 2303 y FJ(\017)34 b FK(as)27 b FM(r)l(ewrite)f FK(rules)g(whic)n(h)f(allo)n(ws)h(us)h(to) f(calculate)f(terms)g(b)n(y)i(reduction)f(to)h(a)f(normal)339 2388 y(form.)64 b(That)37 b(is)f(an)i(op)r(erational,)i FM(dynamic)d FK(viewp)r(oin)n(t,)i(the)e(only)g(truly)f(fruitful)339 2474 y(view)27 b(for)h(this)f(asp)r(ect)h(of)g(logic.)270 2635 y(Of)37 b(course)g(the)f(second)i(viewp)r(oin)n(t)e(is)g (under-dev)n(elop)r(ed)h(b)n(y)g(comparison)g(with)f(the)167 2720 y(\014rst)44 b(one,)49 b(as)44 b(w)n(as)h(the)f(case)g(in)f (Logic!)84 b(F)-6 b(or)45 b(example)e FM(denotational)h FK(seman)n(tics)f(of)167 2805 y(programs)c(\(Scott's)e(seman)n(tics,)j (for)d(example\))g(ab)r(ound:)57 b(for)38 b(this)f(kind)h(of)g(seman)n (tics,)167 2890 y(nothing)h(c)n(hanges)g(throughout)i(the)d(execution)g (of)g(a)h(program.)68 b(On)38 b(the)g(other)h(hand,)167 2975 y(there)d(is)h(hardly)h(an)n(y)g(civilised)c FM(op)l(er)l(ational) 39 b FK(seman)n(tics)d(of)i(programs)g(\(w)n(e)e(exclude)h FM(ad)167 3060 y(ho)l(c)h FK(seman)n(tics)e(whic)n(h)h(crudely)g (paraphrase)i(the)e(steps)h(to)n(w)n(ard)g(normalisation\).)64 b(The)167 3146 y(establishmen)n(t)28 b(of)j(a)f(truly)f(op)r(erational) h(seman)n(tics)f(of)h(algorithms)g(is)f(p)r(erhaps)i(the)e(most)167 3231 y(imp)r(ortan)n(t)e(problem)g(in)g(computer)g(science.)270 3357 y(The)h(corresp)r(ondence)g(b)r(et)n(w)n(een)f(t)n(yp)r(es)h(and)g (prop)r(ositions)g(w)n(as)h(set)e(out)h(in)f([)p FG(?)q FK(].)1385 4101 y(14)p eop PStoPSsaved restore %%Page: (18,19) 10 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 15 18 bop 167 167 a Fz(3.1.)64 b(LAMBD)n(A)27 b(CALCULUS)1549 b FK(15)167 404 y FE(3.1)114 b(Lam)m(b)s(da)28 b(Calculus)167 601 y Fy(3.1.1)95 b(T)m(yp)s(es)167 753 y FK(When)48 b(w)n(e)f(think)g(of)h(pro)r(ofs)h(in)e(the)g(spirit)f(of)i(Heyting,)k (form)n(ulae)47 b(b)r(ecome)g FM(typ)l(es)p FK(.)167 839 y(Sp)r(eci\014cally:)251 1057 y(1.)35 b(A)n(tomic)26 b(t)n(yp)r(es)i FH(T)812 1068 y FD(1)841 1057 y FH(;)12 b(:)g(:)g(:)f(;)h(T)1035 1068 y Fw(n)1096 1057 y FK(are)28 b(t)n(yp)r(es.)251 1236 y(2.)35 b(If)28 b FH(U)35 b FK(and)28 b FH(V)44 b FK(are)27 b(t)n(yp)r(es,)h(then)g FH(U)7 b FJ(\002)p FH(V)43 b FK(and)29 b FH(U)7 b FJ(!)p FH(V)43 b FK(are)28 b(t)n(yp)r(es.)251 1415 y(3.)35 b(The)j(only)h(t)n(yp)r(es) f(are)h(\(for)f(the)g(time)e(b)r(eing\))i(those)h(obtained)f(b)n(y)h (means)g(of)f FG(??)339 1500 y FK(and)29 b FG(??)q FK(.)270 1718 y(This)40 b(corresp)r(onds)g(to)g(the)g(\()p FJ(^)p FH(;)12 b FJ(\))p FK(\))39 b(fragmen)n(t)h(of)g(prop)r(ositional)g (calculus:)58 b(atomic)167 1803 y(prop)r(ositions)43 b(are)g(written)e FH(T)1012 1814 y Fw(i)1032 1803 y FK(,)47 b(\\)p FJ(^)p FK(")c(b)r(ecomes)f(\\)p FJ(\002)q FK(")h(\(Cartesian)f (pro)r(duct\))h(and)h(\\)p FJ(\))p FK(")167 1888 y(b)r(ecomes)27 b(\\)p FJ(!)q FK(".)167 2143 y Fy(3.1.2)95 b(T)-8 b(erms)167 2295 y FK(Pro)r(ofs)27 b(b)r(ecome)f FM(terms)6 b FK(;)26 b(more)g(precisely)-6 b(,)25 b(a)i(pro)r(of)g(of)g FH(A)f FK(\(as)h(a)g(form)n(ula\))f(b)r(ecomes)f(a)i FM(term)167 2380 y(of)h(typ)l(e)g FH(A)g FK(\(as)g(a)g(t)n(yp)r(e\).)35 b(Sp)r(eci\014cally:)251 2598 y(1.)g(The)28 b(v)l(ariables)f FH(x)815 2573 y Fw(T)815 2616 y FD(0)854 2598 y FH(;)12 b(:)g(:)g(:)g(;)g(x)1048 2573 y Fw(T)1048 2616 y(n)1087 2598 y FH(;)g(:)g(:)g(:)27 b FK(are)h(terms)e(of)j(t)n(yp)r(e)e FH(T)10 b FK(.)251 2778 y(2.)35 b(If)27 b FH(u)h FK(and)g FH(v)i FK(are)c(terms)g(of)i(t)n(yp)r(es)f(resp)r(ectiv)n(ely)e FH(U)34 b FK(and)28 b FH(V)16 b FK(,)27 b(then)g FJ(h)p FH(u;)12 b(v)s FJ(i)28 b FK(is)e(a)i(term)e(of)339 2863 y(t)n(yp)r(e)i FH(U)7 b FJ(\002)p FH(V)16 b FK(.)251 3042 y(3.)35 b(If)27 b FH(t)f FK(is)g(a)h(term)e(of)i(t)n(yp)r(e)g FH(U)7 b FJ(\002)p FH(V)42 b FK(then)27 b FH(\031)1400 3016 y FD(1)1427 3042 y FH(t)g FK(and)g FH(\031)1658 3016 y FD(2)1686 3042 y FH(t)f FK(are)h(terms)e(of)i(t)n(yp)r(es)g (resp)r(ectiv)n(ely)339 3127 y FH(U)35 b FK(and)29 b FH(V)15 b FK(.)251 3306 y(4.)35 b(If)25 b FH(v)i FK(is)d(a)h(term)e(of) i(t)n(yp)r(e)g FH(V)40 b FK(and)26 b FH(x)1258 3281 y Fw(U)1258 3324 y(n)1324 3306 y FK(is)e(a)h(v)l(ariable)f(of)h(t)n(yp)r (e)g FH(U)32 b FK(then)24 b FH(\025x)2267 3281 y Fw(U)2267 3324 y(n)2309 3306 y FH(:)12 b(v)28 b FK(is)23 b(a)i(term)339 3391 y(of)h(t)n(yp)r(e)g FH(U)7 b FJ(!)q FH(V)15 b FK(.)35 b(In)26 b(general)f(w)n(e)g(shall)f(supp)r(ose)j(that)f(w)n(e)f(ha)n(v) n(e)i(settled)d(questions)i(of)339 3476 y(the)j(c)n(hoice)g(of)h(b)r (ound)h(v)l(ariables)e(and)h(of)g(substitution,)g(b)n(y)g(some)f(means) g(or)h(other,)339 3562 y(whic)n(h)h(allo)n(ws)g(us)i(to)e(disregard)h (the)g(names)g(of)g(b)r(ound)h(v)l(ariables,)g(the)e(idea)g(b)r(eing) 339 3647 y(that)d(a)h(b)r(ound)g(v)l(ariable)e(has)i(no)f(individualit) n(y)-6 b(.)251 3826 y(5.)35 b(If)c FH(t)f FK(and)h FH(u)g FK(are)f(terms)f(of)i(t)n(yp)r(es)g(resp)r(ectiv)n(ely)d FH(U)7 b FJ(!)q FH(V)46 b FK(and)31 b FH(U)7 b FK(,)31 b(then)g FH(t)12 b(u)30 b FK(is)g(a)g(term)339 3911 y(of)f(t)n(yp)r(e)e FH(V)16 b FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 16 19 bop 167 167 a FK(16)639 b Fz(CHAPTER)26 b(3.)63 b(THE)27 b(CURR)-6 b(Y-HO)n(W)e(ARD)26 b(ISOMORPHISM)167 404 y FE(3.2)114 b(Denotational)30 b(signi\014cance)167 567 y FK(T)n(yp)r(es)k(represen)n(t)f(the)h(kind)g(of)g(ob)t(ject)g (under)g(discussion.)54 b(F)-6 b(or)34 b(example)f(an)i(ob)t(ject)f(of) 167 652 y(t)n(yp)r(e)28 b FH(U)7 b FJ(!)p FH(V)43 b FK(is)27 b(a)h(function)g(from)f FH(U)35 b FK(to)28 b FH(V)15 b FK(,)28 b(and)h(an)f(ob)t(ject)f(of)h(t)n(yp)r(e)g FH(U)7 b FJ(\002)p FH(V)43 b FK(is)27 b(an)h(ordered)167 737 y(pair)34 b(consisting)g(of)h(an)g(ob)t(ject)f(of)h FH(U)42 b FK(and)35 b(an)h(ob)t(ject)e(of)h FH(V)15 b FK(.)56 b(The)34 b(meaning)g(of)h(atomic)167 822 y(t)n(yp)r(es)28 b(is)f(not)h(imp)r(ortan)n(t)f(|)h(it)f(dep)r(ends)h(on)g(the)g(con)n (text.)270 1024 y(The)42 b(terms)f(follo)n(w)h(v)n(ery)g(precisely)e (the)i(\014v)n(e)h(sc)n(hemes)e(whic)n(h)g(w)n(e)h(ha)n(v)n(e)h(used)g (for)167 1109 y(Heyting)27 b(seman)n(tics)g(and)h(natural)g(deduction.) 251 1290 y(1.)35 b(A)28 b(v)l(ariable)g FH(x)722 1265 y Fw(T)790 1290 y FK(of)h(t)n(yp)r(e)f FH(T)38 b FK(represen)n(ts)28 b(an)n(y)i(term)d FH(t)h FK(of)h(t)n(yp)r(e)f FH(T)39 b FK(\(pro)n(vided)28 b(that)h FH(x)2633 1265 y Fw(T)339 1375 y FK(is)e(replaced)g(b)n(y)h FH(t)p FK(\).)251 1531 y(2.)35 b FJ(h)p FH(u;)12 b(v)s FJ(i)29 b FK(is)e(the)g(ordered)h(pair) f(of)h FH(u)g FK(and)h FH(v)s FK(.)251 1687 y(3.)35 b FH(\031)381 1661 y FD(1)409 1687 y FH(t)27 b FK(and)i FH(\031)642 1661 y FD(2)670 1687 y FH(t)e FK(are)h(resp)r(ectiv)n(ely)d (the)j(\014rst)f(and)i(second)f(pro)t(jection)f(of)i FH(t)p FK(.)251 1843 y(4.)35 b FH(\025x)418 1817 y Fw(U)461 1843 y FH(:)12 b(v)30 b FK(is)e(the)g(function)g(whic)n(h)g(to)g(an)n (y)h FH(u)g FK(of)g(t)n(yp)r(e)f FH(U)35 b FK(asso)r(ciates)29 b FH(v)s FK([)p FH(u=x)p FK(],)g(that)g(is)e FH(v)339 1928 y FK(in)g(whic)n(h)g FH(x)665 1902 y Fw(U)735 1928 y FK(is)g(regarded)h(as)g(an)h(abbreviation)f(for)g FH(u)p FK(.)251 2084 y(5.)35 b FH(t)12 b(u)28 b FK(is)f(the)g(result)g(of)h (applying)g(the)g(function)f FH(t)h FK(to)g(the)f(argumen)n(t)h FH(u)p FK(.)270 2315 y(Denotationally)-6 b(,)28 b(w)n(e)f(ha)n(v)n(e)i (the)e(follo)n(wing)g(\()p FM(primary)p FK(\))h(equations)466 2518 y FH(\031)508 2492 y FD(1)535 2518 y FJ(h)p FH(u;)12 b(v)s FJ(i)21 b FK(=)e FH(u)299 b(\031)1169 2492 y FD(2)1197 2518 y FJ(h)p FH(u;)12 b(v)s FJ(i)20 b FK(=)f FH(v)302 b FK(\()p FH(\025x)1891 2492 y Fw(U)1933 2518 y FH(:)12 b(v)s FK(\))p FH(u)19 b FK(=)h FH(v)s FK([)p FH(u=x)p FK(])167 2720 y(together)28 b(with)e(the)i FM(se)l(c)l(ondary)h FK(equations)556 2922 y FJ(h)p FH(\031)625 2896 y FD(1)653 2922 y FH(t;)12 b(\031)751 2896 y FD(2)778 2922 y FH(t)p FJ(i)20 b FK(=)f FH(t)389 b(\025x)1416 2896 y Fw(U)1458 2922 y FH(:)12 b(t)g(x)20 b FK(=)f FH(t)78 b FK(\()p FH(x)28 b FK(not)g(free)f(in)g FH(t)p FK(\))167 3124 y(whic)n(h)g(ha)n(v)n(e)i(nev)n(er)e(b)r(een)g(giv)n(en)h(adequate)h (status.)167 3326 y FG(Theorem)e FK(The)g(system)h(giv)n(en)f(b)n(y)i (these)e(equations)h(is)f(consisten)n(t)h(and)g(decidable.)270 3529 y(By)33 b FM(c)l(onsistent)p FK(,)h(w)n(e)e(mean)g(that)h(the)g (equalit)n(y)f FH(x)23 b FK(=)f FH(y)s FK(,)34 b(where)d FH(x)i FK(and)h FH(y)g FK(are)f(distinct)167 3614 y(v)l(ariables,)28 b(cannot)g(b)r(e)g(pro)n(v)n(ed.)270 3754 y(Although)45 b(this)f(result)e(holds)j(for)f(the)g(whole)f(set)h(of)h(equations,)k (one)44 b(only)h(ev)n(er)167 3840 y(considers)31 b(the)h(\014rst)g (three.)46 b(It)32 b(is)f(a)h(consequence)g(of)g(the)f FM(Chur)l(ch-R)l(osser)i(pr)l(op)l(erty)40 b FK(and)167 3925 y(the)27 b FM(normalisation)i(the)l(or)l(em)f FK(\(c)n(hapter)g FG(??)q FK(\).)p eop PStoPSsaved restore %%Page: (20,21) 11 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 17 20 bop 167 167 a Fz(3.3.)64 b(OPERA)-6 b(TIONAL)26 b(SIGNIFICANCE)1204 b FK(17)167 404 y FE(3.3)114 b(Op)s(erational)29 b(signi\014cance)167 560 y FK(In)22 b(general,)h FM(terms)g FK(will)c(represen)n(t)i FM(pr)l(o)l(gr)l(ams)p FK(.)36 b(The)22 b(purp)r(ose)i(of)e(a)h(program)g(is)e(to)i(calculate)167 645 y(\(or)32 b(at)g(least)g(put)g(in)f(a)i(con)n(v)n(enien)n(t)f (form\))f(its)g(denotation.)50 b(The)31 b FM(typ)l(e)i FK(of)g(a)f(program)h(is)167 730 y(seen)e(as)h(a)g FM(sp)l(e)l(ci\014c) l(ation)p FK(,)h FM(i.e.)e FK(what)h(the)f(program)h(\(abstractly\))f (do)r(es.)47 b FM(A)32 b(priori)g FK(it)e(is)h(a)167 815 y(commen)n(tary)c(of)h(the)g(form)f(\\this)h(program)g(calculates)e (the)i(sum)f(of)i(t)n(w)n(o)e(in)n(tegers".)270 942 y(What)j(is)e(the)h (relev)l(an)n(t)f(part)h(of)h(this)e(commen)n(tary?)38 b(In)29 b(other)g(w)n(ords,)h(when)f(w)n(e)f(giv)n(e)167 1028 y(this)k(kind)g(of)h(information,)g(are)f(w)n(e)g(b)r(eing)g FM(su\016ciently)f FK(precise)f(|)j(for)f(example,)h(ough)n(t)167 1113 y(one)27 b(to)f(sa)n(y)h(in)f(what)g(w)n(a)n(y)h(this)f (calculation)e(is)i(done?)35 b(Or)25 b FM(to)l(o)i FK(precise)e(|)h(is) f(it)g(enough)j(to)167 1198 y(sa)n(y)h(that)f(the)f(program)i(tak)n(es) f(t)n(w)n(o)g(in)n(tegers)f(as)h(argumen)n(ts)g(and)h(returns)e(an)i (in)n(teger?)270 1325 y(In)38 b(terms)d(of)j(syn)n(tax,)j(the)c(answ)n (er)g(is)f(not)h(clear:)53 b(for)37 b(example)f(the)h(t)n(yp)r(e)g (systems)167 1410 y(en)n(visaged)52 b(in)f(this)g(b)r(o)r(ok)i(concern) e(themselv)n(es)g(only)g(with)g(the)g(most)h(elemen)n(tary)167 1495 y(information)36 b(\(sending)h(in)n(tegers)e(to)i(in)n(tegers\),)h (whereas)e(some)h(systems,)i(suc)n(h)e(as)g(that)167 1580 y(of)31 b([)p FG(?)q FK(],)g(giv)n(e)f(information)g(ab)r(out)i (what)f(the)f(program)h(calculates,)f FM(i.e.)h FK(information)f(of)h (a)167 1665 y(denotational)d(kind.)270 1793 y(A)n(t)i(a)g(more)g (general)f(lev)n(el,)g(abstracting)i(a)n(w)n(a)n(y)g(from)f(an)n(y)h(p) r(eculiar)d(syn)n(tactic)i(c)n(hoice,)167 1878 y(one)40 b(should)g(see)f(a)h(t)n(yp)r(e)g(as)g(an)g(instruction)f(for)h FM(plugging)e FK(things)h(together.)72 b(Let)39 b(us)167 1963 y(imagine)g(that)i(w)n(e)f(program)h(with)f FM(mo)l(dules)p FK(,)k FM(i.e.)d FK(closed)f(units,)j(whic)n(h)d(w)n(e)g(can)h(plug)167 2048 y(together.)52 b(A)33 b(mo)r(dule)g(is)f(absolutely)h(closed,)i(w) n(e)d(ha)n(v)n(e)i(no)g(righ)n(t)f(to)h(op)r(en)g(it.)51 b(W)-6 b(e)33 b(just)167 2133 y(ha)n(v)n(e)26 b(the)f(abilit)n(y)e(to)i (use)g(it)f(or)h(not,)i(and)f(to)f(c)n(ho)r(ose)g(the)g(manner)g(of)g (use)g(\(plugging\).)35 b(The)167 2218 y(t)n(yp)r(e)28 b(of)g(a)h(mo)r(dule)e(is)g(of)h(course)g(completely)d(determined)h(b)n (y)j(all)d(the)i(p)r(ossible)f FM(pluggings)167 2303 y FK(it)36 b(allo)n(ws)h(without)g(crashing.)64 b(In)38 b(particular,)g(one)g(can)g(alw)n(a)n(ys)f(substitute)g(a)h(mo)r(dule) 167 2388 y(with)30 b(another)i(of)f(the)g(same)g(t)n(yp)r(e,)h(in)e (the)h(ev)n(en)n(t)g(of)h(a)f(breakdo)n(wn,)j(or)d(for)g(the)g(purp)r (ose)167 2474 y(of)d(optimisation.)270 2601 y(This)38 b(idea)f(of)i FM(arbitr)l(ary)g(pluggings)e FK(seems)g FM(mathematisable)p FK(,)k(but)d(to)g(attempt)g(this)167 2686 y(w)n(ould)28 b(lead)f(us)h(to)r(o)g(far)g(astra)n(y)-6 b(.)270 2861 y(A)35 b(term)e(of)i(t)n(yp)r(e)f FH(T)10 b FK(,)36 b(sa)n(y)g FH(t)p FK(,)g(whic)n(h)e(dep)r(ends)h(on)g(v)l (ariables)f FH(x)2035 2872 y FD(1)2064 2861 y FH(;)12 b(x)2134 2872 y FD(2)2162 2861 y FH(;)g(:)g(:)g(:)f(;)h(x)2355 2872 y Fw(n)2423 2861 y FK(of)35 b(t)n(yp)r(es)167 2946 y(resp)r(ectiv)n(ely)i FH(U)606 2957 y FD(1)634 2946 y FH(;)12 b(:)g(:)g(:)f(;)h(U)835 2957 y Fw(n)868 2946 y FK(,)42 b(should)e(b)r(e)e(seen)h(no)h(longer)f(as)g(the)g(result)f (of)h(substituting)167 3031 y(for)f FH(x)326 3042 y Fw(i)383 3031 y FK(the)f(terms)f FH(u)761 3042 y Fw(i)819 3031 y FK(of)i(t)n(yp)r(es)f FH(U)1155 3042 y Fw(i)1175 3031 y FK(,)j(but)e(as)g(a)f FM(plugging)f FK(instruction.)64 b(The)37 b(term)f(has)167 3117 y(places)31 b(\(sym)n(b)r(olised,)g (according)h(to)f(a)h(v)n(ery)f(ancien)n(t)g(tradition,)g(b)n(y)h(v)l (ariables\))f(in)g(whic)n(h)167 3202 y(w)n(e)k(can)h(plug)f FM(inputs)h FK(of)g(appropriate)g(t)n(yp)r(e:)51 b(for)36 b(example,)h(to)e(eac)n(h)h(o)r(ccurrence)e(of)i FH(x)2652 3213 y Fw(i)167 3287 y FK(corresp)r(onds)g(the)e(p)r(ossibilit)n(y)e (of)j(plugging)g(in)f(a)h(term)e FH(u)1783 3298 y Fw(i)1838 3287 y FK(of)i(t)n(yp)r(e)f FH(U)2141 3298 y Fw(i)2161 3287 y FK(,)i(the)e(same)g(term)167 3372 y(b)r(eing)26 b(sim)n(ultaneously)g(plugged)h(in)f(eac)n(h)h(instance.)34 b(But)27 b(also,)g FH(t)f FK(itself,)f(b)r(eing)h(of)h(t)n(yp)r(e)g FH(T)10 b FK(,)167 3457 y(is)31 b(a)h(plugging)g(instruction,)g(so)g (that)g(it)f(can)h(b)r(e)f(plugged)h(in)g(an)n(y)g(v)l(ariable)g FH(y)h FK(of)f(t)n(yp)r(e)g FH(T)167 3542 y FK(app)r(earing)d(in)e (another)h(term.)270 3669 y(This)i(w)n(a)n(y)h(of)g(seeing)e(v)l (ariables)h(and)h(v)l(alues)g(as)f(dual)h(asp)r(ects)f(of)h(the)f(same) f(plugging)167 3754 y(phenomenon,)36 b(allo)n(ws)c(us)i(to)f(view)f (the)h(execution)g(of)g(an)h(algorithm)f(as)g(a)h(symmetrical)167 3840 y(input/output)e(pro)r(cess.)46 b(The)31 b(true)g(op)r(erational)g (in)n(terpretation)f(of)h(the)g(sc)n(hemes)f(is)h(still)167 3925 y(in)c(an)h(em)n(bry)n(onic)f(state)h(\(see)f(app)r(endix)h FG(??)q FK(\).)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 18 21 bop 167 167 a FK(18)639 b Fz(CHAPTER)26 b(3.)63 b(THE)27 b(CURR)-6 b(Y-HO)n(W)e(ARD)26 b(ISOMORPHISM)270 404 y FK(F)-6 b(or)42 b(w)n(an)n(t)g(of)g(a)f(clearer)f(idea)g(of)i(ho) n(w)g(to)f(explain)g(the)g(terms)f(op)r(erationally)-6 b(,)45 b(w)n(e)167 490 y(ha)n(v)n(e)33 b(an)f FM(ad)g(ho)l(c)g FK(notion,)i(whic)n(h)d(is)g(not)h(so)g(bad:)45 b(w)n(e)31 b(shall)g(mak)n(e)g(the)h(equations)g(of)g FG(??)167 575 y FK(asymmetric)k(and)j(turn)f(them)f(in)n(to)g(rewrite)f(rules.)64 b(This)38 b FM(r)l(ewriting)43 b FK(ma)n(y)38 b(b)r(e)g(seen)f(as)167 660 y(an)e(em)n(bry)n(onic)e(program)i(calculating)e(the)h(terms)f(in)g (question.)56 b(That)34 b(is)f(not)i(to)r(o)g(bad,)167 745 y(b)r(ecause)23 b(the)f(op)r(erational)g(seman)n(tics)g(whic)n(h)f (w)n(e)h(lac)n(k)g(is)g(surely)g(v)n(ery)h(close)e(to)i(this)f(pro)r (cess)167 830 y(of)28 b(calculation,)f(itself)e(based)k(on)f(the)g (fundamen)n(tal)g(symmetries)d(of)j(logic.)270 956 y(So)j(one)e(could)g (hop)r(e)h(to)g(mak)n(e)f(progress)i(at)e(the)g(op)r(erational)g(lev)n (el)f(b)n(y)i(a)g(close)e(study)167 1041 y(of)g(normalisation.)167 1276 y FE(3.4)114 b(Con)m(v)m(ersion)167 1431 y FK(A)27 b(term)g(is)g FM(normal)35 b FK(if)26 b(none)j(of)f(its)f(subterms)g (is)g(of)h(the)g(form:)598 1603 y FH(\031)640 1578 y FD(1)668 1603 y FJ(h)p FH(u;)12 b(v)s FJ(i)432 b FH(\031)1302 1578 y FD(2)1329 1603 y FJ(h)p FH(u;)12 b(v)s FJ(i)432 b FK(\()p FH(\025x)2027 1578 y Fw(U)2069 1603 y FH(:)12 b(v)s FK(\))g FH(u)167 1776 y FK(A)27 b(term)g FH(t)g FM(c)l(onverts)g FK(to)h(a)g(term)f FH(t)1087 1750 y Fv(0)1131 1776 y FK(when)g(one)h(of)h(the)e(follo)n(wing)g(three)g (cases)g(holds:)471 1965 y FH(t)58 b FK(=)h FH(\031)709 1939 y FD(1)736 1965 y FJ(h)p FH(u;)12 b(v)s FJ(i)293 b FH(t)59 b FK(=)f FH(\031)1427 1939 y FD(2)1455 1965 y FJ(h)p FH(u;)12 b(v)s FJ(i)293 b FH(t)59 b FK(=)f(\()p FH(\025x)2210 1939 y Fw(U)2252 1965 y FH(:)12 b(v)s FK(\))p FH(u)454 2050 y(t)479 2025 y Fv(0)554 2050 y FK(=)59 b FH(u)467 b(t)1198 2025 y Fv(0)1273 2050 y FK(=)58 b FH(v)474 b(t)1917 2025 y Fv(0)1992 2050 y FK(=)58 b FH(v)s FK([)p FH(u=x)p FK(])167 2243 y FH(t)27 b FK(is)g(called)f(the)i FM(r)l(e)l(dex)g FK(and)g FH(t)960 2218 y Fv(0)1004 2243 y FK(the)g FM(c)l(ontr)l(actum)p FK(;)g(they)g(are)g(alw)n(a)n(ys)g(of) g(the)f(same)h(t)n(yp)r(e.)270 2416 y(A)f(term)e FH(u)i FM(r)l(e)l(duc)l(es)796 2390 y FD(1)851 2416 y FK(to)g(a)g(term)f FH(v)j FK(when)e(there)e(is)h(a)h(sequence)g(of)g(con)n(v)n(ersions)g (from)g FH(u)167 2501 y FK(to)e FH(v)s FK(,)h(that)f(is)f(a)h(sequence) g FH(u)20 b FK(=)f FH(t)1060 2512 y FD(0)1088 2501 y FH(;)k(t)1155 2512 y FD(1)1183 2501 y FH(;)12 b(:)g(:)g(:)f(;)h(t)1362 2512 y Fw(n)p Fv(\000)p FD(1)1459 2501 y FH(;)24 b(t)1527 2512 y Fw(n)1579 2501 y FK(=)19 b FH(v)28 b FK(suc)n(h)e(that)f(for)g FH(i)19 b FK(=)g(0)p FH(;)12 b FK(1)p FH(;)g(:)g(:)g(:)h(;)f(n)f FJ(\000)g FK(1,)167 2586 y FH(t)192 2597 y Fw(i)p FD(+1)305 2586 y FK(is)28 b(obtained)i(from)f FH(t)864 2597 y Fw(i)913 2586 y FK(b)n(y)h(replacing)e(a)i(redex)f(b)n(y)h(its)e(con)n(tractum.) 40 b(W)-6 b(e)29 b(write)e FH(u)21 b Fu( )g FH(v)167 2671 y FK(for)28 b(\\)p FH(u)g FK(reduces)f(to)h FH(v)s FK(":)36 b(\\)p Fu( )p FK(")29 b(is)e(re\015exiv)n(e)g(and)i(transitiv) n(e.)270 2843 y(A)j FM(normal)g(form)h(for)f FH(t)g FK(is)f(a)i(term)e FH(u)h FK(suc)n(h)g(that)h FH(t)22 b Fu( )h FH(u)33 b FK(and)g(whic)n(h)e(is)g(normal.)48 b(W)-6 b(e)167 2928 y(shall)27 b(see)g(in)g(the)g(follo)n(wing)g(c)n(hapter)h(that)g (normal)f(forms)h(exist)f(and)h(are)g(unique.)270 3101 y(W)-6 b(e)38 b(shall)f(w)n(an)n(t)h(to)g(discuss)g(normal)g(forms)f (in)g(detail,)i(and)g(for)f(this)g(purp)r(ose)g(the)167 3186 y(follo)n(wing)24 b(de\014nition,)g(whic)n(h)g(is)g(essen)n(tial)f (to)i(the)f(study)i(of)f FM(untyp)l(e)l(d)g FH(\025)p FK(-calculus,)f(is)g(useful:)167 3312 y FG(Lemma)h FK(A)i(term)g FH(t)g FK(is)g(normal)g(i\013)g(it)g(is)g(in)g FM(he)l(ad)h(normal)g (form)p FK(:)951 3484 y FH(\025x)1030 3495 y FD(1)1059 3484 y FH(:)12 b(\025x)1169 3495 y FD(2)1197 3484 y FH(:)23 b(:)12 b(:)g(:)g(\025x)1411 3495 y Fw(n)1445 3484 y FH(:)g(y)i(u)1563 3495 y FD(1)1602 3484 y FH(u)1641 3495 y FD(2)1681 3484 y FH(:)e(:)g(:)g(u)1813 3495 y Fw(m)167 3657 y FK(\(where)35 b FH(y)j FK(ma)n(y)-6 b(,)39 b(but)e(need)e(not,)k(b)r(e)d(one)h(of)f (the)g FH(x)1635 3668 y Fw(i)1655 3657 y FK(\),)i(and)f(moreo)n(v)n(er) f(the)g FH(u)2367 3668 y Fw(j)2429 3657 y FK(are)g(also)167 3742 y(normal.)p 167 3790 1003 3 v 246 3833 a FC(1)273 3854 y FB(A)29 b(term)h FA(c)m(onverts)k FB(in)29 b(one)g(step,)h FA(r)m(e)m(duc)m(es)35 b FB(in)28 b(man)n(y)-5 b(.)41 b(In)29 b(c)n(hapter)h Ft(??)f FB(w)n(e)i(shall)d(in)n(tro)r(duce)g(a)i (more)167 3925 y(abstract)e(notion)e(called)h FA(r)m(e)m(ducibility)p FB(,)i(and)e(the)g(reader)h(should)e(b)r(e)h(careful)g(to)h(a)n(v)n (oid)g(confusion.)p eop PStoPSsaved restore %%Page: (22,23) 12 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 19 22 bop 167 167 a Fz(3.5.)64 b(DESCRIPTION)26 b(OF)h(THE)g (ISOMORPHISM)936 b FK(19)167 404 y FG(Pro)r(of)29 b FK(By)g(induction)f (on)i FH(t)p FK(;)g(if)e(it)g(is)g(a)h(v)l(ariable)g(or)g(an)g (abstraction)h(there)e(is)g(nothing)i(to)167 490 y(do.)38 b(If)28 b(it)f(is)g(an)i(application,)e FH(t)20 b FK(=)g FH(uv)s FK(,)28 b(w)n(e)g(apply)h(the)e(induction)h(h)n(yp)r(othesis)h (to)f FH(u)p FK(,)h(whic)n(h)167 575 y(b)n(y)f(normalit)n(y)f(cannot)i (b)r(e)e(an)i(abstraction.)1245 b Fu(\003)167 840 y FG(Corollary)23 b FK(If)j(the)f(t)n(yp)r(es)h(of)h(the)e(free)g(v)l(ariables)g(of)i FH(t)e FK(are)h(strictly)d(simpler)h(than)i(the)g(t)n(yp)r(e)167 926 y(of)i FH(t)p FK(,)g(or)g(in)f(particular)f(if)h FH(t)h FK(is)f(closed,)g(then)h(it)e(is)h(an)h(abstraction.)612 b Fu(\003)167 1216 y FE(3.5)114 b(Description)28 b(of)f(the)i (isomorphism)167 1394 y FK(This)i(is)g(nothing)i(other)f(than)h(the)e (precise)g(statemen)n(t)g(of)h(the)g(corresp)r(ondence)g(b)r(et)n(w)n (een)167 1480 y(pro)r(ofs)44 b(and)f(functional)f(terms,)j(whic)n(h)d (can)h(b)r(e)f(done)h(in)f(a)h(precise)d(w)n(a)n(y)-6 b(,)48 b(no)n(w)43 b(that)167 1565 y(functional)30 b(terms)g(ha)n(v)n (e)h(a)g(precise)e(status.)45 b(On)31 b(one)g(side)f(w)n(e)g(ha)n(v)n (e)h(pro)r(ofs)h(with)e(parcels)167 1650 y(of)f(h)n(yp)r(otheses,)h (these)d(parcels)h(b)r(eing)g(lab)r(elled)e(b)n(y)j(in)n(tegers,)f(on)h (the)f(other)g(side)f(w)n(e)h(ha)n(v)n(e)167 1735 y(the)f(system)h(of)g (t)n(yp)r(ed)g(terms:)251 1958 y(1.)35 b(T)-6 b(o)29 b(the)e(deduction)106 b FH(A)f FK(\()p FH(A)27 b FK(in)h(parcel)e FH(i)p FK(\))h(corresp)r(onds)i(the)e(v)l(ariable)h FH(x)2413 1933 y Fw(A)2413 1975 y(i)2453 1958 y FK(.)251 2244 y(2.)35 b(T)-6 b(o)43 b(the)f(deduction)1071 2120 y FJ(\001)1071 2158 y(\001)1071 2196 y(\001)1055 2253 y FH(A)1272 2120 y FJ(\001)1272 2158 y(\001)1272 2196 y(\001)1254 2253 y FH(B)p 1055 2298 255 4 v 1330 2313 a FJ(^I)1089 2374 y FH(A)16 b FJ(^)f FH(B)1583 2244 y FK(corresp)r(onds)43 b FJ(h)p FH(u;)12 b(v)s FJ(i)43 b FK(where)f FH(u)g FK(and)h FH(v)339 2429 y FK(corresp)r(ond)29 b(to)f(the)f(deductions)h(of)g FH(A)g FK(and)g FH(B)t FK(.)251 2711 y(3.)35 b(T)-6 b(o)22 b(the)f(deduction)1033 2587 y FJ(\001)1033 2625 y(\001)1033 2663 y(\001)950 2720 y FH(A)15 b FJ(^)h FH(B)p 950 2765 186 4 v 1156 2780 a FJ(^)p FK(1)p FJ(E)1017 2841 y FH(A)1381 2711 y FK(\(resp)r(ectiv)n(ely)1943 2587 y FJ(\001)1943 2625 y(\001)1943 2663 y(\001)1859 2720 y FH(A)g FJ(^)f FH(B)p 1859 2765 V 2066 2780 a FJ(^)p FK(2)p FJ(E)1924 2841 y FH(B)2269 2711 y FK(\))21 b(corresp)r(onds)339 2903 y FH(\031)381 2877 y FD(1)409 2903 y FH(t)27 b FK(\(resp)r(ectiv)n (ely)f FH(\031)911 2877 y FD(2)938 2903 y FH(t)p FK(\),)i(where)f FH(t)g FK(corresp)r(onds)i(to)f(the)f(deduction)h(of)g FH(A)15 b FJ(^)h FH(B)t FK(.)251 3224 y(4.)35 b(T)-6 b(o)45 b(the)e(deduction)1127 3076 y([)p FH(A)p FK(])1162 3135 y FJ(\001)1162 3173 y(\001)1162 3211 y(\001)1144 3268 y FH(B)p 1063 3313 218 4 v 1301 3329 a FJ(\))q(I)1063 3389 y FH(A)19 b FJ(\))h FH(B)1582 3224 y FK(corresp)r(onds)45 b FH(\025x)2060 3198 y Fw(A)2060 3241 y(i)2101 3224 y FH(:)12 b(v)s FK(,)47 b(if)c(the)h(deleted)339 3444 y(h)n(yp)r(otheses) 29 b(form)f(parcel)e FH(i)p FK(,)i(and)g FH(v)j FK(corresp)r(onds)e(to) f(the)f(deduction)h(of)g FH(B)t FK(.)251 3726 y(5.)35 b(T)-6 b(o)30 b(the)e(deduction)993 3602 y FJ(\001)993 3640 y(\001)993 3678 y(\001)977 3735 y FH(A)1275 3602 y FJ(\001)1275 3640 y(\001)1275 3678 y(\001)1176 3735 y FH(A)19 b FJ(\))h FH(B)p 977 3780 417 4 v 1414 3796 a FJ(\)E)1157 3856 y FH(B)1639 3726 y FK(corresp)r(onds)30 b(the)e(term)g FH(t)12 b(u)p FK(,)29 b(where)f FH(t)339 3911 y FK(and)h FH(u)f FK(corresp)r(ond)h(to)e(the)h(deductions)g(of)g FH(A)19 b FJ(\))h FH(B)32 b FK(and)c FH(B)t FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 20 23 bop 167 167 a FK(20)639 b Fz(CHAPTER)26 b(3.)63 b(THE)27 b(CURR)-6 b(Y-HO)n(W)e(ARD)26 b(ISOMORPHISM)167 404 y FE(3.6)114 b(Relev)-6 b(ance)28 b(of)f(the)i(isomorphism)167 563 y FK(Strictly)35 b(sp)r(eaking,)41 b(what)c(w)n(as)h(de\014ned)g (in)e FG(??)i FK(is)f(a)h(bijection.)62 b(W)-6 b(e)37 b(cannot)h(sa)n(y)h(it)d(is)167 648 y(an)d(isomorphism:)42 b(this)32 b(requires)e(that)j(structures)e(of)h(the)g(same)f(kind)h (already)g(exist)f(on)167 733 y(either)26 b(side.)270 866 y(In)20 b(fact)f(the)h(tradition)e(of)i(normalisation)f(exists)g (indep)r(enden)n(tly)f(for)i(natural)g(deduction:)167 951 y(a)30 b(pro)r(of)i(is)d(normal)h(when)g(it)f(do)r(es)h(not)h(con)n (tain)f(an)n(y)h(sequence)f(of)h(an)f(in)n(tro)r(duction)g(and)167 1037 y(an)e(elimination)d(rule:)482 1221 y FJ(\001)482 1259 y(\001)482 1297 y(\001)466 1354 y FH(A)683 1221 y FJ(\001)683 1259 y(\001)683 1297 y(\001)665 1354 y FH(B)p 466 1399 255 4 v 741 1414 a FJ(^I)500 1475 y FH(A)15 b FJ(^)h FH(B)p 500 1520 186 4 v 707 1536 a FJ(^)p FK(1)p FJ(E)567 1596 y FH(A)1146 1221 y FJ(\001)1146 1259 y(\001)1146 1297 y(\001)1130 1354 y FH(A)1347 1221 y FJ(\001)1347 1259 y(\001)1347 1297 y(\001)1329 1354 y FH(B)p 1130 1399 255 4 v 1406 1414 a FJ(^I)1165 1475 y FH(A)f FJ(^)h FH(B)p 1165 1520 186 4 v 1371 1536 a FJ(^)p FK(2)p FJ(E)1230 1596 y FH(B)1811 1377 y FJ(\001)1811 1415 y(\001)1811 1453 y(\001)1795 1510 y FH(A)2058 1197 y FK([)p FH(A)p FK(])2093 1256 y FJ(\001)2093 1294 y(\001)2093 1332 y(\001)2075 1389 y FH(B)p 1994 1434 218 4 v 2232 1450 a FJ(\)I)1994 1510 y FH(A)j FJ(\))h FH(B)p 1795 1555 417 4 v 2232 1571 a FJ(\)E)1975 1632 y FH(B)270 1789 y FK(F)-6 b(or)27 b(eac)n(h)f(of)g(these)f(con\014gurations,)j(it)d(is)g(p)r(ossible)g (to)h(de\014ne)g(a)g(notion)g(of)g FM(c)l(onversion)p FK(.)167 1874 y(In)34 b(c)n(hapter)h FG(??)p FK(,)h(w)n(e)e FM(identi\014e)l(d)g FK(deductions)h(b)n(y)g(the)f(w)n(ord)g (\\equals";)39 b(w)n(e)34 b(no)n(w)h(consider)167 1959 y(these)29 b(iden)n(ti\014cations)e(as)j FM(r)l(ewriting)p FK(,)f(the)g(left)f(mem)n(b)r(er)f(of)i(the)g(equalit)n(y)f(b)r(eing)h (rewritten)167 2044 y(to)f(the)f(righ)n(t)h(one.)270 2177 y(That)f(w)n(e)e(ha)n(v)n(e)h(an)h(isomorphism)e(follo)n(ws)g (from)g(the)h(fact)g(that,)g(mo)r(dulo)g(the)f(bijection)167 2262 y(w)n(e)34 b(ha)n(v)n(e)h(already)g(in)n(tro)r(duced,)h(the)e (notions)h(of)f FM(c)l(onversion)p FK(,)i FM(normality)f FK(and)h FM(r)l(e)l(duction)167 2347 y FK(in)n(tro)r(duced)g(in)g(the)g (t)n(w)n(o)h(cases)f(\(and)i(indep)r(enden)n(tly)-6 b(,)38 b(from)e(the)h(historical)d(viewp)r(oin)n(t\))167 2433 y(corresp)r(ond)c(p)r(erfectly)-6 b(.)37 b(In)29 b(particular)f(the)g FM(normal)h(form)h(the)l(or)l(em)f FK(w)n(e)g(announced)h(in)e FG(??)167 2518 y FK(has)j(an)g(exact)f(coun)n(terpart)h(in)f(natural)g (deduction.)43 b(W)-6 b(e)30 b(shall)g(discuss)g(the)g(analogue)i(of) 167 2603 y FM(he)l(ad)c(normal)g(forms)h FK(in)e(section)g FG(??)p FK(.)270 2790 y(Ha)n(ving)34 b(said)e(this,)i(the)e(in)n (terest)f(in)h(an)h(isomorphism)f(lies)f(in)h(a)h(di\013erence)e(b)r (et)n(w)n(een)167 2875 y(the)24 b(t)n(w)n(o)g(participan)n(ts,)h (otherwise)e(what)i(is)f(the)g(p)r(oin)n(t)g(of)h(it?)32 b(In)25 b(the)f(case)g(whic)n(h)f(in)n(terests)167 2960 y(us,)43 b(the)c(functional)g(side)f(p)r(ossesses)j(an)f(op)r (erational)f(asp)r(ect)g(alien)f(to)i(formal)f(pro)r(ofs.)167 3045 y(The)29 b(pro)r(of)h(side)e(is)g(distinguished)g(b)n(y)i(its)e (logical)f(asp)r(ect,)j FM(a)f(priori)g FK(alien)f(to)h(algorithmic)167 3130 y(considerations.)270 3264 y(The)e(comparison)h(of)g(the)f(t)n(w)n (o)g(alien)f(viewp)r(oin)n(ts)h(has)h(some)f(deep)h(consequences)f (from)167 3349 y(a)h(metho)r(dological)e(p)r(oin)n(t)h(of)g(view)f (\(tec)n(hnically)f(none,)j(seen)f(at)g(the)g(w)n(eak)h(tec)n(hnical)d (lev)n(el)167 3434 y(of)j(the)g(t)n(w)n(o)f(traditions\):)270 3605 y FJ(\017)34 b FK(All)26 b(go)r(o)r(d)j(\(constructiv)n(e\))e (logic)f(m)n(ust)i(ha)n(v)n(e)g(an)h(op)r(erational)f(side.)270 3754 y FJ(\017)34 b FK(Con)n(v)n(ersely)-6 b(,)23 b(one)f(cannot)g(w)n (ork)f(with)g(t)n(yp)r(ed)g(calculi)e(without)h(regard)i(to)f(the)g (implicit)339 3840 y(symmetries,)35 b(whic)n(h)g(are)g(those)h(of)f (Logic.)58 b(In)36 b(general,)g(the)f(\\impro)n(v)n(emen)n(ts")h(of)339 3925 y(t)n(yping)29 b(based)f(on)h(logical)d(atro)r(cities)f(do)k(not)f (w)n(ork.)p eop PStoPSsaved restore %%Page: (24,25) 13 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 21 24 bop 167 167 a Fz(3.6.)64 b(RELEV)-8 b(ANCE)27 b(OF)g(THE)g (ISOMORPHISM)994 b FK(21)270 404 y(Basically)-6 b(,)41 b(the)e(t)n(w)n(o)g(sides)g(of)g(the)g(isomorphism)f(are)h(undoubtedly) h(the)f(the)f(same)167 490 y(ob)t(ject,)e(acciden)n(tally)c(represen)n (ted)i(in)g(t)n(w)n(o)g(di\013eren)n(t)f(w)n(a)n(ys.)57 b(It)33 b(seems,)j(in)d(the)h(ligh)n(t)g(of)167 575 y(recen)n(t)d(w)n (ork,)i(that)f(the)f(\\pro)r(of)5 b(")34 b(asp)r(ect)d(is)g(less)g (tied)f(to)i(con)n(tingen)n(t)g(in)n(tuitions,)f(and)i(is)167 660 y(the)j(w)n(a)n(y)h(in)f(whic)n(h)g(one)h(should)g FM(study)g FK(algorithms.)61 b(The)36 b(functional)h(asp)r(ect)f(is)g (more)167 745 y(elo)r(quen)n(t,)28 b(more)f(immediate,)d(and)29 b(should)g(b)r(e)e(k)n(ept)h(to)g(a)g(heuristic)e(r^)-34 b(ole.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 22 25 bop 167 874 a FF(Chapter)28 b(4)167 1168 y(The)g(Normalisation)e (Theorem)167 1487 y FK(This)39 b(c)n(hapter)g(concerns)g(the)g(t)n(w)n (o)g(results)g(whic)n(h)f(ensure)h(that)h(the)e(t)n(yp)r(ed)i FH(\025)p FK(-calculus)167 1573 y(b)r(eha)n(v)n(es)48 b(w)n(ell)c(computationally)-6 b(.)92 b(The)46 b FM(Normalisation)i (The)l(or)l(em)g FK(pro)n(vides)e(for)h(the)167 1658 y(existence)39 b(of)i(a)g(normal)g(form,)i(whilst)c(the)i FM(Chur)l(ch-R)l(osser)h FK(prop)r(ert)n(y)f(guaran)n(tees)h(its)167 1743 y(uniqueness.)e(In)29 b(fact)g(w)n(e)g(shall)f(simply)g(state)h (the)f(latter)g(without)h(pro)r(of,)h(since)e(it)g(is)h(not)167 1828 y(really)d(a)i(matter)f(of)h(t)n(yp)r(e)g(theory)g(and)h(is)e(w)n (ell)e(co)n(v)n(ered)j(in)f(the)g(literature,)f FM(e.g.)h FK([)p FG(?)q FK(].)270 1945 y(The)h(normalisation)f(theorem)g(has)h(t) n(w)n(o)g(forms:)270 2069 y FJ(\017)34 b FK(a)26 b FM(we)l(ak)33 b FK(one)26 b(\(there)f(is)g FM(some)h FK(terminating)e(strategy)i(for) g(normalisation\),)f(whic)n(h)g(w)n(e)339 2154 y(shall)i(pro)n(v)n(e)i (in)e(this)g(c)n(hapter,)270 2289 y FJ(\017)34 b FK(a)e FM(str)l(ong)37 b FK(one)31 b(\()p FM(al)t(l)e(p)l(ossible)i FK(strategies)f(for)h(normalisation)f(terminate\),)g(pro)n(v)n(ed)i(in) 339 2374 y(c)n(hapter)c FG(??)q FK(.)167 2604 y FE(4.1)114 b(The)28 b(Ch)m(urc)m(h-Rosser)g(prop)s(ert)m(y)167 2759 y FK(This)40 b(prop)r(ert)n(y)h(states)f(the)g(uniqueness)h(of)f(the)g (normal)g(form,)k(indep)r(enden)n(tly)39 b(of)i(its)167 2844 y(existence.)i(In)31 b(fact,)h(it)e(has)h(a)h(meaning)e(for)h (calculi)e(|)h(suc)n(h)i(as)f FM(untyp)l(e)l(d)39 b FH(\025)p FK(-calculus)30 b(|)167 2930 y(where)d(the)g(normalisation)g(theorem)g (is)g(false.)167 3084 y FG(Theorem)g FK(If)h FH(t)19 b Fu( )h FH(u;)12 b(v)31 b FK(one)d(can)g(\014nd)g FH(w)i FK(suc)n(h)e(that)g FH(u;)12 b(v)23 b Fu( )d FH(w)r FK(.)1407 3206 y FH(t)1233 3367 y(u)297 b(v)1394 3534 y(w)1327 3277 y Fs(\000)1286 3318 y(\000)-59 b(\011)1286 3444 y(@)1327 3485 y(@)g(R)1453 3277 y(@)1494 3318 y(@)g(R)1494 3444 y(\000)1453 3485 y(\000)g(\011)167 3685 y FG(Corollary)25 b FK(A)i(term)g FH(t)g FK(has)i(at)f(most)f(one)h(normal)g(form.)167 3840 y FG(Pro)r(of)j FK(If)g FH(t)22 b Fu( )h FH(u;)12 b(v)34 b FK(normal,)e(then)f FH(u;)12 b(v)25 b Fu( )d FH(w)34 b FK(for)d(some)g FH(w)r FK(,)h(but)g(since)e FH(u;)12 b(v)34 b FK(are)d(normal,)167 3925 y(they)d(cannot)g(b)r(e)g (reduced)f(except)g(to)h(themselv)n(es,)f(so)h FH(u)20 b FK(=)f FH(w)j FK(=)d FH(v)s FK(.)600 b Fu(\003)1385 4101 y FK(22)p eop PStoPSsaved restore %%Page: (26,27) 14 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 23 26 bop 167 167 a Fz(4.1.)64 b(THE)27 b(CHUR)n(CH-R)n(OSSER)f(PR)n (OPER)-6 b(TY)1068 b FK(23)270 404 y(The)32 b(Ch)n(urc)n(h-Rosser)h (theorem)e(is)h(rather)g(delicate)e(to)j(pro)n(v)n(e)g(\(at)f(least)f (if)h(w)n(e)g(try)g(to)167 490 y(do)27 b(it)d(b)n(y)j(brute)f(force\).) 34 b(It)26 b(can)g(b)r(e)g(stated)g(for)g(a)g(great)g(v)l(ariet)n(y)g (of)g(systems)g(and)h(its)e(pro)r(of)167 575 y(is)i(alw)n(a)n(ys)h(m)n (uc)n(h)g(the)f(same.)270 701 y(An)h(immediate)c(corollary)i(of)i(Ch)n (urc)n(h-Rosser)g(is)e(the)h FM(c)l(onsistency)g FK(of)h(the)f (calculus:)34 b(it)167 786 y(is)h(not)g(the)g(case)h(that)f(ev)n(ery)h (equation)g FH(u)25 b FK(=)f FH(v)39 b FK(\(with)34 b FH(u)h FK(and)i FH(v)h FK(of)d(the)g(same)h(t)n(yp)r(e\))f(is)167 871 y(deducible)26 b(from)i(the)f(equations)h(of)h FG(??)p FK(.)36 b(Indeed,)28 b(let)e(us)i(note)g(that:)270 1033 y FJ(\017)34 b FK(If)24 b FH(u)c Fu( )g FH(v)26 b FK(then)d(the)g (equalit)n(y)g FH(u)d FK(=)f FH(v)26 b FK(is)d(deriv)l(able)f(from)h FG(??)i FK(and)f(the)f(general)g(axioms)339 1118 y(for)28 b(equalit)n(y)-6 b(.)270 1261 y FJ(\017)34 b FK(Con)n(v)n(ersely)-6 b(,)35 b(if)d(from)g FG(??)h FK(and)h(the)f(axioms)f(for)h(equalit)n(y) f(one)h(can)g(deduce)g FH(u)23 b FK(=)g FH(v)s FK(,)339 1347 y(then)41 b(it)e(is)g(easy)i(to)f(see)g(that)g(there)g(are)g (terms)f FH(u)29 b FK(=)f FH(t)1961 1358 y FD(0)1988 1347 y FH(;)k(t)2064 1358 y FD(1)2091 1347 y FH(;)12 b(:)g(:)g(:)g(;)g(t)2271 1358 y FD(2)p Fw(n)p Fv(\000)p FD(1)2393 1347 y FH(;)31 b(t)2468 1358 y FD(2)p Fw(n)2554 1347 y FK(=)d FH(v)339 1432 y FK(suc)n(h)41 b(that,)j(for)c FH(i)28 b FK(=)g(0)p FH(;)12 b FK(1)p FH(;)g(:::;)g(n)20 b FJ(\000)f FK(1,)44 b(w)n(e)c(ha)n(v)n(e)h FH(t)1727 1443 y FD(2)p Fw(i)1771 1432 y FH(;)12 b(t)1827 1443 y FD(2)p Fw(i)p FD(+2)1964 1432 y Fu( )29 b FH(t)2088 1443 y FD(2)p Fw(i)p FD(+1)2197 1432 y FK(.)72 b(By)40 b(rep)r(eated)339 1517 y(application)24 b(of)h(the)f(Ch)n(urc)n (h-Rosser)h(theorem,)g(w)n(e)f(obtain)h(the)f(existence)f(of)i FH(w)i FK(suc)n(h)339 1602 y(that)h FH(u;)12 b(v)23 b Fu( )d FH(w)r FK(.)1480 2444 y FH(w)1465 1764 y(:)12 b(:)g(:)695 1777 y(u)20 b FK(=)f FH(t)852 1788 y FD(0)1145 1777 y FH(t)1170 1788 y FD(2)978 1944 y FH(t)1003 1955 y FD(1)1312 1944 y FH(t)1337 1955 y FD(3)879 1861 y Fs(@)904 1886 y(@)-59 b(R)1071 1861 y(\000)1046 1886 y(\000)g(\011)1213 1861 y(@)1238 1886 y(@)g(R)1046 2028 y(@)1071 2053 y(@)g(R)1238 2028 y(\000)1213 2053 y(\000)g(\011)1381 2362 y(@)1405 2387 y(@)g(R)1229 2177 y FJ(\001)1245 2194 y(\001)1262 2210 y(\001)2068 1777 y FH(t)2093 1788 y FD(2)p Fw(n)2171 1777 y FK(=)19 b FH(v)1766 1774 y(t)1791 1785 y FD(2)p Fw(n)p Fv(\000)p FD(2)1933 1941 y FH(t)1958 1952 y FD(2)p Fw(n)p Fv(\000)p FD(1)1599 1941 y FH(t)1624 1952 y FD(2)p Fw(n)p Fv(\000)p FD(3)2073 1861 y Fs(\000)2049 1886 y(\000)-59 b(\011)1882 1861 y(@)1906 1886 y(@)g(R)1739 1861 y(\000)1715 1886 y(\000)g(\011)1906 2028 y(\000)1882 2053 y(\000)g(\011)1715 2028 y(@)1739 2053 y(@)g(R)1572 2362 y(\000)1548 2387 y(\000)g(\011)1763 2177 y FJ(\001)1747 2194 y(\001)1730 2210 y(\001)339 2619 y FK(No)n(w,)25 b(if)f FH(u)g FK(and)h FH(v)i FK(are)c(t)n(w)n(o)i(distinct)d(normal)i(forms)g(of)g(the)g (same)g(t)n(yp)r(e)g(\(for)g(example)339 2704 y(t)n(w)n(o)34 b(distinct)e(v)l(ariables\))h(no)h(suc)n(h)f FH(w)j FK(exists,)e(so)g (the)f(equation)h FH(u)24 b FK(=)f FH(v)36 b FK(cannot)e(b)r(e)339 2790 y(pro)n(v)n(ed.)i(So)27 b(Ch)n(urc)n(h-Rosser)f(sho)n(ws)g(the)g (denotational)g(consistency)f(of)h(the)f(system.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 24 27 bop 167 167 a FK(24)776 b Fz(CHAPTER)26 b(4.)63 b(THE)27 b(NORMALISA)-6 b(TION)26 b(THEOREM)167 404 y FE(4.2)114 b(The)28 b(w)m(eak)h(normalisation)e(theorem)167 562 y FK(This)d(result)g(states)h(the)f FM(existenc)l(e)g FK(of)h(a)g(normal)g(form)f(|)h(whic)n(h)f(is)g(necessarily)f(unique)i (|)167 647 y(for)h(ev)n(ery)f(term.)33 b(Its)25 b(immediate)e (corollary)h(is)h(the)g FM(de)l(cidability)h FK(of)g(denotational)f (equalit)n(y)-6 b(.)167 732 y(Indeed)31 b(w)n(e)f(ha)n(v)n(e)i(seen)e (that)h(the)g(equation)g FH(u)22 b FK(=)f FH(v)34 b FK(is)c(pro)n(v)l (able)h(exactly)f(when)h FH(u;)12 b(v)25 b Fu( )d FH(w)167 818 y FK(for)36 b(some)f FH(w)r FK(;)40 b(but)c(suc)n(h)g FH(w)i FK(has)e(a)g(normal)f(form,)j(whic)n(h)d(then)g(b)r(ecomes)g (the)g(common)167 903 y(normal)h(form)g(for)h FH(u)f FK(and)i FH(v)s FK(.)61 b(T)-6 b(o)37 b(decide)e(the)h(denotational)h (equalit)n(y)f(of)g FH(u)h FK(and)g FH(v)j FK(w)n(e)167 988 y(pro)r(ceed)27 b(th)n(us:)270 1157 y FJ(\017)34 b FK(in)27 b(the)h(\014rst)g(step,)f(calculate)f(the)i(normal)f(forms)h (of)g FH(u)g FK(and)g FH(v)s FK(,)270 1306 y FJ(\017)34 b FK(in)27 b(the)h(second)g(step,)g(compare)f(them.)270 1475 y(There)37 b(is)f(p)r(erhaps)i(a)g(small)d(di\016cult)n(y)i (hidden)g(in)g(calculating)e(the)i(normal)g(forms,)167 1560 y(since)32 b(the)g(reduction)h(is)f(not)i(a)f(deterministic)c (algorithm.)50 b(That)34 b(is,)f(for)h(\014xed)f FH(t)p FK(,)h(man)n(y)167 1645 y(con)n(v)n(ersions)39 b(\(but)f(only)g(a)h (\014nite)e(n)n(um)n(b)r(er\))h(are)g(p)r(ossible)f(on)i(the)f (subterms)f(of)i FH(t)p FK(.)66 b(So)167 1730 y(the)42 b(theorem)f(states)h(the)f(p)r(ossibilit)n(y)f(of)j(\014nding)f(the)g (normal)f(form)h(b)n(y)g(appropriate)167 1815 y(con)n(v)n(ersions,)30 b(but)f(do)r(es)g(not)g(exclude)e(the)i(p)r(ossibilit)n(y)d(of)j(bad)h (reductions,)e(whic)n(h)g(do)i(not)167 1900 y(lead)d(to)h(a)g(normal)f (form.)36 b(That)28 b(is)f(wh)n(y)h(one)g(sp)r(eaks)h(of)f FM(we)l(ak)f(normalisation)p FK(.)270 2032 y(Ha)n(ving)g(said)e(that,)i (it)d(is)h(p)r(ossible)g(to)h(\014nd)h(the)e(normal)g(form)h(b)n(y)g (en)n(umerating)f(all)f(the)167 2117 y(reductions)29 b(in)h(one)g(step,)g(all)f(the)g(reductions)h(in)f(t)n(w)n(o)h(steps,)h (and)g(so)f(on)h(un)n(til)d(a)i(normal)167 2203 y(form)25 b(is)f(found.)36 b(This)25 b(inelegan)n(t)f(pro)r(cedure)h(is)f (justi\014ed)h(b)n(y)h(the)f(fact)g(that)g(there)g(are)g(only)167 2288 y(\014nitely)h(man)n(y)j(reductions)e(of)h(length)g FH(n)f FK(starting)h(from)f(a)i(\014xed)f(term)e FH(t)p FK(.)270 2420 y(The)31 b(strong)h(normalisation)e(theorem)f(will)f (simplify)h(the)h(situation)h(b)n(y)g(guaran)n(teeing)167 2505 y(that)26 b(all)d(normalisation)i(strategies)f(are)h(go)r(o)r(d,)j (in)c(the)h(sense)g(they)h(all)d(lead)i(to)h(the)e(normal)167 2590 y(form.)43 b(Ob)n(viously)-6 b(,)31 b(some)f(are)g(more)g (e\016cien)n(t)f(than)i(others,)g(in)f(terms)f(of)i(the)e(n)n(um)n(b)r (er)i(of)167 2675 y(steps,)d(but)g(if)f(one)h(ignores)g(this)f(\(essen) n(tial\))f(asp)r(ect,)h(one)h(alw)n(a)n(ys)h(gets)e(to)h(the)g(result!) 167 2917 y FE(4.3)114 b(Pro)s(of)27 b(of)h(the)g(w)m(eak)h (normalisation)e(theorem)167 3075 y FK(The)g FM(de)l(gr)l(e)l(e)h FH(@)t FK(\()p FH(T)10 b FK(\))28 b(of)g(a)g FM(typ)l(e)g FK(is)f(de\014ned)i(b)n(y:)270 3244 y FJ(\017)34 b FH(@)t FK(\()p FH(T)446 3255 y Fw(i)467 3244 y FK(\))19 b(=)g(1)28 b(if)f FH(T)756 3255 y Fw(i)804 3244 y FK(is)g(atomic.)270 3393 y FJ(\017)34 b FH(@)t FK(\()p FH(U)7 b FJ(\002)p FH(V)16 b FK(\))j(=)h FH(@)t FK(\()p FH(U)7 b FJ(!)p FH(V)16 b FK(\))j(=)g(max)q(\()p FH(@)t FK(\()p FH(U)7 b FK(\))p FH(;)12 b(@)t FK(\()p FH(V)j FK(\)\))g(+)h(1.)167 3607 y(The)27 b FM(de)l(gr)l(e)l(e)h FH(@)t FK(\()p FH(r)r FK(\))g(of)g(a)g FM(r)l(e)l(dex)g FK(is)f(de\014ned)h(b)n(y:)270 3776 y FJ(\017)34 b FH(@)t FK(\()p FH(\031)448 3750 y FD(1)476 3776 y FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(\))20 b(=)f FH(@)t FK(\()p FH(\031)865 3750 y FD(2)893 3776 y FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(\))20 b(=)f FH(@)t FK(\()p FH(U)7 b FJ(\002)p FH(V)16 b FK(\))27 b(where)g FH(U)7 b FJ(\002)p FH(V)43 b FK(is)27 b(the)h(t)n(yp)r(e)f(of)i FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(.)270 3925 y FJ(\017)34 b FH(@)t FK(\(\()p FH(\025x:)12 b(v)s FK(\))g FH(u)p FK(\))20 b(=)f FH(@)t FK(\()p FH(U)7 b FJ(!)q FH(V)15 b FK(\))28 b(where)e FH(U)7 b FJ(!)q FH(V)43 b FK(is)27 b(the)g(t)n(yp)r(e)h(of)g(\()p FH(\025x:)12 b(v)s FK(\).)p eop PStoPSsaved restore %%Page: (28,29) 15 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 25 28 bop 167 167 a Fz(4.3.)64 b(PR)n(OOF)27 b(OF)g(THE)g(WEAK)g (NORMALISA)-6 b(TION)26 b(THEOREM)442 b FK(25)167 404 y(The)27 b FM(de)l(gr)l(e)l(e)h FH(d)p FK(\()p FH(t)p FK(\))f(of)h(a)g FM(term)g FK(is)f(the)g(sup)h(of)g(the)g(degrees)f(of) h(the)f(redexes)g(it)g(con)n(tains.)36 b(By)167 490 y(con)n(v)n(en)n (tion,)29 b(a)f(normal)f(term)f(\()p FM(i.e.)i FK(one)g(con)n(taining)g (no)g(redex\))f(has)i(degree)e(0.)167 632 y FG(NB)49 b FK(A)24 b(redex)h FH(r)h FK(has)g(t)n(w)n(o)f(degrees:)33 b(one)25 b(as)g(redex,)h(another)f(as)g(term,)f(for)h(the)f(redex)h(ma) n(y)167 717 y(con)n(tain)f(others;)i(the)d(second)i(degree)e(is)h (greater)f(than)i(or)f(equal)g(to)g(the)g(\014rst:)34 b FH(@)t FK(\()p FH(r)r FK(\))19 b FJ(\024)g FH(d)p FK(\()p FH(r)r FK(\).)167 941 y Fy(4.3.1)95 b(Degree)28 b(and)f(substitution) 167 1080 y FG(Lemma)e FK(If)i FH(x)h FK(is)f(of)h(t)n(yp)r(e)g FH(U)35 b FK(then)28 b FH(d)p FK(\()p FH(t)p FK([)p FH(u=x)p FK(]\))20 b FJ(\024)f FK(max)q(\()p FH(d)p FK(\()p FH(t)p FK(\))p FH(;)12 b(d)p FK(\()p FH(u)p FK(\))p FH(;)g(@)t FK(\()p FH(U)7 b FK(\)\).)167 1286 y FG(Pro)r(of)28 b FK(Inside)f FH(t)p FK([)p FH(u=x)p FK(],)i(one)f(\014nds:)270 1469 y FJ(\017)34 b FK(the)28 b(redexes)f(of)h FH(t)g FK(\(in)f(whic)n(h)g FH(x)g FK(has)i(b)r(ecome)e FH(u)p FK(\))270 1626 y FJ(\017)34 b FK(the)28 b(redexes)f(of)h FH(u)g FK(\(proliferated)e(according)i(to)g(the)f(o)r(ccurrences)g(of)h FH(x)p FK(\))270 1784 y FJ(\017)34 b FK(p)r(ossibly)49 b(new)f(redexes,)53 b(in)48 b(the)g(case)h(where)e FH(x)i FK(app)r(ears)g(in)f(a)h(con)n(text)f FH(\031)2605 1758 y FD(1)2633 1784 y FH(x)339 1869 y FK(\(resp)r(ectiv)n(ely)35 b FH(\031)798 1843 y FD(2)825 1869 y FH(x)i FK(or)g FH(x)12 b(v)s FK(\))36 b(and)h FH(u)g FK(is)f FJ(h)p FH(u)1521 1843 y Fv(0)1538 1869 y FH(;)12 b(u)1608 1843 y Fv(00)1638 1869 y FJ(i)37 b FK(\(resp)r(ectiv)n(ely)d FJ(h)p FH(u)2184 1843 y Fv(0)2201 1869 y FH(;)12 b(u)2271 1843 y Fv(00)2301 1869 y FJ(i)37 b FK(or)g FH(\025y)s(:)12 b(u)2610 1843 y Fv(0)2626 1869 y FK(\).)339 1954 y(These)28 b(new)f(redexes)g(ha)n(v) n(e)i(the)e(degree)g(of)i FH(U)7 b FK(.)1016 b Fu(\003)167 2178 y Fy(4.3.2)95 b(Degree)28 b(and)f(con)m(v)m(ersion)167 2316 y FK(First)g(note)g(that,)i(if)d FH(r)k FK(is)d(a)h(redex)f(of)i (t)n(yp)r(e)e FH(T)10 b FK(,)28 b(then)g FH(@)t FK(\()p FH(r)r FK(\))19 b FH(>)h(@)t FK(\()p FH(T)10 b FK(\))27 b(\(ob)n(vious\).)167 2522 y FG(Lemma)e FK(If)i FH(t)20 b Fu( )g FH(u)28 b FK(then)f FH(d)p FK(\()p FH(u)p FK(\))20 b FJ(\024)f FH(d)p FK(\()p FH(t)p FK(\).)167 2728 y FG(Pro)r(of)33 b FK(W)-6 b(e)32 b(need)h(only)g(consider)f(the)g(case)h(where)f(there) g(is)g(only)h(one)g(con)n(v)n(ersion)g(step:)167 2813 y FH(u)f FK(is)f(obtained)h(from)f FH(t)g FK(b)n(y)i(replacing)d FH(r)k FK(b)n(y)e FH(c)p FK(.)47 b(The)31 b(situation)g(is)g(v)n(ery)h (close)f(to)h(that)g(of)167 2898 y(lemma)26 b FG(??)q FK(,)h FM(i.e.)h FK(in)f FH(u)h FK(w)n(e)f(\014nd:)270 3082 y FJ(\017)34 b FK(redexes)27 b(whic)n(h)f(w)n(ere)f(in)h FH(t)h FK(but)g(not)g(in)f FH(r)r FK(,)h(mo)r(di\014ed)g(b)n(y)g(the)f (replacemen)n(t)f(of)i FH(r)i FK(b)n(y)e FH(c)339 3167 y FK(\(whic)n(h)g(do)r(es)h(not)h(a\013ect)e(the)g(degree\),)270 3324 y FJ(\017)34 b FK(redexes)i(of)h FH(c)p FK(.)61 b(But)37 b FH(c)f FK(is)f(obtained)i(b)n(y)g(simpli\014cation)d(of)j FH(r)r FK(,)i(or)d(b)n(y)h(an)g(in)n(ternal)339 3409 y(substitution)j(in)g FH(r)r FK(:)60 b(\()p FH(\025x:)12 b(s)p FK(\))g FH(s)1190 3384 y Fv(0)1247 3409 y FK(b)r(ecomes)40 b FH(s)p FK([)p FH(s)1622 3384 y Fv(0)1639 3409 y FH(=x)p FK(])h(and)g(lemma)d FG(??)j FK(tells)d(us)j(that)339 3494 y FH(d)p FK(\()p FH(c)p FK(\))19 b FJ(\024)h FK(max\()p FH(d)p FK(\()p FH(s)p FK(\))p FH(;)12 b(d)p FK(\()p FH(s)956 3469 y Fv(0)972 3494 y FK(\))p FH(;)g(@)t FK(\()p FH(T)e FK(\)\),)27 b(where)g FH(T)38 b FK(is)27 b(the)g(t)n(yp)r(e)h(of)g FH(x)p FK(.)36 b(But)27 b FH(@)t FK(\()p FH(T)10 b FK(\))20 b FH(<)f(d)p FK(\()p FH(r)r FK(\),)27 b(so)339 3579 y FH(d)p FK(\()p FH(c)p FK(\))19 b FJ(\024)h FH(d)p FK(\()p FH(r)r FK(\).)270 3737 y FJ(\017)34 b FK(redexes)f(whic)n(h)g(come)f (from)h(the)g(replacemen)n(t)f(of)i FH(r)h FK(b)n(y)f FH(c)p FK(.)52 b(The)33 b(situation)g(is)f(the)339 3822 y(same)e(as)h(in)f(lemma)e FG(??)q FK(:)40 b(these)30 b(redexes)g(ha)n(v)n(e)h(degree)f(equal)g(to)g FH(@)t FK(\()p FH(T)10 b FK(\))30 b(where)g FH(T)40 b FK(is)339 3907 y(the)28 b(t)n(yp)r(e)g(of)g FH(r)r FK(,)f(and)i FH(@)t FK(\()p FH(T)10 b FK(\))20 b FH(<)f(@)t FK(\()p FH(r)r FK(\).)1310 b Fu(\003)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 26 29 bop 167 167 a FK(26)776 b Fz(CHAPTER)26 b(4.)63 b(THE)27 b(NORMALISA)-6 b(TION)26 b(THEOREM)167 404 y Fy(4.3.3)95 b(Con)m(v)m(ersion)27 b(of)g(maximal)g(degree)167 549 y FG(Lemma)32 b FK(Let)i FH(r)j FK(b)r(e)e(a)g(redex)g(of)g (maximal)e(degree)i FH(n)g FK(in)f FH(t)p FK(,)j(and)e(supp)r(ose)i (that)e(all)e(the)167 634 y(redexes)26 b(strictly)f(con)n(tained)h(in)g FH(r)j FK(ha)n(v)n(e)e(degree)f(less)g(than)h FH(n)p FK(.)36 b(If)26 b FH(u)h FK(is)f(obtained)h(from)f FH(t)g FK(b)n(y)167 719 y(con)n(v)n(erting)i FH(r)h FK(to)f FH(c)g FK(then)f FH(u)h FK(has)h(strictly)c(few)n(er)i(redexes)g(of)h (degree)g FH(n)p FK(.)167 948 y FG(Pro)r(of)g FK(When)f(the)h(con)n(v)n (ersion)g(is)f(made,)h(the)f(follo)n(wing)g(things)h(happ)r(en:)270 1147 y FJ(\017)34 b FK(The)28 b(redexes)f(outside)h FH(r)h FK(remain.)270 1314 y FJ(\017)34 b FK(The)48 b(redexes)g(strictly)e (inside)h FH(r)j FK(are)e(in)f(general)h(conserv)n(ed,)54 b(but)48 b(sometimes)339 1399 y(proliferated:)42 b(for)31 b(example)g(if)f(one)i(replaces)e(\()p FH(\025x:)12 b FJ(h)p FH(x;)g(x)p FJ(i)p FK(\))g FH(s)32 b FK(b)n(y)h FJ(h)p FH(s;)12 b(s)p FJ(i)p FK(,)33 b(the)e(redexes)339 1484 y(of)d FH(s)g FK(are)f(duplicated.)34 b(The)27 b(h)n(yp)r(othesis) h(made)f(do)r(es)h(not)g(exclude)e(duplication,)h(but)339 1570 y(it)g(is)g(limited)d(to)k(degrees)g(less)e(than)j FH(n)p FK(.)270 1737 y FJ(\017)34 b FK(The)d(redex)g FH(r)i FK(is)d(destro)n(y)n(ed)i(and)g(p)r(ossibly)f(replaced)f(b)n(y)i (some)f(redexes)g(of)g(strictly)339 1822 y(smaller)26 b(degree.)1824 b Fu(\003)167 2059 y Fy(4.3.4)95 b(Pro)s(of)26 b(of)h(the)h(theorem)167 2204 y FK(If)g FH(t)f FK(is)g(a)h(term,)f (consider)g FH(\026)p FK(\()p FH(t)p FK(\))19 b(=)h(\()p FH(n;)12 b(m)p FK(\))27 b(with)549 2433 y FH(n)20 b FK(=)f FH(d)p FK(\()p FH(t)p FK(\))381 b FH(m)20 b FK(=)f(n)n(um)n(b)r(er)28 b(of)g(redexes)f(of)h(degree)f FH(n)167 2662 y FK(Lemma)k FG(??)i FK(sa)n(ys)g(that)f(it)f(is)g(p)r(ossible)h(to)g(c)n(ho)r(ose)h (a)f(redex)g FH(r)h FK(of)g FH(t)f FK(in)f(suc)n(h)h(a)h(w)n(a)n(y)g (that,)167 2747 y(after)d(con)n(v)n(ersion)h(of)g FH(r)h FK(to)e FH(c)p FK(,)h(the)f(result)f FH(t)1350 2722 y Fv(0)1397 2747 y FK(satis\014es)h FH(\026)p FK(\()p FH(t)1751 2722 y Fv(0)1767 2747 y FK(\))22 b FH(<)f(\026)p FK(\()p FH(t)p FK(\))30 b(for)g(the)g(lexicographic)167 2832 y(order,)e FM(i.e.)g FK(if)f FH(\026)p FK(\()p FH(t)655 2807 y Fv(0)671 2832 y FK(\))20 b(=)f(\()p FH(n)859 2807 y Fv(0)876 2832 y FH(;)12 b(m)967 2807 y Fv(0)983 2832 y FK(\))28 b(then)g FH(n)1241 2807 y Fv(0)1277 2832 y FH(<)19 b(n)28 b FK(or)g(\()p FH(n)1576 2807 y Fv(0)1612 2832 y FK(=)20 b FH(n)28 b FK(and)g FH(m)1953 2807 y Fv(0)1990 2832 y FH(<)19 b(m)p FK(\).)36 b(So)29 b(the)e(result)g(is) 167 2918 y(established)g(b)n(y)h(a)g(double)g(induction.)1400 b Fu(\003)167 3186 y FE(4.4)114 b(The)28 b(strong)g(normalisation)g (theorem)167 3355 y FK(The)j(w)n(eak)h(normalisation)e(theorem)h(is)f (in)h(fact)g(a)h(bit)e(b)r(etter)g(than)i(its)f(statemen)n(t)f(leads) 167 3440 y(us)j(to)h(b)r(eliev)n(e,)e(b)r(ecause)h(w)n(e)f(ha)n(v)n(e)i (a)f(simple)e(algorithm)h(for)h(c)n(ho)r(osing)h(at)f(eac)n(h)g(step)g (an)167 3525 y(appropriate)38 b(redex)g(whic)n(h)f(leads)h(us)g(to)g (the)g(normal)g(form.)66 b(Ha)n(ving)38 b(said)g(this,)i(it)d(is)167 3611 y(in)n(teresting)26 b(to)i(ask)h(whether)e FM(al)t(l)33 b FK(normalisation)27 b(strategies)g(con)n(v)n(erge.)270 3840 y(A)h(term)f FH(t)i FK(is)e FM(str)l(ongly)i(normalisable)f FK(when)g(there)g(is)f(no)i(in\014nite)e(reduction)h(sequence)167 3925 y(b)r(eginning)g(with)e FH(t)p FK(.)p eop PStoPSsaved restore %%Page: (30,31) 16 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 27 30 bop 167 167 a Fz(4.4.)64 b(THE)27 b(STR)n(ONG)g(NORMALISA)-6 b(TION)26 b(THEOREM)771 b FK(27)167 404 y FG(Lemma)30 b FH(t)k FK(is)e(strongly)i(normalisable)e(i\013)g(there)h(is)f(a)i(n)n (um)n(b)r(er)f FH(\027)t FK(\()p FH(t)p FK(\))g(whic)n(h)f(b)r(ounds)j (the)167 490 y(length)27 b(of)h(ev)n(ery)g(normalisation)f(sequence)g (b)r(eginning)h(with)f FH(t)p FK(.)167 663 y FG(Pro)r(of)44 b FK(F)-6 b(rom)45 b(the)f(existence)f(of)i FH(\027)t FK(\()p FH(t)p FK(\),)k(it)43 b(follo)n(ws)h(immediately)d(that)j FH(t)h FK(is)e(strongly)167 748 y(normalisable.)270 874 y(The)23 b(con)n(v)n(erse)g(uses)h(K\177)-34 b(onig's)23 b(lemma)1283 848 y FD(1)1309 874 y FK(:)33 b(one)23 b(can)h(represen)n (t)e(a)h(sequence)g(of)g(con)n(v)n(ersions)167 959 y(b)n(y)35 b(sp)r(ecifying)f(a)h(redex)g FH(r)904 970 y FD(0)966 959 y FK(of)h FH(t)1082 970 y FD(0)1109 959 y FK(,)h(then)e(a)g(redex)f FH(r)1631 970 y FD(1)1694 959 y FK(of)h FH(t)1809 970 y FD(1)1837 959 y FK(,)h(and)g(so)f(on.)57 b(The)35 b(p)r(ossible)167 1044 y(sequences)c(can)h(then)g(b)r(e)f(arranged)i(in)d(the)i(form)f (of)h(a)f(tree,)h(and)g(the)f(fact)h(that)g(a)f(term)167 1129 y(has)26 b(only)f(a)h(\014nite)e(n)n(um)n(b)r(er)h(of)g(subterms)g (assures)h(us)f(that)g(the)g(tree)f(is)g(\014nitely-branc)n(hing.)167 1214 y(No)n(w,)38 b(the)e(strong)h(normalisation)e(h)n(yp)r(othesis)h (tells)e(us)i(that)h(the)e(tree)g(has)i(no)f(in\014nite)167 1300 y(branc)n(h,)30 b(and)f(b)n(y)g(K\177)-34 b(onig's)29 b(lemma,)e(the)h(whole)f(tree)h(m)n(ust)g(b)r(e)g(\014nite,)g(whic)n(h) f(giv)n(es)i(us)f(the)167 1385 y(existence)e(of)i FH(\027)t FK(\()p FH(t)p FK(\).)1933 b Fu(\003)270 1558 y FK(There)29 b(are)f(sev)n(eral)h(metho)r(ds)g(to)g(pro)n(v)n(e)h(that)f(ev)n(ery)g (term)f(\(of)h(the)g(t)n(yp)r(ed)g FH(\025)p FK(-calculus\))167 1643 y(is)e(strongly)h(normalisable:)270 1804 y FJ(\017)34 b FM(internalisation)5 b FK(:)48 b(this)34 b(consists)g(of)g(a)g (tortuous)h(translation)f(of)h(the)e(calculus)g(in)n(to)339 1889 y(itself)k(in)g(suc)n(h)i(a)g(w)n(a)n(y)g(as)g(to)f(pro)n(v)n(e)i (strong)f(normalisation)f(b)n(y)h(means)f(of)h(w)n(eak)339 1975 y(normalisation.)c(Gandy)29 b(w)n(as)g(the)e(\014rst)h(to)g(use)f (this)g(tec)n(hnique)g([)p FG(?)q FK(].)270 2118 y FJ(\017)34 b FM(r)l(e)l(ducibility)6 b FK(:)65 b(w)n(e)41 b(in)n(tro)r(duce)g(a)h (prop)r(ert)n(y)g(of)g(\\hereditary)g(calculabilit)n(y")d(whic)n(h)339 2204 y(allo)n(ws)g(us)g(to)g(manipulate)g(complex)f(com)n(binatorial)g (information.)69 b(This)38 b(is)g(the)339 2289 y(metho)r(d)c(w)n(e)g (shall)f(follo)n(w,)i(since)e(it)g(is)h(the)f(only)i(one)f(whic)n(h)g (generalises)e(to)j(v)n(ery)339 2374 y(complicated)26 b(situations.)36 b(This)27 b(metho)r(d)g(will)e(b)r(e)j(the)f(sub)t (ject)g(of)h(c)n(hapter)g FG(??)q FK(.)p 167 3790 1003 3 v 246 3833 a FC(1)273 3854 y FB(A)d(\014nitely)e(branc)n(hing)i(tree) g(with)g(no)g(in\014nite)e(branc)n(h)i(is)g(\014nite.)32 b(Unless)25 b(the)g(branc)n(hes)g(are)h(lab)r(elled)167 3925 y(\(as)i(they)f(usually)f(are\),)i(this)f(requires)f(the)h(axiom)h (of)g(Choice.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 28 31 bop 167 874 a FF(Chapter)28 b(5)167 1168 y(Sequen)-5 b(t)28 b(Calculus)167 1487 y FK(The)22 b FM(se)l(quent)f(c)l(alculus)p FK(,)h(due)h(to)f(Gen)n(tzen,)g(is)g(the)f(prettiest)f(illustration)g (of)j(the)e(symmetries)167 1573 y(of)33 b(Logic.)51 b(It)33 b(presen)n(ts)g(n)n(umerous)g(analogies)g(with)f(natural)h(deduction,)i (without)d(b)r(eing)167 1658 y(limited)24 b(to)k(the)g(in)n (tuitionistic)c(case.)270 1831 y(This)37 b(calculus)f(is)h(generally)f (ignored)h(b)n(y)h(computer)f(scien)n(tists)2071 1805 y FD(1)2097 1831 y FK(.)64 b(Y)-6 b(et)36 b(it)h(underlies)167 1916 y(essen)n(tial)22 b(ideas:)33 b(for)24 b(example,)f Fr(PROLOG)i FK(is)d(an)i(implemen)n(tation)d(of)j(a)f(fragmen)n(t)h(of) g(sequen)n(t)167 2001 y(calculus,)h(and)i(the)f(\\tableaux")h(used)f (in)f(automatic)h(theorem-pro)n(ving)g(are)f(just)h(a)h(sp)r(ecial)167 2086 y(case)i(of)h(this)e(calculus.)39 b(In)29 b(other)h(w)n(ords,)g (it)e(is)g(used)i(un)n(wittingly)e(b)n(y)i(man)n(y)g(p)r(eople,)f(but) 167 2171 y(mixed)k(with)f FM(c)l(ontr)l(ol)41 b FK(features,)36 b FM(i.e.)d FK(programming)h(devices.)52 b(What)34 b(mak)n(es)g(ev)n (erything)167 2256 y(w)n(ork)c(is)g(the)f(sequen)n(t)i(calculus)d(with) h(its)g(deep)h(symmetries,)f(and)h(not)h(particular)e(tric)n(ks.)167 2341 y(So)24 b(it)e(is)g(di\016cult)g(to)i(consider,)f(sa)n(y)-6 b(,)26 b(the)d(theory)g(of)h Fr(PROLOG)h FK(without)d(kno)n(wing)j (thoroughly)167 2427 y(the)i(subtleties)f(of)i(sequen)n(t)g(calculus.) 270 2600 y(F)-6 b(rom)40 b(an)f(algorithmic)e(viewp)r(oin)n(t,)k(the)e (sequen)n(t)h(calculus)e(has)i(no)f FM(Curry-Howar)l(d)167 2685 y(isomorphism)p FK(,)d(b)r(ecause)c(of)g(the)g(m)n(ultitude)e(of)j (w)n(a)n(ys)g(of)g(writing)d(the)i(same)g(pro)r(of.)50 b(This)167 2770 y(prev)n(en)n(ts)31 b(us)g(from)g(using)g(it)f(as)i(a)f (t)n(yp)r(ed)g FH(\025)p FK(-calculus,)g(although)h(w)n(e)e(glimpse)g (some)g(deep)167 2855 y(structure)k(of)h(this)f(kind,)j(probably)f (link)n(ed)e(with)g(parallelism.)53 b(But)35 b(it)f(requires)f(a)i(new) 167 2940 y(approac)n(h)30 b(to)d(the)h(syn)n(tax,)h(for)f(example)f (natural)h(deductions)g(with)e(sev)n(eral)h(conclusions.)p 167 3860 1003 3 v 246 3903 a FC(1)273 3925 y FB(An)g(exception)f(is)h ([)p Ft(?)q FB(].)1385 4101 y FK(28)p eop PStoPSsaved restore %%Page: (32,33) 17 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 29 32 bop 167 167 a Fz(5.1.)64 b(THE)27 b(CALCULUS)1710 b FK(29)167 404 y FE(5.1)114 b(The)28 b(calculus)167 580 y Fy(5.1.1)95 b(Sequen)m(ts)167 710 y FK(A)26 b FM(se)l(quent)g FK(is)g(an)h(expression)998 711 y FH(A)p 1001 731 39 3 v 1069 710 a FJ(`)1132 711 y FH(B)p 1135 731 43 3 v 1214 710 a FK(where)1417 711 y FH(A)p 1420 731 39 3 v 1495 710 a FK(and)1632 711 y FH(B)p 1636 731 43 3 v 1715 710 a FK(are)f(\014nite)g(sequences)h(of)g(form)n(ulae)167 796 y FH(A)219 807 y FD(1)247 796 y FH(;)12 b(:)g(:)g(:)f(;)h(A)453 807 y Fw(n)514 796 y FK(and)28 b FH(B)704 807 y FD(1)733 796 y FH(;)12 b(:)g(:)g(:)f(;)h(B)939 807 y Fw(m)986 796 y FK(.)270 918 y(The)44 b(na)-8 b(\177)-27 b(\020v)n(e)45 b(\(denotational\))f(in)n(terpretation)f(is)g(that)h(the)g(conjunction) g(of)h(the)f FH(A)2653 929 y Fw(i)167 1003 y FK(implies)25 b(the)i(disjunction)g(of)i(the)e FH(B)1147 1014 y Fw(j)1173 1003 y FK(.)36 b(In)27 b(particular,)270 1148 y FJ(\017)34 b FK(if)407 1149 y FH(A)p 411 1168 39 3 v 487 1148 a FK(is)26 b(empt)n(y)-6 b(,)28 b(the)g(sequen)n(t)g(asserts)g(the)f (disjunction)g(of)i(the)e FH(B)2136 1159 y Fw(j)2162 1148 y FK(;)270 1287 y FJ(\017)34 b FK(if)407 1288 y FH(A)p 411 1308 V 487 1287 a FK(is)26 b(empt)n(y)i(and)915 1288 y FH(B)p 918 1308 43 3 v 998 1287 a FK(is)f(just)h FH(B)1265 1298 y FD(1)1293 1287 y FK(,)g(it)f(asserts)h FH(B)1694 1298 y FD(1)1722 1287 y FK(;)270 1427 y FJ(\017)34 b FK(if)407 1428 y FH(B)p 411 1448 V 491 1427 a FK(is)27 b(empt)n(y)-6 b(,)27 b(it)g(asserts)h(the)f(negation)i(of)f(the)f (conjunction)h(of)h(the)e FH(A)2346 1438 y Fw(i)2366 1427 y FK(;)270 1567 y FJ(\017)34 b FK(if)407 1568 y FH(A)p 411 1587 39 3 v 487 1567 a FK(and)625 1568 y FH(B)p 629 1587 43 3 v 709 1567 a FK(are)27 b(empt)n(y)-6 b(,)28 b(it)f(asserts)h(con)n(tradiction.)167 1769 y Fy(5.1.2)95 b(Structural)27 b(rules)167 1899 y FK(These)38 b(rules,)j(whic)n(h)e (seem)e(not)j(to)f(sa)n(y)h(an)n(ything)g(at)f(all,)i(imp)r(ose)d(a)h (certain)f(w)n(a)n(y)i(of)167 1984 y(managing)29 b(the)e(\\slots")i(in) e(whic)n(h)g(one)h(writes)e(form)n(ulae.)35 b(They)27 b(are:)251 2129 y(1.)35 b(The)28 b FM(exchange)e FK(rules)719 2312 y FH(A)p 723 2332 39 3 v -1 x(;)12 b(C)q(;)g(D)r(;)973 2312 y(A)p 977 2332 V -30 x Fv(0)1061 2311 y FJ(`)1124 2312 y FH(B)p 1127 2332 43 3 v 719 2356 461 4 v 1200 2372 a FJ(L)p Fq(X)719 2434 y FH(A)p 723 2453 39 3 v -1 x(;)g(D)r(;)g(C)q(;)973 2434 y(A)p 977 2453 V -31 x Fv(0)1061 2433 y FJ(`)1124 2434 y FH(B)p 1127 2453 43 3 v 1674 2311 a(A)19 b FJ(`)1808 2312 y FH(B)p 1812 2332 V 1864 2311 a(;)12 b(C)q(;)g(D)r(;)2066 2312 y(B)p 2070 2332 V 2122 2282 a Fv(0)p 1674 2356 465 4 v 2160 2372 a FJ(R)p Fq(X)1674 2433 y FH(A)19 b FJ(`)1808 2434 y FH(B)p 1812 2453 43 3 v 1864 2433 a(;)12 b(D)r(;)g(C)q(;)2066 2434 y(B)p 2070 2453 V 2122 2403 a Fv(0)339 2615 y FK(These)38 b(rules)f(express)h(in)g(some)f(w)n(a)n(y)i(the)f FM(c)l(ommutativity)h FK(of)g(logic,)g(b)n(y)g(allo)n(wing)339 2700 y(p)r(erm)n(utation)28 b(of)g(form)n(ulae)f(on)h(either)e(side)h(of)h(the)g(sym)n(b)r(ol)f(\\) p FJ(`)p FK(".)251 2840 y(2.)35 b(The)28 b FM(we)l(akening)e FK(rules)875 3016 y FH(A)p 878 3036 39 3 v 946 3015 a FJ(`)1009 3016 y FH(B)p 1012 3036 43 3 v 832 3060 276 4 v 1128 3076 a FJ(L)p Fq(W)832 3138 y FH(A)p 836 3157 39 3 v -1 x(;)12 b(C)25 b FJ(`)1051 3138 y FH(B)p 1055 3157 43 3 v 1775 3016 a(A)p 1779 3036 39 3 v 1847 3015 a FJ(`)1909 3016 y FH(B)p 1913 3036 43 3 v 1735 3060 272 4 v 2027 3076 a FJ(R)p Fq(W)1735 3138 y FH(A)p 1738 3157 39 3 v 1806 3137 a FJ(`)19 b FH(C)q(;)1949 3138 y(B)p 1953 3157 43 3 v 339 3319 a FK(as)29 b(their)d(name)i(suggests,)h (allo)n(w)d(replacemen)n(t)g(of)i(a)g(sequen)n(t)g(b)n(y)h(a)f(w)n(eak) n(er)f(one.)251 3459 y(3.)35 b(The)28 b FM(c)l(ontr)l(action)g FK(rules)792 3622 y FH(A)p 796 3642 39 3 v -1 x(;)12 b(C)q(;)g(C)25 b FJ(`)1093 3622 y FH(B)p 1096 3642 43 3 v 792 3666 357 4 v 1169 3681 a FJ(L)p Fq(C)833 3743 y FH(A)p 836 3763 39 3 v -1 x(;)12 b(C)24 b FJ(`)1052 3743 y FH(B)p 1056 3763 43 3 v 1715 3622 a(A)p 1718 3642 39 3 v 1786 3621 a FJ(`)c FH(C)q(;)12 b(C)q(;)2011 3622 y(B)p 2015 3642 43 3 v 1715 3666 353 4 v 2088 3681 a FJ(R)p Fq(C)1755 3743 y FH(A)p 1759 3763 39 3 v 1827 3742 a FJ(`)19 b FH(C)q(;)1970 3743 y(B)p 1974 3763 43 3 v 339 3925 a FK(express)28 b(the)g(idemp)r(otence)e(of)i(conjunction) g(and)h(disjunction.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 30 33 bop 167 167 a FK(30)1200 b Fz(CHAPTER)26 b(5.)63 b(SEQUENT)27 b(CALCULUS)270 404 y FK(In)41 b(fact,)j(con)n(trary)d(to)g (p)r(opular)h(b)r(elief,)f(these)g(rules)e(are)i(the)f(most)g(imp)r (ortan)n(t)h(of)167 490 y(the)32 b(whole)f(calculus,)h(for,)h(without)f (ha)n(ving)h(written)d(a)i(single)f(logical)g(sym)n(b)r(ol,)i(w)n(e)e (ha)n(v)n(e)167 575 y(practically)g(determined)g(the)h(future)h(b)r (eha)n(viour)h(of)f(the)g(logical)e(op)r(erations.)51 b(Y)-6 b(et)32 b(these)167 660 y(rules,)25 b(if)e(they)i(are)g(ob)n (vious)h(from)f(the)f(denotational)h(p)r(oin)n(t)g(of)g(view,)g(should) g(b)r(e)g(examined)167 745 y(closely)h(from)i(the)f(op)r(erational)h(p) r(oin)n(t)f(of)i(view,)d(esp)r(ecially)g(the)h FM(c)l(ontr)l(action)p FK(.)270 867 y(It)f(is)g(p)r(ossible)f(to)h(en)n(visage)h(v)l(arian)n (ts)g(on)g(the)e(sequen)n(t)i(calculus,)e(in)h(whic)n(h)f(these)h (rules)167 953 y(are)34 b(ab)r(olished)g(or)g(extremely)e(restricted.) 52 b(That)34 b(seems)f(to)h(ha)n(v)n(e)h(some)e(v)n(ery)i(b)r (ene\014cial)167 1038 y(e\013ects,)27 b(leading)h(to)g(linear)f(logic)g ([)p FG(?)p FK(].)37 b(But)28 b(without)f(going)i(that)f(far,)h (certain)e(w)n(ell-kno)n(wn)167 1123 y(restrictions)20 b(on)j(the)f(sequen)n(t)h(calculus)e(seem)g(to)h(ha)n(v)n(e)h(no)g (purp)r(ose)g(apart)g(from)f(con)n(trolling)167 1208 y(the)27 b(structural)g(rules,)g(as)i(w)n(e)e(shall)g(see)g(in)g(the)g (follo)n(wing)g(sections.)167 1410 y Fy(5.1.3)95 b(The)27 b(in)m(tuitionistic)i(case)167 1541 y FK(Essen)n(tially)-6 b(,)30 b(the)g(in)n(tuitionistic)d(sequen)n(t)k(calculus)e(is)h (obtained)h(b)n(y)g(restricting)d(the)i(form)167 1626 y(of)g(sequen)n(ts:)38 b(an)30 b FM(intuitionistic)f(se)l(quent)f FK(is)h(a)g(sequen)n(t)1739 1627 y FH(A)p 1743 1647 39 3 v 1811 1626 a FJ(`)1875 1627 y FH(B)p 1878 1647 43 3 v 1980 1626 a FK(where)2186 1627 y FH(B)p 2189 1647 V 2270 1626 a FK(is)g(a)g(sequence)167 1711 y(formed)f(from)h FM(at)f(most)i(one)e FK(form)n(ula.)38 b(In)29 b(the)f(in)n (tuitionistic)d(sequen)n(t)30 b(calculus,)d(the)i(only)167 1796 y(structural)e(rule)g(on)i(the)f(righ)n(t)g(is)f FJ(R)p Fq(W)i FK(since)e FJ(R)p Fq(X)g FK(and)i FJ(R)p Fq(C)f FK(assume)g(sev)n(eral)g(form)n(ulae)f(on)167 1881 y(the)g(righ)n(t.)270 2004 y(The)43 b(in)n(tuitionistic)d (restriction)h(is)i(in)f(fact)h(a)h(mo)r(di\014cation)f(to)g(the)g (managemen)n(t)167 2089 y(of)i(the)f(form)n(ulae)h(|)f(the)g (particular)g(place)g(distinguished)g(b)n(y)h(the)g(sym)n(b)r(ol)f FJ(`)h FK(is)f(a)167 2174 y(place)g(where)f(con)n(traction)i(is)f (forbidden)g(|)h(and)g(from)g(that,)k(n)n(umerous)c(prop)r(erties)167 2259 y(follo)n(w.)50 b(On)33 b(the)f(other)h(hand,)j(this)c(c)n(hoice)f (is)i(made)f(at)h(the)g(exp)r(ense)f(of)i(the)e(left/righ)n(t)167 2344 y(symmetry.)50 b(A)33 b(b)r(etter)f(result)g(is)g(without)h(doubt) h(obtained)f(b)n(y)h(forbidding)f(con)n(traction)167 2429 y(\(and)c(w)n(eak)n(ening\))e(altogether,)h(whic)n(h)f(allo)n(ws)g (the)g(symmetry)g(to)h(reapp)r(ear.)270 2552 y(Otherwise,)36 b(the)f(in)n(tuitionistic)d(sequen)n(t)j(calculus)g(will)d(b)r(e)j (obtained)h(b)n(y)g(restricting)167 2637 y(to)29 b(the)g(in)n (tuitionistic)d(sequen)n(ts,)31 b(and)f(preserving)f(|)g(apart)h(from)f (one)h(exception)e(|)h(the)167 2722 y(classical)d(rules)g(of)j(the)e (calculus.)167 2924 y Fy(5.1.4)95 b(The)27 b(\\iden)m(tit)m(y")j(group) 251 3055 y FK(1.)35 b(F)-6 b(or)30 b(ev)n(ery)g(form)n(ula)f FH(C)34 b FK(there)29 b(is)g(the)g FM(identity)g(axiom)51 b FH(C)26 b FJ(`)21 b FH(C)26 b FK(.)41 b(In)29 b(fact)g(one)h(could) 339 3140 y(limit)25 b(it)h(to)i(the)g(case)f(of)h(atomic)f FH(C)5 b FK(,)28 b(but)g(this)f(is)g(rarely)g(done.)251 3280 y(2.)35 b(The)28 b FM(cut)f(rule)1101 3450 y FH(A)p 1104 3470 39 3 v 1172 3449 a FJ(`)20 b FH(C)q(;)1316 3450 y(B)p 1320 3470 43 3 v 82 w(A)p 1454 3470 39 3 v -30 x Fv(0)1518 3449 y FH(;)12 b(C)25 b FJ(`)1686 3450 y FH(B)p 1689 3470 43 3 v 1742 3420 a Fv(0)p 1101 3494 658 4 v 1779 3510 a Fq(Cut)1233 3572 y FH(A)p 1237 3591 39 3 v -1 x(;)1316 3572 y(A)p 1319 3591 V -30 x Fv(0)1404 3571 y FJ(`)1466 3572 y FH(B)p 1470 3591 43 3 v 1522 3571 a(;)1553 3572 y(B)p 1557 3591 V 1609 3542 a Fv(0)339 3754 y FK(is)32 b(another)g(w)n(a)n(y)h(of)f(expressing)g(the)g(iden)n (tit)n(y)-6 b(.)47 b(The)31 b(iden)n(tit)n(y)g(axiom)g(sa)n(ys)j(that)e FH(C)339 3840 y FK(\(on)d(the)f(left\))f(is)h(stronger)h(than)g FH(C)34 b FK(\(on)29 b(the)f(righ)n(t\);)g(this)g(rule)f(states)i(the)f (con)n(v)n(erse)339 3925 y(truth,)g FM(i.e.)g FH(C)33 b FK(\(on)28 b(the)g(righ)n(t\))f(is)g(stronger)h(than)g FH(C)33 b FK(\(on)28 b(the)g(left\).)p eop PStoPSsaved restore %%Page: (34,35) 18 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 31 34 bop 167 167 a Fz(5.1.)64 b(THE)27 b(CALCULUS)1710 b FK(31)270 404 y(The)34 b(iden)n(tit)n(y)f(axiom)h(is)f(absolutely)h (necessary)g(to)h(an)n(y)g(pro)r(of,)i(to)d(start)g(things)g(o\013.)167 490 y(That)41 b(is)e(undoubtedly)j(wh)n(y)f(the)f(cut)g(rule,)j(whic)n (h)d(represen)n(ts)f(the)i(dual,)i(symmetric)167 575 y(asp)r(ect)29 b(can)f(b)r(e)h(eliminated,)d(b)n(y)j(means)g(of)g(a)g (di\016cult)e(theorem)h(\(pro)n(v)n(ed)h(in)f(c)n(hapter)g FG(??)q FK(\))167 660 y(whic)n(h)23 b(is)f(related)g(to)i(the)f (normalisation)f(theorem.)33 b(The)23 b(deep)g(con)n(ten)n(t)h(of)g (the)e(t)n(w)n(o)i(results)167 745 y(is)j(the)g(same;)h(they)g(only)g (di\013er)e(in)h(their)g(syn)n(tactic)g(dressing.)167 961 y Fy(5.1.5)95 b(Logical)28 b(rules)167 1096 y FK(There)23 b(is)f(tradition)h(whic)n(h)g(w)n(ould)g(ha)n(v)n(e)i(it)d(that)i (Logic)f(is)g(a)g(formal)g(game,)i(a)e(succession)h(of)167 1181 y(more)j(or)h(less)f(arbitrary)h(axioms)f(and)i(rules.)35 b(Sequen)n(t)28 b(calculus)f(\(and)h(natural)g(deduction)167 1267 y(as)g(w)n(ell\))c(sho)n(ws)k(this)f(is)f(not)h(at)h(all)d(so:)36 b(one)27 b(can)h(am)n(use)f(oneself)f(b)n(y)i(in)n(v)n(en)n(ting)f (one's)g(o)n(wn)167 1352 y(logical)34 b(op)r(erations,)39 b(but)d(they)g(ha)n(v)n(e)h(to)f(resp)r(ect)f(the)g(left/righ)n(t)g (symmetry,)i(otherwise)167 1437 y(one)c(creates)f(a)i(logical)d(atro)r (cit)n(y)i(without)f(in)n(terest.)50 b(Concretely)-6 b(,)33 b(the)g(symmetry)f(is)g(the)167 1522 y(fact)c(that)g(w)n(e)f (can)h FM(eliminate)f FK(the)g(cut)h(rule.)251 1696 y(1.)35 b FM(Ne)l(gation)p FK(:)44 b(the)31 b(rules)f(for)i(negation)g(allo)n (w)f(us)g(to)h(pass)h(from)e(the)g(righ)n(t)g(hand)i(side)339 1781 y(of)c(\\)p FJ(`)p FK(")f(to)g(the)f(left,)g(and)i(con)n(v)n (ersely:)839 1989 y FH(A)p 842 2008 39 3 v 910 1988 a FJ(`)19 b FH(C)q(;)1053 1989 y(B)p 1057 2008 43 3 v 813 2033 323 4 v 1156 2048 a FJ(L:)813 2110 y FH(A)p 817 2130 39 3 v -1 x(;)12 b FJ(:)p FH(C)25 b FJ(`)1079 2110 y FH(B)p 1083 2130 43 3 v 1747 1989 a(A)p 1750 2008 39 3 v 1798 1988 a(;)12 b(C)25 b FJ(`)1966 1989 y FH(B)p 1969 2008 43 3 v 1725 2033 319 4 v 2064 2048 a FJ(R:)1725 2110 y FH(A)p 1729 2130 39 3 v 1796 2109 a FJ(`)20 b(:)p FH(C)q(;)1987 2110 y(B)p 1991 2130 43 3 v 251 2356 a FK(2.)35 b FM(Conjunction)p FK(:)h(on)28 b(the)f(left,)g(t)n(w)n(o)h (unary)h(rules;)e(on)h(the)f(righ)n(t,)h(one)g(binary)g(rule:)801 2563 y FH(A)p 805 2583 39 3 v -1 x(;)12 b(C)25 b FJ(`)1020 2563 y FH(B)p 1024 2583 43 3 v 732 2607 413 4 v 1166 2623 a FJ(L)p FK(1)p FJ(^)732 2684 y FH(A)p 736 2704 39 3 v -1 x(;)12 b(C)21 b FJ(^)16 b FH(D)21 b FJ(`)1089 2684 y FH(B)p 1092 2704 43 3 v 1755 2563 a(A)p 1758 2583 39 3 v 1806 2562 a(;)12 b(D)22 b FJ(`)1979 2563 y FH(B)p 1982 2583 43 3 v 1688 2607 413 4 v 2122 2623 a FJ(L)p FK(2)p FJ(^)1688 2684 y FH(A)p 1692 2704 39 3 v -1 x(;)12 b(C)21 b FJ(^)16 b FH(D)21 b FJ(`)2045 2684 y FH(B)p 2049 2704 43 3 v 1097 2904 a(A)p 1101 2924 39 3 v 1168 2903 a FJ(`)f FH(C)q(;)1312 2904 y(B)p 1316 2924 43 3 v 83 w(A)p 1450 2924 39 3 v 1498 2874 a Fv(0)1534 2903 y FJ(`)g FH(D)r(;)1687 2904 y(B)p 1691 2924 43 3 v 1743 2874 a Fv(0)p 1097 2948 663 4 v 1780 2963 a FJ(R^)1121 3025 y FH(A)p 1124 3045 39 3 v -1 x(;)1204 3025 y(A)p 1207 3045 V 1255 2995 a Fv(0)1291 3024 y FJ(`)g FH(C)h FJ(^)15 b FH(D)r(;)1576 3025 y(B)p 1580 3045 43 3 v 1632 3024 a(;)1663 3025 y(B)p 1667 3045 V 1719 2995 a Fv(0)251 3271 y FK(3.)35 b FM(Disjunction)p FK(:)h(obtained)28 b(from)f(conjunction)h(b)n(y)h(in)n(terc)n(hanging)f(righ)n(t)f(and)i (left:)1101 3484 y FH(A)p 1104 3504 39 3 v 1152 3483 a(;)12 b(C)25 b FJ(`)1320 3484 y FH(B)p 1323 3504 43 3 v 82 w(A)p 1458 3504 39 3 v -30 x Fv(0)1522 3483 y FH(;)12 b(D)22 b FJ(`)1695 3484 y FH(B)p 1698 3504 43 3 v 1751 3454 a Fv(0)p 1101 3528 667 4 v 1788 3544 a FJ(L_)1126 3606 y FH(A)p 1130 3625 39 3 v -1 x(;)1209 3606 y(A)p 1213 3625 V -30 x Fv(0)1277 3605 y FH(;)12 b(C)21 b FJ(_)16 b FH(D)21 b FJ(`)1582 3606 y FH(B)p 1586 3625 43 3 v 1638 3605 a(;)1669 3606 y(B)p 1672 3625 V 1725 3576 a Fv(0)796 3819 y FH(A)p 799 3839 39 3 v 867 3818 a FJ(`)e FH(C)q(;)1010 3819 y(B)p 1014 3839 43 3 v 725 3863 413 4 v 1158 3879 a FJ(R)p FK(1)p FJ(_)725 3940 y FH(A)p 728 3960 39 3 v 796 3939 a FJ(`)h FH(C)h FJ(_)15 b FH(D)r(;)1081 3940 y(B)p 1085 3960 43 3 v 1751 3819 a(A)p 1755 3839 39 3 v 1822 3818 a FJ(`)20 b FH(D)r(;)1975 3819 y(B)p 1979 3839 43 3 v 1685 3863 413 4 v 2118 3879 a FJ(R)p FK(2)p FJ(_)1685 3940 y FH(A)p 1688 3960 39 3 v 1756 3939 a FJ(`)g FH(C)h FJ(_)15 b FH(D)r(;)2041 3940 y(B)p 2045 3960 43 3 v eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 32 35 bop 167 167 a FK(32)1200 b Fz(CHAPTER)26 b(5.)63 b(SEQUENT)27 b(CALCULUS)339 404 y FG(Sp)r(ecial)f(case:)72 b FK(The)27 b(in)n(tuitionistic)e(rule)h FJ(L_)h FK(is)g(written:)1109 583 y FH(A)p 1113 603 39 3 v -1 x(;)12 b(C)25 b FJ(`)1328 583 y FH(B)p 1332 603 43 3 v 82 w(A)p 1466 603 39 3 v -30 x Fv(0)1531 582 y FH(;)12 b(D)21 b FJ(`)1703 583 y FH(B)p 1706 603 43 3 v 1109 627 650 4 v 1779 643 a FJ(L_)1178 705 y FH(A)p 1182 724 39 3 v -1 x(;)1261 705 y(A)p 1264 724 V 1312 675 a Fv(0)1329 704 y FH(;)12 b(C)21 b FJ(_)15 b FH(D)22 b FJ(`)1634 705 y FH(B)p 1637 724 43 3 v 339 883 a FK(where)544 884 y FH(B)p 547 903 V 628 883 a FK(con)n(tains)29 b(zero)f(or)h(one)f(form)n(ula.)38 b(This)27 b(rule)h(is)f(not)i(a)g(sp)r(ecial)e(case)h(of)h(its)339 968 y(classical)h(analogue,)k(since)c(a)i(classical)d FJ(L_)i FK(leads)g(to)1846 969 y FH(B)p 1849 988 V 1902 968 a(;)1933 969 y(B)p 1936 988 V 2020 968 a FK(on)h(the)f(righ)n(t.)46 b(This)31 b(is)339 1053 y(the)e(only)h(case)f(where)g(the)g(in)n (tuitionistic)d(rule)i(is)h(not)h(simply)e(a)h(restriction)f(of)h(the) 339 1138 y(classical)d(one.)251 1276 y(4.)35 b FM(Implic)l(ation)p FK(:)42 b(here)30 b(w)n(e)h(ha)n(v)n(e)g(on)h(the)e(left)f(a)j(rule)d (with)h(t)n(w)n(o)h(premises)e(and)j(on)f(the)339 1361 y(righ)n(t)k(a)f(rule)g(with)f(one)i(premise.)54 b(They)35 b(matc)n(h)f(again,)j(but)e(in)f(a)h(di\013eren)n(t)e(w)n(a)n(y)339 1446 y(from)24 b(the)g(case)g(of)g(conjunction:)34 b(the)24 b(rule)f(with)g(one)h(premise)e(uses)i FM(two)g FK(o)r(ccurrences)339 1531 y(in)j(the)h(premise:)642 1710 y FH(A)p 646 1730 39 3 v 713 1709 a FJ(`)20 b FH(C)q(;)857 1710 y(B)p 861 1730 43 3 v 83 w(A)p 995 1730 39 3 v 1043 1680 a Fv(0)1060 1709 y FH(;)12 b(D)22 b FJ(`)1232 1710 y FH(B)p 1236 1730 43 3 v 1288 1680 a Fv(0)p 642 1754 663 4 v 1325 1770 a FJ(L\))650 1832 y FH(A)p 654 1851 39 3 v -1 x(;)733 1832 y(A)p 736 1851 V -30 x Fv(0)801 1831 y FH(;)12 b(C)25 b FJ(\))20 b FH(D)i FJ(`)1137 1832 y FH(B)p 1141 1851 43 3 v 1193 1831 a(;)1224 1832 y(B)p 1228 1851 V 1280 1802 a Fv(0)1786 1707 y FH(A)p 1790 1727 39 3 v -1 x(;)12 b(C)25 b FJ(`)20 b FH(D)r(;)2096 1707 y(B)p 2099 1727 43 3 v 1747 1751 444 4 v 2212 1767 a FJ(R\))1747 1829 y FH(A)p 1751 1848 39 3 v 1818 1828 a FJ(`)g FH(C)25 b FJ(\))20 b FH(D)r(;)2135 1829 y(B)p 2139 1848 43 3 v 251 2036 a FK(5.)35 b FM(Universal)27 b(quanti\014c)l(ation)p FK(:)34 b(t)n(w)n(o)27 b(unary)h(rules)e(whic)n(h)g(matc)n(h)g(in)h (the)f(sense)h(that)g(one)339 2121 y(uses)h(a)g FM(variable)f FK(and)i(the)e(other)h(a)g FM(term)p FK(:)768 2284 y FH(A)p 771 2304 39 3 v 819 2283 a(;)12 b(C)5 b FK([)p FH(a=\030)s FK(])22 b FJ(`)1129 2284 y FH(B)p 1133 2304 43 3 v 768 2328 418 4 v 1206 2344 a FJ(L8)787 2405 y FH(A)p 791 2425 39 3 v -1 x(;)12 b FJ(8)p FH(\030)s(:)g(C)24 b FJ(`)1110 2405 y FH(B)p 1113 2425 43 3 v 1774 2282 a(A)p 1777 2302 39 3 v 1845 2281 a FJ(`)c FH(C)q(;)1989 2282 y(B)p 1993 2302 43 3 v 1722 2326 375 4 v 2117 2342 a FJ(R8)1722 2403 y FH(A)p 1725 2423 39 3 v 1793 2402 a FJ(`)g(8)p FH(\030)s(:)12 b(C)q(;)2041 2403 y(B)p 2044 2423 43 3 v 339 2583 a FJ(R8)27 b FK(is)g(sub)t(ject)g(to)h(a)g (restriction:)34 b FH(\030)d FK(m)n(ust)c(not)h(b)r(e)g(free)f(in)1981 2584 y FH(A)p 1984 2604 39 3 v 2032 2583 a(;)2063 2584 y(B)p 2067 2604 43 3 v 2119 2583 a FK(.)251 2721 y(6.)35 b FM(Existential)27 b(quanti\014c)l(ation)p FK(:)35 b(the)27 b(mirror)g(image)f(of)j FG(??)p FK(:)818 2896 y FH(A)p 822 2916 39 3 v -1 x(;)12 b(C)25 b FJ(`)1037 2896 y FH(B)p 1041 2916 43 3 v 766 2940 379 4 v 1166 2956 a FJ(L9)766 3017 y FH(A)p 770 3037 39 3 v -1 x(;)12 b FJ(9)p FH(\030)s(:)g(C)26 b FJ(`)1089 3017 y FH(B)p 1093 3037 43 3 v 1680 2898 a(A)p 1684 2918 39 3 v 1752 2897 a FJ(`)19 b FH(C)5 b FK([)p FH(a=\030)s FK(])p FH(;)2040 2898 y(B)p 2046 2918 43 3 v 1680 2942 418 4 v 2119 2958 a FJ(R9)1702 3019 y FH(A)p 1705 3039 39 3 v 1773 3018 a FJ(`)20 b(9)p FH(\030)s(:)12 b(C)q(;)2020 3019 y(B)p 2024 3039 43 3 v 339 3197 a FJ(L9)28 b FK(is)f(sub)t(ject)g(to)h(the)f(same)h(restriction)d(as)k FJ(R8)p FK(:)34 b FH(\030)d FK(m)n(ust)c(not)i(b)r(e)e(free)g(in)2424 3198 y FH(A)p 2427 3218 39 3 v -1 x(;)2507 3198 y(B)p 2510 3218 43 3 v 2562 3197 a FK(.)167 3429 y FE(5.2)114 b(Some)27 b(prop)s(erties)h(of)g(the)g(system)f(without)j(cut)167 3584 y FK(Gen)n(tzen's)23 b(calculus)e(is)h(a)h(p)r(ossible)f(form)n (ulation)h(of)g(\014rst)g(order)f(logic.)33 b(Gen)n(tzen's)23 b(theorem,)167 3669 y(whic)n(h)31 b(is)h(pro)n(v)n(ed)h(in)e(c)n (hapter)i FG(??)p FK(,)h(sa)n(ys)f(that)f(the)g(cut)g(rule)f(is)g (redundan)n(t,)k(sup)r(er\015uous.)167 3754 y(The)27 b(pro)r(of)h(is)f(v)n(ery)g(delicate,)e(and)k(dep)r(ends)e(on)h(the)f (p)r(erfect)f(righ)n(t/left)g(symmetry)h(whic)n(h)167 3840 y(w)n(e)41 b(ha)n(v)n(e)i(seen.)78 b(Let)42 b(us)g(b)r(e)g(con)n (ten)n(t)g(with)f(seeing)h(some)f(of)i(the)e(more)h(sp)r(ectacular)167 3925 y(consequences.)p eop PStoPSsaved restore %%Page: (36,37) 19 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 33 36 bop 167 167 a Fz(5.2.)64 b(SOME)28 b(PR)n(OPER)-6 b(TIES)27 b(OF)g(THE)g(SYSTEM)h(WITHOUT)e(CUT)410 b FK(33)167 404 y Fy(5.2.1)95 b(The)27 b(last)h(rule)167 539 y FK(If)c(w)n(e)f(can) h(pro)n(v)n(e)h FH(A)f FK(in)f(the)h(predicate)e(calculus,)i(then)g(it) f(is)g(p)r(ossible)g(to)h(sho)n(w)h(the)f(sequen)n(t)167 625 y FJ(`)c FH(A)45 b FM(without)27 b(cut)p FK(.)35 b(What)27 b(is)f(the)g(last)g(rule)g(used?)35 b(Surely)26 b(not)h FJ(R)p Fq(W)q FK(,)f(b)r(ecause)h(the)f(empt)n(y)167 710 y(sequen)n(t)h(is)f(not)h(pro)n(v)l(able.)36 b(P)n(erhaps)27 b(it)f(is)g(the)g(logical)f(rule)h FJ(R)p FH(i)p Fq(s)g FK(where)g Fq(s)h FK(is)e(the)i(principal)167 795 y(sym)n(b)r(ol)j(of)h FH(A)p FK(,)f(and)i(this)d(case)h(is)g(v)n(ery)g(imp)r(ortan)n(t.)43 b(But)30 b(it)f(ma)n(y)i(also)f(b)r(e)g FJ(R)p Fq(C)p FK(,)h(in)f(whic)n(h)167 880 y(case)24 b(w)n(e)g(are)g(led)f(to)44 b FJ(`)20 b FH(A;)12 b(A)43 b FK(and)25 b(all)e(is)h(lost!)33 b(That)25 b(is)f(wh)n(y)g(the)g(in)n(tuitionistic)d(case,)k(with)167 965 y(its)i(sp)r(ecial)f(managemen)n(t)h(whic)n(h)g(forbids)h(con)n (traction)g(on)g(the)f(righ)n(t,)h(is)e(v)n(ery)i(imp)r(ortan)n(t:)167 1050 y(if)e FH(A)g FK(is)g(pro)n(v)l(able)i(in)e(the)g(in)n (tuitionistic)e(sequen)n(t)j(calculus)e(b)n(y)j(a)f(cut-free)e(pro)r (of,)k(then)d(the)167 1135 y(last)h(rule)g(is)g(a)h(righ)n(t)f(logical) f(rule.)167 1326 y(Tw)n(o)i(particularly)e(famous)j(cases:)270 1499 y FJ(\017)34 b FK(If)j FH(A)f FK(is)g(a)i(disjunction)e FH(A)1085 1473 y Fv(0)1119 1499 y FJ(_)19 b FH(A)1237 1473 y Fv(00)1266 1499 y FK(,)39 b(the)e(last)f(rule)g(m)n(ust)g(b)r(e) h FJ(R)p FK(1)p FJ(_)p FK(,)i(in)d(whic)n(h)g(case)339 1584 y FJ(`)21 b FH(A)455 1558 y Fv(0)522 1584 y FK(is)29 b(pro)n(v)l(able,)i(or)f FJ(R)p FK(2)p FJ(_)p FK(,)h(in)e(whic)n(h)g (case)50 b FJ(`)21 b FH(A)1762 1558 y Fv(00)1842 1584 y FK(is)29 b(pro)n(v)l(able:)41 b(this)29 b(is)g(what)h(is)339 1669 y(called)c(the)i FM(Disjunction)f(Pr)l(op)l(erty)p FK(.)270 1820 y FJ(\017)34 b FK(If)26 b FH(A)f FK(is)f(an)i(existence)e FJ(9)p FH(\030)s(:)12 b(A)1108 1795 y Fv(0)1125 1820 y FK(,)26 b(the)f(last)g(rule)f(m)n(ust)h(b)r(e)g FJ(R)p FK(1)p FJ(9)p FK(,)i(whic)n(h)d(means)i(that)f(the)339 1905 y(premise)32 b(is)g(of)i(the)f(form)56 b FJ(`)24 b FH(A)1215 1880 y Fv(0)1231 1905 y FK([)p FH(a=\030)s FK(])h(;)36 b(in)c(other)h(w)n(ords,)j(a)d(term)f FH(t)h FK(can)h(b)r(e)f(found)339 1990 y(suc)n(h)c(that)47 b FJ(`)20 b FH(A)788 1965 y Fv(0)804 1990 y FK([)p FH(a=\030)s FK(])49 b(is)27 b(pro)n(v)l(able:)36 b(this)27 b(is)g(the)g FM(Existenc)l(e)g(Pr)l(op)l(erty)p FK(.)270 2164 y(These)21 b(t)n(w)n(o)g(examples)f(fully)g(justify)h(the)g(in)n(terest)e(of)i (limiting)d(the)j(use)g(of)g(the)g(structural)167 2249 y(rules,)27 b(a)h(limitation)d(whic)n(h)i(leads)g(to)h(linear)e(logic.) 167 2463 y Fy(5.2.2)95 b(Subform)m(ula)26 b(prop)s(ert)m(y)167 2598 y FK(Let)k(us)h(consider)f(the)g(last)g(rule)f(of)i(a)g(pro)r(of:) 42 b(can)30 b(one)h(someho)n(w)g(predict)e(the)h(premises?)167 2683 y(The)c(cut)f(rule)g(is)h(absolutely)g(unpredictable,)f(since)g (an)i(arbitrary)f(form)n(ula)g FH(C)31 b FK(disapp)r(ears:)167 2769 y(it)c(cannot)i(b)r(e)g(reco)n(v)n(ered)e(from)h(the)g (conclusions.)38 b(It)27 b(is)h(the)g(only)g(rule)g(whic)n(h)f(b)r(eha) n(v)n(es)i(so)167 2854 y(badly)-6 b(.)35 b(Indeed,)25 b(all)e(the)h(other)h(rules)e(ha)n(v)n(e)i(the)f(prop)r(ert)n(y)h(that) g(the)f(unsp)r(eci\014ed)g(\\con)n(text")167 2939 y(part)36 b(\(written)609 2940 y FH(A)p 612 2959 39 3 v -1 x FK(,)717 2940 y FH(B)p 720 2959 43 3 v 773 2939 a FK(,)h FM(etc.)p FK(\))57 b(is)35 b(preserv)n(ed)g(in)n(tact.)57 b(The)35 b(rule)f(actually)h(concerns)g(only)167 3024 y(a)g(few)g(of)h(the)e (form)n(ulae.)58 b(But)35 b(the)f(form)n(ulae)h(in)f(the)h(premises)f (are)h(simpler)d(than)k(the)167 3109 y(corresp)r(onding)e(ones)f(in)f (the)h(conclusions.)51 b(F)-6 b(or)33 b(example,)h(for)f FH(A)17 b FJ(^)g FH(B)36 b FK(as)e(a)f(conclusion,)167 3194 y FH(A)e FK(and)h FH(B)k FK(m)n(ust)31 b(ha)n(v)n(e)h(b)r(een)f (used)h(as)g(premises,)e(or)i(for)g FJ(8)p FH(\030)s(:)12 b(A)30 b FK(as)i(a)g(conclusion,)g FH(A)p FK([)p FH(a=\030)s FK(])167 3279 y(m)n(ust)26 b(ha)n(v)n(e)i(b)r(een)e(used)h(as)g(a)g (premise.)33 b(In)27 b(other)f(w)n(ords,)i(one)e(has)i(to)e(use)h FM(subformulae)f FK(as)167 3364 y(premises:)270 3537 y FJ(\017)34 b FK(The)28 b(immediate)d(subform)n(ulae)j(of)g FH(A)15 b FJ(^)h FH(B)t FK(,)27 b FH(A)16 b FJ(_)f FH(B)32 b FK(and)d FH(A)19 b FJ(\))h FH(B)31 b FK(are)d FH(A)f FK(and)i FH(B)t FK(.)270 3688 y FJ(\017)34 b FK(The)28 b(only)g(immediate)d(subform)n(ula)j(of)g FJ(:)p FH(A)f FK(is)g FH(A)p FK(.)270 3840 y FJ(\017)34 b FK(The)42 b(immediate)d(subform)n(ulae)i(of)i FJ(8)p FH(\030)s(:)12 b(A)40 b FK(and)j FJ(9)p FH(\030)s(:)12 b(A)42 b FK(are)f(the)h(form)n (ulae)f FH(A)p FK([)p FH(a=\030)s FK(])339 3925 y(where)27 b FH(a)h FK(is)f(an)n(y)i(term.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 34 37 bop 167 167 a FK(34)1200 b Fz(CHAPTER)26 b(5.)63 b(SEQUENT)27 b(CALCULUS)270 404 y FK(No)n(w)39 b(it)f(is)g(clear)g (that)h(all)f(the)h(rules)f(|)h(except)f(the)h(cut)f(|)h(ha)n(v)n(e)h (the)e(prop)r(ert)n(y)167 490 y(that)c(the)f(premises)e(are)i(made)h (up)f(of)h(subform)n(ulae)g(of)g(the)f(conclusion.)52 b(In)33 b(particular,)167 575 y(a)38 b(cut-free)e(pro)r(of)i(of)g(a)g (sequen)n(t)f(uses)h(only)f(subform)n(ulae)h(of)g(its)e(form)n(ulae.)64 b(W)-6 b(e)37 b(shall)167 660 y(pro)n(v)n(e)32 b(the)g(corresp)r (onding)g(result)f(for)h(natural)f(deduction)h(in)f(section)g FG(??)q FK(.)47 b(This)31 b(is)g(v)n(ery)167 745 y(in)n(teresting)37 b(for)h FM(automate)l(d)i(de)l(duction)p FK(.)68 b(Of)38 b(course,)j(it)c(is)h(not)h(enough)g(to)g(mak)n(e)f(the)167 830 y(predicate)i(calculus)h FM(de)l(cidable)p FK(,)j(since)d(w)n(e)f (ha)n(v)n(e)j(an)f(in\014nit)n(y)f(of)h(subform)n(ulae)g(for)f(the)167 915 y(sen)n(tences)27 b(with)g(quan)n(ti\014ers.)167 1230 y Fy(5.2.3)95 b(Asymmetrical)27 b(in)m(terpretation)167 1365 y FK(W)-6 b(e)43 b(ha)n(v)n(e)g(describ)r(ed)f(the)h(iden)n(tit)n (y)f(axiom)g(and)i(the)f(cut)g(rule)e(as)j(the)f(t)n(w)n(o)g(faces)g (of)167 1450 y(\\)p FH(A)34 b FK(is)e FH(A)p FK(".)53 b(No)n(w,)35 b(in)e(the)h(absence)f(of)h(cut,)h(the)e(situation)g(is)g (suddenly)h(v)n(ery)g(di\013eren)n(t:)167 1535 y(w)n(e)c(can)h(no)g (longer)f(express)g(that)h FH(A)f FK(\(on)h(the)f(righ)n(t\))g(is)f (stronger)i(than)h FH(A)d FK(\(on)i(the)f(left\).)167 1620 y(Then)k(there)f(arises)g(the)g(p)r(ossibilit)n(y)f(of)j (splitting)d FH(A)h FK(in)n(to)h(t)n(w)n(o)g(in)n(terpretations)e FH(A)2490 1594 y Fv(L)2561 1620 y FK(and)167 1705 y FH(A)219 1679 y Fv(R)264 1705 y FK(,)c(whic)n(h)f(need)g(not)i(necessarily)d (coincide.)34 b(Let)27 b(us)h(b)r(e)f(more)g(precise.)270 1839 y(In)41 b(a)g(sen)n(tence,)i(w)n(e)d(can)h(de\014ne)f(the)g FM(signatur)l(e)h FK(of)g(an)g(o)r(ccurrence)e(of)i(an)g(atomic)167 1924 y(predicate,)27 b(+1)h(or)g FJ(\000)p FK(1:)36 b(the)27 b(signature)h(is)f(the)h(parit)n(y)g(of)g(the)f(n)n(um)n(b)r(er)h(of)g (times)e(that)j(this)167 2009 y(sym)n(b)r(ol)f(has)h(b)r(een)f (negated.)37 b(Concretely)-6 b(,)28 b FH(P)38 b FK(retains)27 b(the)h(signature)g(whic)n(h)g(it)f(had)i(in)e FH(A)p FK(,)167 2094 y(when)k(it)f(is)g(considered)g(in)h FH(A)16 b FJ(^)h FH(B)t FK(,)31 b FH(B)21 b FJ(^)16 b FH(A)p FK(,)32 b FH(A)16 b FJ(_)h FH(B)t FK(,)31 b FH(B)21 b FJ(_)16 b FH(A)p FK(,)32 b FH(B)26 b FJ(\))c FH(A)p FK(,)32 b FJ(8)p FH(\030)s(:)12 b(A)30 b FK(and)i FJ(9)p FH(\030)s(:)12 b(A)p FK(,)167 2180 y(and)29 b(rev)n(erses)e(it)f(in)h FJ(:)p FH(A)h FK(and)g FH(A)20 b FJ(\))g FH(B)t FK(.)270 2314 y(In)29 b(a)g(sequen)n(t)g(to)r(o,)g(w)n(e)f(can)h(de\014ne)f(the) g(signature)h(of)g(an)g(o)r(ccurrence)e(of)i(a)g(predicate:)167 2399 y(if)f FH(P)39 b FK(o)r(ccurs)29 b(in)g FH(A)f FK(on)i(the)f(left) f(of)h(\\)p FJ(`)p FK(",)i(the)e(signature)g(is)f(rev)n(ersed,)h(if)f FH(P)40 b FK(o)r(ccurs)29 b(on)g(the)167 2484 y(righ)n(t,)e(it)g(is)g (conserv)n(ed.)270 2618 y(The)h(rules)f(of)h(the)f(sequen)n(t)h (calculus)e(\(apart)j(from)e(the)h(iden)n(tit)n(y)e(axiom)h(and)i(the)f (cut\))167 2703 y(preserv)n(e)37 b(the)g(signature:)56 b(in)37 b(other)g(w)n(ords,)k(they)d(relate)e(o)r(ccurrences)g(with)h (the)g(same)167 2788 y(signature.)44 b(The)30 b(iden)n(tit)n(y)f(axiom) h(sa)n(ys)i(that)f(the)f(negativ)n(e)g(o)r(ccurrences)g(\(signature)g FJ(\000)p FK(1\))167 2873 y(are)f(stronger)g(than)h(the)f(p)r(ositiv)n (e)f(ones;)i(the)e(cut)h(sa)n(ys)h(the)f(opp)r(osite.)39 b(So)30 b(in)e(the)h(absence)167 2958 y(of)38 b(cut,)j(there)c(is)g (the)h(p)r(ossibilit)n(y)e(of)i(giving)g(asymmetric)e(in)n (terpretations)h(to)h(sequen)n(t)167 3044 y(calculus:)c FH(A)26 b FK(do)r(es)h(not)g(ha)n(v)n(e)g(the)f(same)h(meaning)f(when)g (it)g(is)f(on)j(the)e(righ)n(t)g(as)h(when)f(it)g(is)167 3129 y(on)i(the)g(left)e(of)i(\\)p FJ(`)p FK(".)270 3347 y FJ(\017)34 b FH(A)391 3321 y Fv(R)466 3347 y FK(is)29 b(obtained)h(b)n(y)h(replacing)d(the)h(p)r(ositiv)n(e)g(o)r(ccurrences) g(of)h(the)f(predicate)g FH(P)39 b FK(b)n(y)339 3432 y FH(P)393 3407 y Fv(R)467 3432 y FK(and)28 b(the)g(negativ)n(e)f(ones) i(b)n(y)f FH(P)1318 3407 y Fv(L)1355 3432 y FK(.)270 3583 y FJ(\017)34 b FH(A)391 3557 y Fv(L)459 3583 y FK(is)29 b(obtained)i(b)n(y)g(replacing)e(the)h(p)r(ositiv)n(e)g(o)r(ccurrences) f(of)i(the)f(predicate)f FH(P)40 b FK(b)n(y)339 3668 y FH(P)393 3642 y Fv(L)458 3668 y FK(and)29 b(the)e(negativ)n(e)h(ones) g(b)n(y)h FH(P)1310 3642 y Fv(R)1355 3668 y FK(.)270 3840 y(The)38 b(atomic)f(sym)n(b)r(ols)i FH(P)1001 3814 y Fv(R)1084 3840 y FK(and)g FH(P)1287 3814 y Fv(L)1363 3840 y FK(are)f(tied)f(together)h(b)n(y)h(a)f(condition,)j(namely)167 3925 y FH(P)221 3899 y Fv(L)278 3925 y FJ(\))20 b FH(P)422 3899 y Fv(R)467 3925 y FK(.)p eop PStoPSsaved restore %%Page: (38,39) 20 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 35 38 bop 167 167 a Fz(5.3.)64 b(SEQUENT)27 b(CALCULUS)g(AND)f(NA)-6 b(TURAL)27 b(DEDUCTION)500 b FK(35)270 404 y(It)37 b(is)f(easy)h(to)g (see)f(that)h(this)f(kind)h(of)g(asymmetrical)d(in)n(terpretation)h(is) h(consisten)n(t)167 490 y(with)27 b(the)g(system)g(without)h(cut,)f(in) n(terpreting)1491 491 y FH(A)p 1494 510 39 3 v 1562 490 a FJ(`)1625 491 y FH(B)p 1628 510 43 3 v 1728 490 a FK(b)n(y)1848 491 y FH(A)p 1851 510 39 3 v 1899 461 a Fv(L)1956 490 y FJ(`)2019 491 y FH(B)p 2022 510 43 3 v 2075 461 a Fv(R)2140 490 y FK(.)270 627 y(The)18 b(sequen)n(t)g(calculus)e(seems)h(to)h (lend)f(itself)f(to)h(some)h(m)n(uc)n(h)f(more)g(subtle)g(asymmetrical) 167 712 y(in)n(terpretations,)27 b(esp)r(ecially)e(in)i(linear)f (logic.)167 960 y FE(5.3)114 b(Sequen)m(t)29 b(Calculus)g(and)f (Natural)h(Deduction)167 1121 y FK(W)-6 b(e)28 b(shall)g(consider)g (here)g(the)h(noble)f(part)h(of)g(natural)g(deduction,)g(that)g(is,)g (the)f(fragmen)n(t)167 1206 y(without)33 b FJ(_)p FK(,)i FJ(9)f FK(or)g FJ(:)p FK(.)53 b(W)-6 b(e)33 b(restrict)e(ourselv)n(es)j (to)f(sequen)n(ts)i(of)f(the)f(form)2299 1207 y FH(A)p 2302 1226 39 3 v 2374 1206 a FJ(`)24 b FH(B)k FK(;)36 b(the)167 1291 y(corresp)r(ondence)28 b(with)f(natural)h(deduction)f (is)g(giv)n(en)h(as)g(follo)n(ws:)270 1467 y FJ(\017)34 b FK(T)-6 b(o)31 b(a)f(pro)r(of)h(of)806 1468 y FH(A)p 810 1488 V 879 1467 a FJ(`)21 b FH(B)56 b FK(corresp)r(onds)31 b(a)f(deduction)g(of)h FH(B)i FK(under)e(the)f(h)n(yp)r(otheses,)339 1552 y(or)e(rather)g(parcels)f(of)h(h)n(yp)r(otheses,)1333 1553 y FH(A)p 1336 1573 V -1 x FK(.)270 1705 y FJ(\017)34 b FK(Con)n(v)n(ersely)-6 b(,)36 b(a)f(deduction)f(of)g FH(B)k FK(under)c(the)g(\(parcels)f(of)5 b(\))34 b(h)n(yp)r(otheses) 2378 1706 y FH(A)p 2382 1726 V 2464 1705 a FK(can)g(b)r(e)339 1790 y(represen)n(ted)27 b(in)g(the)h(sequen)n(t)g(calculus,)e(but)j (unfortunately)f(not)g(uniquely)-6 b(.)270 1985 y(F)g(rom)29 b(a)g(pro)r(of)h(of)810 1986 y FH(A)p 813 2006 V 882 1985 a FJ(`)20 b FH(B)k FK(,)29 b(w)n(e)f(build)g(a)h(deduction)g(of)g FH(B)t FK(,)g(of)g(whic)n(h)e(the)i(h)n(yp)r(otheses)167 2070 y(are)f(parcels,)f(eac)n(h)g(parcel)g(corresp)r(onding)i(in)e(a)h (precise)e(w)n(a)n(y)i(to)g(a)g(form)n(ula)g(of)2370 2071 y FH(A)p 2373 2091 V 2421 2070 a FK(.)251 2246 y(1.)35 b(The)28 b(axiom)47 b FH(A)19 b FJ(`)h FH(A)47 b FK(b)r(ecomes)27 b(the)g(deduction)106 b FH(A)78 b FK(.)251 2399 y(2.)35 b(If)28 b(the)f(last)h(rule)e(is)h(a)h(cut)1150 2601 y FH(A)p 1153 2621 V 1221 2600 a FJ(`)20 b FH(B)1418 2601 y(A)p 1421 2621 V 1469 2571 a Fv(0)1486 2600 y FH(;)12 b(B)23 b FJ(`)d FH(C)p 1150 2645 560 4 v 1730 2661 a Fq(Cut)1286 2723 y FH(A)p 1289 2742 39 3 v 1337 2722 a(;)1368 2723 y(A)p 1372 2742 V -30 x Fv(0)1456 2722 y FJ(`)g FH(C)339 3031 y FK(and)37 b(the)e(deductions)h FH(\016)i FK(of)1238 2941 y FH(A)p 1241 2960 V 1254 3001 a FJ(\001)1254 3039 y(\001)1254 3077 y(\001)1236 3134 y FH(B)1428 3031 y FK(and)e FH(\016)1608 3005 y Fv(0)1659 3031 y FK(of)1851 2945 y FH(A)p 1855 2964 V -30 x Fv(0)1919 2944 y FH(;)12 b(B)1919 3005 y FJ(\001)1919 3043 y(\001)1919 3081 y(\001)1902 3138 y FH(C)2142 3031 y FK(are)36 b(asso)r(ciated)g (to)339 3193 y(the)c(sub-pro)r(ofs)i(ab)r(o)n(v)n(e)f(the)e(t)n(w)n(o)h (premises,)f(then)h(w)n(e)f(asso)r(ciate)h(to)f(our)i(pro)r(of)f(the) 339 3278 y(deduction)g FH(\016)700 3253 y Fv(0)747 3278 y FK(where)f(all)g(the)g(o)r(ccurrences)g(of)h FH(B)k FK(in)31 b(the)h(parcel)e(it)h(represen)n(ts)g(are)339 3363 y(replaced)c(b)n(y)h FH(\016)s FK(:)1397 3766 y FH(A)p 1401 3786 V -30 x Fv(0)1465 3765 y FH(;)1533 3572 y(A)p 1536 3591 V 1549 3632 a FJ(\001)1549 3670 y(\001)1549 3708 y(\001)1531 3765 y FH(B)1482 3827 y FJ(\001)1482 3865 y(\001)1482 3903 y(\001)1465 3960 y FH(C)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 36 39 bop 167 167 a FK(36)1200 b Fz(CHAPTER)26 b(5.)63 b(SEQUENT)27 b(CALCULUS)339 404 y FK(In)d(general)f(the)g(h)n(yp)r (otheses)h(in)f(the)g(parcel)f(in)1618 405 y FH(A)p 1622 425 39 3 v 1693 404 a FK(are)h(proliferated,)g(but)h(the)f(n)n(um)n(b)r (er)339 490 y(is)28 b(preserv)n(ed)g(b)n(y)h(putting)g(in)f(the)g(same) g(parcel)f(afterw)n(ards)i(the)f(h)n(yp)r(otheses)i(whic)n(h)339 575 y(came)c(from)h(the)f(same)h(parcel)f(b)r(efore)g(and)i(ha)n(v)n(e) g(b)r(een)e(duplicated.)34 b(No)27 b(regrouping)339 660 y(o)r(ccurs)h(b)r(et)n(w)n(een)828 661 y FH(A)p 831 680 V 907 660 a FK(and)1046 661 y FH(A)p 1049 680 V -30 x Fv(0)1114 660 y FK(.)251 796 y(3.)35 b(The)28 b(rule)e FJ(L)p Fq(X)1204 958 y FH(A)p 1208 978 V -1 x(;)12 b(C)q(;)g(D)r(;)1458 958 y(A)p 1462 978 V -30 x Fv(0)1546 957 y FJ(`)20 b FH(B)p 1204 1002 461 4 v 1685 1018 a FJ(L)p Fq(X)1204 1079 y FH(A)p 1208 1099 39 3 v -1 x(;)12 b(D)r(;)g(C)q(;)1458 1079 y(A)p 1462 1099 V -30 x Fv(0)1546 1078 y FJ(`)20 b FH(B)339 1253 y FK(is)27 b(in)n(terpreted)f(as)j(the)e(iden)n(tit)n (y:)34 b(the)28 b(same)f(deduction)h(b)r(efore)f(and)i(after)e(the)h (rule.)251 1390 y(4.)35 b(The)28 b(rule)e FJ(L)p Fq(W)1330 1545 y FH(A)p 1333 1565 V 1401 1544 a FJ(`)19 b FH(B)p 1287 1589 276 4 v 1583 1605 a FJ(L)p Fq(W)1287 1666 y FH(A)p 1290 1686 39 3 v -1 x(;)12 b(C)25 b FJ(`)19 b FH(B)339 1840 y FK(is)25 b(in)n(terpreted)g(as)h(the)g(creation)f(of)h (a)g(mo)r(c)n(k)g(parcel)f(formed)g(from)h(zero)f(o)r(ccurrences)339 1925 y(of)k FH(C)5 b FK(.)35 b(W)-6 b(eak)n(ening)29 b(is)e(then)g(the)h(p)r(ossibilit)n(y)e(of)i(forming)f(empt)n(y)g (parcels.)251 2062 y(5.)35 b(The)28 b(rule)e FJ(L)p Fq(C)1257 2217 y FH(A)p 1261 2237 V -1 x(;)12 b(C)q(;)g(C)25 b FJ(`)20 b FH(B)p 1257 2261 357 4 v 1634 2277 a FJ(L)p Fq(C)1298 2338 y FH(A)p 1301 2358 39 3 v 1349 2337 a(;)12 b(C)25 b FJ(`)20 b FH(B)339 2512 y FK(is)33 b(in)n(terpreted)f(as)i (the)g(uni\014cation)f(of)h(t)n(w)n(o)g FH(C)5 b FK(-parcels)33 b(in)n(to)g(one.)54 b(Con)n(traction)34 b(is)339 2597 y(then)28 b(the)f(p)r(ossibilit)n(y)f(of)j(forming)e(big)h(parcels.)251 2734 y(6.)35 b(The)28 b(rule)e FJ(R^)1192 2895 y FH(A)p 1195 2915 V 1263 2894 a FJ(`)20 b FH(B)1460 2895 y(A)p 1464 2915 V -30 x Fv(0)1548 2894 y FJ(`)f FH(C)p 1192 2939 473 4 v 1685 2955 a FJ(R^)1218 3017 y FH(A)p 1221 3036 39 3 v 1269 3016 a(;)1300 3017 y(A)p 1304 3036 V -30 x Fv(0)1388 3016 y FJ(`)g FH(B)h FJ(^)c FH(C)339 3191 y FK(will)23 b(b)r(e)j(in)n(terpreted)e(b)n(y)i FJ(^I)5 b FK(:)35 b(supp)r(ose)27 b(that)f(deductions)g(ending)g(in)f FH(B)k FK(and)e FH(C)k FK(ha)n(v)n(e)339 3276 y(b)r(een)g(constructed)g (to)h(represen)n(t)e(the)h(pro)r(ofs)h(ab)r(o)n(v)n(e)g(the)f(t)n(w)n (o)g(premises;)g(then)h(our)339 3361 y(pro)r(of)d(is)e(in)n(terpreted)f (b)n(y:)1306 3536 y FH(A)p 1310 3556 V 1322 3597 a FJ(\001)1322 3635 y(\001)1322 3673 y(\001)1304 3730 y FH(B)1507 3536 y(A)p 1511 3556 V -30 x Fv(0)1532 3597 y FJ(\001)1532 3635 y(\001)1532 3673 y(\001)1514 3730 y FH(C)p 1304 3774 265 4 v 1589 3790 a FJ(^I)1342 3851 y FH(B)20 b FJ(^)15 b FH(C)p eop PStoPSsaved restore %%Page: (40,41) 21 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 37 40 bop 167 167 a Fz(5.3.)64 b(SEQUENT)27 b(CALCULUS)g(AND)f(NA)-6 b(TURAL)27 b(DEDUCTION)500 b FK(37)251 404 y(7.)35 b(The)28 b(rule)e FJ(R\))i FK(will)d(b)r(e)i(in)n(terpreted)f(b)n(y)j FJ(\)I)5 b FK(:)677 757 y FH(A)p 681 776 39 3 v -1 x(;)12 b(B)24 b FJ(`)19 b FH(C)p 638 800 354 4 v 1013 816 a FJ(R\))638 878 y FH(A)p 642 898 39 3 v 709 877 a FJ(`)h FH(B)j FJ(\))d FH(C)1441 751 y FK(b)r(ecomes)2013 672 y FH(A)p 2016 691 V -1 x(;)12 b FK([)p FH(B)t FK(])2091 732 y FJ(\001)2091 770 y(\001)2091 808 y(\001)2074 865 y FH(C)p 1991 910 220 4 v 2232 926 a FJ(\)I)1991 987 y FH(B)24 b FJ(\))c FH(C)339 1235 y FK(where)27 b(a)h(complete)e FH(B)t FK(-parcel)h(is)g(disc)n(harged)h(at)g(one)g(go.)251 1409 y(8.)35 b(The)28 b(rule)e FJ(R8)h FK(will)e(b)r(e)i(in)n (terpreted)f(b)n(y)i FJ(8I)5 b FK(:)736 1766 y FH(A)p 739 1785 39 3 v 807 1765 a FJ(`)20 b FH(B)p 684 1809 294 4 v 998 1825 a FJ(R8)684 1887 y FH(A)p 687 1907 39 3 v 755 1886 a FJ(`)g(8)p FH(\030)s(:)12 b(B)1441 1760 y FK(b)r(ecomes)2091 1671 y FH(A)p 2095 1691 V 2107 1732 a FJ(\001)2107 1769 y(\001)2107 1807 y(\001)2089 1865 y FH(B)p 2037 1909 160 4 v 2217 1925 a FJ(8I)2037 1986 y(8)p FH(\030)s(:)g(B)251 2293 y FK(9.)35 b(With)21 b(the)h(left)f (rules)g(app)r(ears)i(one)f(of)h(the)e(hidden)h(prop)r(erties)f(of)i (natural)f(deduction,)339 2378 y(namely)k(that)h(the)f(elimination)d (rules)i(\(whic)n(h)h(corresp)r(ond)h FM(gr)l(osso)g(mo)l(do)h FK(to)e(the)g(left)339 2463 y(rules)j(of)h(sequen)n(ts\))g(are)g (written)e(bac)n(kw)n(ards!)43 b(This)29 b(is)g(no)n(where)h(seen)g(b)r (etter)e(than)339 2548 y(in)h(linear)g(logic,)g(whic)n(h)g(mak)n(es)h (the)f(lost)g(symmetries)f(reapp)r(ear.)42 b(Here)28 b(concretely)-6 b(,)339 2633 y(this)31 b(is)g(re\015ected)g(in)g(the)g (fact)h(that)g(the)f(left)f(rules)h(are)h(translated)f(b)n(y)i(actions) e(on)339 2718 y(parcels)c(of)h(h)n(yp)r(otheses.)339 2913 y(The)g(rule)e FJ(L)p FK(1)p FJ(^)i FK(b)r(ecomes)f FJ(^)p FK(1)p FJ(E)6 b FK(:)602 3249 y FH(A)p 605 3269 39 3 v -1 x(;)12 b(B)23 b FJ(`)d FH(D)p 536 3293 413 4 v 969 3309 a FJ(L)p FK(1)p FJ(^)536 3371 y FH(A)p 539 3390 39 3 v 587 3370 a(;)12 b(B)20 b FJ(^)15 b FH(C)25 b FJ(`)20 b FH(D)1295 3244 y FK(is)27 b(in)n(terpreted)f(b)n(y)1997 3283 y FH(A)p 2001 3303 V -1 x(;)2114 3161 y(B)20 b FJ(^)15 b FH(C)p 2114 3206 189 4 v 2323 3222 a FJ(^)p FK(1)p FJ(E)2180 3282 y FH(B)2007 3344 y FJ(\001)2007 3382 y(\001)2007 3420 y(\001)1987 3477 y FH(D)339 3729 y FJ(^)p FK(1)p FJ(E)35 b FK(allo)n(ws)27 b(us)h(to)g(pass)h(from)e(a)h(\()p FH(B)20 b FJ(^)15 b FH(C)5 b FK(\)-parcel)27 b(to)h(a)g FH(B)t FK(-parcel.)339 3925 y(Similarly)-6 b(,)26 b(the)h(rule)f FJ(L)p FK(2)p FJ(^)i FK(b)r(ecomes)f FJ(^)p FK(2)p FJ(E)6 b FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 38 41 bop 167 167 a FK(38)1200 b Fz(CHAPTER)26 b(5.)63 b(SEQUENT)27 b(CALCULUS)217 404 y FK(10.)35 b(The)28 b(rule)e FJ(L\))i FK(b)r(ecomes)f FJ(\)E)6 b FK(:)449 765 y FH(A)p 453 784 39 3 v 521 764 a FJ(`)19 b FH(B)718 765 y(A)p 721 784 V 769 735 a Fv(0)786 764 y FH(;)12 b(C)25 b FJ(`)19 b FH(D)p 449 808 563 4 v 1033 824 a FJ(L\))459 886 y FH(A)p 463 906 39 3 v -1 x(;)542 886 y(A)p 546 906 V -30 x Fv(0)610 885 y FH(;)12 b(B)24 b FJ(\))c FH(C)25 b FJ(`)19 b FH(D)1262 756 y FK(is)27 b(in)n(terpreted)f(b)n(y)1878 892 y FH(A)p 1881 912 V 1929 862 a Fv(0)1946 891 y FH(;)2013 576 y(A)p 2017 596 V 2030 637 a FJ(\001)2030 675 y(\001)2030 713 y(\001)2011 770 y FH(B)117 b(B)24 b FJ(\))c FH(C)p 2011 815 389 4 v 2421 831 a FJ(\)E)2178 891 y FH(C)1912 953 y FJ(\001)1912 991 y(\001)1912 1029 y(\001)1892 1086 y FH(D)339 1262 y FK(Here)34 b(again,)k(a)e FH(C)5 b FK(-parcel)35 b(is)f(replaced)g(b) n(y)i(a)g(\()p FH(B)29 b FJ(\))c FH(C)5 b FK(\)-parcel;)38 b(something)d(m)n(ust)339 1348 y(also)28 b(b)r(e)g(done)g(ab)r(out)h (the)e(proliferation)g(of)h FH(A)p FK(-parcels,)f(as)h(in)f(case)h FG(??)p FK(.)217 1515 y(11.)35 b(Finally)27 b(the)g(rule)g FJ(L8)f FK(b)r(ecomes)h FJ(8E)6 b FK(:)553 1791 y FH(A)p 557 1811 39 3 v -1 x(;)12 b(B)t FK([)p FH(a=\030)s FK(])21 b FJ(`)e FH(C)p 553 1835 418 4 v 991 1851 a FJ(L8)573 1912 y FH(A)p 576 1932 39 3 v 624 1911 a(;)12 b FJ(8)p FH(\030)s(:)g(B)23 b FJ(`)d FH(C)1293 1783 y FK(is)27 b(in)n(terpreted)f(b)n(y)2012 1824 y FH(A)p 2016 1843 V -1 x(;)2149 1701 y FJ(8)p FH(\030)s(:)12 b(B)p 2129 1746 199 4 v 2348 1762 a FJ(8E)2129 1823 y FH(B)t FK([)p FH(a=\030)s FK(])2093 1884 y FJ(\001)2093 1922 y(\001)2093 1960 y(\001)2076 2017 y FH(C)167 2288 y FE(5.4)114 b(Prop)s(erties)27 b(of)h(the)g(translation)167 2443 y FK(The)f(translation)g(from)h (sequen)n(t)f(calculus)g(in)n(to)g(natural)g(deduction)h(is)e(not)i (1{1:)37 b(di\013eren)n(t)167 2528 y(pro)r(ofs)29 b(giv)n(e)e(the)h (same)f(deduction,)h(for)g(example)546 2685 y FH(A)19 b FJ(`)h FH(A)78 b(B)23 b FJ(`)d FH(B)p 546 2730 458 4 v 1025 2746 a FJ(R^)572 2806 y FH(A;)12 b(B)23 b FJ(`)c FH(A)d FJ(^)f FH(B)p 499 2851 554 4 v 1072 2867 a FJ(L)p FK(1)p FJ(^)499 2928 y FH(A)g FJ(^)h FH(A)681 2898 y Fv(0)697 2928 y FH(;)c(B)23 b FJ(`)d FH(A)15 b FJ(^)h FH(B)p 423 2972 704 4 v 1148 2988 a FJ(L)p FK(1)p FJ(^)423 3049 y FH(A)g FJ(^)f FH(A)605 3020 y Fv(0)621 3049 y FH(;)d(B)20 b FJ(^)15 b FH(B)842 3020 y Fv(0)878 3049 y FJ(`)20 b FH(A)15 b FJ(^)h FH(B)1657 2685 y(A)j FJ(`)h FH(A)78 b(B)23 b FJ(`)d FH(B)p 1657 2730 458 4 v 2135 2746 a FJ(R^)1682 2806 y FH(A;)12 b(B)24 b FJ(`)19 b FH(A)d FJ(^)f FH(B)p 1607 2851 558 4 v 2185 2867 a FJ(L)p FK(1)p FJ(^)1607 2928 y FH(A;)d(B)19 b FJ(^)d FH(B)1880 2898 y Fv(0)1916 2928 y FJ(`)j FH(A)d FJ(^)f FH(B)p 1534 2972 704 4 v 2258 2988 a FJ(L)p FK(1)p FJ(^)1534 3049 y FH(A)g FJ(^)h FH(A)1716 3020 y Fv(0)1732 3049 y FH(;)c(B)20 b FJ(^)15 b FH(B)1953 3020 y Fv(0)1989 3049 y FJ(`)20 b FH(A)15 b FJ(^)h FH(B)167 3206 y FK(whic)n(h)27 b(di\013er)g(only)h (in)f(the)g(order)h(of)g(the)f(rules,)g(ha)n(v)n(e)i(the)e(same)h (translation:)984 3369 y FH(A)16 b FJ(^)f FH(A)1166 3340 y Fv(0)p 984 3414 199 4 v 1203 3429 a FJ(^)p FK(1)p FJ(E)1057 3490 y FH(A)1475 3369 y(B)20 b FJ(^)15 b FH(B)1665 3340 y Fv(0)p 1475 3414 207 4 v 1702 3429 a FJ(^)p FK(1)p FJ(E)1550 3490 y FH(B)p 1057 3535 550 4 v 1627 3551 a FJ(^I)1239 3611 y FH(A)g FJ(^)h FH(B)167 3754 y FK(In)35 b(particular,)h(it)e(w)n(ould)h(b)r(e)g(v)l(ain)g(to)g(lo)r(ok)g(for)h (an)f(in)n(v)n(erse)f(transformation.)58 b(What)36 b(is)167 3840 y(true)25 b(is)g(that)h(for)f(a)h(giv)n(en)g(deduction)f FH(\016)s FK(,)g(there)g(is)g(at)g(least)g(one)h(pro)r(of)g(in)f (sequen)n(t)h(calculus)167 3925 y(whose)i(translation)g(is)f FH(\016)s FK(.)p eop PStoPSsaved restore %%Page: (42,43) 22 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 39 42 bop 167 167 a Fz(5.4.)64 b(PR)n(OPER)-6 b(TIES)27 b(OF)g(THE)g(TRANSLA)-6 b(TION)975 b FK(39)270 404 y(In)30 b(some)f(sense,)g(w)n(e)g(should)h(think)f(of)h(the)f(natural)g (deductions)h(as)f(the)g(true)g(\\pro)r(of)5 b(")167 490 y(ob)t(jects.)38 b(The)29 b(sequen)n(t)g(calculus)e(is)h(only)h(a)g (system)g(whic)n(h)f(enable)g(us)h(to)g(w)n(ork)g(on)g(these)167 575 y(ob)t(jects:)454 576 y FH(A)p 458 595 39 3 v 525 575 a FJ(`)20 b FH(B)51 b FK(tells)26 b(us)i(that)g(w)n(e)f(ha)n(v)n(e) h(a)h(deduction)e(of)h FH(B)k FK(under)c(the)f(h)n(yp)r(otheses)2589 576 y FH(A)p 2593 595 V -1 x FK(.)270 741 y(A)h(rule)e(suc)n(h)i(as)h (the)e(cut)1064 884 y FH(A)p 1068 904 V 1135 883 a FJ(`)20 b FH(C)1331 884 y(A)p 1334 904 V 1382 854 a Fv(0)1399 883 y FH(;)12 b(C)25 b FJ(`)19 b FH(B)p 1064 928 559 4 v 1643 944 a Fq(Cut)1199 1006 y FH(A)p 1202 1025 39 3 v -1 x(;)1282 1006 y(A)p 1285 1025 V 1333 976 a Fv(0)1369 1005 y FJ(`)h FH(B)167 1161 y FK(allo)n(ws)27 b(us)i(to)f(construct)g (a)g(new)g(deduction)f(from)h(t)n(w)n(o)g(others,)h(in)e(a)h(sense)g (made)g(explicit)167 1247 y(b)n(y)g(the)g(translation.)270 1369 y(In)41 b(other)g(w)n(ords,)k(the)40 b(system)h(of)g(sequen)n(ts)g (is)f(not)h(primitiv)n(e,)h(and)f(the)g(rules)f(of)167 1454 y(the)d(calculus)e(are)i(in)f(fact)h(more)f(or)h(less)f(complex)g (com)n(binations)h(of)g(rules)f(of)i(natural)167 1540 y(deduction:)251 1769 y(1.)d(The)28 b(logical)e(rules)h(on)h(the)f FM(right)h FK(corresp)r(ond)h(to)e FM(intr)l(o)l(ductions)p FK(.)251 1909 y(2.)35 b(Those)28 b(on)g(the)e FM(left)h FK(to)g FM(eliminations)p FK(.)35 b(Here)26 b(the)h(direction)e(of)j (the)e(rules)g(is)h(in)n(v)n(erted)339 1994 y(in)h(the)g(case)h(of)g FM(natur)l(al)f(de)l(duction)p FK(,)h(since)e(in)h(fact,)h(the)f(tree)f (of)i(natural)g(deduction)339 2079 y(gro)n(ws)g(b)n(y)f(its)f(lea)n(v)n (es)g(at)h(the)g(elimination)c(stage.)339 2230 y(The)h(corresp)r (ondence)g FJ(R)19 b FK(=)g FJ(I)5 b FK(,)26 b FJ(L)19 b FK(=)g FJ(E)32 b FK(is)24 b(extremely)e(precise,)i(for)h(example)f(w) n(e)g(ha)n(v)n(e)339 2315 y FJ(R^)c FK(=)f FJ(^I)33 b FK(and)c FJ(L)p FK(1)p FJ(^)19 b FK(=)g FJ(^)p FK(1)p FJ(E)6 b FK(.)251 2455 y(3.)35 b(The)c(con)n(traction)f(rule)f FJ(L)p Fq(C)i FK(corresp)r(onds)g(to)g(the)f(formation)h(of)g(parcels,) f(and)i FJ(L)p Fq(W)q FK(,)339 2541 y(in)27 b(some)h(cases,)g(to)g(the) f(formation)h(of)g(mo)r(c)n(k)g(parcels.)251 2681 y(4.)35 b(The)28 b(exc)n(hange)g(rule)f(corresp)r(onds)i(to)f(nothing)g(at)g (all.)251 2821 y(5.)35 b(The)28 b(cut)f(rule)f(do)r(es)i(not)g(corresp) r(ond)g(to)g(a)g(rule)e(of)i(natural)g(deduction,)g(but)g(to)f(the)339 2906 y(need)35 b(to)g(mak)n(e)g(deductions)g(gro)n(w)h(at)f(the)g(ro)r (ot.)57 b(Let)35 b(us)g(giv)n(e)g(an)g(example:)49 b(the)339 2992 y(strict)23 b(translation)i(of)g FJ(L\))f FK(giv)n(es)h(us)g (\\from)f(a)h(deduction)g(of)g FH(A)f FK(and)h(one)g(of)g FH(C)30 b FK(\(with)339 3077 y(a)e FH(B)t FK(-parcel)f(as)h(h)n(yp)r (othesis\),)h(the)e(deduction)1250 3250 y FJ(\001)1250 3288 y(\001)1250 3326 y(\001)1234 3383 y FH(A)113 b(A)19 b FJ(\))h FH(B)p 1234 3428 381 4 v 1636 3444 a FJ(\)E)1397 3498 y FH(B)1415 3539 y FJ(\001)1415 3577 y(\001)1415 3615 y(\001)1397 3672 y FH(C)339 3840 y FK(is)34 b(formed")g(whic)n(h)g (gro)n(ws)h(in)e(the)h(wrong)h(direction)e(\(to)n(w)n(ards)i(the)f(lea) n(v)n(es\).)55 b(Y)-6 b(et,)339 3925 y(the)28 b(full)e(p)r(o)n(w)n(er)i (of)g(the)f(calculus)g(is)g(only)h(obtained)g(with)f(the)g(\\top-do)n (wn")j(rule)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 40 43 bop 167 167 a FK(40)1200 b Fz(CHAPTER)26 b(5.)63 b(SEQUENT)27 b(CALCULUS)1233 375 y FJ(\001)1233 413 y(\001)1233 451 y(\001)1217 508 y FH(A)1514 375 y FJ(\001)1514 413 y(\001)1514 451 y(\001)1416 508 y FH(A)19 b FJ(\))h FH(B)p 1217 553 417 4 v 1653 569 a FJ(\))q(E)1397 629 y FH(B)339 795 y FK(whic)n(h)27 b(is)g(the)h(translation)f(of)h(the)g(blo)r(c)n(k) f(of)i(pro)r(of:)880 981 y FH(A)p 884 1001 39 3 v -30 x Fv(0)968 980 y FJ(`)19 b FH(A)78 b(B)24 b FJ(`)c FH(B)p 880 1025 475 4 v 1375 1041 a FJ(L\))890 1102 y FH(A)p 894 1122 39 3 v -30 x Fv(0)958 1101 y FH(;)12 b(A)19 b FJ(\))h FH(B)k FJ(`)c FH(B)1607 1103 y(B)p 1610 1122 43 3 v 1663 1072 a Fv(0)1699 1102 y FJ(`)g FH(A)f FJ(\))h FH(B)p 890 1146 1089 4 v 1999 1162 a Fq(Cut)1280 1224 y FH(A)p 1283 1243 39 3 v 1331 1194 a Fv(0)1348 1223 y FH(;)1379 1224 y(B)p 1382 1243 43 3 v 1435 1194 a Fv(0)1471 1223 y FJ(`)f FH(B)270 1485 y FK(The)32 b(cut)g(corresp)r(onds)h FM(so)g FK(w)n(ell)d(to)i(a)h(rev)n(ersal)e(of)i(the)f(direction)e(of)j (the)f(deductions,)167 1570 y(that,)45 b(if)40 b(w)n(e)h(translate)g(a) g(cut-free)f(pro)r(of,)46 b(it)40 b(is)g(almost)h(immediate)d(that)j (the)g(result)167 1655 y(is)g(a)i(normal)f(deduction.)78 b(Indeed)42 b(non-normalit)n(y)h(comes)e(from)h(a)g(con\015ict)g(b)r (et)n(w)n(een)167 1740 y(an)36 b(in)n(tro)r(duction)e(and)i(an)f (elimination,)f(whic)n(h)g(only)h(arises)g(b)r(ecause)g(the)f(t)n(w)n (o)h(sorts)h(of)167 1825 y(rules)d(ev)n(olv)n(e)h(from)f(top)h(to)h(b)r (ottom.)54 b(But)33 b(just)i(try)e(to)h(pro)r(duce)h(a)f(redex,)h (writing)d(the)167 1910 y(in)n(tro)r(duction)e(rules)f(from)h(top)h(to) g(b)r(ottom)f(and)h(the)f(elimination)e(rules)h(from)h(b)r(ottom)h(to) 167 1995 y(top!)k(Once)25 b(again,)i(linear)d(logic)g(clari\014es)g (the)h(empirical)d(con)n(ten)n(t)k(of)g(this)f(kind)g(of)h(remark.)270 2163 y(W)-6 b(e)28 b(come)f(to)h(the)f(moral)g(equiv)l(alence:)1112 2331 y(normal)47 b(=)g(cut-free)270 2499 y(In)25 b(fact,)g(whilst)e(a)i (cut-free)e(pro)r(of)i(giv)n(es)g(a)f(normal)g(deduction,)h(n)n (umerous)g(pro)r(ofs)h(with)167 2584 y(cut)h(also)h(giv)n(e)g(normal)f (deductions,)h(for)g(example)1119 2735 y FH(A)19 b FJ(`)g FH(A)78 b(A)20 b FJ(`)f FH(A)p 1119 2779 450 4 v 1589 2795 a Fq(Cut)1250 2856 y FH(A)h FJ(`)f FH(A)167 2993 y FK(is)27 b(translated)h(b)n(y)g(the)f(deduction)106 b FH(A)78 b FK(!)270 3161 y(In)48 b(particular,)j(w)n(e)46 b(see)h(that)h(the)e(sequen)n(t)i(calculus)e(sometimes)f(incon)n(v)n (enien)n(tly)167 3246 y(complicates)c(situations,)48 b(b)n(y)c(making)f(cuts)g(app)r(ear)i(when)e(there)f(is)h(no)h(need.)82 b(The)167 3331 y(cut-elimination)25 b(theorem)h(\(Hauptsatz\))i(in)f (fact)h(reiterates)e(the)h(normalisation)g(theorem,)167 3417 y(but)c(with)f(some)h(tec)n(hnical)e(complications)g(whic)n(h)h (re\015ect)g(the)g(lesser)g(purit)n(y)g(of)i(the)e(syn)n(tax.)270 3584 y(As)27 b(w)n(e)e(ha)n(v)n(e)j(already)e(said,)h(ev)n(ery)g (deduction)f(is)g(the)g(translation)g(of)h(some)f(pro)r(of,)i(but)167 3669 y(this)g(pro)r(of)i(is)e(not)i(unique.)39 b(Moreo)n(v)n(er)30 b(a)f(normal)g(deduction)g(is)f(the)g(image)g(of)i(a)f(cut-free)167 3754 y(pro)r(of.)47 b(This)31 b(is)f(established)h(b)n(y)h(induction)e (on)i(the)f(deduction)g FH(\016)i FK(of)f FH(B)j FK(from)c(parcels)g (of)167 3840 y(h)n(yp)r(otheses)520 3841 y FH(A)p 524 3860 39 3 v -1 x FK(:)j(w)n(e)24 b(construct)h(a)g(pro)r(of)h FH(\031)h FK(of)1440 3841 y FH(A)p 1443 3860 V 1511 3840 a FJ(`)20 b FH(B)48 b FK(whose)25 b(translation)g(is)f FH(\016)s FK(;)h(moreo)n(v)n(er,)167 3925 y(w)n(e)i(w)n(an)n(t)h FH(\031)j FK(to)c(b)r(e)h(cut-free)e(in)i(the)f(case)h(where)e FH(\016)k FK(is)d(normal.)p eop PStoPSsaved restore %%Page: (44,45) 23 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 41 44 bop 167 879 a FF(Chapter)28 b(6)167 1177 y(Strong)g (Normalisation)e(Theorem)167 1501 y FK(In)35 b(this)f(c)n(hapter)h(w)n (e)f(shall)g(pro)n(v)n(e)i(the)f(strong)g(normalisation)g(theorem)f (for)h(the)f(simple)167 1586 y(t)n(yp)r(ed)h FH(\025)p FK(-calculus,)g(but)f(since)f(w)n(e)h(ha)n(v)n(e)h(already)g(discussed) f(this)f(topic)h(at)g(length,)i(and)167 1671 y(in)c(particular)f(pro)n (v)n(ed)j(w)n(eak)f(normalisation,)g(the)f(purp)r(ose)i(of)f(the)f(c)n (hapter)h(is)f(really)f(to)167 1756 y(in)n(tro)r(duce)c(the)h(tec)n (hnique)e(whic)n(h)h(w)n(e)h(shall)e(later)h(apply)h(to)g(system)f FG(F)p FK(.)270 1896 y(F)-6 b(or)29 b(simple)c(t)n(yp)r(ed)k FH(\025)p FK(-calculus,)e(there)g(is)g(pro)r(of)i(theoretic)d(tec)n (hniques)h(whic)n(h)g(mak)n(e)h(it)167 1981 y(p)r(ossible)j(to)i (express)f(the)f(argumen)n(t)i(of)f(the)g(pro)r(of)h(in)e(arithmetic,)g (and)i(ev)n(en)f(in)f(a)i(v)n(ery)167 2066 y(w)n(eak)g(system.)51 b(Ho)n(w)n(ev)n(er)32 b(our)h(metho)r(d)g(extends)g(straigh)n(tforw)n (ardly)h(to)f(G\177)-34 b(odel's)32 b(system)167 2151 y FG(T)p FK(,)j(whic)n(h)f(includes)g(a)h(t)n(yp)r(e)g(of)g(in)n (tegers)f(and)i(hence)f(co)r(des)g(P)n(eano)g(Arithmetic.)54 b(As)35 b(a)167 2236 y(result,)f(strong)h(normalisation)e(implies)d (the)k(consistency)f(of)h FG(P)-23 b(A)p FK(,)35 b(whic)n(h)e(means)g (that)h(it)167 2321 y(cannot)29 b(itself)c(b)r(e)j(pro)n(v)n(ed)h(in)e FG(P)-23 b(A)27 b FK(\(Second)h(Incompleteness)e(Theorem\).)270 2461 y(Accordingly)44 b(w)n(e)g(ha)n(v)n(e)h(to)g(use)f(a)h(strong)h (induction)e(h)n(yp)r(othesis,)49 b(for)c(whic)n(h)f(w)n(e)167 2546 y(in)n(tro)r(duce)27 b(an)h(abstract)g(notion)g(called)e FM(r)l(e)l(ducibility)p FK(,)i(originally)e(due)h(to)h([)p FG(?)q FK(].)35 b(Some)27 b(of)h(the)167 2631 y(tec)n(hnical)e(impro)n (v)n(emen)n(ts,)h(suc)n(h)h(as)g FM(neutr)l(ality)p FK(,)g(are)f(due)h (to)g([)p FG(?)p FK(].)36 b(Besides)26 b(pro)n(ving)j(strong)167 2716 y(normalisation,)c(w)n(e)e(iden)n(tify)h(the)g(three)f(imp)r (ortan)n(t)h(prop)r(erties)g(\()p FG(CR)g(1-3)p FK(\))g(of)h (reducibilit)n(y)167 2802 y(whic)n(h)i(w)n(e)g(shall)g(use)h(for)g (system)f FG(F)g FK(in)g(c)n(hapter)h FG(??)q FK(.)167 3053 y FE(6.1)114 b(Reducibilit)m(y)167 3215 y FK(W)-6 b(e)26 b(de\014ne)g(a)h(set)f Fq(RED)798 3226 y Fw(T)863 3215 y FK(\(\\reducible)1198 3189 y FD(1)1250 3215 y FK(terms)f(of)i(t)n(yp)r(e)f FH(T)10 b FK("\))26 b(b)n(y)h(induction)f (on)h(the)f FM(typ)l(e)32 b FH(T)10 b FK(.)251 3394 y(1.)35 b(F)-6 b(or)29 b FH(t)e FK(of)h(atomic)f(t)n(yp)r(e)h FH(T)10 b FK(,)27 b FH(t)h FK(is)f(reducible)e(if)i(it)g(is)g(strongly) h(normalisable.)251 3549 y(2.)35 b(F)-6 b(or)29 b FH(t)e FK(of)h(t)n(yp)r(e)g FH(U)7 b FJ(\002)p FH(V)16 b FK(,)27 b FH(t)h FK(is)f(reducible)e(if)i FH(\031)1510 3524 y FD(1)1538 3549 y FH(t)g FK(and)i FH(\031)1771 3524 y FD(2)1798 3549 y FH(t)f FK(are)f(reducible.)251 3704 y(3.)35 b(F)-6 b(or)34 b FH(t)f FK(of)h(t)n(yp)r(e)f FH(U)7 b FJ(!)q FH(V)15 b FK(,)35 b FH(t)e FK(is)g(reducible)e(if,)j (for)f(all)f(reducible)f FH(u)j FK(of)f(t)n(yp)r(e)h FH(U)7 b FK(,)35 b FH(t)12 b(u)33 b FK(is)339 3789 y(reducible)26 b(of)i(t)n(yp)r(e)g FH(V)16 b FK(.)p 167 3860 1003 3 v 246 3903 a FC(1)273 3925 y FB(This)27 b(is)g(an)g(abstract)h(notion)f (whic)n(h)g(should)f(not)h(b)r(e)g(confused)g(with)g FA(r)m(e)m(duction)p FB(.)1385 4101 y FK(41)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 42 45 bop 167 167 a FK(42)628 b Fz(CHAPTER)26 b(6.)63 b(STR)n(ONG)27 b(NORMALISA)-6 b(TION)26 b(THEOREM)270 404 y FK(The)k(deep)h(reason)g(wh)n(y)g(reducibilit)n(y)c(w)n(orks)k (where)e(com)n(binatorial)h(in)n(tuition)e(fails)i(is)167 490 y(its)d(logical)f(complexit)n(y)-6 b(.)34 b(Indeed,)28 b(w)n(e)f(ha)n(v)n(e:)451 642 y FH(t)20 b FJ(2)f Fq(RED)697 653 y Fw(U)5 b Fv(!)p Fw(V)1113 642 y FK(i\013)284 b FJ(8)p FH(u)19 b FK(\()p FH(u)g FJ(2)h Fq(RED)1842 653 y Fw(U)1903 642 y FJ(\))g FH(t)12 b(u)20 b FJ(2)f Fq(RED)2290 653 y Fw(V)2333 642 y FK(\))167 794 y(W)-6 b(e)43 b(see)g(that)h(in)f (passing)i(to)f FH(U)7 b FJ(!)p FH(V)16 b FK(,)47 b Fq(RED)1459 805 y Fw(U)1544 794 y FK(has)d(b)r(een)g(negated,)k(and)d(a)f(univ)n (ersal)167 879 y(quan)n(ti\014er)f(has)h(b)r(een)f(added.)83 b(In)43 b(particular)f(the)h(normalisation)g(argumen)n(t)g(cannot)167 964 y(b)r(e)c(directly)e(formalised)h(in)g(arithmetic)f(b)r(ecause)i FH(t)28 b FJ(2)f Fq(RED)1871 975 y Fw(T)1949 964 y FK(is)39 b(not)g(expressed)h(as)f(an)167 1049 y(arithmetic)25 b(form)n(ula)i(in)g FH(t)h FK(and)h FH(T)10 b FK(.)167 1279 y FE(6.2)114 b(Prop)s(erties)27 b(of)h(reducibilit)m(y)167 1434 y FK(First)i(w)n(e)g(in)n(tro)r(duce)h(a)g(notion)h(of)f FM(neutr)l(ality)6 b FK(:)43 b(a)31 b(term)f(is)g(called)g FM(neutr)l(al)38 b FK(if)30 b(it)g(is)g(not)i(of)167 1519 y(the)27 b(form)h FJ(h)p FH(u;)12 b(v)s FJ(i)28 b FK(or)g FH(\025x:)12 b(v)s FK(.)36 b(In)27 b(other)h(w)n(ords,)h (neutral)e(terms)f(are)i(those)g(of)g(the)f(form:)602 1671 y FH(x)435 b(\031)1118 1645 y FD(1)1145 1671 y FH(t)g(\031)1647 1645 y FD(2)1674 1671 y FH(t)g(t)12 b(u)270 1853 y FK(The)28 b(conditions)f(that)h(in)n(terest)e(us)j(are)e(the)g(follo)n(wing:)201 1972 y(\()p FG(CR)h(1)p FK(\))f(If)h FH(t)19 b FJ(2)h Fq(RED)786 1983 y Fw(T)825 1972 y FK(,)28 b(then)f FH(t)h FK(is)f(strongly)h(normalisable.)201 2106 y(\()p FG(CR)g(2)p FK(\))f(If)h FH(t)19 b FJ(2)h Fq(RED)786 2117 y Fw(T)852 2106 y FK(and)29 b FH(t)20 b Fu( )g FH(t)1151 2080 y Fv(0)1167 2106 y FK(,)28 b(then)f FH(t)1400 2080 y Fv(0)1436 2106 y FJ(2)20 b Fq(RED)1638 2117 y Fw(T)1677 2106 y FK(.)201 2239 y(\()p FG(CR)30 b(3)p FK(\))e(If)i FH(t)f FK(is)f(neutral,)h(and)i(whenev)n(er)e(w)n(e)f(con)n(v)n(ert)i(a)f (redex)g(of)h FH(t)f FK(w)n(e)g(obtain)h(a)f(term)339 2324 y FH(t)364 2298 y Fv(0)400 2324 y FJ(2)20 b Fq(RED)602 2335 y Fw(T)641 2324 y FK(,)28 b(then)f FH(t)20 b FJ(2)f Fq(RED)1095 2335 y Fw(T)1134 2324 y FK(.)167 2443 y(As)27 b(a)i(sp)r(ecial)d(case)h(of)h(the)g(last)f(clause:)201 2562 y(\()p FG(CR)h(4)p FK(\))f(If)h FH(t)f FK(is)g(neutral)g(and)i (normal,)f(then)f FH(t)20 b FJ(2)f Fq(RED)1712 2573 y Fw(T)1751 2562 y FK(.)270 2681 y(W)-6 b(e)28 b(shall)f(v)n(erify)g(b)n (y)h(induction)f(on)i(the)e FM(typ)l(e)34 b FK(that)28 b Fq(RED)f FK(satis\014es)h(these)f(conditions.)167 2880 y Fy(6.2.1)95 b(A)m(tomic)27 b(t)m(yp)s(es)167 3011 y FK(A)34 b(term)g(of)h(atomic)f(t)n(yp)r(e)h(is)f(reducible)f(i\013)h (it)g(is)g(strongly)i(normalisable.)55 b(So)36 b(w)n(e)e(m)n(ust)167 3096 y(sho)n(w)k(that)g(the)f(set)g(of)h(strongly)g(normalisable)e (terms)g(of)i(t)n(yp)r(e)f FH(T)47 b FK(satis\014es)38 b(the)f(three)167 3181 y(conditions:)201 3300 y(\()p FG(CR)28 b(1)p FK(\))f(is)g(a)h(tautology)-6 b(.)201 3433 y(\()p FG(CR)35 b(2)p FK(\))f(If)g FH(t)g FK(is)g(strongly)h (normalisable)e(then)h(ev)n(ery)h(term)e FH(t)1955 3408 y Fv(0)2005 3433 y FK(to)i(whic)n(h)f FH(t)g FK(reduces)g(is)339 3519 y(also.)201 3652 y(\()p FG(CR)26 b(3)p FK(\))f(A)g(reduction)g (path)h(lea)n(ving)f FH(t)g FK(m)n(ust)h(pass)g(through)h(one)f(of)g (the)f(terms)f FH(t)2436 3626 y Fv(0)2453 3652 y FK(,)i(whic)n(h)339 3737 y(are)i(strongly)f(normalisable,)f(and)j(so)f(is)e(\014nite.)35 b(In)27 b(fact,)g(it)g(is)f(immediate)e(that)k FH(\027)t FK(\()p FH(t)p FK(\))339 3822 y(\(see)j FG(??)q FK(\))g(is)f(equal)h (to)h(the)e(greatest)h(of)h(the)f(n)n(um)n(b)r(ers)g FH(\027)t FK(\()p FH(t)1964 3796 y Fv(0)1981 3822 y FK(\))16 b(+)h(1,)32 b(as)g FH(t)2298 3796 y Fv(0)2346 3822 y FK(v)l(aries)f(o)n(v)n(er)339 3907 y(the)d(\(one-step\))f(con)n(v)n (ersions)i(of)f FH(t)p FK(.)p eop PStoPSsaved restore %%Page: (46,47) 24 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 43 46 bop 167 167 a Fz(6.2.)64 b(PR)n(OPER)-6 b(TIES)27 b(OF)g(REDUCIBILITY)1142 b FK(43)167 404 y Fy(6.2.2)95 b(Pro)s(duct)26 b(t)m(yp)s(e)167 535 y FK(A)h(term)g(of)h(pro)r(duct)g (t)n(yp)r(e)g(is)f(reducible)e(i\013)i(its)g(pro)t(jections)h(are.)201 688 y(\()p FG(CR)f(1)p FK(\))g(Supp)r(ose)h(that)f FH(t)p FK(,)g(of)h(t)n(yp)r(e)f FH(U)7 b FJ(\002)p FH(V)15 b FK(,)28 b(is)e(reducible;)f(then)i FH(\031)2010 663 y FD(1)2038 688 y FH(t)f FK(is)g(reducible)f(and)j(b)n(y)339 773 y(induction)h(h)n(yp)r(othesis)h(\()p FG(CR)g(1)p FK(\))e(for)i FH(U)7 b FK(,)30 b FH(\031)1523 748 y FD(1)1551 773 y FH(t)f FK(is)f(strongly)i(normalisable.)39 b(Moreo)n(v)n(er)339 859 y FH(\027)t FK(\()p FH(t)p FK(\))21 b FJ(\024)f FH(\027)t FK(\()p FH(\031)659 833 y FD(1)687 859 y FH(t)p FK(\),)29 b(since)e(to)i(an)n(y)h(reduction)e(sequence)h FH(t;)12 b(t)1872 870 y FD(1)1899 859 y FH(;)g(t)1955 870 y FD(2)1983 859 y FH(;)g(:)g(:)g(:)p FK(,)29 b(one)g(can)g(apply)h FH(\031)2645 833 y FD(1)339 944 y FK(to)h(construct)e(a)i(reduction)e (sequence)h FH(\031)1453 918 y FD(1)1480 944 y FH(t;)12 b(\031)1578 918 y FD(1)1606 944 y FH(t)1631 955 y FD(1)1658 944 y FH(;)g(\031)1731 918 y FD(1)1759 944 y FH(t)1784 955 y FD(2)1812 944 y FH(;)g(:)g(:)g(:)29 b FK(\(in)g(whic)n(h)g(the)h FH(\031)2439 918 y FD(1)2496 944 y FK(is)g(not)339 1029 y(reduced\).)35 b(So)29 b FH(\027)t FK(\()p FH(t)p FK(\))e(is)g (\014nite,)g(and)i FH(t)f FK(is)f(strongly)h(normalisable.)201 1171 y(\()p FG(CR)44 b(2)p FK(\))f(If)g FH(t)31 b Fu( )g FH(t)769 1145 y Fv(0)785 1171 y FK(,)48 b(then)43 b FH(\031)1071 1145 y FD(1)1099 1171 y FH(t)31 b Fu( )g FH(\031)1298 1145 y FD(1)1325 1171 y FH(t)1350 1145 y Fv(0)1410 1171 y FK(and)45 b FH(\031)1607 1145 y FD(2)1634 1171 y FH(t)31 b Fu( )g FH(\031)1833 1145 y FD(2)1860 1171 y FH(t)1885 1145 y Fv(0)1902 1171 y FK(.)83 b(As)43 b FH(t)g FK(is)g(reducible)e(b) n(y)339 1256 y(h)n(yp)r(othesis,)28 b(so)f(are)f FH(\031)950 1230 y FD(1)977 1256 y FH(t)g FK(and)h FH(\031)1207 1230 y FD(2)1235 1256 y FH(t)p FK(.)34 b(The)26 b(induction)g(h)n(yp)r (othesis)h(\()p FG(CR)f(2)p FK(\))f(for)i FH(U)33 b FK(and)339 1341 y FH(V)44 b FK(sa)n(ys)29 b(that)f(the)f FH(\031)893 1315 y FD(1)920 1341 y FH(t)945 1315 y Fv(0)989 1341 y FK(and)i FH(\031)1170 1315 y FD(2)1198 1341 y FH(t)1223 1315 y Fv(0)1267 1341 y FK(are)e(reducible,)f(and)j(so)f FH(t)1958 1315 y Fv(0)2002 1341 y FK(is)f(reducible.)201 1483 y(\()p FG(CR)33 b(3)p FK(\))f(Let)g FH(t)g FK(b)r(e)g(neutral)g (and)i(supp)r(ose)g(all)d(the)h FH(t)1687 1457 y Fv(0)1736 1483 y FK(one)h(step)f(from)g FH(t)h FK(are)f(reducible.)339 1568 y(Applying)c(a)g(con)n(v)n(ersion)g(inside)f FH(\031)1288 1542 y FD(1)1316 1568 y FH(t)p FK(,)g(the)h(result)e(is)i(a)g FH(\031)1886 1542 y FD(1)1913 1568 y FH(t)1938 1542 y Fv(0)1955 1568 y FK(,)f(since)g FH(\031)2217 1542 y FD(1)2245 1568 y FH(t)g FK(cannot)i(itself)339 1653 y(b)r(e)k(a)h(redex)f(\()p FH(t)g FK(is)f(not)i(a)g(pair\),)g(and)g FH(\031)1457 1627 y FD(1)1485 1653 y FH(t)1510 1627 y Fv(0)1559 1653 y FK(is)f(reducible,)g(since)f FH(t)2169 1627 y Fv(0)2218 1653 y FK(is.)52 b(But)33 b(as)h FH(\031)2620 1627 y FD(1)2647 1653 y FH(t)339 1738 y FK(is)29 b(neutral,)g(and)i(all)d(the) h(terms)f(one)i(step)f(from)g FH(\031)1740 1712 y FD(1)1767 1738 y FH(t)h FK(are)f(reducible,)f(the)h(induction)339 1823 y(h)n(yp)r(othesis)f(\()p FG(CR)e(3)p FK(\))g(for)h FH(U)33 b FK(ensures)27 b(that)g FH(\031)1575 1797 y FD(1)1602 1823 y FH(t)f FK(is)g(reducible.)33 b(Lik)n(ewise)25 b FH(\031)2375 1797 y FD(2)2402 1823 y FH(t)p FK(,)i(and)g(so)339 1908 y FH(t)h FK(is)f(reducible.)167 2111 y Fy(6.2.3)95 b(Arro)m(w)26 b(t)m(yp)s(e)167 2242 y FK(A)34 b(term)e(of)j(arro)n(w)f (t)n(yp)r(e)g(is)g(reducible)e(i\013)h(all)g(its)g(applications)g(to)h (reducible)e(terms)h(are)167 2327 y(reducible.)201 2480 y(\()p FG(CR)40 b(1)p FK(\))e(If)h FH(t)g FK(is)f(reducible)f(of)j(t)n (yp)r(e)f FH(U)7 b FJ(!)p FH(V)16 b FK(,)42 b(let)c FH(x)h FK(b)r(e)g(a)g(v)l(ariable)g(of)g(t)n(yp)r(e)g FH(U)7 b FK(;)45 b(the)339 2565 y(induction)31 b(h)n(yp)r(othesis)h(\()p FG(CR)f(3)p FK(\))g(for)g FH(U)39 b FK(sa)n(ys)32 b(that)g(the)e(term)g FH(x)p FK(,)j(whic)n(h)d(is)h(neutral)339 2650 y(and)45 b(normal,)i(is)c(reducible.)81 b(So)44 b FH(t)12 b(x)43 b FK(is)g(reducible.)81 b(Just)44 b(as)g(in)f(the)g(case)h(of)339 2736 y(the)32 b(pro)r(duct)h(t)n(yp)r(e,)h(w)n(e)e(remark)g(that)g FH(\027)t FK(\()p FH(t)p FK(\))23 b FJ(\024)g FH(\027)t FK(\()p FH(t)12 b(x)p FK(\).)49 b(The)32 b(induction)g(h)n(yp)r (othesis)339 2821 y(\()p FG(CR)d(1)p FK(\))g(for)g FH(V)44 b FK(guaran)n(tees)30 b(that)f FH(\027)t FK(\()p FH(t)12 b(x)p FK(\))29 b(is)f(\014nite,)h(and)g(so)h FH(\027)t FK(\()p FH(t)p FK(\))f(is)f(\014nite,)g(and)i FH(t)f FK(is)339 2906 y(strongly)g(normalisable.)201 3048 y(\()p FG(CR)38 b(2)p FK(\))e(If)h FH(t)26 b Fu( )g FH(t)740 3022 y Fv(0)794 3048 y FK(and)38 b FH(t)e FK(is)h(reducible,)g(tak)n(e) g FH(u)h FK(reducible)d(of)i(t)n(yp)r(e)g FH(U)7 b FK(;)42 b(then)37 b FH(t)12 b(u)37 b FK(is)339 3133 y(reducible)26 b(and)j FH(t)12 b(u)20 b Fu( )g FH(t)989 3107 y Fv(0)1017 3133 y FH(u)p FK(.)36 b(The)28 b(induction)f(h)n(yp)r(othesis)h(\()p FG(CR)g(2)p FK(\))g(for)g FH(V)43 b FK(giv)n(es)28 b(that)339 3218 y FH(t)364 3192 y Fv(0)393 3218 y FH(u)f FK(is)g(reducible.)34 b(So)28 b FH(t)985 3192 y Fv(0)1029 3218 y FK(is)f(reducible.)201 3360 y(\()p FG(CR)21 b(3)p FK(\))f(Let)g FH(t)g FK(b)r(e)g(neutral)g (and)h(supp)r(ose)h(all)d(the)h FH(t)1566 3334 y Fv(0)1603 3360 y FK(one)h(step)f(from)g FH(t)h FK(are)f(reducible.)31 b(Let)20 b FH(u)339 3445 y FK(b)r(e)32 b(a)g(reducible)e(term)h(of)h(t) n(yp)r(e)g FH(U)7 b FK(;)34 b(w)n(e)d(w)n(an)n(t)h(to)h(sho)n(w)f(that) g FH(t)12 b(u)32 b FK(is)f(reducible.)46 b(By)339 3530 y(induction)23 b(h)n(yp)r(othesis)h(\()p FG(CR)f(1)p FK(\))f(for)i FH(U)7 b FK(,)24 b(w)n(e)f(kno)n(w)h(that)f FH(u)g FK(is)g(strongly)g(normalisable;)339 3615 y(so)29 b(w)n(e)e(can)h(reason)g(b)n(y)h(induction)e(on)h FH(\027)t FK(\()p FH(u)p FK(\).)339 3767 y(In)g(one)g(step,)g FH(t)12 b(u)27 b FK(con)n(v)n(erts)i(to)421 3925 y FJ(\017)35 b FH(t)516 3899 y Fv(0)544 3925 y FH(u)28 b FK(with)f FH(t)798 3899 y Fv(0)842 3925 y FK(one)h(step)f(from)h FH(t)p FK(;)f(but)h FH(t)1518 3899 y Fv(0)1562 3925 y FK(is)f(reducible,)f(so)i FH(t)2069 3899 y Fv(0)2098 3925 y FH(u)f FK(is.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 44 47 bop 167 167 a FK(44)628 b Fz(CHAPTER)26 b(6.)63 b(STR)n(ONG)27 b(NORMALISA)-6 b(TION)26 b(THEOREM)421 404 y FJ(\017)35 b FH(t)12 b(u)567 379 y Fv(0)584 404 y FK(,)33 b(with)f FH(u)842 379 y Fv(0)891 404 y FK(one)h(step)f(from)h FH(u)p FK(.)50 b FH(u)1502 379 y Fv(0)1551 404 y FK(is)32 b(reducible)e(b)n(y)j(induction)f(h)n(yp)r(othesis)491 490 y(\()p FG(CR)25 b(2)p FK(\))f(for)g FH(U)7 b FK(,)26 b(and)f FH(\027)t FK(\()p FH(u)1194 464 y Fv(0)1211 490 y FK(\))20 b FH(<)f(\027)t FK(\()p FH(u)p FK(\);)26 b(so)f(the)f (induction)g(h)n(yp)r(othesis)h(for)g FH(u)2508 464 y Fv(0)2549 490 y FK(tells)491 575 y(us)j(that)g FH(t)12 b(u)814 549 y Fv(0)858 575 y FK(is)27 b(reducible.)421 678 y FJ(\017)35 b FK(There)c(is)f(no)i(other)g(p)r(ossibilit)n(y)-6 b(,)31 b(for)g FH(t)12 b(u)31 b FK(cannot)i(itself)c(b)r(e)i(a)h(redex) f(\()p FH(t)g FK(is)g(not)491 763 y(of)d(the)g(form)f FH(\025x:)12 b(v)s FK(\).)339 901 y(In)26 b(ev)n(ery)g(case,)h(w)n(e)e (ha)n(v)n(e)i(seen)e(that)i(the)e(neutral)h(term)e FH(t)12 b(u)26 b FK(con)n(v)n(erts)g(in)n(to)g(reducible)339 986 y(terms)k(only)-6 b(.)46 b(The)31 b(induction)g(h)n(yp)r(othesis)g (\()p FG(CR)g(3)p FK(\))g(for)g FH(V)47 b FK(allo)n(ws)30 b(us)h(to)h(conclude)339 1071 y(that)c FH(t)12 b(u)28 b FK(is)f(reducible,)f(and)i(so)h FH(t)e FK(is)g(reducible.)980 b Fu(\003)167 1301 y FE(6.3)114 b(Reducibilit)m(y)28 b(theorem)167 1476 y Fy(6.3.1)95 b(P)m(airing)167 1607 y FG(Lemma)25 b FK(If)i FH(u)h FK(and)h FH(v)h FK(are)e(reducible,)e (then)i(so)g(is)f FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(.)167 1757 y FG(Pro)r(of)33 b FK(Because)g(of)g(\()p FG(CR)g(1)p FK(\),)h(w)n(e)e(can)h(reason)h(b)n(y)g(induction)e(on)i FH(\027)t FK(\()p FH(u)p FK(\))17 b(+)g FH(\027)t FK(\()p FH(v)s FK(\))33 b(to)g(sho)n(w)167 1842 y(that)28 b FH(\031)363 1816 y FD(1)391 1842 y FJ(h)p FH(u;)12 b(v)s FJ(i)28 b FK(is)f(reducible.)33 b(This)27 b(term)g(con)n(v)n(erts)h(to:)270 1957 y FJ(\017)34 b FH(u)p FK(,)28 b(whic)n(h)f(is)g(reducible.)270 2089 y FJ(\017)34 b FH(\031)381 2064 y FD(1)409 2089 y FJ(h)p FH(u)475 2064 y Fv(0)492 2089 y FH(;)12 b(v)s FJ(i)p FK(,)30 b(with)e FH(u)837 2064 y Fv(0)883 2089 y FK(one)i(step)f(from)h FH(u)p FK(.)40 b FH(u)1475 2064 y Fv(0)1521 2089 y FK(is)29 b(reducible)e(b)n(y)j(\()p FG(CR)g(2)p FK(\),)f(and)h(w)n(e)f(ha)n(v)n(e)339 2175 y FH(\027)t FK(\()p FH(u)443 2149 y Fv(0)460 2175 y FK(\))20 b FH(<)f(\027)t FK(\()p FH(u)p FK(\);)27 b(so)f(the)e(induction)h(h)n (yp)r(othesis)h(tells)d(us)j(that)g(this)e(term)g(is)h(reducible.)270 2307 y FJ(\017)34 b FH(\031)381 2281 y FD(1)409 2307 y FJ(h)p FH(u;)12 b(v)542 2281 y Fv(0)559 2307 y FJ(i)p FK(,)28 b(with)e FH(v)830 2281 y Fv(0)874 2307 y FK(one)i(step)f(from)g FH(v)s FK(:)35 b(this)27 b(term)f(is)h(reducible)e(for)j(similar)d (reasons.)167 2422 y(In)30 b(ev)n(ery)f(case,)h(the)f(neutral)g(term)f FH(\031)1202 2397 y FD(1)1230 2422 y FJ(h)p FH(u;)12 b(v)s FJ(i)30 b FK(con)n(v)n(erts)g(to)f(reducible)f(terms)g(only)-6 b(,)31 b(and)f(b)n(y)167 2507 y(\()p FG(CR)e(3)p FK(\))f(it)f(is)h (reducible.)34 b(Lik)n(ewise)26 b FH(\031)1230 2482 y FD(2)1257 2507 y FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(,)29 b(and)f(so)h FJ(h)p FH(u;)12 b(v)s FJ(i)28 b FK(is)f(reducible.)369 b Fu(\003)167 2706 y Fy(6.3.2)95 b(Abstraction)167 2836 y FG(Lemma)25 b FK(If)i(for)h(all)f(reducible)e FH(u)j FK(of)g(t)n(yp)r(e)g FH(U)7 b FK(,)28 b FH(v)s FK([)p FH(u=x)p FK(])h(is)e(reducible,)f(then)h(so)i(is)e FH(\025x:)12 b(v)s FK(.)167 2986 y FG(Pro)r(of)30 b FK(W)-6 b(e)29 b(w)n(an)n(t)h(to)g(sho)n(w)g(that)g(\()p FH(\025x:)12 b(v)s FK(\))g FH(u)29 b FK(is)g(reducible)f(for)i(all)e(reducible)g FH(u)p FK(.)41 b(Again)30 b(w)n(e)167 3071 y(reason)f(b)n(y)f (induction)f(on)h FH(\027)t FK(\()p FH(v)s FK(\))16 b(+)f FH(\027)t FK(\()p FH(u)p FK(\).)270 3174 y(The)28 b(term)e(\()p FH(\025x:)12 b(v)s FK(\))g FH(u)28 b FK(con)n(v)n(erts)g(to)270 3289 y FJ(\017)34 b FH(v)s FK([)p FH(u=x)p FK(],)29 b(whic)n(h)e(is)g (reducible)f(b)n(y)i(h)n(yp)r(othesis.)270 3422 y FJ(\017)34 b FK(\()p FH(\025x:)12 b(v)512 3396 y Fv(0)529 3422 y FK(\))g FH(u)31 b FK(with)f FH(v)839 3396 y Fv(0)887 3422 y FK(one)i(step)f(from)g FH(v)s FK(;)i(so)f FH(v)1564 3396 y Fv(0)1611 3422 y FK(is)f(reducible,)f FH(\027)t FK(\()p FH(v)2113 3396 y Fv(0)2130 3422 y FK(\))22 b FH(<)g(\027)t FK(\()p FH(v)s FK(\),)32 b(and)g(the)339 3507 y(induction)c(h)n(yp)r(othesis)g(tells)e(us)i(that)g(this)f(term)f (is)h(reducible.)270 3639 y FJ(\017)34 b FK(\()p FH(\025x:)12 b(v)s FK(\))g FH(u)590 3614 y Fv(0)644 3639 y FK(with)35 b FH(u)853 3614 y Fv(0)907 3639 y FK(one)i(step)g(from)g FH(u)p FK(:)54 b FH(u)1535 3614 y Fv(0)1589 3639 y FK(is)36 b(reducible,)h FH(\027)t FK(\()p FH(u)2106 3614 y Fv(0)2123 3639 y FK(\))26 b FH(<)g(\027)t FK(\()p FH(u)p FK(\),)40 b(and)e(w)n(e)339 3724 y(conclude)28 b(similarly)-6 b(.)167 3840 y(In)30 b(ev)n(ery)f(case)g(the)g(neutral)g(term)f(\()p FH(\025x:)12 b(v)s FK(\))g FH(u)29 b FK(con)n(v)n(erts)h(to)g (reducible)d(terms)h(only)-6 b(,)31 b(and)f(b)n(y)167 3925 y(\()p FG(CR)e(3)p FK(\))f(it)f(is)h(reducible.)34 b(So)28 b FH(\025x:)12 b(v)31 b FK(is)c(reducible.)1070 b Fu(\003)p eop PStoPSsaved restore %%Page: (48,49) 25 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 45 48 bop 167 167 a Fz(6.3.)64 b(REDUCIBILITY)26 b(THEOREM)1354 b FK(45)167 404 y Fy(6.3.3)95 b(The)27 b(theorem)167 535 y FK(No)n(w)h(w)n(e)f(can)h(pro)n(v)n(e)g(the)167 661 y FG(Theorem)f FK(All)f(terms)g(are)i(reducible.)167 787 y(Hence,)f(b)n(y)h(\()p FG(CR)g(1)p FK(\),)f(w)n(e)g(ha)n(v)n(e)i (the)167 914 y FG(Corollary)c FK(All)h(terms)g(are)i(strongly)g (normalisable.)270 1087 y(In)d(the)e(pro)r(of)i(of)g(the)f(theorem,)g (w)n(e)f(need)h(a)h(stronger)f(induction)g(h)n(yp)r(othesis)h(to)f (handle)167 1172 y(the)35 b(case)g(of)g(abstraction.)58 b(This)35 b(is)f(the)h(purp)r(ose)h(of)f(the)g(follo)n(wing)f(prop)r (osition,)j(from)167 1257 y(whic)n(h)27 b(the)g(theorem)g(follo)n(ws)g (b)n(y)i(putting)e FH(u)1385 1268 y Fw(i)1425 1257 y FK(=)19 b FH(x)1537 1268 y Fw(i)1557 1257 y FK(.)167 1430 y FG(Prop)r(osition)28 b FK(Let)i FH(t)h FK(b)r(e)f FM(any)37 b FK(term)29 b(\()p FM(not)37 b FK(assumed)31 b(to)g(b)r(e)g(reducible\),)e(and)i(supp)r(ose)h(all)167 1515 y(the)d(free)g(v)l(ariables)h(of)g FH(t)f FK(are)h(among)h FH(x)1253 1526 y FD(1)1281 1515 y FH(;)12 b(:)g(:)g(:)f(;)h(x)1474 1526 y Fw(n)1537 1515 y FK(of)30 b(t)n(yp)r(es)g FH(U)1858 1526 y FD(1)1886 1515 y FH(;)12 b(:)g(:)g(:)g(;)g(U)2088 1526 y Fw(n)2121 1515 y FK(.)41 b(If)30 b FH(u)2296 1526 y FD(1)2324 1515 y FH(;)12 b(:)g(:)g(:)f(;)h(u)2517 1526 y Fw(n)2580 1515 y FK(are)167 1600 y(reducible)26 b(terms)g(of)i(t)n (yp)r(es)g FH(U)980 1611 y FD(1)1008 1600 y FH(;)12 b(:)g(:)g(:)g(;)g (U)1210 1611 y Fw(n)1270 1600 y FK(then)28 b FH(t)p FK([)p FH(u)1515 1611 y FD(1)1543 1600 y FH(=x)1616 1611 y FD(1)1645 1600 y FH(;)12 b(:)g(:)g(:)f(;)h(u)1838 1611 y Fw(n)1872 1600 y FH(=x)1945 1611 y Fw(n)1978 1600 y FK(])28 b(is)f(reducible.)167 1774 y FG(Pro)r(of)h FK(By)g(induction)f(on)h FH(t)p FK(.)35 b(W)-6 b(e)28 b(write)e FH(t)p FK([)1351 1775 y FH(u)p 1354 1794 26 3 v -1 x(=)1424 1775 y(x)p 1428 1794 V -1 x FK(])i(for)g FH(t)p FK([)p FH(u)1703 1785 y FD(1)1731 1774 y FH(=x)1804 1785 y FD(1)1833 1774 y FH(;)12 b(:)g(:)g(:)f(;)h(u)2026 1785 y Fw(n)2060 1774 y FH(=x)2133 1785 y Fw(n)2167 1774 y FK(].)251 1935 y(1.)35 b FH(t)43 b FK(is)f FH(x)535 1946 y Fw(i)555 1935 y FK(:)65 b(one)43 b(has)g(to)g(c)n(hec)n(k)f(the)h(tautology)h(\\if)e FH(u)1859 1946 y Fw(i)1921 1935 y FK(is)g(reducible,)j(then)d FH(u)2563 1946 y Fw(i)2626 1935 y FK(is)339 2020 y(reducible";)27 b(details)f(are)i(left)e(to)i(the)f(reader.)251 2164 y(2.)35 b FH(t)30 b FK(is)g FH(\031)513 2138 y FD(1)540 2164 y FH(w)r FK(:)40 b(b)n(y)31 b(induction)f(h)n(yp)r(othesis,)h(for) g(ev)n(ery)f(sequence)2027 2165 y FH(u)p 2031 2185 V 2097 2164 a FK(of)g(reducible)e(terms,)339 2249 y FH(w)r FK([)421 2250 y FH(u)p 425 2270 V 461 2249 a(=)495 2250 y(x)p 499 2270 V -1 x FK(])e(is)e(reducible.)33 b(That)25 b(means)g(that)h FH(\031)1557 2223 y FD(1)1584 2249 y FK(\()p FH(w)r FK([)1693 2250 y FH(u)p 1697 2270 V -1 x(=)1766 2250 y(x)p 1770 2270 V 1806 2249 a FK(]\))f(is)g(reducible,)e (but)j(this)e(term)339 2334 y(is)j(nothing)i(other)f(than)g FH(\031)1063 2309 y FD(1)1091 2334 y FH(w)r FK([)1173 2335 y FH(u)p 1176 2355 V -1 x(=)1246 2335 y(x)p 1250 2355 V 1286 2334 a FK(])19 b(=)h FH(t)p FK([)1454 2335 y FH(u)p 1457 2355 V -1 x(=)1527 2335 y(x)p 1531 2355 V -1 x FK(].)251 2478 y(3.)35 b FH(t)28 b FK(is)f FH(\031)508 2452 y FD(2)535 2478 y FH(w)r FK(:)36 b(as)28 b FG(??)q FK(.)251 2622 y(4.)35 b FH(t)c FK(is)f FJ(h)p FH(v)s(;)12 b(w)r FJ(i)p FK(:)43 b(b)n(y)31 b(induction)g(h)n(yp)r(othesis)g(b)r (oth)h FH(v)s FK([)1709 2623 y FH(u)p 1712 2642 V -1 x(=)1782 2623 y(x)p 1786 2642 V -1 x FK(])f(and)h FH(w)r FK([)2095 2623 y FH(u)p 2099 2642 V 2135 2622 a(=)2169 2623 y(x)p 2173 2642 V -1 x FK(])f(are)g(reducible.)339 2707 y(Lemma)c FG(??)i FK(sa)n(ys)g(that)f FH(t)p FK([)1054 2708 y FH(u)p 1057 2728 V -1 x(=)1127 2708 y(x)p 1131 2728 V -1 x FK(])20 b(=)f FJ(h)p FH(v)s FK([)1372 2708 y FH(u)p 1376 2728 V 1412 2707 a(=)1446 2708 y(x)p 1450 2728 V -1 x FK(])p FH(;)12 b(w)r FK([)1617 2708 y FH(u)p 1621 2728 V 1657 2707 a(=)1691 2708 y(x)p 1695 2728 V -1 x FK(])p FJ(i)29 b FK(is)e(reducible.)251 2851 y(5.)35 b FH(t)k FK(is)g FH(w)14 b(v)s FK(:)58 b(b)n(y)40 b(induction)f(h)n(yp) r(othesis)g FH(w)r FK([)1537 2852 y FH(u)p 1541 2871 V 1577 2851 a(=)1611 2852 y(x)p 1615 2871 V -1 x FK(])h(and)g FH(v)s FK([)1926 2852 y FH(u)p 1929 2871 V -1 x(=)1999 2852 y(x)p 2003 2871 V 2039 2851 a FK(])f(are)g(reducible,)h(and)339 2936 y(so)c(\(b)n(y)g(de\014nition\))e(is)h FH(w)r FK([)1080 2937 y FH(u)p 1083 2956 V -1 x(=)1153 2937 y(x)p 1157 2956 V 1193 2936 a FK(])12 b(\()p FH(v)s FK([)1318 2937 y FH(u)p 1321 2956 V 1356 2936 a(=)1390 2937 y(x)p 1394 2956 V 1430 2936 a FK(]\);)39 b(but)c(this)g(term)f(is)g(nothing)i (other)f(than)339 3021 y FH(t)p FK([)395 3022 y FH(u)p 399 3042 V -1 x(=)468 3022 y(x)p 472 3042 V 508 3021 a FK(].)251 3165 y(6.)g FH(t)30 b FK(is)e FH(\025y)s(:)12 b(w)31 b FK(of)f(t)n(yp)r(e)g FH(V)15 b FJ(!)q FH(W)10 b FK(:)38 b(b)n(y)31 b(induction)e(h)n(yp)r(othesis,)h FH(w)r FK([)2025 3166 y FH(u)p 2029 3185 V 2065 3165 a(=)2099 3166 y(x)p 2103 3185 V -1 x(;)12 b(v)s(=y)s FK(])29 b(is)g(reducible)339 3250 y(for)22 b(all)f FH(v)j FK(of)f(t)n(yp)r(e)f FH(V)15 b FK(.)33 b(Lemma)21 b FG(??)i FK(sa)n(ys)g(that)f FH(t)p FK([)1625 3251 y FH(u)p 1628 3270 V -1 x(=)1698 3251 y(x)p 1702 3270 V 1738 3250 a FK(])d(=)h FH(\025y)s(:)12 b FK(\()p FH(w)r FK([)2067 3251 y FH(u)p 2069 3270 V 2105 3250 a(=)2139 3251 y(x)p 2143 3270 V 2179 3250 a FK(]\))21 b(is)g(reducible.)10 b Fu(\003)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 46 49 bop 167 874 a FF(Chapter)28 b(7)167 1168 y(G\177)-82 b(odel's)27 b(system)g(T)167 1487 y FK(The)e(extremely)e(rudimen)n (tary)i(t)n(yp)r(e)g(system)g(w)n(e)g(ha)n(v)n(e)h(studied)f(has)h(v)n (ery)g(little)c(expressiv)n(e)167 1573 y(p)r(o)n(w)n(er.)38 b(F)-6 b(or)28 b(example,)g(can)h(w)n(e)f(use)g(it)f(to)i(represen)n(t) e(the)h(in)n(tegers)g(or)g(the)h(b)r(o)r(oleans,)g(and)167 1658 y(if)d(so)i(can)f(w)n(e)g(represen)n(t)f(su\016cien)n(tly)h(man)n (y)g(functions)h(on)f(them?)34 b(The)27 b(answ)n(er)g(is)g(clearly)167 1743 y FM(no)p FK(.)270 1869 y(T)-6 b(o)24 b(obtain)f(more)f (expressivit)n(y)-6 b(,)24 b(w)n(e)e(are)h(inexorably)g(led)f(to)h(the) f(consideration)h(of)g(other)167 1954 y(sc)n(hemes:)48 b(new)34 b(t)n(yp)r(es,)j(or)e(new)f(terms,)h(often)g(b)r(oth)g (together.)56 b(So)35 b(it)e(is)h(quite)g(natural)167 2039 y(that)d(systems)f(suc)n(h)h(as)g(that)f(of)h(G\177)-34 b(odel)30 b(app)r(ear,)i(whic)n(h)e(w)n(e)g(shall)f(lo)r(ok)i(at)f (brie\015y)-6 b(.)44 b(That)167 2124 y(said,)28 b(w)n(e)f(come)g(up)h (against)h(a)f(t)n(w)n(o-fold)g(di\016cult)n(y:)270 2286 y FJ(\017)34 b FK(Systems)g(lik)n(e)e FG(T)h FK(are)h(a)f(step)h(bac)n (kw)n(ards)h(from)e(the)g(logical)f(viewp)r(oin)n(t:)46 b(the)33 b(new)339 2371 y(sc)n(hemes)39 b(do)i(not)f(corresp)r(ond)g (to)g(pro)r(ofs)h(in)e(an)h(extended)g(logical)e(system.)71 b(In)339 2456 y(particular,)27 b(that)h(mak)n(es)g(it)f(di\016cult)f (to)i(study)h(them.)270 2600 y FJ(\017)34 b FK(By)51 b(prop)r(osing)i(impro)n(v)n(emen)n(ts)d(of)h(expressivit)n(y)-6 b(,)56 b(these)51 b(systems)f(suggest)i(the)339 2685 y(p)r(ossibilit)n(y)28 b(of)i(further)f(impro)n(v)n(emen)n(ts.)39 b(F)-6 b(or)30 b(example,)e(it)h(is)f(w)n(ell)f(kno)n(wn)k(that)e(the) 339 2770 y(language)j Fr(PASCAL)g FK(do)r(es)f(not)g(ha)n(v)n(e)g(the)f (t)n(yp)r(e)h(of)g(lists)e(built)g(in!)43 b(So)31 b(w)n(e)f(are)g(led)g (to)339 2855 y(endless)g(impro)n(v)n(emen)n(t,)f(in)g(order)g(to)h(b)r (e)g(able)f(to)h(consider,)g(b)r(esides)f(the)g(b)r(o)r(oleans,)339 2940 y(the)g(in)n(tegers,)g(lists,)f(trees,)h FM(etc.)39 b FK(Of)28 b(course,)i(all)e(this)g(is)h(done)g(to)h(the)e(detrimen)n (t)g(of)339 3025 y(conceptual)g(simplicit)n(y)c(and)29 b(mo)r(dularit)n(y.)270 3187 y(The)i(system)f FG(F)h FK(resolv)n(es)f(these)h(questions)g(in)f(a)h(v)n(ery)g(satisfying)g (manner,)h(as)f(it)f(will)167 3272 y(b)r(e)d(seen)g(that)g(the)g (addition)g(of)g(a)h(new)e(logical)g(sc)n(heme)g(allo)n(ws)g(us)h(to)h (deal)e(with)g(common)167 3357 y(data)38 b(t)n(yp)r(es.)64 b(But)37 b(\014rst,)i(let)d(us)h(concen)n(trate)g(on)g(the)g(system)g FG(T)p FK(,)g(whic)n(h)f(already)h(has)167 3442 y(considerable)27 b(expressiv)n(e)g(p)r(o)n(w)n(er.)1385 4101 y(46)p eop PStoPSsaved restore %%Page: (50,51) 26 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 47 50 bop 167 167 a Fz(7.1.)64 b(THE)27 b(CALCULUS)1710 b FK(47)167 404 y FE(7.1)114 b(The)28 b(calculus)167 582 y Fy(7.1.1)95 b(T)m(yp)s(es)167 716 y FK(In)25 b(c)n(hapter)g FG(??)h FK(w)n(e)e(allo)n(w)n(ed)g(for)h(giv)n(en)g(additional)g (constan)n(t)h(t)n(yp)r(es;)g(w)n(e)e(shall)g(no)n(w)i(sp)r(ecify)167 801 y(t)n(w)n(o)i(suc)n(h)g(t)n(yp)r(es,)g(namely)f Fq(Int)h FK(\(in)n(tegers\))e(and)j Fq(Bo)r(ol)e FK(\(b)r(o)r(oleans\).)167 1011 y Fy(7.1.2)95 b(T)-8 b(erms)167 1144 y FK(Besides)30 b(the)h(usual)g(\014v)n(e,)h(there)e(are)h(sc)n(hemes)f(for)i(the)e(sp) r(eci\014c)g(constan)n(ts)i Fq(Int)f FK(and)h Fq(Bo)r(ol)p FK(.)167 1229 y(W)-6 b(e)29 b(ha)n(v)n(e)h(retained)e(the)h FM(intr)l(o)l(duction/elimination)g FK(terminology)-6 b(,)29 b(as)h(these)f(sc)n(hemes)f(will)167 1314 y(app)r(ear)h(later)d (in)h FG(F)p FK(:)251 1483 y(1.)35 b Fq(Int)p FM(-intr)l(o)l(duction)5 b FK(:)421 1650 y FJ(\017)35 b Fq(O)28 b FK(is)f(a)h(constan)n(t)g(of)h (t)n(yp)r(e)e Fq(Int)p FK(;)421 1766 y FJ(\017)35 b FK(if)27 b FH(t)g FK(is)g(of)i(t)n(yp)r(e)e Fq(Int)p FK(,)h(then)g Fq(S)12 b FH(t)27 b FK(is)g(of)h(t)n(yp)r(e)g Fq(Int)p FK(.)251 1933 y(2.)35 b Fq(Int)p FM(-elimination)5 b FK(:)39 b(if)28 b FH(u)p FK(,)j FH(v)s FK(,)e FH(t)g FK(are)h(of)g(t)n(yp)r(es)f(resp)r(ectiv)n(ely)e FH(U)7 b FK(,)30 b FH(U)7 b FJ(!)q FK(\()p Fq(Int)p FJ(!)p FH(U)g FK(\))30 b(and)g Fq(Int)p FK(,)339 2018 y(then)e Fq(R)12 b FH(u)g(v)j(t)27 b FK(is)g(of)h(t)n(yp)r(e)g FH(U)7 b FK(.)251 2167 y(3.)35 b Fq(Bo)r(ol)p FM(-intr)l(o)l(duction)5 b FK(:)37 b Fq(T)27 b FK(and)i Fq(F)f FK(are)f(constan)n(ts)i(of)f(t)n (yp)r(e)g Fq(Bo)r(ol)p FK(.)251 2315 y(4.)35 b Fq(Bo)r(ol)p FM(-elimination)5 b FK(:)46 b(if)33 b FH(u)p FK(,)h FH(v)s FK(,)h FH(t)e FK(are)g(of)g(t)n(yp)r(es)h(resp)r(ectiv)n(ely)d FH(U)7 b FK(,)34 b FH(U)40 b FK(and)35 b Fq(Bo)r(ol)o FK(,)g(then)339 2400 y Fq(D)12 b FH(u)g(v)i(t)28 b FK(is)f(of)h(t)n(yp) r(e)g FH(U)7 b FK(.)167 2610 y Fy(7.1.3)95 b(In)m(tended)28 b(meaning)251 2743 y FK(1.)35 b Fq(O)28 b FK(and)h Fq(S)39 b FK(are)28 b(resp)r(ectiv)n(ely)d(zero)i(and)i(the)f(successor)f (function.)251 2891 y(2.)35 b Fq(R)28 b FK(is)f(a)h(recursion)f(op)r (erator:)37 b Fq(R)12 b FH(u)g(v)i FK(0)20 b(=)g FH(u)p FK(,)28 b Fq(R)12 b FH(u)g(v)i FK(\()p FH(n)i FK(+)f(1\))20 b(=)f FH(v)c FK(\()p Fq(R)d FH(u)g(v)j(n)p FK(\))d FH(n)p FK(.)251 3039 y(3.)35 b Fq(T)28 b FK(and)h Fq(F)f FK(are)f(the)g(truth) h(v)l(alues.)251 3187 y(4.)35 b Fq(D)f FK(is)f(the)h(op)r(eration)g (\\if)g(.)11 b(.)g(.)g(then)35 b(.)11 b(.)g(.)g(else")35 b(|)f(de\014nition)g(b)n(y)g(case:)48 b Fq(D)12 b FH(u)g(v)i Fq(T)24 b FK(=)g FH(u)p FK(,)339 3272 y Fq(D)12 b FH(u)g(v)i Fq(F)20 b FK(=)f FH(v)s FK(.)167 3483 y Fy(7.1.4)95 b(Con)m(v)m (ersions)167 3616 y FK(T)-6 b(o)28 b(the)g(classical)d(redexes,)j(w)n (e)f(add:)645 3814 y Fq(R)12 b FH(u)g(v)i Fq(O)59 b Fu( )g FH(u)761 b Fq(D)12 b FH(u)g(v)i Fq(T)59 b Fu( )g FH(u)567 3899 y Fq(R)12 b FH(u)g(v)j FK(\()p Fq(S)d FH(t)p FK(\))58 b Fu( )h FH(v)15 b FK(\()p Fq(R)d FH(u)g(v)i(t)p FK(\))e FH(t)490 b Fq(D)12 b FH(u)g(v)i Fq(F)59 b Fu( )g FH(v)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 48 51 bop 167 167 a FK(48)1244 b Fz(CHAPTER)26 b(7.)64 b(G)2038 149 y(\177)2025 167 y(ODEL'S)27 b(SYSTEM)h(T)167 404 y FE(7.2)114 b(Normalisation)27 b(theorem)167 559 y FK(In)h FG(T)p FK(,)g(all)e(the)h(reduction)h(sequences)f(are)h (\014nite)f(and)h(lead)f(to)h(the)g(same)f(normal)g(form.)167 720 y FG(Pro)r(of)k FK(P)n(art)h(of)g(the)f(result)f(is)g(the)h (extension)h(of)f(Ch)n(urc)n(h-Rosser;)j(it)c(is)h(not)h(di\016cult)e (to)167 805 y(extend)25 b(the)g(pro)r(of)h(for)g(the)f(simple)e(system) i(to)g(this)g(more)g(complex)f(case.)35 b(The)24 b(other)i(part)167 890 y(is)i(a)h(strong)g(normalisation)f(result,)g(for)h(whic)n(h)f (reducibilit)n(y)d(is)j(w)n(ell)f(adapted)i(\(it)f(w)n(as)h(for)167 975 y FG(T)f FK(that)g(T)-6 b(ait)27 b(in)n(v)n(en)n(ted)g(the)h (notion\).)270 1095 y(First,)g(the)h(notion)g(of)g FM(neutr)l(ality)g FK(is)f(extended:)37 b(a)29 b(term)e(is)h(called)f FM(neutr)l(al)h FK(if)g(it)g(is)g(not)167 1180 y(of)34 b(the)g(form)f FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(,)36 b FH(\025x:)12 b(v)s FK(,)36 b Fq(O)p FK(,)f Fq(S)12 b FH(t)p FK(,)35 b Fq(T)f FK(or)g Fq(F)p FK(.)53 b(Then,)36 b(without)d(c)n(hanging)i(an)n (ything,)i(w)n(e)167 1265 y(sho)n(w)28 b(successiv)n(ely:)251 1401 y(1.)35 b Fq(O)p FK(,)28 b Fq(T)g FK(and)g Fq(F)g FK(are)g(reducible)d(|)j(they)g(are)f(normal)g(terms)g(of)h(atomic)f(t) n(yp)r(e.)251 1539 y(2.)35 b(If)28 b FH(t)f FK(of)h(t)n(yp)r(e)g Fq(Int)g FK(is)f(reducible)e(\()p FM(i.e.)j FK(strongly)g (normalisable\),)e(then)i Fq(S)12 b FH(t)27 b FK(is)g(reducible)339 1624 y(|)h(that)g(comes)f(from)g FH(\027)t FK(\()p Fq(S)12 b FH(t)p FK(\))20 b(=)f FH(\027)t FK(\()p FH(t)p FK(\).)251 1761 y(3.)35 b(If)j FH(u)p FK(,)k FH(v)s FK(,)e FH(t)e FK(are)h(reducible,)f(then)h Fq(D)12 b FH(u)g(v)i(t)38 b FK(is)f(reducible)f(|)i FH(u)p FK(,)k FH(v)s FK(,)e FH(t)e FK(are)g(strongly)339 1846 y(normalisable)24 b(b)n(y)i(\()p FG(CR)f(1)p FK(\),)h(and)g(so)g(one)f(can)h(reason)g(b)n(y)g(induction) e(on)i(the)f(n)n(um)n(b)r(er)339 1932 y FH(\027)t FK(\()p FH(u)p FK(\))16 b(+)e FH(\027)t FK(\()p FH(v)s FK(\))h(+)g FH(\027)t FK(\()p FH(t)p FK(\).)35 b(The)27 b(neutral)f(term)g Fq(D)12 b FH(u)g(v)i(t)27 b FK(con)n(v)n(erts)h(to)f(one)g(of)h(the)f (follo)n(wing)339 2017 y(terms:)421 2165 y FJ(\017)35 b Fq(D)12 b FH(u)592 2140 y Fv(0)620 2165 y FH(v)656 2140 y Fv(0)684 2165 y FH(t)709 2140 y Fv(0)762 2165 y FK(with)35 b FH(u)p FK(,)j FH(v)s FK(,)h FH(t)d FK(reduced)f(resp)r (ectiv)n(ely)f(to)j FH(u)1978 2140 y Fv(0)1995 2165 y FK(,)h FH(v)2088 2140 y Fv(0)2104 2165 y FK(,)h FH(t)2187 2140 y Fv(0)2203 2165 y FK(.)61 b(In)36 b(this)g(case,)491 2251 y(w)n(e)j(ha)n(v)n(e)i FH(\027)t FK(\()p FH(u)889 2225 y Fv(0)906 2251 y FK(\))19 b(+)f FH(\027)t FK(\()p FH(v)1125 2225 y Fv(0)1142 2251 y FK(\))h(+)g FH(\027)t FK(\()p FH(t)1351 2225 y Fv(0)1367 2251 y FK(\))28 b FH(<)g(\027)t FK(\()p FH(u)p FK(\))19 b(+)g FH(\027)t FK(\()p FH(v)s FK(\))g(+)g FH(\027)t FK(\()p FH(t)p FK(\),)43 b(and)d(b)n(y)h(induction)491 2336 y(h)n(yp)r(othesis,)29 b(the)e(term)f(is)h(reducible.)421 2444 y FJ(\017)35 b FH(u)28 b FK(or)g FH(v)i FK(if)d FH(t)h FK(is)f Fq(T)g FK(or)h Fq(F)p FK(;)g(these)f(t)n(w)n(o)h(terms)f(are)g(reducible.)339 2593 y(W)-6 b(e)28 b(conclude)f(b)n(y)h(\()p FG(CR)g(3)p FK(\))f(that)h Fq(D)12 b FH(u)g(v)i(t)28 b FK(is)e(reducible.)251 2730 y(4.)35 b(If)k FH(u)p FK(,)j FH(v)s FK(,)g FH(t)d FK(are)f(reducible,)i(then)f Fq(R)12 b FH(u)g(v)j(t)39 b FK(is)f(reducible)f(|)h(here)h(also)g(w)n(e)f(reason)339 2815 y(b)n(y)32 b(induction,)f(but)g(on)h FH(\027)t FK(\()p FH(u)p FK(\))17 b(+)f FH(\027)t FK(\()p FH(v)s FK(\))g(+)g FH(\027)t FK(\()p FH(t)p FK(\))h(+)f FH(`)p FK(\()p FH(t)p FK(\),)31 b(where)f FH(`)p FK(\()p FH(t)p FK(\))g(is)g(the)h(n)n(um)n (b)r(er)g(of)339 2900 y(sym)n(b)r(ols)d(of)g(the)g(normal)f(form)h(of)g FH(t)p FK(.)35 b(In)28 b(one)g(step,)g Fq(R)12 b FH(u)g(v)i(t)28 b FK(con)n(v)n(erts)g(to:)421 3049 y FJ(\017)35 b Fq(R)12 b FH(u)586 3023 y Fv(0)615 3049 y FH(v)651 3023 y Fv(0)679 3049 y FH(t)704 3023 y Fv(0)748 3049 y FK(with)26 b FM(etc.)35 b FK(|)28 b(reducible)d(b)n(y)k(induction.)421 3157 y FJ(\017)35 b FH(u)28 b FK(\(if)f FH(t)19 b FK(=)g Fq(O)p FK(\))28 b(|)f(reducible.)421 3265 y FJ(\017)35 b FH(v)15 b FK(\()p Fq(R)d FH(u)g(v)i(w)r FK(\))e FH(w)r FK(,)41 b(where)c Fq(S)12 b FH(w)29 b FK(=)d FH(t)p FK(;)43 b(since)37 b FH(\027)t FK(\()p FH(w)r FK(\))27 b(=)g FH(\027)t FK(\()p FH(t)p FK(\))37 b(and)i FH(`)p FK(\()p FH(w)r FK(\))27 b FH(<)f(`)p FK(\()p FH(t)p FK(\),)40 b(the)491 3350 y(induction)27 b(h)n(yp)r(othesis)h(tells)d(us)j(that)f Fq(R)12 b FH(u)g(v)j(w)29 b FK(is)e(reducible.)33 b(As)27 b FH(v)j FK(and)f FH(w)g FK(are,)491 3435 y FH(v)15 b FK(\()p Fq(R)d FH(u)g(v)i(w)r FK(\))e FH(w)30 b FK(is)d(reducible)e(b)n (y)k(the)e(de\014nition)g(for)h FH(U)7 b FJ(!)q FH(V)15 b FK(.)511 b Fu(\003)270 3584 y FK(The)32 b(use)f(of)h(the)g(induction) f(h)n(yp)r(othesis)h(in)f(the)g(\014nal)h(case)f(is)g(really)f(essen)n (tial:)42 b(it)31 b(is)167 3669 y(the)f(only)g(o)r(ccasion,)h(in)e(all) f(the)i(uses)g(so)g(far)h(made)e(of)i(reducibilit)n(y)-6 b(,)27 b(where)i(w)n(e)h(truly)f(use)167 3754 y(an)35 b(induction)f(on)i(reducibilit)n(y)-6 b(.)53 b(F)-6 b(or)35 b(the)g(other)f(cases,)j(the)d(cognoscen)n(ti)h(will)d(see)i(that)167 3840 y(w)n(e)g(really)g(ha)n(v)n(e)i(no)f(need)g(for)g(induction)f(on)i (a)f(complex)f(predicate,)h(b)n(y)h(reform)n(ulating)167 3925 y(\()p FG(CR)28 b(3)p FK(\))f(in)g(an)h(appropriate)g(w)n(a)n(y)-6 b(.)p eop PStoPSsaved restore %%Page: (52,53) 27 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 49 52 bop 167 167 a Fz(7.3.)64 b(EXPRESSIVE)27 b(PO)n(WER:)g(EXAMPLES) 1092 b FK(49)167 404 y FE(7.3)114 b(Expressiv)m(e)28 b(p)s(o)m(w)m(er:)40 b(examples)167 580 y Fy(7.3.1)95 b(Bo)s(oleans)167 710 y FK(The)27 b(t)n(ypical)g(example)g(is)g(giv)n (en)g(b)n(y)i(the)e(logical)f(connectors:)381 864 y Fq(neg)q FK(\()p FH(u)p FK(\))20 b(=)f Fq(D)12 b(F)g(T)g FH(u)213 b Fq(disj)p FK(\()p FH(u;)12 b(v)s FK(\))19 b(=)g Fq(D)12 b(T)g FH(v)i(u)214 b Fq(conj)p FK(\()p FH(u;)12 b(v)s FK(\))20 b(=)f Fq(D)12 b FH(v)i Fq(F)e FH(u)167 1017 y FK(F)-6 b(or)27 b(example,)f Fq(disj)p FK(\()p Fq(T)p FH(;)12 b(x)p FK(\))19 b Fu( )h Fq(T)26 b FK(and)i Fq(disj)p FK(\()p Fq(F)p FH(;)12 b(x)p FK(\))19 b Fu( )h FH(x)p FK(;)27 b(but)g(on)g(the)f(other)h(hand,)h(faced)e(with)167 1102 y(the)h(expression)h Fq(disj)p FK(\()p FH(x;)12 b Fq(T)p FK(\),)28 b(w)n(e)f(do)h(not)h(kno)n(w)f(what)g(to)g(do.)167 1218 y FG(Question)55 b FK(Is)27 b(it)g(p)r(ossible)g(to)h(de\014ne)g (another)g(disjunction)f(whic)n(h)g(is)g(symmetrical?)270 1334 y(W)-6 b(e)36 b(shall)e(see)h(in)g FG(??)q FK(,)i(b)n(y)g(seman)n (tic)d(metho)r(ds,)k(that)d(there)g(is)g(no)h(term)e FH(G)i FK(of)g(t)n(yp)r(e)167 1419 y Fq(Bo)r(ol)p FH(;)12 b Fq(Bo)r(ol)f FJ(!)i Fq(Bo)r(ol)27 b FK(suc)n(h)h(that:)494 1572 y FH(G)12 b FJ(h)p Fq(T)p FH(;)g(x)p FJ(i)21 b Fu( )f Fq(T)327 b FH(G)12 b FJ(h)p FH(x;)g Fq(T)p FJ(i)21 b Fu( )f Fq(T)327 b FH(G)12 b FJ(h)p Fq(F)p FH(;)g Fq(F)p FJ(i)21 b Fu( )f Fq(F)167 1839 y Fy(7.3.2)95 b(In)m(tegers)167 1970 y FK(First)36 b(w)n(e)h(m)n(ust)g(represen)n(t)g(the)g(in)n (tegers:)54 b(the)38 b(c)n(hoice)e(of)p 1847 1931 42 3 v 38 w FH(n)26 b FK(=)h Fq(S)2033 1944 y Fw(n)2078 1970 y Fq(O)37 b FK(to)h(represen)n(t)e(the)167 2055 y(in)n(teger)27 b FH(n)g FK(is)g(ob)n(vious.)270 2208 y(The)i(classical)d(functions)j(are)g(de\014ned)g(b)n(y)g(simple)e (recurrence)g(relations.)37 b(Let)28 b(us)h(giv)n(e)167 2293 y(the)36 b(example)f(of)h(the)g(addition:)52 b(w)n(e)36 b(ha)n(v)n(e)h(to)f(w)n(ork)h(from)f(the)f(de\014ning)i(equations)g(w)n (e)167 2378 y(already)28 b(kno)n(w:)701 2531 y FH(x)16 b FK(+)g Fq(O)j FK(=)g FH(x)535 b(x)16 b FK(+)f Fq(S)d FH(y)22 b FK(=)d Fq(S)12 b FK(\()p FH(x)k FK(+)f FH(y)s FK(\))270 2684 y(Consider)28 b FH(t)p FK([)p FH(x;)12 b(y)s FK(])19 b(=)g Fq(R)12 b FH(x)g FK(\()p FH(\025z)1034 2659 y Fp(Int)1095 2684 y FH(:)g(\025z)1201 2659 y Fv(0)f Fp(Int)1286 2684 y FH(:)h Fq(S)g FH(z)s FK(\))g FH(y)s FK(:)402 2837 y FH(t)p FK([)p FH(x;)g Fq(O)p FK(])20 b Fu( )g FH(x)236 b(t)p FK([)p FH(x;)12 b Fq(S)g FH(y)s FK(])19 b Fu( )h FK(\()p FH(\025z)1402 2812 y Fp(Int)1463 2837 y FH(:)12 b(\025z)1569 2812 y Fv(0)f Fp(Int)1654 2837 y FH(:)h Fq(S)g FH(z)s FK(\))g(\()p FH(t)p FK([)p FH(x;)g(y)s FK(]\))g FH(y)21 b Fu( )f Fq(S)12 b FH(t)p FK([)p FH(x;)g(y)s FK(])167 2990 y(This)27 b(sho)n(ws)i(that)f(one)g (can)g(tak)n(e)g FH(t)p FK([)p FH(x;)12 b(y)s FK(])27 b(as)h(a)g(de\014nition)f(of)i FH(x)15 b FK(+)h FH(y)s FK(.)270 3106 y(Among)52 b(easy)f(exercises)f(in)g(this)g(st)n(yle,)57 b(one)51 b(can)g(am)n(use)g(oneself)g(b)n(y)h(de\014ning)167 3192 y(m)n(ultiplication,)24 b(exp)r(onen)n(tial,)k(predecessor)f FM(etc.)270 3308 y FK(Predicates)g(on)h(in)n(tegers)f(can)h(also)g(b)r (e)f(de\014ned,)i(for)f(example)751 3461 y Fq(null)o FK(\()p Fq(O)p FK(\))19 b(=)g Fq(T)585 b(null)o FK(\()p Fq(S)12 b FH(x)p FK(\))19 b(=)g Fq(F)167 3567 y FK(giv)n(es)926 3687 y Fq(null)o FK(\()p FH(x)p FK(\))1141 3647 y FD(def)1149 3687 y FK(=)27 b Fq(R)12 b(T)g FK(\()p FH(\025z)1447 3661 y Fp(Bo)q(ol)1546 3687 y FH(:)g(\025z)1652 3661 y Fv(0)f Fp(Int)1738 3687 y FH(:)h Fq(F)p FK(\))g FH(x)167 3840 y FK(whic)n(h)27 b(allo)n(ws)g(us)h(to)g(turn)f(a)h(c)n (haracteristic)e(function)h(\(t)n(yp)r(e)h Fq(Int)p FK(\))f(in)n(to)h (a)g(predicate)e(\(t)n(yp)r(e)167 3925 y Fq(Bo)r(ol)p FK(\).)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 50 53 bop 167 167 a FK(50)1244 b Fz(CHAPTER)26 b(7.)64 b(G)2038 149 y(\177)2025 167 y(ODEL'S)27 b(SYSTEM)h(T)270 404 y FK(None)34 b(of)h(these)e(examples)g(mak)n(es)h(serious)f(use)h (of)g(higher)g(t)n(yp)r(es.)54 b(Ho)n(w)n(ev)n(er,)35 b(as)f(the)167 490 y(t)n(yp)r(es)25 b(used)h(in)f(the)f(recursion)h (increase,)g(more)f(and)i(more)f(functions)g(b)r(ecome)f(expressible.) 167 575 y(F)-6 b(or)28 b(example,)f(if)g FH(f)35 b FK(is)27 b(of)h(t)n(yp)r(e)g Fq(Int)p FJ(!)12 b Fq(Int)p FK(,)28 b(one)g(can)g(de\014ne)g Fq(it)o FK(\()p FH(f)8 b FK(\))27 b(of)h(t)n(yp)r(e)g Fq(Int)p FJ(!)12 b Fq(Int)27 b FK(b)n(y)527 809 y Fq(it)o FK(\()p FH(f)8 b FK(\))k FH(x)18 b FK(=)h Fq(R)p 862 755 35 3 v 12 w FK(1)13 b(\()p FH(\025z)1011 784 y Fp(Int)1072 809 y FH(:)f(\025z)1178 784 y Fv(0)f Fp(Int)1263 809 y FH(:)h(f)19 b(z)s FK(\))12 b FH(x)360 b FK(\()p Fq(it)o FK(\()p FH(f)8 b FK(\))p 1996 770 42 3 v 12 w FH(n)26 b FK(is)h FH(f)2179 784 y Fw(n)p 2224 755 35 3 v 2224 809 a FK(1\))167 1044 y(As)g(an)i(ob)t(ject)e(of)h(t)n (yp)r(e)g(\()p Fq(Int)p FJ(!)12 b Fq(Int)p FK(\))p FJ(!)q FK(\()p Fq(Int)o FJ(!)h Fq(Int)p FK(\),)27 b(the)h(function)f Fq(it)p FK(,)g(is:)1200 1278 y FH(\025x)1279 1252 y Fp(Int)p Fv(!)p Fp(Int)1447 1278 y FH(:)12 b Fq(it)o FK(\()p FH(x)p FK(\))270 1546 y(It)26 b(is)f(easy)h(to)g(see)g(that)g(b)n(y)g (\014nite)f(iteration)f(of)j(some)e(reasonable)i(function)e FH(f)2391 1557 y FD(0)2419 1546 y FK(,)h(w)n(e)g(can)167 1631 y(exceed)33 b(ev)n(ery)g(primitiv)n(e)d(recursiv)n(e)i(function.) 52 b(The)33 b(function)h(whic)n(h,)g(giv)n(en)f FH(n)p FK(,)i(returns)167 1716 y Fq(it)208 1687 y Fw(n)253 1716 y FH(f)287 1727 y FD(0)342 1716 y FK(\(Ac)n(k)n(ermann's)27 b(function\),)h(gro)n(ws)g(more)e(quic)n(kly)h(than)h(all)e(the)h (primitiv)n(e)d(recursiv)n(e)167 1801 y(functions.)270 1958 y(This)h(kind)f(of)i(function)e(is)g(easily)g(de\014nable)h(in)f FG(T)p FK(,)h(pro)n(vided)g(w)n(e)f(use)h(a)g(recursion)f(on)i(a)167 2043 y(complex)e(t)n(yp)r(e,)h(suc)n(h)h(as)f Fq(Int)p FJ(!)12 b Fq(Int)p FK(:)34 b(tak)n(e)25 b Fq(R)12 b FH(f)1393 2054 y FD(0)1433 2043 y FK(\()p FH(\025x)1539 2018 y Fp(Int)p Fv(!)p Fp(Int)1707 2043 y FH(:)g(\025z)1813 2018 y Fp(Int)1874 2043 y FH(:)g Fq(it)o FK(\()p FH(x)p FK(\)\))g FH(y)s FK(,)24 b(whic)n(h)g(normalises)167 2128 y(for)k FH(y)22 b FK(=)d Fq(O)27 b FK(to)h FH(f)607 2139 y FD(0)635 2128 y FK(,)g(and)h(for)p 931 2090 42 3 v 28 w FH(n)e FK(to)h Fq(it)1129 2099 y Fw(n)1174 2128 y FH(f)1208 2139 y FD(0)1236 2128 y FK(.)270 2363 y(T)-6 b(o)30 b(\014nish,)f(let)f(us)h(remark)f(that)i(the)e(second)i(argumen) n(t)f(of)g FH(v)j FK(in)c Fq(R)12 b FH(u)g(v)j(t)28 b FK(is)g(frequen)n(tly)167 2448 y(un)n(used.)43 b(One)29 b(w)n(ould)h(prefer)f(an)i(iterator)d Fq(It)i FK(instead)g(of)g(the)f (recursor)h Fq(R)p FK(,)h(applying)f(to)g FH(u)167 2533 y FK(of)e(t)n(yp)r(e)g FH(T)10 b FK(,)28 b FH(v)i FK(of)e(t)n(yp)r(e)g FH(T)10 b FJ(!)p FH(T)g FK(,)28 b(and)h FH(t)e FK(of)i(t)n(yp)r(e)e Fq(Int)p FK(,)h(with)f(the)g(rule:)1070 2767 y Fq(It)11 b FH(u)h(v)j FK(\()p Fq(S)d FH(t)p FK(\))19 b Fu( )h FH(v)14 b FK(\()p Fq(It)e FH(u)g(v)i(t)p FK(\))270 3002 y(The)33 b FM(one-step)g(pr)l(e)l(de)l(c)l(essor)h FK(satisfying)g(the) e(equations)i Fq(p)n(red)q FK(\()p Fq(O)p FK(\))23 b(=)g Fq(O)p FK(,)35 b Fq(p)n(red)q FK(\()p Fq(S)12 b FH(x)p FK(\))23 b(=)g FH(x)167 3087 y FK(cannot)32 b(b)r(e)e(constructed)h (using)g(the)g(iterator:)40 b Fq(R)31 b FK(is)f(essen)n(tial.)44 b(In)30 b(fact,)i(if)e(one)h(has)h(only)167 3172 y(the)c(iterator)f (one)i(can)f(de\014ne)h(the)f(same)g(functions)g(but)h(a)f(certain)f(n) n(um)n(b)r(er)i(of)f(equations)167 3257 y(with)c(v)l(ariables)h(disapp) r(ear.)35 b(So)26 b(the)e(predecessor)h(will)d(still)h(b)r(e)h (de\014nable,)i(but)g(will)c(satisfy)167 3342 y Fq(p)n(red)q FK(\()p Fq(S)12 b FH(t)p FK(\))22 b Fu( )i FH(t)32 b FK(only)g(when)h FH(t)f FK(is)g(of)g(the)g(form)p 1465 3304 V 32 w FH(n)q FK(,)h(in)f(other)g(w)n(ords)h FM(by)g(values)p FK(.)48 b(This)32 b(is)g(a)167 3427 y(little)c(anno)n(ying)33 b(\(in)e(particular)f(for)i FG(F)p FK(,)f(where)g(w)n(e)g(shall)f(no)i (longer)g(ha)n(v)n(e)g(an)n(ything)h(but)167 3513 y(the)e(iterator\),)f (for)h(it)f(sho)n(ws)i(that)f(to)g(calculate)e Fq(p)n(red)q FK(\()p 1687 3474 V FH(n)p FK(\),)j(the)e(program)i(mak)n(es)f FH(n)g FK(steps,)167 3598 y(whic)n(h)38 b(is)g(manifestly)f(excessiv)n (e.)67 b(W)-6 b(e)38 b(do)i(not)f(kno)n(w)g(ho)n(w)g(to)g(t)n(yp)r(e)g (the)f(predecessor,)167 3683 y(except)27 b(in)g(systems)h(lik)n(e)e FG(T)p FK(,)i(where)e(the)i(solution)f(is)g(visibly)g FM(ad)h(ho)l(c)p FK(.)270 3840 y(As)34 b(an)g(exercise,)f(de\014ne)g Fq(R)h FK(from)f Fq(It)g FK(and)h(pairing)f(\(b)n(y)h(v)l(alues)g (only\).)52 b(W)-6 b(e)33 b(shall)g(use)167 3925 y(this)27 b(in)g(system)g FG(F)h FK(\(see)f FG(??)q FK(\).)p eop PStoPSsaved restore %%Page: (54,55) 28 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 51 54 bop 167 167 a Fz(7.4.)64 b(EXPRESSIVE)27 b(PO)n(WER:)g(RESUL)-6 b(TS)1168 b FK(51)167 404 y FE(7.4)114 b(Expressiv)m(e)28 b(p)s(o)m(w)m(er:)40 b(results)167 580 y Fy(7.4.1)95 b(Canonical)28 b(forms)167 710 y FK(First)c(a)i(question:)35 b(what)25 b(guaran)n(tee)i(do)f(w)n(e)f(ha)n(v)n(e)h(that)g Fq(Int)f FK(represen)n(ts)g(the)g(in)n(tegers,)g Fq(Bo)r(ol)167 796 y FK(the)i(b)r(o)r(oleans,)h FM(etc.)p FK(?)34 b(It)27 b(is)g(not)g(b)r(ecause)h(w)n(e)e(ha)n(v)n(e)j(represen)n(ted)d(the)h (in)n(tegers)f(in)h(the)g(t)n(yp)r(e)167 881 y Fq(Int)33 b FK(that)h(this)e(t)n(yp)r(e)h(can)h(immediately)c(claim)g(to)k (represen)n(t)e(the)h(in)n(tegers.)51 b(The)33 b(answ)n(er)167 966 y(lies)26 b(in)h(the)g(follo)n(wing)g(lemma:)167 1085 y FG(Lemma)e FK(Let)i FH(t)h FK(b)r(e)f(a)h(closed)f(normal)h (term:)270 1216 y FJ(\017)34 b FK(If)28 b FH(t)f FK(is)g(of)i(t)n(yp)r (e)e Fq(Int)p FK(,)h(then)g FH(t)f FK(is)g(of)h(the)g(form)p 1570 1177 42 3 v 27 w FH(n)p FK(.)270 1353 y FJ(\017)34 b FK(If)28 b FH(t)f FK(is)g(of)i(t)n(yp)r(e)e Fq(Bo)r(ol)p FK(,)h(then)g FH(t)f FK(is)g(of)h(the)g(form)f Fq(T)h FK(or)g Fq(F)p FK(.)270 1489 y FJ(\017)34 b FK(If)28 b FH(t)f FK(is)g(of)i(t)n(yp)r(e)e FH(U)7 b FJ(\002)p FH(V)16 b FK(,)28 b(then)f FH(t)h FK(is)f(of)h(the)f(form)h FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(.)270 1625 y FJ(\017)34 b FK(If)28 b FH(t)f FK(is)g(of)i(t)n(yp)r(e)e FH(U)7 b FJ(!)q FH(V)15 b FK(,)28 b(then)g FH(t)f FK(is)g(of)i(the)e(form)g FH(\025x:)12 b(v)s FK(.)167 1791 y FG(Pro)r(of)34 b FK(By)h(induction)e (on)i(the)f(n)n(um)n(b)r(er)h(of)f(sym)n(b)r(ols)h(of)g FH(t)p FK(.)55 b(If)34 b FH(t)g FK(is)f Fq(S)12 b FH(w)r FK(,)37 b(the)d(induction)167 1876 y(h)n(yp)r(othesis)27 b(applied)f(to)h FH(w)i FK(giv)n(es)e FH(w)21 b FK(=)p 1238 1837 V 20 w FH(n)p FK(,)27 b(so)g FH(t)20 b FK(=)p 1531 1822 161 3 v 19 w FH(n)c FK(+)f(1.)35 b(So)28 b(w)n(e)e(supp)r (ose)i(that)f FH(t)f FK(is)g(not)i(of)167 1961 y(the)f(form)h Fq(O)p FK(,)f Fq(T)p FK(,)h Fq(F)p FK(,)g FJ(h)p FH(u;)12 b(v)s FJ(i)29 b FK(or)e FH(\025x:)12 b(v)s FK(:)270 2092 y FJ(\017)34 b FK(If)d FH(t)g FK(is)f Fq(R)12 b FH(u)g(v)i(w)r FK(,)32 b(then)f(the)g(induction)f(h)n(yp)r(othesis)h(sa)n(ys)h(that)g FH(w)g FK(is)f(of)g(the)f(form)p 2612 2054 42 3 v 31 w FH(n)p FK(,)339 2177 y(and)f(then)f FH(t)f FK(is)g(not)h(normal.)270 2314 y FJ(\017)34 b FK(If)c FH(t)f FK(is)g Fq(D)12 b FH(u)g(v)i(w)r FK(,)30 b(then)g(b)n(y)g(the)f(induction)g(h)n(yp)r (othesis)h FH(w)i FK(is)d Fq(T)g FK(or)h Fq(F)p FK(,)g(and)h(then)e FH(t)h FK(is)339 2399 y(not)f(normal.)270 2535 y FJ(\017)34 b FK(If)28 b FH(t)f FK(is)g FH(\031)581 2510 y Fw(i)601 2535 y FH(w)r FK(,)h(then)g(again)g FH(w)i FK(is)d(of)h(the)f(form)h FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(,)28 b(and)h FH(t)f FK(is)e(not)j (normal.)270 2672 y FJ(\017)34 b FK(If)28 b FH(t)f FK(is)g FH(w)14 b(u)p FK(,)28 b(then)g FH(w)i FK(is)d(of)h(the)f(form)h FH(\025x:)12 b(v)s FK(,)28 b(and)g FH(t)g FK(is)f(not)h(normal.)425 b Fu(\003)167 2872 y Fy(7.4.2)95 b(Represen)m(table)28 b(functions)167 3003 y FK(In)h(particular,)f(if)g FH(t)g FK(is)g(a)i(closed)e(term)f(of)i(t)n(yp)r(e)g Fq(Int)p FJ(!)12 b Fq(Int)29 b FK(of)g FG(T)p FK(,)g(it)f(induces)g(a)h (function)g FJ(j)p FH(t)p FJ(j)167 3088 y FK(from)e(I)-12 b(N)28 b(to)g(I)-12 b(N)27 b(de\014ned)h(b)n(y:)641 3246 y FJ(j)p FH(t)p FJ(j)p FK(\()p FH(n)p FK(\))19 b(=)g FH(m)475 b FK(i\013)454 b FH(t)p 1979 3207 V 12 w(n)19 b Fu( )p 2129 3207 61 3 v 20 w FH(m)167 3404 y FK(Lik)n(ewise,)26 b(a)i(closed)f(term)f(of)j(t)n(yp)r(e)e Fq(Int)p FJ(!)13 b Fq(Bo)r(ol)27 b FK(induces)g(a)h(predicate)f FJ(j)p FH(t)p FJ(j)f FK(on)j(I)-12 b(N:)627 3563 y FJ(j)p FH(t)p FJ(j)p FK(\()p FH(n)p FK(\))26 b(holds)461 b(i\013)e FH(t)p 1987 3524 42 3 v 12 w(n)20 b Fu( )g Fq(T)270 3754 y FK(The)j(functions)g FJ(j)p FH(t)p FJ(j)f FK(are)h(clearly)e (calculable:)31 b(the)23 b(normalisation)f(algorithm)g(giv)n(es)h FJ(j)p FH(t)p FJ(j)p FK(\()p FH(n)p FK(\))167 3840 y(as)31 b(a)g(function)g(of)g FH(n)p FK(.)45 b(So)31 b(those)g(functions)g (represen)n(table)f(in)g FG(T)g FK(are)h FM(r)l(e)l(cursive)p FK(.)44 b(Can)32 b(w)n(e)167 3925 y(c)n(haracterise)26 b(the)i(class)f(of)h(suc)n(h)g(functions?)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 52 55 bop 167 167 a FK(52)1244 b Fz(CHAPTER)26 b(7.)64 b(G)2038 149 y(\177)2025 167 y(ODEL'S)27 b(SYSTEM)h(T)270 404 y FK(In)43 b(general,)i(recursiv)n(e)40 b(functions)j(are)f (de\014ned)g(using)g(partial)g(algorithms,)j(whose)167 490 y(con)n(v)n(ergence)29 b(is)g(not)h(assured,)g(but)g(whic)n(h)e(ha) n(v)n(e)i(nice)e(closure)g(prop)r(erties)h(not)g(shared)h(b)n(y)167 575 y(total)22 b(ones.)34 b(Seen)22 b(as)h(a)g(partial)e(algorithm,)i FJ(j)p FH(t)p FJ(j)e FK(amoun)n(ts)j(to)e(lo)r(oking)h(for)f(the)g (normal)g(form,)167 660 y(and,)j(in)d(the)h(case)g(where)f(this)g (succeeds,)h(writing)f(it.)33 b(The)22 b(normalisation)g(theorem)g(is)g (th)n(us)167 745 y(a)34 b FM(pr)l(o)l(of)h(of)e(pr)l(o)l(gr)l(am)j FK(guaran)n(teeing)e(termination)e(of)h(all)f(algorithms)h(obtained)h (from)f FG(T)p FK(.)167 830 y(No)n(w,)c(what)h(are)f(the)f (mathematical)f(principles)g(necessary)i(to)g(pro)n(v)n(e)h(the)f (reducibilit)n(y)d(of)167 915 y(a)i FM(\014xe)l(d)f FK(term)g FH(t)p FK(?)270 1041 y(W)-6 b(e)28 b(need)270 1203 y FJ(\017)34 b FK(to)29 b(b)r(e)f(able)f(to)i(express)f(the)g (reducibilit)n(y)d(of)j FH(t)g FK(and)h(of)g(its)e(subterms:)36 b(one)28 b(m)n(ust)g(b)r(e)339 1288 y(able)i(to)g(write)f(a)h(\014nite) f(n)n(um)n(b)r(er)h(of)h(reducibilities,)26 b(whic)n(h)k(can)g(b)r(e)g (done)h(in)e(P)n(eano)339 1373 y(arithmetic)c(\()p FG(P)-23 b(A)p FK(\).)270 1517 y FJ(\017)34 b FK(to)j(b)r(e)f(able)h(to)f (reason)i(b)n(y)f(mathematical)d(induction)i(on)i(this)d(\014nite)h(n)n (um)n(b)r(er)h(of)339 1602 y(reducibilit)n(y)30 b(predicates;)35 b(that)e(can)g(again)h(b)r(e)e(done)i(in)e FG(P)-23 b(A)p FK(,)34 b(mo)r(dulo)f(some)f(a)n(wful)339 1687 y(co)r(ding)c(without)g (signi\014can)n(t)f(in)n(terest)f(\(G\177)-34 b(odel)27 b(n)n(um)n(b)r(ering\).)270 1848 y(Summing)38 b(up,)j(the)d (termination)f(is)g(pro)n(v)l(able)i(in)e(arithmetic:)54 b(w)n(e)37 b(sa)n(y)i(that)g FJ(j)p FH(t)p FJ(j)e FK(is)167 1933 y FM(pr)l(ovably)28 b(total)35 b FK(in)27 b FG(P)-23 b(A)p FK(.)270 2107 y(The)27 b(con)n(v)n(erse)h(is)e(true:)35 b(let)26 b FH(f)34 b FK(b)r(e)27 b(a)h(recursiv)n(e)e(function,)h(pro)n (v)l(ably)i(total)e(in)f FG(P)-23 b(A)p FK(,)27 b(then)167 2192 y(one)32 b(can)g(\014nd)g(a)g(term)e(of)i(t)n(yp)r(e)f Fq(Int)p FJ(!)12 b Fq(Int)32 b FK(in)e FG(T)p FK(,)i(suc)n(h)g(that)g FH(f)8 b FK(\()p FH(n)p FK(\))21 b(=)h FJ(j)p FH(t)p FJ(j)p FK(\()p FH(n)p FK(\))30 b(for)i(all)e FH(n)p FK(.)47 b(In)167 2277 y(other)30 b(w)n(ords,)i(the)d(expressiv)n(e)h(p)r(o)n(w) n(er)g(of)h(the)f(system)f FG(T)i FK(is)e(enormous,)j(and)f(m)n(uc)n(h) f(more)167 2362 y(than)f(what)g(is)f(feasible)808 2336 y FD(1)863 2362 y FK(on)h(a)g(computer!)37 b(The)28 b(further)g (generalisations)g(are)g(not)h(aiming)167 2447 y(to)e(increase)e(the)h (class)g(of)h(represen)n(table)f(functions,)h(whic)n(h)f(is)f(already)i (to)r(o)g(big,)g(but)g(only)167 2532 y(to)36 b(enlarge)f(the)h(class)f (of)i(particular)d(algorithms)i(calculating)e(simple)g(giv)n(en)i (functions.)167 2617 y(F)-6 b(or)28 b(example,)f(\014nding)i(a)f(t)n (yp)r(e)f(system)h(where)f(the)g(predecessor)g(is)g(w)n(ell-b)r(eha)n (v)n(ed.)270 2744 y(W)-6 b(e)33 b(do)g(not)g(w)n(an)n(t)g(to)f(giv)n(e) g(a)h(pro)r(of)h(of)f(this)e(con)n(v)n(erse)i(here,)g(since)f(w)n(e)f (consider)h(the)167 2829 y(\(more)27 b(delicate\))e(case)j(of)g(system) f FG(F)h FK(in)f FG(??)q FK(.)p 167 3790 1003 3 v 246 3833 a FC(1)273 3854 y FB(In)34 b(the)g(sense)h(of)g FA(c)m(omplexity)p FB(.)57 b(Th)n(us)35 b(for)g(instance)e FA(hyp)m(er)m(exp)m(onential)j FB(algorithms,)g(suc)n(h)e(as)i(the)167 3925 y(pro)r(of)27 b(of)h(cut)f(elimination,)e(are)j(not)g(feasible.)p eop PStoPSsaved restore %%Page: (56,57) 29 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 53 56 bop 167 881 a FF(Chapter)28 b(8)167 1182 y(Coherence)g(Spaces)167 1508 y FK(The)40 b(earliest)e(w)n(ork)i(in)g(denotational)g(seman)n (tics)f(w)n(as)i(done)f(b)n(y)h([)p FG(?)q FK(])f(for)g(the)g(un)n(t)n (yp)r(ed)167 1594 y FH(\025)p FK(-calculus,)22 b(and)h(m)n(uc)n(h)e (has)i(b)r(een)e(written)f(since)g(then.)34 b(His)20 b(approac)n(h)k(is)d(c)n(haracterised)f(b)n(y)167 1679 y FM(c)l(ontinuity)p FK(,)29 b FM(i.e.)f FK(the)h(preserv)l(ation)f(of) h(directed)e(joins.)38 b(In)28 b(this)g(c)n(hapter,)h(a)g(no)n(v)n(el)f (kind)h(of)167 1764 y(domain)c(theory)g(is)g(in)n(tro)r(duced,)g(in)f (whic)n(h)g(w)n(e)h(also)g(ha)n(v)n(e)h(\(and)g(preserv)n(e\))e(meets)f (b)r(ounded)167 1849 y(ab)r(o)n(v)n(e)30 b(\()p FM(pul)t(lb)l(acks)p FK(\).)38 b(This)29 b(prop)r(ert)n(y)-6 b(,)30 b(called)d FM(stability)p FK(,)j(w)n(as)f(originally)f(in)n(tro)r(duced)h(b)n(y)g ([)p FG(?)q FK(])167 1934 y(in)34 b(an)h(attempt)e(to)i(giv)n(e)f(a)h (seman)n(tic)e(c)n(haracterisation)g(of)i FM(se)l(quential)f FK(algorithms.)54 b(W)-6 b(e)167 2019 y(shall)31 b(\014nd)h(that)g (this)f(seman)n(tics)g(is)g(w)n(ell)e(adapted)k(to)f(system)g FG(F)f FK(and)i(leads)e(us)h(to)n(w)n(ards)167 2104 y(linear)26 b(logic.)167 2365 y FE(8.1)114 b(General)27 b(ideas)167 2530 y FK(The)18 b(fundamen)n(tal)g(idea)g(of)g(denotational)h(seman)n (tics)e(is)g(to)h(in)n(terpret)f(reduction)g(\(a)h(dynamic)167 2615 y(notion\))35 b(b)n(y)g(equalit)n(y)g(\(a)g(static)e(notion\).)57 b(T)-6 b(o)35 b(put)h(it)d(in)h(another)i(w)n(a)n(y)-6 b(,)38 b(w)n(e)c(mo)r(del)f(the)167 2700 y(in)n(v)l(arian)n(ts)j(of)f (the)g(calculi.)56 b(This)35 b(said,)i(there)d(are)i(mo)r(dels)e(and)i (mo)r(dels:)50 b(it)34 b(has)i(b)r(een)167 2786 y(kno)n(wn)46 b(since)f(G\177)-34 b(odel)44 b(\(1930\))j(ho)n(w)f(to)f(construct)g (mo)r(dels)f(as)i(maximally)d(consisten)n(t)167 2871 y(extensions.)36 b(This)27 b(is)g(certainly)f(not)i(what)g(w)n(e)f (mean,)h(b)r(ecause)f(it)g(giv)n(es)h(no)g FM(information)p FK(.)270 3018 y(W)-6 b(e)32 b(ha)n(v)n(e)i(in)d(mind)h(rather)g(to)h (tak)n(e)f(literally)d(the)j(na)-8 b(\177)-27 b(\020v)n(e)34 b(in)n(terpretation)c(|)j(that)f(an)167 3103 y(ob)t(ject)j(of)h(t)n(yp) r(e)f FH(U)25 b FJ(!)18 b FH(V)51 b FK(is)34 b(a)i(function)f(from)g FH(U)43 b FK(to)35 b FH(V)51 b FK(|)35 b(and)h(see)f(if)f(w)n(e)h(can)h (giv)n(e)f(a)167 3188 y(reasonable)i(meaning)g(to)g(the)g(w)n(ord)g (\\function".)64 b(In)37 b(this)f(w)n(a)n(y)i(of)f(lo)r(oking)h(at)f (things,)167 3273 y(w)n(e)k(try)g(to)g(a)n(v)n(oid)h(b)r(eing)f (obsessed)h(b)n(y)g(completeness,)i(but)d(instead)g(lo)r(ok)h(for)f (simple)167 3358 y(geometrical)25 b(ideas.)270 3574 y(The)j(\014rst)g (idea)f(whic)n(h)g(comes)g(to)h(mind)e(is)h(the)h(follo)n(wing:)270 3763 y FJ(\017)34 b FK(t)n(yp)r(e)28 b(=)f(set.)270 3925 y FJ(\017)34 b FH(U)23 b FJ(!)16 b FH(V)43 b FK(is)27 b(the)h(set)f(of)h(all)f(functions)h(\(in)e(the)i(set-theoretic)d (sense\))j(from)f FH(U)35 b FK(to)28 b FH(V)15 b FK(.)1385 4101 y(53)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 54 57 bop 167 167 a FK(54)1205 b Fz(CHAPTER)27 b(8.)63 b(COHERENCE)26 b(SP)-6 b(A)n(CES)270 404 y FK(This)37 b(in)n(terpretation)e(is)h(all)f(v)n(ery)i(w)n(ell,)g(but)g(it)f(do)r (es)h(not)g(explain)f(an)n(ything.)64 b(The)167 490 y(computationally) 41 b(in)n(teresting)f(ob)t(jects)i(just)f(get)h(dro)n(wned)g(in)f(a)h (sea)g(of)g(set-theoretic)167 575 y(functions.)36 b(The)27 b(function)h(spaces)g(also)g(quic)n(kly)f(b)r(ecome)g(enormous.)270 783 y(Kreisel)e(had)k(the)e(follo)n(wing)g(idea)g(\(hereditarily)f (e\013ectiv)n(e)f(op)r(erations\):)270 1020 y FJ(\017)34 b FK(t)n(yp)r(e)28 b(=)f(partial)g(equiv)l(alence)g(relation)f(on)j(I) -12 b(N.)270 1178 y FJ(\017)34 b FH(U)25 b FJ(!)19 b FH(V)50 b FK(is)35 b(the)g(set)g(of)g(\(co)r(des)h(of)5 b(\))35 b(partial)f(recursiv)n(e)g(functions)i FH(f)43 b FK(suc)n(h)35 b(that,)j(if)339 1263 y FH(x)12 b(U)19 b(y)s FK(,)27 b(then)h FH(f)8 b FK(\()p FH(x)p FK(\))k FH(V)26 b(f)8 b FK(\()p FH(y)s FK(\),)26 b(sub)t(ject)i(to)g(the)f (equiv)l(alence)g(relation:)604 1502 y FH(f)20 b FK(\()p FH(U)i FJ(!)16 b FH(V)g FK(\))c FH(g)267 b FK(i\013)e FJ(8)p FH(x;)12 b(y)21 b FK(\()p FH(x)12 b(U)18 b(y)k FJ(\))e FH(f)8 b FK(\()p FH(x)p FK(\))k FH(V)26 b(g)s FK(\()p FH(y)s FK(\)\))270 1804 y(This)40 b(stic)n(ks)g(more)f(closely) g(to)i(the)f(computational)g(paradigm)h(whic)n(h)e(w)n(e)h(seek)g(to) 167 1889 y(mo)r(del)25 b(|)h(a)g(bit)f(to)r(o)h(closely)-6 b(,)26 b(it)e(seems,)i(for)g(in)f(fact)h(it)f(hardly)h(do)r(es)h(more)e (than)i(in)n(terpret)167 1974 y(the)g(syn)n(tax)j(b)n(y)e(itself,)e(mo) r(dulo)i(some)f(unexciting)g(co)r(ding.)270 2182 y(Scott's)i(idea)e(is) g(m)n(uc)n(h)g(b)r(etter:)270 2367 y FJ(\017)34 b FK(t)n(yp)r(e)28 b(=)f(top)r(ological)h(space.)270 2525 y FJ(\017)34 b FH(U)23 b FJ(!)16 b FH(V)43 b FK(=)28 b(con)n(tin)n(uous)h(functions)e (from)h FH(U)35 b FK(to)28 b FH(V)15 b FK(.)270 2710 y(No)n(w)24 b(it)e(is)h(w)n(ell)e(kno)n(wn)k(that)f(top)r(ology)h(do)r (es)f(not)g(lend)f(itself)e(w)n(ell)g(to)j(the)f(construction)167 2795 y(of)j(function)f(spaces.)35 b(When)26 b(should)g(w)n(e)f(sa)n(y)h (that)g(a)g(sequence)f(of)g(functions)h(con)n(v)n(erges)g(|)167 2880 y(p)r(oin)n(t)n(wise,)h(or)h(uniformly)e(in)h(some)h(w)n(a)n(y) 1282 2854 y FD(1)1311 2880 y FK(?)270 3024 y(T)-6 b(o)25 b(resolv)n(e)f(these)g(problems,)h(Scott)f(w)n(as)h(led)f(to)g(imp)r (osing)g(drastic)g(restrictions)e(on)j(his)167 3109 y(top)r(ological)g (spaces)h(whic)n(h)e(are)h(far)h(remo)n(v)n(ed)f(from)g(the)g (traditional)g(geometrical)e(spirit)h(of)167 3194 y(top)r(ology)426 3168 y FD(2)455 3194 y FK(.)47 b(In)32 b(fact)g(his)f(spaces)h(are)f (really)f(only)i(partially)e(ordered)i(sets)f(with)g(directed)167 3279 y(joins:)j(the)25 b(top)r(ology)h(is)e(an)h(inciden)n(tal)e (feature.)34 b(So)25 b(it)f(is)g(natural)h(to)g(ask)h(oneself)e (whether)167 3364 y(p)r(erhaps)29 b(the)e(top)r(ological)g(in)n (tuition)f(is)h(itself)f(false,)h(and)i(lo)r(ok)f(for)g(something)f (else.)p 167 3438 1003 3 v 246 3481 a FC(1)273 3502 y FB(The)g(most)h(common)g(\(but)e(b)n(y)i(no)f(means)h(the)f(univ)n (ersal\))f(answ)n(er)i(to)g(this)e(question)h(is)g(to)g(use)h(the)167 3573 y FA(c)m(omp)m(act-op)m(en)k FB(top)r(ology)-5 b(,)32 b(in)e(whic)n(h)h(a)g(function)f(lies)g(in)g(a)i(basic)f(op)r(en)f(set) h(if,)h(when)f(restricted)f(to)i(a)167 3643 y(sp)r(eci\014ed)24 b(compact)h(set,)h(its)f(v)m(alues)g(lie)f(in)g(a)i(sp)r(eci\014ed)d (op)r(en)i(set.)34 b(This)25 b(top)r(ology)g(is)g(only)f(w)n(ell-b)r (eha)n(v)n(ed)167 3713 y(when)h(the)f(spaces)i(are)f(lo)r(cally)e (compact)j(\(ev)n(ery)f(p)r(oin)n(t)f(has)h(a)g(base)h(of)f(compact)g (neigh)n(b)r(ourho)r(o)r(ds\),)f(and)167 3784 y(ev)n(en)k(then)e(the)i (function)d(space)j(need)f(not)h(itself)e(b)r(e)h(lo)r(cally)f (compact.)246 3833 y FC(2)273 3854 y FB(There)36 b(is,)j(ho)n(w)n(ev)n (er,)h(a)d(logical)f(view)g(of)h(top)r(ology)-5 b(,)39 b(whic)n(h)c(has)i(b)r(een)f(set)g(out)g(in)g(a)h(computer)167 3925 y(science)27 b(con)n(text)h(b)n(y)f([)p Ft(?)p FB(,)h Ft(?)p FB(,)g Ft(?)p FB(,)g Ft(?)p FB(].)p eop PStoPSsaved restore %%Page: (58,59) 30 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 55 58 bop 167 167 a Fz(8.2.)64 b(COHERENCE)26 b(SP)-6 b(A)n(CES)1526 b FK(55)167 404 y FE(8.2)114 b(Coherence)28 b(Spaces)167 559 y FK(A)f FM(c)l(oher)l(enc)l(e)h(sp)l(ac)l(e)714 534 y FD(3)770 559 y FK(is)f(a)h(set)g(\(of)g(sets\))f FJ(A)h FK(whic)n(h)f(satis\014es:)201 718 y(i\))g(Do)n(wn-closure:)35 b(if)27 b FH(a)20 b FJ(2)f(A)28 b FK(and)h FH(a)1182 693 y Fv(0)1218 718 y FJ(\032)19 b FH(a)p FK(,)28 b(then)g FH(a)1573 693 y Fv(0)1609 718 y FJ(2)20 b(A)p FK(.)201 862 y(ii\))41 b(Binary)h(completeness:)62 b(if)42 b FH(M)37 b FJ(\032)29 b(A)42 b FK(and)h(if)f FJ(8)p FH(a)1710 873 y FD(1)1737 862 y FH(;)12 b(a)1804 873 y FD(2)1862 862 y FJ(2)29 b FH(M)37 b FK(\()p FH(a)2105 873 y FD(1)2153 862 y FJ([)20 b FH(a)2256 873 y FD(2)2313 862 y FJ(2)30 b(A)p FK(\),)46 b(then)339 894 y Fo(S)410 947 y FH(M)27 b FJ(2)19 b(A)p FK(.)270 1106 y(In)28 b(particular,)f(w)n(e)g(ha)n(v)n (e)i(the)e FM(unde\014ne)l(d)g(obje)l(ct)p FK(,)h Fn(?)19 b FJ(2)h(A)p FK(.)270 1232 y(The)31 b(reader)g(ma)n(y)g(consider)g(a)h (coherence)e(space)h(as)h(a)f(\\domain")h(\(partially)e(ordered)167 1317 y(b)n(y)35 b(inclusion\);)i(as)e(suc)n(h)g(it)f(is)f FM(algebr)l(aic)h FK(\(an)n(y)i(set)e(is)g(the)g(directed)f(union)i(of) g(its)f(\014nite)167 1402 y(subsets\))28 b(and)h(satis\014es)e(the)h (binary)g(condition)f(\(ii\),)f(so)i(that)808 1785 y Fn(?)617 1585 y FJ(f)p FG(t)p FJ(g)233 b(f)p FG(f)7 b FJ(g)743 1734 y Fs(@)701 1692 y(@)868 1734 y(\000)910 1692 y(\000)1643 1785 y Fn(?)1618 1585 y FJ(f)p FK(0)p FJ(g)146 b(f)p FK(1)p FJ(g)h(f)p FK(2)p FJ(g)2298 1570 y FH(:)12 b(:)g(:)p 1669 1717 3 67 v 1720 1734 a Fs(\021)1779 1695 y(\021)1812 1673 y(\021)1770 1734 y(\020)1829 1714 y(\020)1888 1695 y(\020)1946 1675 y(\020)2005 1656 y(\020)2012 1653 y(\020)167 1927 y FK(are)28 b(\(v)n(ery)f(basic\))h(coherence)e (spaces,)j(resp)r(ectiv)n(ely)c(called)h FJ(B)-10 b FM(o)l(ol)36 b FK(and)29 b FJ(I)-7 b FM(nt)7 b FK(,)28 b(but)1392 2509 y Fn(?)1117 2342 y FJ(f)p FK(0)p FJ(g)146 b(f)p FK(1)p FJ(g)h(f)p FK(2)p FJ(g)1084 2092 y(f)p FK(1)p FH(;)12 b FK(2)q FJ(g)80 b(f)p FK(0)p FH(;)12 b FK(2)q FJ(g)81 b(f)p FK(0)p FH(;)12 b FK(1)q FJ(g)1311 2458 y Fs(Q)1252 2419 y(Q)1219 2397 y(Q)p 1418 2442 V 1470 2458 a(\021)1528 2419 y(\021)1561 2397 y(\021)1311 2275 y(@)1252 2216 y(@)1219 2183 y(@)1470 2275 y(\000)1528 2216 y(\000)1561 2183 y(\000)1219 2275 y(\000)1278 2216 y(\000)1311 2183 y(\000)1236 2291 y(\010)1295 2262 y(\010)1353 2233 y(\010)1412 2203 y(\010)1471 2174 y(\010)1528 2145 y(\010)1561 2275 y(@)1503 2216 y(@)1470 2183 y(@)1545 2291 y(H)1486 2262 y(H)1427 2233 y(H)1369 2203 y(H)1310 2174 y(H)1253 2145 y(H)167 2651 y FK(is)44 b(not.)87 b(Ho)n(w)n(ev)n(er)45 b(w)n(e)f(shall)g(see)g(that)h(coherence)f (spaces)h(are)g(b)r(etter)e(regarded)i(as)167 2736 y(undirected)27 b(graphs.)167 2940 y Fy(8.2.1)95 b(The)27 b(w)m(eb)h(of)g(a)f (coherence)i(space)167 3087 y FK(Consider)c FJ(jAj)572 3047 y FD(def)580 3087 y FK(=)660 3034 y Fo(S)731 3087 y FJ(A)20 b FK(=)f FJ(f)p FH(\013)h FK(:)39 b FJ(f)p FH(\013)p FJ(g)21 b(2)e(Ag)p FK(.)35 b(The)25 b(elemen)n(ts)e(of)j FJ(jAj)f FK(are)g(called)f FM(tokens)p FK(,)h(and)167 3172 y(the)i FM(c)l(oher)l(enc)l(e)h(r)l(elation)g(mo)l(dulo)g FJ(A)g FK(is)f(de\014ned)h(b)r(et)n(w)n(een)f(tok)n(ens)i(b)n(y)553 3344 y FH(\013)617 3322 y(_)617 3365 y(^)705 3344 y(\013)749 3319 y Fv(0)813 3344 y FK(\(mo)r(d)24 b FJ(A)p FK(\))386 b(i\013)f FJ(f)p FH(\013;)12 b(\013)2064 3319 y Fv(0)2081 3344 y FJ(g)20 b(2)f(A)167 3516 y FK(whic)n(h)36 b(is)h(a)g(re\015exiv) n(e)g(symmetric)d(relation,)39 b(so)e FJ(jAj)g FK(equipp)r(ed)g(with) 2193 3494 y FH(_)2193 3537 y(^)2326 3516 y FK(is)f(a)i(graph,)167 3601 y(called)26 b(the)h FM(web)g FK(of)h FJ(A)p FK(.)p 167 3649 1003 3 v 246 3692 a FC(3)273 3713 y FB(The)d(term)g FA(esp)m(ac)m(e)g(c)m(oh)n(\023)-29 b(er)m(ent)26 b FB(is)f(used)f(in)g (the)h(F)-5 b(renc)n(h)25 b(text,)h(and)f(indeed)e(Plotkin)h(has)h (also)g(used)g(the)167 3784 y(w)n(ord)30 b FA(c)m(oher)m(ent)f FB(to)h(refer)f(to)g(this)f(binary)g(condition.)38 b(Ho)n(w)n(ev)n(er) 31 b FA(c)m(oher)m(ent)e(sp)m(ac)m(e)g FB(is)g(established,)f(alb)r (eit)167 3854 y(p)r(eculiar,)33 b(usage)g(for)h(a)f(space)h(with)e(a)h (basis)g(of)g(compact)h(op)r(en)e(sets,)j(also)e(called)f(a)h FA(sp)m(e)m(ctr)m(al)h(sp)m(ac)m(e)p FB(.)167 3925 y(Consequen)n(tly)-5 b(,)27 b(the)g(term)h(w)n(as)h(mo)r(di\014ed)c(in)i(translation.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 56 59 bop 167 167 a FK(56)1205 b Fz(CHAPTER)27 b(8.)63 b(COHERENCE)26 b(SP)-6 b(A)n(CES)270 404 y FK(F)g(or)44 b(example,)h(the)e(w)n(eb)f(of)i FJ(B)-10 b FM(o)l(ol)51 b FK(consists)43 b(of)g(the)f(tok)n(ens)i FG(t)e FK(and)i FG(f)7 b FK(,)47 b(whic)n(h)42 b(are)167 490 y(incoheren)n(t;)j (similarly)36 b(the)j(w)n(eb)g(of)h FJ(I)-7 b FM(nt)46 b FK(is)39 b(a)h FM(discr)l(ete)f(gr)l(aph)46 b FK(whose)39 b(p)r(oin)n(ts)h(are)f(the)167 575 y(in)n(tegers.)c(Suc)n(h)28 b(domains)g(w)n(e)f(call)f FM(\015at)p FK(.)270 792 y(The)43 b(construction)g(of)h(the)f(w)n(eb)g(of)h(a)f(coherence)g(space)g(is)f (a)i(bijection)e(b)r(et)n(w)n(een)167 877 y(coherence)28 b(spaces)i(and)g(\(re\015exiv)n(e-symmetric\))c(graphs.)41 b(F)-6 b(rom)29 b(the)g(w)n(eb)g(w)n(e)g(reco)n(v)n(er)f(the)167 962 y(coherence)f(space)h(b)n(y:)627 1179 y FH(a)20 b FJ(2)f(A)d(,)g FH(a)k FJ(\032)g(jAj)15 b(^)g(8)p FH(\013)1295 1190 y FD(1)1322 1179 y FH(;)d(\013)1397 1190 y FD(2)1444 1179 y FJ(2)20 b FH(a)g FK(\()p FH(\013)1638 1190 y FD(1)1685 1157 y FH(_)1685 1200 y(^)1773 1179 y(\013)1817 1190 y FD(2)1892 1179 y FK(\(mo)r(d)j FJ(A)p FK(\)\))270 1397 y(So)39 b(in)e(the)h(terminology)f(of)h(Graph)h(Theory)-6 b(,)41 b(a)d(p)r(oin)n(t)g(is)f(exactly)g(a)i FM(clique)p FK(,)g FM(i.e.)f FK(a)167 1482 y(complete)26 b(subgraph.)167 1712 y Fy(8.2.2)95 b(In)m(terpretation)167 1854 y FK(The)30 b(aim)g(is)f(to)i(in)n(terpret)e(a)i(t)n(yp)r(e)f(b)n(y)h(a)g (coherence)f(space)g FJ(A)p FK(,)i(and)f(a)g(term)e(of)i(this)f(t)n(yp) r(e)167 1939 y(b)n(y)f(a)f(p)r(oin)n(t)h(of)f FJ(A)g FK(\(coheren)n(t)g(subset)h(of)f FJ(jAj)p FK(,)g(in\014nite)f(in)g (general:)36 b(w)n(e)28 b(write)e FJ(A)2374 1950 y Fm(\014n)2466 1939 y FK(for)i(the)167 2024 y(set)f(of)h FM(\014nite)f FK(p)r(oin)n(ts\).)270 2241 y(T)-6 b(o)30 b(w)n(ork)g(in)f(an)h (e\013ectiv)n(e)d(manner)i(with)g(p)r(oin)n(ts)g(of)h FJ(A)p FK(,)g(it)e(is)h(necessary)g(to)h(in)n(tro)r(duce)167 2326 y(a)f(notion)g(of)g FM(\014nite)f(appr)l(oximation)p FK(.)40 b(An)29 b(appro)n(ximan)n(t)h(of)f FH(a)20 b FJ(2)h(A)28 b FK(is)g(an)n(y)i(subset)f FH(a)2487 2301 y Fv(0)2533 2326 y FK(of)g FH(a)p FK(.)167 2412 y(Condition)23 b(\(i\))f(for)i(coherence)f(spaces)h(ensures)f(that)h(appro)n(ximan)n (ts)h(are)e(still)e(in)i FJ(A)p FK(.)34 b(Ab)r(o)n(v)n(e)167 2497 y(all,)27 b(there)f(are)i(enough)h FM(\014nite)e FK(appro)n(ximan)n(ts)i(to)f FH(a)p FK(:)270 2688 y FJ(\017)34 b FH(a)28 b FK(is)f(the)h(union)g(of)g(its)f(set)g(of)h(\014nite)f (appro)n(ximan)n(ts.)270 2850 y FJ(\017)34 b FK(The)28 b(set)f FH(I)34 b FK(of)28 b(\014nite)f(appro)n(ximan)n(ts)i(is)e FM(dir)l(e)l(cte)l(d)p FK(.)36 b(In)28 b(other)f(w)n(ords,)374 3037 y(i\))f FH(I)34 b FK(is)27 b(nonempt)n(y)h(\()p Fn(?)20 b FJ(2)f FH(I)6 b FK(\).)374 3159 y(ii\))26 b(If)h FH(a)576 3133 y Fv(0)593 3159 y FH(;)12 b(a)660 3133 y Fv(00)710 3159 y FJ(2)19 b FH(I)6 b FK(,)28 b(one)g(can)g(\014nd)g FH(a)20 b FJ(2)g FH(I)33 b FK(suc)n(h)28 b(that)g FH(a)1799 3133 y Fv(0)1816 3159 y FH(;)12 b(a)1883 3133 y Fv(00)1933 3159 y FJ(\032)19 b FH(a)28 b FK(\(tak)n(e)g FH(a)19 b FK(=)h FH(a)2417 3133 y Fv(0)2449 3159 y FJ([)c FH(a)2548 3133 y Fv(00)2578 3159 y FK(\).)270 3402 y(This)28 b(comes)f(from)g (the)g(follo)n(wing)g(idea:)270 3592 y FJ(\017)34 b FK(On)h(the)f(one)h (hand)g(w)n(e)f(ha)n(v)n(e)h(the)g FM(true)f FK(\(or)g FM(total)p FK(\))g(ob)t(jects)g(of)h FJ(A)p FK(.)56 b(F)-6 b(or)35 b(example,)339 3677 y(in)27 b FJ(B)-10 b FM(o)l(ol)9 b FK(,)28 b(the)f(singletons)g FJ(f)p FG(t)p FJ(g)h FK(and)h FJ(f)p FG(f)7 b FJ(g)p FK(,)29 b(in)e FJ(I)-7 b FM(nt)7 b FK(,)28 b FJ(f)p FK(0)p FJ(g)p FK(,)g FJ(f)p FK(1)p FJ(g)p FK(,)h FJ(f)p FK(2)p FJ(g)p FK(,)g FM(etc.)270 3840 y FJ(\017)34 b FK(On)c(the)f(other)g(hand,)i(the)e(appro)n(ximan)n (ts,)i(of)f(whic)n(h,)f(in)g(the)g(t)n(w)n(o)g(simplistic)d(cases)339 3925 y(considered,)i Fn(?)f FK(is)g(the)g(only)h(example.)35 b(They)28 b(are)f FM(p)l(artial)i FK(ob)t(jects.)p eop PStoPSsaved restore %%Page: (60,61) 31 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 57 60 bop 167 167 a Fz(8.3.)64 b(ST)-6 b(ABLE)28 b(FUNCTIONS)1547 b FK(57)270 404 y(The)27 b(addition)h(of)f(partial)g(ob)t(jects)g(has)h (m)n(uc)n(h)g(the)f(same)g(signi\014cance)f(as)i(in)f(recursion)167 490 y(theory)-6 b(,)27 b(where)d(w)n(e)h(shift)g(from)g(total)f(to)i (partial)e(functions:)35 b(for)26 b(example,)e(to)i(the)f(in)n(tegers) 167 575 y(\(represen)n(ted)i(b)n(y)h(singletons\))f(w)n(e)g(add)i(the)f (\\unde\014ned")h Fn(?)p FK(.)270 714 y(One)i(should)i(not,)g(ho)n(w)n (ev)n(er,)f(attac)n(h)h(to)r(o)f(m)n(uc)n(h)f(imp)r(ortance)f(to)i (this)f(\014rst)g(in)n(tuition.)167 799 y(F)-6 b(or)32 b(example,)h(it)d(is)i(misguided)f(to)h(seek)g(to)g(iden)n(tify)f(the)g (total)h(p)r(oin)n(ts)g(of)g(an)h(arbitrary)167 884 y(coherence)d (space)g FJ(A)p FK(.)44 b(One)30 b(migh)n(t)f(p)r(erhaps)j(think)e (that)h(the)f(total)g(p)r(oin)n(ts)h(of)g FJ(A)f FK(are)g(the)167 969 y(maximal)c(p)r(oin)n(ts,)i FM(i.e.)g FK(suc)n(h)g(that:)715 1169 y FJ(8)p FH(\013)19 b FJ(2)g(jAj)g FK(\()p FJ(8)p FH(\013)1110 1143 y Fv(0)1146 1169 y FJ(2)g FH(a)h(\013)1332 1146 y(_)1332 1189 y(^)1420 1169 y(\013)1464 1143 y Fv(0)1528 1169 y FK(\(mo)r(d)k FJ(A)p FK(\)\))19 b FJ(\))h FH(\013)g FJ(2)f FH(a)167 1368 y FK(whic)n(h)30 b(indeed)g(they)g(are)h(|)f(in)g (the)g(simple)f(cases)h(\(in)n(tegers,)h(b)r(o)r(oleans,)h FM(etc.)p FK(\).)43 b(Ho)n(w)n(ev)n(er)167 1453 y(w)n(e)28 b(w)n(ould)h(lik)n(e)e(to)i(de\014ne)g(totalit)n(y)e(in)i(coherence)e (spaces)i(whic)n(h)f(are)h(the)f(in)n(terpretations)167 1538 y(of)j(complex)e(t)n(yp)r(es,)j(using)e(form)n(ulae)g(analogous)j (to)d(the)g(ones)h(for)g(reducibilit)n(y)c(\(see)i FG(??)q FK(\).)167 1623 y(These)23 b(are)h(of)h(greater)e(and)i(greater)f (logical)e(complexit)n(y)1711 1598 y FD(4)1738 1623 y FK(,)i(and)h(altogether)f(unpredictable,)167 1708 y(whilst)30 b(the)g(notion)i(of)g(maximalit)n(y)d(remains)h(desp)r(erately)h(\005) 1875 1683 y FD(0)1875 1726 y(2)1902 1708 y FK(,)h(so)g(one)g(cannot)g (hop)r(e)g(for)167 1793 y(a)g(coincidence.)47 b(In)32 b(fact,)h(for)f(an)n(y)h(giv)n(en)f(coherence)f(space)h(there)f(are)h (man)n(y)h(notions)g(of)167 1879 y(totalit)n(y)-6 b(,)31 b(just)g(as)g(there)e(are)i(man)n(y)g FM(r)l(e)l(ducibility)g(c)l (andidates)g FK(\(c)n(hapter)f FG(??)q FK(\))g(for)h(the)f(same)167 1964 y(t)n(yp)r(e.)38 b(In)29 b(fact)g(the)f(seman)n(tics)g (partialises)f(ev)n(erything,)i(and)g(the)g(total)f(ob)t(jects)g(get)h (a)g(bit)167 2049 y(lost)e(inside)g(it.)270 2248 y(The)40 b(functions)g(from)g FJ(A)g FK(to)g FJ(B)i FK(will)37 b(b)r(e)j(seen)g(as)g(functions)g(de\014ned)h(uniquely)e(b)n(y)167 2333 y(their)33 b(appro)n(ximan)n(ts,)38 b(and)d(in)f(this)f(w)n(a)n(y) i(\\con)n(tin)n(uous".)58 b(Here)33 b(it)g(is)h(p)r(ossible)g(to)g(use) h(a)167 2418 y(top)r(ological)28 b(language)i(where)d(the)h(subsets)h FJ(f)p FH(a)21 b FK(:)40 b FH(a)1575 2429 y Fv(\016)1623 2418 y FJ(\032)20 b FH(a)p FJ(g)29 b FK(of)f FJ(A)p FK(,)h(for)g FH(a)2132 2429 y Fv(\016)2188 2418 y FK(\014nite,)f(are)g(op)r(en.)167 2503 y(Ho)n(w)n(ev)n(er)e(whereas)h(in)f(Scott-st)n(yle)g(domain)h (theory)g(the)f(functions)h(b)r(et)n(w)n(een)f(domains)h(are)167 2589 y(exactly)35 b(those)i(whic)n(h)e(are)h(con)n(tin)n(uous)h(for)f (this)g(top)r(ology)-6 b(,)40 b(this)35 b(will)e(no)k(longer)f(b)r(e)f (so)167 2674 y(here.)167 2925 y FE(8.3)114 b(Stable)29 b(functions)167 3086 y FK(Giv)n(en)e(t)n(w)n(o)h(coherence)f(spaces)h FJ(A)g FK(and)h FJ(B)r FK(,)f(a)g(function)g FH(F)36 b FK(from)28 b FJ(A)g FK(to)g FJ(B)h FK(is)e FM(stable)g FK(if:)201 3265 y(i\))g FH(a)311 3239 y Fv(0)347 3265 y FJ(\032)20 b FH(a)f FJ(2)h(A)g(\))g FH(F)10 b FK(\()p FH(a)828 3239 y Fv(0)843 3265 y FK(\))20 b FJ(\032)f FH(F)10 b FK(\()p FH(a)p FK(\))201 3420 y(ii\))26 b FH(F)10 b FK(\()376 3367 y Fo(S)434 3385 y Fv(")434 3440 y Fw(i)p Fv(2)p Fw(I)524 3420 y FH(a)560 3431 y Fw(i)580 3420 y FK(\))20 b(=)700 3367 y Fo(S)759 3385 y Fv(")759 3440 y Fw(i)p Fv(2)p Fw(I)849 3420 y FH(F)10 b FK(\()p FH(a)967 3431 y Fw(i)986 3420 y FK(\))106 b(\(directed)25 b(union\))201 3574 y(iii\))g FH(a)349 3585 y FD(1)393 3574 y FJ([)16 b FH(a)492 3585 y FD(2)539 3574 y FJ(2)k(A)g(\))g FH(F)10 b FK(\()p FH(a)890 3585 y FD(1)932 3574 y FJ(\\)16 b FH(a)1031 3585 y FD(2)1059 3574 y FK(\))k(=)f FH(F)10 b FK(\()p FH(a)1297 3585 y FD(1)1324 3574 y FK(\))15 b FJ(\\)h FH(F)10 b FK(\()p FH(a)1547 3585 y FD(2)1574 3574 y FK(\))106 b(\()p FG(St)p FK(\))p 167 3649 1003 3 v 246 3692 a FC(4)273 3713 y FB(The)23 b(logical)g(complexit)n(y)g (of)g(a)h(form)n(ula)g(is)f(essen)n(tially)f(determined)g(b)n(y)h(the)h (n)n(um)n(b)r(er)e(of)i(alternations)167 3784 y(of)33 b(quan)n(ti\014ers.)49 b(In)32 b(particular,)h(w)n(e)h(sa)n(y)f(that)f (a)i(form)n(ula)e Fl(8)p Fx(x:)10 b Fl(9)p Fx(x)1775 3763 y Fk(0)1789 3784 y Fx(:)g Fl(8)p Fx(x)1883 3763 y Fk(00)1911 3784 y Fx(:)20 b(:)10 b(:)g(:)g(P)e FB(\()p Fx(x;)i(x)2188 3763 y Fk(0)2204 3784 y Fx(;)g(x)2264 3763 y Fk(00)2293 3784 y Fx(;)g(:)g(:)g(:)q FB(\))32 b(where)h Fx(P)167 3854 y FB(is)j(a)i(primitiv)n(e)c(recursiv)n(e)j (predicate,)i(is)d(of)h(logical)f(complexit)n(y)g(\005)1852 3833 y FC(0)1852 3869 y Fj(n)1884 3854 y FB(,)k(where)d Fx(n)g FB(is)f(the)h(n)n(um)n(b)r(er)f(of)167 3925 y(quan)n(ti\014ers.) d(Similarly)-5 b(,)25 b Fl(9)p Fx(x:)10 b Fl(8)p Fx(x)915 3903 y Fk(0)929 3925 y Fx(:)g Fl(9)p Fx(x)1022 3903 y Fk(00)1051 3925 y Fx(:)20 b(:)10 b(:)g(:)h(P)d FB(\()p Fx(x;)i(x)1329 3903 y Fk(0)1344 3925 y Fx(;)g(x)1404 3903 y Fk(00)1434 3925 y Fx(;)g(:)g(:)g(:)p FB(\))28 b(is)f(of)g(logical)g(complexit)n(y)f(\006)2259 3903 y FC(0)2259 3939 y Fj(n)2292 3925 y FB(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 58 61 bop 167 167 a FK(58)1205 b Fz(CHAPTER)27 b(8.)63 b(COHERENCE)26 b(SP)-6 b(A)n(CES)270 404 y FK(The)32 b(\014rst)g(condition)f(sa)n(ys)i(that)g FH(F)40 b FK(preserv)n(es)32 b(appro)n(ximation:)45 b(if)30 b(w)n(e)i(pro)n(vide)g(more)167 490 y(information)25 b(to)g(start)g(o\013)h(with)f(\()p FH(a)g FK(rather)g(than)h FH(a)1552 464 y Fv(0)1569 490 y FK(\))f(then)g(w)n(e)g(get)g(more)f(bac)n(k)i(at)g(the)f(end.)167 575 y(Alternativ)n(ely)-6 b(,)26 b FH(F)36 b FK(only)28 b(uses)g FM(p)l(ositive)h FK(information)e(ab)r(out)i(its)d(argumen)n (ts.)270 734 y(The)i(second)g(states)g(con)n(tin)n(uit)n(y:)839 973 y FH(F)10 b FK(\()p FH(a)p FK(\))19 b(=)1076 920 y Fo(S)1135 939 y Fv(")1163 973 y FJ(f)p FH(F)10 b FK(\()p FH(a)1316 984 y Fv(\016)1343 973 y FK(\))19 b(:)40 b FH(a)1484 984 y Fv(\016)1531 973 y FJ(\032)20 b FH(a;)31 b(a)1728 984 y Fv(\016)1784 973 y FK(\014nite)o FJ(g)167 1212 y FK(This)c(sp)r(ecial)f(case)i(of)g(\(ii\))d(is)i(in)g(fact)h (equiv)l(alen)n(t)f(to)h(it.)270 1371 y(Considering)i(a)h(coherence)e (space)h(as)h(a)g(category)f(in)g(whic)n(h)f(the)h(morphisms)g(from)f FH(a)2655 1345 y Fv(0)167 1456 y FK(to)34 b FH(a)h FK(are)f(inclusions) f FH(a)821 1430 y Fv(0)862 1456 y FJ(\032)24 b FH(a)p FK(,)36 b(the)e(\014rst)g(condition)g(states)g(that)h(a)f(stable)g (function)g(is)g(a)167 1541 y FM(functor)29 b FK(and)h(the)f(second)h (that)g(this)e(preserv)n(es)h FM(\014lter)l(e)l(d)g(c)l(olimits)p FK(.)41 b(These)29 b(t)n(w)n(o)g(conditions)167 1626 y(are)37 b(en)n(tirely)d(familiar)h(from)h(the)h(top)r(ological)f (setting;)41 b(this)36 b(is)g(no)h(longer)g(true)f(of)h(the)167 1711 y(last)28 b(condition)f(|)h(the)g(stabilit)n(y)e(prop)r(ert)n(y)j (itself)d(|)h(whic)n(h)h(has)h(no)f(ob)n(vious)i(top)r(ological)167 1796 y(signi\014cance.)k(It)26 b(lo)r(oks)g(a)h(bit)e(p)r(eculiar)f(at) i(\014rst)g(sigh)n(t,)h(but)f(in)f(terms)g(of)i(categories)e(it)g(just) 167 1882 y(sa)n(ys)k(that)f(the)f(pullbac)n(k)1316 2055 y FH(a)1352 2066 y FD(1)1396 2055 y FJ([)16 b FH(a)1495 2066 y FD(2)1137 2301 y FH(a)1173 2312 y FD(1)1638 2301 y FH(a)1674 2312 y FD(2)1316 2556 y FH(a)1352 2567 y FD(1)1396 2556 y FJ(\\)g FH(a)1495 2567 y FD(2)1219 2241 y Fs(\000)1278 2182 y(\000)1311 2149 y(\000)-59 b(\022)1561 2241 y(@)1503 2182 y(@)1470 2149 y(@)g(I)1311 2492 y(@)1252 2433 y(@)1219 2400 y(@)g(I)1470 2492 y(\000)1528 2433 y(\000)1561 2400 y(\000)g(\022)167 2755 y FK(m)n(ust)28 b(b)r(e)f(preserv)n(ed.)37 b(The)27 b(in)n(ten)n(tion)g(is)g(that)i (this)e(should)i(hold)f(for)g(an)n(y)h(set)f FJ(f)p FH(a)2402 2766 y FD(1)2430 2755 y FH(;)12 b(a)2497 2766 y FD(2)2525 2755 y FH(;)g(:)g(:)g(:)p FJ(g)167 2840 y FK(whic)n(h)27 b(is)g(b)r(ounded)i(ab)r(o)n(v)n(e,)g(not)g(just)f(\014nite)f(ones,)h (but)g(in)f(the)h(con)n(text)f(of)i(strongly)f(\014nite)167 2926 y(appro)n(ximation)35 b(\()p FM(i.e.)g FK(the)f(fact)h(that)g(the) g(appro)n(ximating)g(elemen)n(ts)e(ha)n(v)n(e)i(only)g(\014nitely)167 3011 y(man)n(y)h(elemen)n(ts)e(b)r(elo)n(w)g(them,)j(whic)n(h)e(is)f (not)i(in)f(general)g(true)g(in)g(Scott's)h(theory\))g(w)n(e)167 3096 y(don't)29 b(need)e(to)h(sa)n(y)h(this.)270 3255 y(Let)h(us)h(giv)n(e)f(an)h(example)f(to)h(sho)n(w)g(that)g(the)f(h)n (yp)r(othesis)h(of)g(coherence)e(b)r(et)n(w)n(een)h FH(a)2644 3266 y FD(1)167 3340 y FK(and)e FH(a)341 3351 y FD(2)396 3340 y FK(cannot)g(b)r(e)e(lifted.)34 b(W)-6 b(e)26 b(w)n(an)n(t)i(to)f (b)r(e)f(able)h(to)g(represen)n(t)f(all)f(functions)j(from)e(I)-12 b(N)27 b(to)167 3425 y(I)-12 b(N)24 b(as)g(stable)g(functions)g(from)g FJ(I)-7 b FM(nt)31 b FK(to)24 b FJ(I)-7 b FM(nt)8 b FK(,)24 b(in)g(particular)f FH(f)8 b FK(\(0\))19 b(=)g FH(f)8 b FK(\(1\))19 b(=)h(0,)25 b FH(f)8 b FK(\()p FH(n)i FK(+)g(2\))19 b(=)g(1.)167 3510 y(This)41 b(forces)h FH(F)10 b FK(\()p FJ(f)p FK(0)p FJ(g)p FK(\))29 b(=)g FH(F)10 b FK(\()p FJ(f)p FK(1)p FJ(g)p FK(\))30 b(=)f FJ(f)p FK(0)p FJ(g)p FK(,)46 b FH(F)10 b FK(\()p FJ(f)p FH(n)15 b FK(+)g(2)q FJ(g)p FK(\))29 b(=)h FJ(f)p FK(1)p FJ(g)p FK(,)46 b(and)d(b)n(y)f (monotonicit)n(y)-6 b(,)167 3595 y FH(F)10 b FK(\()p Fn(?)p FK(\))20 b(=)g Fn(?)p FK(.)41 b(No)n(w,)30 b FH(F)10 b FK(\()p FJ(f)p FK(0)p FJ(g)16 b(\\)g(f)p FK(1)p FJ(g)p FK(\))22 b(=)e FH(F)10 b FK(\()p Fn(?)p FK(\))20 b(=)g Fn(?)h FJ(6)p FK(=)f FH(F)10 b FK(\()p FJ(f)p FK(0)p FJ(g)p FK(\))16 b FJ(\\)g FH(F)10 b FK(\()p FJ(f)p FK(1)p FJ(g)p FK(\);)30 b(w)n(e)f(are)h(sa)n(v)n(ed)g(b)n(y)167 3680 y(the)d(incoherence)g(of)h(0)g(and)h(1,)f(whic)n(h)f(mak)n(es)h FJ(f)p FK(0)p FJ(g)16 b([)g(f)p FK(1)p FJ(g)28 b FH(=)-42 b FJ(2)20 b(I)-7 b FM(nt)7 b FK(.)270 3840 y(W)-6 b(e)30 b(shall)f(see)g(that)h(this)f(prop)r(ert)n(y)h(forces)g(the)f (existence)f(of)i(a)g FM(le)l(ast)g FK(appro)n(ximan)n(t)h(in)167 3925 y(certain)26 b(cases,)i(simply)f(b)n(y)h(taking)g(the)g(in)n (tersection)d(of)k(a)f(set)f(whic)n(h)g(is)g(b)r(ounded)i(ab)r(o)n(v)n (e.)p eop PStoPSsaved restore %%Page: (62,63) 32 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 59 62 bop 167 167 a Fz(8.3.)64 b(ST)-6 b(ABLE)28 b(FUNCTIONS)1547 b FK(59)167 404 y Fy(8.3.1)95 b(Stable)28 b(functions)f(on)g(a)g (\015at)h(space)167 536 y FK(Let)f(us)h(lo)r(ok)g(at)g(the)g(stable)f (functions)h FH(F)37 b FK(from)27 b FJ(I)-7 b FM(nt)35 b FK(to)28 b FJ(I)-7 b FM(nt)7 b FK(:)270 700 y FJ(\017)34 b FK(If)28 b FH(F)10 b FK(\()p Fn(?)p FK(\))18 b(=)h FJ(f)p FH(n)p FJ(g)p FK(,)29 b(then)e FH(F)10 b FK(\()p FH(a)p FK(\))19 b(=)g FJ(f)p FH(n)p FJ(g)28 b FK(for)g(all)f FH(a)20 b FJ(2)f(I)-7 b FM(nt)7 b FK(.)270 845 y FJ(\017)34 b FK(Otherwise,)23 b FH(F)10 b FK(\()p Fn(?)p FK(\))19 b(=)g Fn(?)p FK(:)33 b(w)n(e)24 b(consider)g(the)g(partial)f(function)h FH(f)8 b FK(,)25 b(de\014ned)g(exactly)e(on)339 930 y(the)f(in)n (tegers)f FH(n)i FK(suc)n(h)f(that)h FH(F)10 b FK(\()p FJ(f)p FH(n)p FJ(g)p FK(\))19 b FJ(6)p FK(=)g Fn(?)p FK(,)k(in)f(whic)n(h)f(case)h(w)n(e)f(put)i FJ(f)p FH(f)8 b FK(\()p FH(n)p FK(\))p FJ(g)19 b FK(=)g FH(F)10 b FK(\()p FJ(f)p FH(n)p FJ(g)p FK(\),)339 1023 y(and)29 b(w)n(e)e(write)f FH(F)j FK(=)925 1004 y Fo(e)912 1023 y FH(f)8 b FK(.)270 1186 y(So)29 b(w)n(e)e(ha)n(v)n(e)i(found:)270 1350 y FJ(\017)34 b FK(the)28 b(constan)n(ts)h(\\b)n(y)g(v)n(o)r(cation")40 b(_)-30 b FH(n)p FK(:)46 b(_)-30 b FH(n)p FK(\()p FH(a)p FK(\))20 b(=)f FJ(f)p FH(n)p FJ(g)p FK(;)270 1503 y FJ(\017)34 b FK(the)19 b(functions)759 1485 y Fo(e)746 1503 y FH(f)8 b FK(,)20 b(amongst)g(whic)n(h)e(are)g(the)g(\\constan)n(ts")1898 1485 y Fo(e)1886 1503 y FH(f)7 b FK(\()p Fn(?)p FK(\))19 b(=)h Fn(?)p FK(,)2235 1485 y Fo(e)2223 1503 y FH(f)7 b FK(\()p FJ(f)p FH(m)p FJ(g)p FK(\))20 b(=)f FJ(f)p FH(n)p FJ(g)p FK(,)339 1588 y(whic)n(h)27 b(only)h(di\013er)f(from)g (the)h(\014rst)g(b)n(y)g(the)f(v)l(alue)h(at)g Fn(?)p FK(.)167 1794 y Fy(8.3.2)95 b(P)m(arallel)29 b(Or)167 1926 y FK(Let)f(us)h(lo)r(ok)g(for)g(all)f(the)g(stable)g(functions)h (of)g(t)n(w)n(o)g(argumen)n(ts)h(from)e FJ(B)-10 b FM(o)l(ol)9 b FK(,)29 b FJ(B)-10 b FM(o)l(ol)37 b FK(to)29 b FJ(B)-10 b FM(o)l(ol)167 2011 y FK(whic)n(h)25 b(represen)n(t)g(the)h (disjunction)g(in)f(the)h(sense)f(that)i FH(F)10 b FK(\()p FJ(f)p FH(\013)p FJ(g)p FH(;)i FJ(f)p FH(\014)t FJ(g)p FK(\))19 b(=)g FJ(f)p FH(\013)d FJ(_)g FH(\014)t FJ(g)26 b FK(for)g(ev)n(ery)167 2096 y(substitution)i(of)g FG(t)f FK(and)i FG(f)35 b FK(for)28 b FH(\013)g FK(and)g FH(\014)t FK(.)270 2273 y(W)-6 b(e)42 b(m)n(ust)f(ha)n(v)n(e)i FH(F)10 b FK(\()p FH(a)893 2247 y Fv(0)909 2273 y FH(;)i(b)969 2247 y Fv(0)985 2273 y FK(\))30 b FJ(\032)f FH(F)10 b FK(\()p FH(a;)i(b)p FK(\))41 b(when)h FH(a)1607 2247 y Fv(0)1653 2273 y FJ(\032)29 b FH(a)42 b FK(and)h FH(b)1997 2247 y Fv(0)2043 2273 y FJ(\032)29 b FH(b)p FK(.)78 b(In)42 b(particular,)167 2358 y(if)53 b FH(F)10 b FK(\()p Fn(?)p FH(;)i Fn(?)p FK(\))36 b(=)i FJ(f)p FG(t)p FJ(g)54 b FK(\(or)f FJ(f)p FG(f)7 b FJ(g)p FK(\),)61 b(then)54 b FH(F)63 b FK(tak)n(es)54 b(constan)n(tly)g(the)g(v)l(alue)g FG(t)f FK(\(or)h FG(f)7 b FK(\),)167 2443 y(whic)n(h)44 b(is)g(imp)r(ossible.)85 b(Similarly)42 b(w)n(e)i(ha)n(v)n(e)i FH(F)10 b FK(\()p FJ(f)p FG(f)d FJ(g)p FH(;)12 b Fn(?)p FK(\))31 b(=)h FH(F)10 b FK(\()p Fn(?)p FH(;)i FJ(f)p FG(f)7 b FJ(g)p FK(\))31 b(=)g Fn(?)45 b FK(b)r(ecause)167 2528 y FH(F)10 b FK(\()p FJ(f)p FG(f)d FJ(g)p FH(;)12 b Fn(?)p FK(\))19 b FJ(\032)g FH(F)10 b FK(\()p FJ(f)p FG(f)d FJ(g)p FH(;)12 b FJ(f)p FG(t)p FJ(g)p FK(\))20 b(=)f FJ(f)p FG(t)p FJ(g)28 b FK(and)h FH(F)10 b FK(\()p FJ(f)p FG(f)d FJ(g)p FH(;)12 b Fn(?)p FK(\))18 b FJ(\032)i FH(F)10 b FK(\()p FJ(f)p FG(f)d FJ(g)p FH(;)12 b FJ(f)p FG(f)7 b FJ(g)p FK(\))20 b(=)f FJ(f)p FG(f)7 b FJ(g)p FK(.)270 2656 y FH(F)j FK(\()p FJ(f)p FG(t)p FJ(g)p FH(;)i Fn(?)p FK(\))21 b(=)h FJ(f)p FG(t)p FJ(g)31 b FK(is)f(p)r(ossible,)h (but)g(then)g FH(F)10 b FK(\()p Fn(?)p FH(;)i FJ(f)p FG(t)p FJ(g)p FK(\))21 b(=)g Fn(?)p FK(:)42 b(indeed,)31 b(if)f(w)n(e)g(write)f(the)167 2741 y(third)e(condition)g(for)h(t)n(w)n (o)g(argumen)n(ts:)283 2917 y FH(a)319 2928 y FD(1)363 2917 y FJ([)16 b FH(a)462 2928 y FD(2)509 2917 y FJ(2)k(B)-10 b FM(o)l(ol)24 b FJ(^)15 b FH(b)811 2928 y FD(1)855 2917 y FJ([)h FH(b)947 2928 y FD(2)995 2917 y FJ(2)j(B)-10 b FM(o)l(ol)28 b FJ(\))20 b FH(F)10 b FK(\()p FH(a)1417 2928 y FD(1)1460 2917 y FJ(\\)16 b FH(a)1559 2928 y FD(2)1587 2917 y FH(;)c(b)1647 2928 y FD(1)1691 2917 y FJ(\\)j FH(b)1782 2928 y FD(2)1810 2917 y FK(\))20 b(=)f FH(F)10 b FK(\()p FH(a)2048 2928 y FD(1)2075 2917 y FH(;)i(b)2135 2928 y FD(1)2163 2917 y FK(\))k FJ(\\)f FH(F)10 b FK(\()p FH(a)2386 2928 y FD(2)2413 2917 y FH(;)i(b)2473 2928 y FD(2)2502 2917 y FK(\))167 3094 y(and)30 b(apply)f(it)f(for)h FH(a)724 3105 y FD(1)772 3094 y FK(=)20 b FJ(f)p FG(t)p FJ(g)p FK(,)30 b FH(a)1032 3105 y FD(2)1080 3094 y FK(=)20 b Fn(?)p FK(,)29 b FH(b)1286 3105 y FD(1)1334 3094 y FK(=)20 b Fn(?)p FK(,)29 b FH(b)1540 3105 y FD(2)1589 3094 y FK(=)20 b FJ(f)p FG(t)p FJ(g)p FK(,)29 b(then)g FH(F)10 b FK(\()p Fn(?)p FH(;)i FJ(f)p FG(t)p FJ(g)p FK(\))19 b(=)h FJ(f)p FG(t)p FJ(g)29 b FK(w)n(ould)167 3179 y(giv)n(e)e(us)h FH(F)10 b FK(\()p Fn(?)p FH(;)i Fn(?)p FK(\))18 b(=)i FJ(f)p FG(t)p FJ(g)p FK(.)270 3307 y(By)28 b(symmetry)-6 b(,)28 b(w)n(e)f(ha)n(v)n(e)h(obtained)g(t)n(w)n (o)g(functions:)270 3471 y FJ(\017)34 b FH(F)384 3482 y FD(1)412 3471 y FK(\()p FJ(f)p FG(t)p FJ(g)p FH(;)12 b Fn(?)p FK(\))19 b(=)g FH(F)790 3482 y FD(1)818 3471 y FK(\()p FJ(f)p FG(t)p FJ(g)p FH(;)12 b FJ(f)p FG(t)p FJ(g)p FK(\))19 b(=)h FH(F)1243 3482 y FD(1)1270 3471 y FK(\()p FJ(f)p FG(t)p FJ(g)p FH(;)12 b FJ(f)p FG(f)7 b FJ(g)p FK(\))20 b(=)g FH(F)1696 3482 y FD(1)1723 3471 y FK(\()p FJ(f)p FG(f)7 b FJ(g)p FH(;)12 b FJ(f)p FG(t)p FJ(g)p FK(\))20 b(=)g FJ(f)p FG(t)p FJ(g)270 3616 y(\017)34 b FH(F)384 3627 y FD(1)412 3616 y FK(\()p FJ(f)p FG(f)7 b FJ(g)p FH(;)12 b FJ(f)p FG(f)7 b FJ(g)p FK(\))21 b(=)e FJ(f)p FG(f)7 b FJ(g)270 3761 y(\017)34 b FH(F)384 3772 y FD(1)412 3761 y FK(\()p Fn(?)p FH(;)12 b Fn(?)p FK(\))19 b(=)g FH(F)744 3772 y FD(1)771 3761 y FK(\()p FJ(f)p FG(f)7 b FJ(g)p FH(;)12 b Fn(?)p FK(\))20 b(=)f FH(F)1150 3772 y FD(1)1178 3761 y FK(\()p Fn(?)p FH(;)12 b FJ(f)p FG(t)p FJ(g)p FK(\))19 b(=)g FH(F)1556 3772 y FD(1)1584 3761 y FK(\()p Fn(?)p FH(;)12 b FJ(f)p FG(f)7 b FJ(g)p FK(\))19 b(=)h Fn(?)167 3925 y FK(and)29 b FH(F)351 3936 y FD(2)378 3925 y FK(\()p FH(a;)12 b(b)p FK(\))20 b(=)f FH(F)666 3936 y FD(1)694 3925 y FK(\()p FH(b;)12 b(a)p FK(\).)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 60 63 bop 167 167 a FK(60)1205 b Fz(CHAPTER)27 b(8.)63 b(COHERENCE)26 b(SP)-6 b(A)n(CES)270 404 y FK(There)27 b(remains)g(another)h(solution:)270 521 y FJ(\017)34 b FH(F)384 532 y FD(3)412 521 y FK(\()p FJ(f)p FG(t)p FJ(g)p FH(;)12 b FJ(f)p FG(t)p FJ(g)p FK(\))20 b(=)f FH(F)837 532 y FD(3)864 521 y FK(\()p FJ(f)p FG(f)7 b FJ(g)p FH(;)12 b FJ(f)p FG(t)p FJ(g)p FK(\))21 b(=)e FH(F)1290 532 y FD(3)1317 521 y FK(\()p FJ(f)p FG(t)p FJ(g)p FH(;)12 b FJ(f)p FG(f)7 b FJ(g)p FK(\))20 b(=)g FJ(f)p FG(t)p FJ(g)270 654 y(\017)34 b FH(F)384 665 y FD(3)412 654 y FK(\()p FJ(f)p FG(f)7 b FJ(g)p FH(;)12 b FJ(f)p FG(f)7 b FJ(g)p FK(\))21 b(=)e FJ(f)p FG(f)7 b FJ(g)270 786 y(\017)34 b Fn(?)28 b FK(otherwise.)270 933 y(The)g(stabilit)n(y)e(condition)h(w)n(as)h(used)h(to)e(eliminate)e (the)i(case)h(of:)270 1049 y FJ(\017)34 b FH(F)384 1060 y FD(0)412 1049 y FK(\()p FJ(f)p FG(t)p FJ(g)p FH(;)12 b Fn(?)p FK(\))19 b(=)g FH(F)790 1060 y FD(0)818 1049 y FK(\()p Fn(?)p FH(;)12 b FJ(f)p FG(t)p FJ(g)p FK(\))19 b(=)g FJ(f)p FG(t)p FJ(g)270 1166 y FK(What)31 b(ha)n(v)n(e)f(w)n(e)g (got)g(against)h(this)e(example?)41 b(It)29 b(violates)g(a)i(principle) c(of)j FM(le)l(ast)g(data)5 b FK(:)167 1251 y(w)n(e)33 b(ha)n(v)n(e)i FH(F)494 1262 y FD(0)522 1251 y FK(\()p FJ(f)p FG(t)p FJ(g)p FH(;)12 b FJ(f)p FG(t)p FJ(g)p FK(\))24 b(=)g FJ(f)p FG(t)p FJ(g)p FK(;)37 b(w)n(e)d(seek)f(to)h(\014nd)h(a)g (least)e(appro)n(ximan)n(t)i(to)f(the)g(pair)g(of)167 1336 y(argumen)n(ts)e FJ(f)p FG(t)p FJ(g)p FH(;)12 b FJ(f)p FG(t)p FJ(g)31 b FK(whic)n(h)g(already)g(giv)n(es)g FJ(f)p FG(t)p FJ(g)p FK(;)i(no)n(w)f(w)n(e)f(ha)n(v)n(e)h(at)f(our)h (disp)r(osal)f Fn(?)p FH(;)12 b FJ(f)p FG(t)p FJ(g)167 1421 y FK(and)29 b FJ(f)p FG(t)p FJ(g)p FH(;)12 b Fn(?)27 b FK(whic)n(h)g(are)h(minimal)c(\()p Fn(?)p FH(;)12 b Fn(?)27 b FK(do)r(es)i(not)f(w)n(ork\))g(and)g(distinct.)270 1536 y(Of)c(course,)i(kno)n(wing)f(that)g(w)n(e)f(alw)n(a)n(ys)g(ha)n (v)n(e)i(a)f(distinguished)e(\()p FM(le)l(ast)p FK(\))h(solution)g (\(rather)167 1621 y(than)k(man)n(y)g FM(minimal)g FK(solutions\))f (for)g(a)h(problem)e(of)i(this)e(kind)i(radically)d(simpli\014es)g(a)j (lot)167 1707 y(of)g(calculations.)167 1936 y FE(8.4)114 b(Direct)27 b(pro)s(duct)i(of)f(t)m(w)m(o)g(coherence)f(spaces)167 2091 y FK(A)g(function)h FH(F)37 b FK(of)28 b(t)n(w)n(o)g(argumen)n (ts,)g(mapping)g FJ(A)p FH(;)12 b FJ(B)31 b FK(to)c FJ(C)32 b FK(is)27 b(stable)g(when:)201 2208 y(i\))g FH(a)311 2182 y Fv(0)347 2208 y FJ(\032)20 b FH(a)f FJ(2)h(A)c(^)f FH(b)707 2182 y Fv(0)744 2208 y FJ(\032)k FH(b)h FJ(2)g(B)i(\))e FH(F)10 b FK(\()p FH(a)1210 2182 y Fv(0)1225 2208 y FH(;)i(b)1285 2182 y Fv(0)1302 2208 y FK(\))19 b FJ(\032)h FH(F)10 b FK(\()p FH(a;)i(b)p FK(\))201 2340 y(ii\))26 b FH(F)10 b FK(\()376 2287 y Fo(S)434 2306 y Fv(")434 2361 y Fw(i)p Fv(2)p Fw(I)524 2340 y FH(a)560 2351 y Fw(i)580 2340 y FH(;)611 2287 y Fo(S)670 2306 y Fv(")670 2361 y Fw(j)s Fv(2)p Fw(J)772 2340 y FH(b)801 2351 y Fw(j)828 2340 y FK(\))19 b(=)947 2287 y Fo(S)1006 2306 y Fv(")1006 2362 y FD(\()p Fw(i;j)s FD(\))p Fv(2)p Fw(I)t Fv(\002)p Fw(J)1242 2340 y FH(F)10 b FK(\()p FH(a)1360 2351 y Fw(i)1379 2340 y FH(;)i(b)1439 2351 y Fw(j)1465 2340 y FK(\))106 b(\(directed)26 b(union\))201 2479 y(iii\))f FH(a)349 2490 y FD(1)393 2479 y FJ([)16 b FH(a)492 2490 y FD(2)539 2479 y FJ(2)k(A)c(^)f FH(b)769 2490 y FD(1)813 2479 y FJ([)h FH(b)905 2490 y FD(2)953 2479 y FJ(2)j(B)j(\))e FH(F)10 b FK(\()p FH(a)1295 2490 y FD(1)1338 2479 y FJ(\\)16 b FH(a)1437 2490 y FD(2)1465 2479 y FH(;)c(b)j FJ(\\)h FH(b)1632 2490 y FD(2)1660 2479 y FK(\))k(=)f FH(F)10 b FK(\()p FH(a)1898 2490 y FD(1)1925 2479 y FH(;)i(b)1985 2490 y FD(1)2013 2479 y FK(\))k FJ(\\)f FH(F)10 b FK(\()p FH(a)2236 2490 y FD(2)2263 2479 y FH(;)i(b)2323 2490 y FD(2)2351 2479 y FK(\))270 2596 y(Lik)n(ewise)43 b(w)n(e)g(de\014ne)h (stabilit)n(y)f(in)g(an)n(y)i(n)n(um)n(b)r(er)f(of)h(argumen)n(ts.)85 b(Observ)n(e)44 b(that,)167 2681 y(whereas)24 b(separate)g FM(c)l(ontinuity)31 b FK(su\016ces)25 b(for)f(join)n(t)g(con)n(tin)n (uit)n(y)-6 b(,)25 b(stabilit)n(y)e(in)g(t)n(w)n(o)h(argumen)n(ts)167 2766 y(is)h(equiv)l(alen)n(t)f(to)i(stabilit)n(y)e(in)g(eac)n(h)i (separately)-6 b(,)26 b(together)f(with)g(the)g(additional)f(condition) 167 2851 y(that)k(the)f(pullbac)n(k)1345 2895 y(\()p FH(a;)12 b(b)p FK(\))1019 3212 y(\()p FH(a;)g(b)1142 3187 y Fv(0)1159 3212 y FK(\))468 b(\()p FH(a)1717 3187 y Fv(0)1733 3212 y FH(;)12 b(b)p FK(\))1328 3530 y(\()p FH(a)1391 3504 y Fv(0)1408 3530 y FH(;)g(b)1468 3504 y Fv(0)1484 3530 y FK(\))1186 3111 y Fs(\000)1244 3053 y(\000)1277 3020 y(\000)-59 b(\022)1595 3111 y(@)1536 3053 y(@)1503 3020 y(@)g(I)1277 3429 y(@)1219 3370 y(@)1186 3337 y(@)g(I)1503 3429 y(\000)1562 3370 y(\000)1595 3337 y(\000)g(\022)167 3604 y FK(\(where)27 b FH(a)434 3578 y Fv(0)470 3604 y FJ(\032)19 b FH(a)h FJ(2)g(A)27 b FK(and)i FH(b)918 3578 y Fv(0)954 3604 y FJ(\032)20 b FH(b)g FJ(2)f(B)r FK(\))28 b(b)r(e)f(preserv)n(ed.)270 3754 y(W)-6 b(e)34 b(w)n(ould)g(lik)n(e)e(to)i(a)n(v)n(oid)g(studying)h(stable)e (functions)h(of)h(t)n(w)n(o)f(\(or)f(more\))g(v)l(ariables)167 3840 y(and)h(so)g(reduce)f(them)f(to)i(the)f(unary)h(case.)52 b(F)-6 b(or)34 b(this)f(w)n(e)g(shall)f(in)n(tro)r(duce)h(the)g(\()p FM(dir)l(e)l(ct)p FK(\))167 3925 y FM(pr)l(o)l(duct)c FJ(A)16 b FK(&)f FJ(B)30 b FK(of)e(t)n(w)n(o)g(coherence)f(spaces.)36 b(The)27 b(notation)i(comes)e(from)g(linear)f(logic.)p eop PStoPSsaved restore %%Page: (64,65) 33 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 61 64 bop 167 167 a Fz(8.5.)64 b(THE)27 b(FUNCTION-SP)-6 b(A)n(CE)1461 b FK(61)270 404 y(If)28 b FJ(A)g FK(and)h FJ(B)h FK(are)d(t)n(w)n(o)h(coherence)f(spaces,)h(w)n(e)f(de\014ne)h FJ(A)16 b FK(&)f FJ(B)30 b FK(b)n(y:)743 607 y FJ(jA)16 b FK(&)f FJ(B)r(j)k FK(=)h FJ(jAj)15 b FK(+)g FJ(jB)r(j)k FK(=)g FJ(f)p FK(1)p FJ(g)e(\002)e(jAj)g([)h(f)p FK(2)p FJ(g)g(\002)g(jB)r(j)518 826 y FK(\(1)p FH(;)c(\013)p FK(\))701 804 y FH(_)701 847 y(^)790 826 y FK(\(1)p FH(;)g(\013)926 801 y Fv(0)943 826 y FK(\))47 b(\(mo)r(d)23 b FJ(A)16 b FK(&)f FJ(B)s FK(\))86 b(i\013)27 b FH(\013)1653 804 y(_)1653 847 y(^)1741 826 y(\013)1785 801 y Fv(0)1849 826 y FK(\(mo)r(d)c FJ(A)p FK(\))520 997 y(\(2)p FH(;)12 b(\014)t FK(\))701 975 y FH(_)701 1017 y(^)790 997 y FK(\(2)p FH(;)g(\014)925 971 y Fv(0)941 997 y FK(\))47 b(\(mo)r(d)24 b FJ(A)16 b FK(&)f FJ(B)r FK(\))88 b(i\013)27 b FH(\014)1651 975 y(_)1651 1017 y(^)1740 997 y(\014)1783 971 y Fv(0)1846 997 y FK(\(mo)r(d)c FJ(B)r FK(\))527 1167 y(\(1)p FH(;)12 b(\013)p FK(\))710 1145 y FH(_)710 1188 y(^)799 1167 y FK(\(2)p FH(;)g(\014)t FK(\))47 b(\(mo)r(d)23 b FJ(A)16 b FK(&)f FJ(B)s FK(\))95 b(for)28 b(all)e FH(\013)20 b FJ(2)g(jAj)27 b FK(and)h FH(\014)c FJ(2)19 b(jB)r(j)167 1388 y FK(In)33 b(particular,)h(the)f(p)r(oin)n(ts)g(of)h FJ(A)17 b FK(&)g FJ(B)36 b FK(\(coheren)n(t)c(subsets)i(of)g FJ(jA)15 b FK(&)g FJ(B)s(j)p FK(\))32 b(can)i(b)r(e)f(written)167 1473 y(uniquely)e(as)h FJ(f)p FK(1)p FJ(g)18 b(\002)e FH(a)h FJ([)g(f)p FK(2)p FJ(g)g(\002)g FH(b)31 b FK(with)g FH(a)22 b FJ(2)g(A)p FK(,)33 b FH(b)23 b FJ(2)f(B)r FK(.)47 b(The)31 b(reader)g(is)f(in)n(vited)h(to)g(sho)n(w)167 1558 y(that)j(this)f(is)g(the)g(pro)r(duct)h(in)f(the)h(categorical)e (sense)i(\(w)n(e)e(shall)h(return)h(to)f(this)g(in)g(the)167 1643 y(next)28 b(c)n(hapter)g(when)f(w)n(e)g(de\014ne)h(the)g(in)n (terpretation\).)270 1808 y(Giv)n(en)f(a)g(stable)f(function)h FH(F)35 b FK(from)27 b FJ(A)p FH(;)12 b FJ(B)29 b FK(to)e FJ(C)t FK(,)g(w)n(e)f(de\014ne)h(a)g(function)f FH(G)h FK(from)g FJ(A)14 b FK(&)g FJ(B)167 1893 y FK(to)28 b FJ(C)k FK(b)n(y:)940 2059 y FH(G)p FK(\()p FJ(f)p FK(1)p FJ(g)17 b(\002)f FH(a)f FJ([)h(f)p FK(2)p FJ(g)h(\002)e FH(b)p FK(\))20 b(=)f FH(F)10 b FK(\()p FH(a;)i(b)p FK(\))167 2224 y(It)37 b(is)f(immediate)f(that)i FH(G)h FK(is)f(stable;)k(con)n (v)n(ersely)c(the)g(same)g(form)n(ula)g(de\014nes,)k(from)c(a)167 2309 y(stable)26 b(unary)i(function)f FH(G)p FK(,)g(a)h(stable)e (binary)h(function)g FH(F)10 b FK(,)26 b(and)i(the)e(t)n(w)n(o)h (transformations)167 2394 y(are)h(in)n(v)n(erse.)167 2627 y FE(8.5)114 b(The)28 b(F)-10 b(unction-Space)167 2782 y FK(W)k(e)33 b(started)g(with)f(the)h(idea)g(that)g(\\t)n(yp)r(e) h(=)f(coherence)f(space".)53 b(The)32 b(previous)i(section)167 2867 y(de\014nes)29 b(a)h(pro)r(duct)f(of)g(coherence)f(spaces)i (corresp)r(onding)f(to)h(the)e(pro)r(duct)i(of)f(t)n(yp)r(es,)h(but)167 2952 y(what)35 b(do)g(w)n(e)g(do)g(with)f(the)g(arro)n(w?)57 b(W)-6 b(e)34 b(w)n(ould)h(lik)n(e)e(to)i(de\014ne)g FJ(A)17 b(!)i(B)37 b FK(as)e(the)f(set)h(of)167 3038 y(stable)h(functions)h(from)g FJ(A)f FK(to)h FJ(B)r FK(,)j(but)d(this)f (is)g(not)h(presen)n(ted)g(as)g(a)g(coherence)f(space.)167 3123 y(So)30 b(w)n(e)e(shall)h(giv)n(e)g(a)g(particular)f(represen)n (tation)h(of)h(the)f(set)f(of)i(stable)f(functions)g(in)g(suc)n(h)167 3208 y(a)f(w)n(a)n(y)h(as)f(to)g(mak)n(e)f(it)g(a)h(coherence)f(space.) 167 3410 y Fy(8.5.1)95 b(The)27 b(trace)i(of)e(a)h(stable)g(function) 167 3541 y FG(Lemma)d FK(Let)i FH(F)37 b FK(b)r(e)27 b(a)h(stable)g(function)f(from)h FJ(A)g FK(to)g FJ(B)r FK(,)g(and)g(let)f FH(a)19 b FJ(2)h(A)p FK(,)28 b FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(a)p FK(\);)27 b(then)201 3686 y(i\))g(it)g(is)g(p)r(ossible)g(to)g(\014nd)i FH(a)954 3697 y Fv(\016)1002 3686 y FJ(\032)19 b FH(a)28 b FK(\014nite)f(suc)n (h)h(that)g FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(a)1882 3697 y Fv(\016)1909 3686 y FK(\).)201 3826 y(ii\))29 b(if)h FH(a)404 3837 y Fv(\016)462 3826 y FK(is)g(c)n(hosen)h(minimal)d (for)j(the)f(inclusion)f(among)j(the)e(solutions)h(to)f(\(i\),)g(then)h FH(a)2644 3837 y Fv(\016)339 3911 y FK(is)c FM(le)l(ast)p FK(,)h(and)h(is)e(in)g(particular)g FM(unique)p FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 62 65 bop 167 167 a FK(62)1205 b Fz(CHAPTER)27 b(8.)63 b(COHERENCE)26 b(SP)-6 b(A)n(CES)167 404 y FG(Pro)r(of)201 586 y FK(i\))53 b(W)-6 b(rite)53 b FH(a)38 b FK(=)690 534 y Fo(S)749 552 y Fv(")749 607 y Fw(i)p Fv(2)p Fw(I)839 586 y FH(a)875 597 y Fw(i)895 586 y FK(,)61 b(where)53 b(the)g FH(a)1390 597 y Fw(i)1464 586 y FK(are)h(the)g(\014nite)f (subsets)h(of)h FH(a)p FK(.)114 b(Then)339 683 y FH(F)10 b FK(\()p FH(a)p FK(\))19 b(=)576 630 y Fo(S)635 648 y Fv(")635 703 y Fw(i)p Fv(2)p Fw(I)725 683 y FH(F)10 b FK(\()p FH(a)843 694 y Fw(i)862 683 y FK(\),)28 b(and)h(if)d FH(\014)e FJ(2)19 b FH(F)10 b FK(\()p FH(a)p FK(\),)27 b FH(\014)d FJ(2)19 b FH(F)10 b FK(\()p FH(a)1709 694 y Fw(i)1726 701 y Fi(0)1753 683 y FK(\))27 b(for)h(some)g FH(i)2119 694 y FD(0)2165 683 y FJ(2)20 b FH(I)6 b FK(.)201 839 y(ii\))50 b(Supp)r(ose)i FH(a)652 850 y Fv(\016)731 839 y FK(is)f(minimal,)j(and)e(let)e FH(a)1476 814 y Fv(0)1528 839 y FJ(\032)36 b FH(a)52 b FK(suc)n(h)f(that)h FH(\014)40 b FJ(2)c FH(F)10 b FK(\()p FH(a)2348 814 y Fv(0)2364 839 y FK(\).)105 b(Then)339 924 y FH(a)375 935 y Fv(\016)422 924 y FJ([)18 b FH(a)523 899 y Fv(0)566 924 y FJ(\032)26 b FH(a)h FJ(2)f(A)p FK(,)40 b(so)d FH(a)1032 935 y Fv(\016)1079 924 y FJ([)18 b FH(a)1180 899 y Fv(0)1223 924 y FJ(2)26 b(A)37 b FK(and)i FH(\014)30 b FJ(2)c FH(F)10 b FK(\()p FH(a)1798 935 y Fv(\016)1825 924 y FK(\))18 b FJ(\\)h FH(F)10 b FK(\()p FH(a)2054 899 y Fv(0)2069 924 y FK(\))26 b(=)g FH(F)10 b FK(\()p FH(a)2320 935 y Fv(\016)2366 924 y FJ(\\)18 b FH(a)2467 899 y Fv(0)2484 924 y FK(\).)63 b(As)339 1009 y FH(a)375 1020 y Fv(\016)438 1009 y FK(is)34 b(minimal,)g(this)g(forces)g FH(a)1207 1020 y Fv(\016)1260 1009 y FJ(\032)24 b FH(a)1375 1020 y Fv(\016)1421 1009 y FJ([)17 b FH(a)1521 984 y Fv(0)1538 1009 y FK(,)36 b(so)g FH(a)1726 1020 y Fv(\016)1778 1009 y FJ(\032)25 b FH(a)1894 984 y Fv(0)1910 1009 y FK(,)37 b(and)e FH(a)2147 1020 y Fv(\016)2210 1009 y FK(is)f(indeed)g FM(le)l(ast)p FK(.)339 1095 y(T)-6 b(o)29 b(put)f(this)f(another)h(w)n (a)n(y)-6 b(,)29 b(w)n(e)f(ha)n(v)n(e)g(said)g(that)g(w)n(e)f(in)n (tend)h(stabilit)n(y)e(to)i(mean)f(the)339 1180 y(in)n(tersection)f(of) i(an)g FM(arbitr)l(ary)g FK(family)e(whic)n(h)h(is)f(b)r(ounded)j(ab)r (o)n(v)n(e,)g(and)g(here)d(w)n(e)h(are)339 1265 y(just)h(taking)h(the)e (in)n(tersection)f(of)i(the)f(\014nite)g FH(a)1619 1239 y Fv(0)1655 1265 y FJ(\032)20 b FH(a)28 b FK(suc)n(h)g(that)g FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(a)2355 1239 y Fv(0)2370 1265 y FK(\).)201 b Fu(\003)270 1498 y FK(The)28 b FM(tr)l(ac)l(e)g FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))27 b(is)g(the)g(set)h(of)g(pairs)f(\()p FH(a)1418 1509 y Fv(\016)1446 1498 y FH(;)12 b(\014)t FK(\))28 b(suc)n(h)g(that:)201 1680 y(i\))f FH(a)311 1691 y Fv(\016)367 1680 y FK(is)g(a)h(\014nite)f(p)r(oin)n(t)g(of)h FJ(A)g FK(and)h FH(\014)23 b FJ(2)d(jB)r(j)201 1836 y FK(ii\))26 b FH(\014)e FJ(2)19 b FH(F)10 b FK(\()p FH(a)541 1847 y Fv(\016)568 1836 y FK(\))201 1993 y(iii\))25 b(if)i FH(a)417 1968 y Fv(0)453 1993 y FJ(\032)20 b FH(a)564 2004 y Fv(\016)619 1993 y FK(and)29 b FH(\014)24 b FJ(2)19 b FH(F)10 b FK(\()p FH(a)1005 1968 y Fv(0)1021 1993 y FK(\))27 b(then)h FH(a)1273 1968 y Fv(0)1309 1993 y FK(=)19 b FH(a)1418 2004 y Fv(\016)1446 1993 y FK(.)270 2226 y FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))28 b(determines)d FH(F)37 b FK(uniquely)27 b(b)n(y)i(the)e(form)n(ula)700 2430 y(\()p FG(App)p FK(\))78 b FH(F)10 b FK(\()p FH(a)p FK(\))18 b(=)h FJ(f)p FH(\014)24 b FK(:)39 b FJ(9)p FH(a)1447 2441 y Fv(\016)1495 2430 y FJ(\032)20 b FH(a)f FK(\()p FH(a)1688 2441 y Fv(\016)1716 2430 y FH(;)12 b(\014)t FK(\))19 b FJ(2)h(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))p FJ(g)167 2634 y FK(whic)n(h)26 b(results)f(immediately)e(from)k(the)f (lemma.)33 b(In)27 b(particular)e(the)h(function)h FH(F)h FJ(7!)20 b(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))167 2719 y(is)27 b(1{1.)270 2923 y(Consider)22 b(for)g(example)f(the)h (stable)f(function)h FH(F)1560 2934 y FD(1)1609 2923 y FK(from)g FJ(B)-10 b FM(o)l(ol)15 b FK(&)7 b FJ(B)-10 b FM(o)l(ol)30 b FK(to)22 b FJ(B)-10 b FM(o)l(ol)30 b FK(in)n(tro)r(duced)167 3008 y(in)55 b FG(??)p FK(.)36 b(The)27 b(elemen)n(ts)f(of)i(its)f(trace)g FJ(T)-6 b FH(r)r FK(\()p FH(F)1340 3019 y FD(1)1368 3008 y FK(\))27 b(are:)423 3212 y(\()p FJ(f)p FK(\(1)p FH(;)12 b FG(t)p FK(\))p FJ(g)p FH(;)32 b FG(t)p FK(\))255 b(\()p FJ(f)p FK(\(1)p FH(;)12 b FG(f)7 b FK(\))p FH(;)25 b FK(\(2)p FH(;)12 b FG(t)p FK(\))o FJ(g)p FH(;)32 b FG(t)p FK(\))256 b(\()p FJ(f)p FK(\(1)p FH(;)12 b FG(f)7 b FK(\))p FH(;)24 b FK(\(2)p FH(;)12 b FG(f)7 b FK(\))p FJ(g)p FH(;)32 b FG(f)7 b FK(\))167 3416 y(W)-6 b(e)27 b(can)h(read)g(this)f(as)i(the) e(sp)r(eci\014cation:)270 3598 y FJ(\017)34 b FK(if)27 b(the)h(\014rst)f(argumen)n(t)h(is)f FM(true)p FK(,)h(the)f(result)g (is)g FM(true)p FK(;)270 3754 y FJ(\017)34 b FK(if)27 b(the)h(\014rst)f(argumen)n(t)h(is)f FM(false)h FK(and)g(the)g(second)g FM(true)p FK(,)f(the)h(result)e(is)h FM(true)p FK(;)270 3911 y FJ(\017)34 b FK(if)27 b(the)h(\014rst)f(argumen)n(t)h(is)f FM(false)h FK(and)g(the)g(second)g FM(false)p FK(,)g(the)f(result)g(is) g FM(false)p FK(.)p eop PStoPSsaved restore %%Page: (66,67) 34 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 63 66 bop 167 167 a Fz(8.5.)64 b(THE)27 b(FUNCTION-SP)-6 b(A)n(CE)1461 b FK(63)167 404 y Fy(8.5.2)95 b(Represen)m(tation)28 b(of)f(the)h(function)f(space)167 535 y FG(Prop)r(osition)d FK(As)i FH(F)35 b FK(v)l(aries)26 b(o)n(v)n(er)h(the)f(stable)g (functions)g(from)g FJ(A)g FK(to)h FJ(B)r FK(,)g(their)e(traces)g(giv)n (e)167 620 y(the)i(p)r(oin)n(ts)h(of)g(a)g(coherence)f(space,)h (written)e FJ(A)16 b(!)g(B)r FK(.)167 773 y FG(Pro)r(of)29 b FK(Let)g(us)h(de\014ne)g(the)f(coherence)f(space)i FJ(C)j FK(b)n(y)d FJ(jC)t(j)20 b FK(=)h FJ(A)1859 784 y Fm(\014n)1938 773 y FJ(\002)16 b(jB)r(j)29 b FK(\()p FJ(A)2209 784 y Fm(\014n)2302 773 y FK(is)g(the)g(set)g(of)167 858 y(\014nite)e(p)r(oin)n(ts)h(of)g FJ(A)p FK(\))g(where)e(\()p FH(a)1020 869 y FD(1)1048 858 y FH(;)12 b(\014)1118 869 y FD(1)1146 858 y FK(\))1192 836 y FH(_)1192 879 y(^)1281 858 y FK(\()p FH(a)1344 869 y FD(2)1372 858 y FH(;)g(\014)1442 869 y FD(2)1470 858 y FK(\))46 b(\(mo)r(d)24 b FJ(C)t FK(\))j(if)201 979 y(i\))g FH(a)311 990 y FD(1)355 979 y FJ([)15 b FH(a)453 990 y FD(2)501 979 y FJ(2)20 b(A)f(\))h FH(\014)772 990 y FD(1)820 957 y FH(_)820 999 y(^)908 979 y(\014)947 990 y FD(2)1022 979 y FK(\(mo)r(d)k FJ(B)r FK(\))201 1112 y(ii\))i FH(a)330 1123 y FD(1)374 1112 y FJ([)16 b FH(a)473 1123 y FD(2)520 1112 y FJ(2)k(A)c(^)f FH(a)757 1123 y FD(1)805 1112 y FJ(6)p FK(=)k FH(a)914 1123 y FD(2)962 1112 y FJ(\))h FH(\014)1091 1123 y FD(1)1138 1112 y FJ(6)p FK(=)f FH(\014)1250 1123 y FD(2)1325 1112 y FK(\(mo)r(d)24 b FJ(B)r FK(\))270 1233 y(In)k FG(??)q FK(,)g(w)n(e)f(shall)g(see)g(a)h(more)f(symmetrical)e(w)n(a)n(y)j(of)h (writing)d(this.)270 1349 y(If)34 b FH(F)42 b FK(is)33 b(stable,)i(then)e FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))34 b(is)e(a)i(subset)g(of)g FJ(jC)t(j)f FK(b)n(y)h(construction.) 53 b(W)-6 b(e)33 b(v)n(erify)g(the)167 1434 y(coherence)27 b(mo)r(dulo)h FJ(C)j FK(of)d(\()p FH(a)952 1445 y FD(1)980 1434 y FH(;)12 b(\014)1050 1445 y FD(1)1078 1434 y FK(\))27 b(and)i(\()p FH(a)1334 1445 y FD(2)1362 1434 y FH(;)12 b(\014)1432 1445 y FD(2)1460 1434 y FK(\))19 b FJ(2)h(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\):)201 1555 y(i\))27 b(If)h FH(a)385 1566 y FD(1)428 1555 y FJ([)16 b FH(a)527 1566 y FD(2)575 1555 y FJ(2)j(A)28 b FK(then)g FJ(f)p FH(\014)961 1566 y FD(1)989 1555 y FH(;)12 b(\014)1059 1566 y FD(2)1086 1555 y FJ(g)20 b(\032)g FH(F)10 b FK(\()p FH(a)1334 1566 y FD(1)1376 1555 y FJ([)16 b FH(a)1475 1566 y FD(2)1503 1555 y FK(\))27 b(so)i FH(\014)1686 1566 y FD(1)1733 1533 y FH(_)1733 1575 y(^)1822 1555 y(\014)1861 1566 y FD(2)1935 1555 y FK(\(mo)r(d)24 b FJ(B)r FK(\).)201 1688 y(ii\))k(If)h FH(\014)410 1699 y FD(1)459 1688 y FK(=)20 b FH(\014)572 1699 y FD(2)629 1688 y FK(and)31 b FH(a)806 1699 y FD(1)850 1688 y FJ([)16 b FH(a)949 1699 y FD(2)998 1688 y FJ(2)21 b(A)p FK(,)30 b(then)f(the)g(lemma)f (applied)h(to)g FH(\014)2065 1699 y FD(1)2114 1688 y FJ(2)21 b FH(F)10 b FK(\()p FH(a)2300 1699 y FD(1)2343 1688 y FJ([)16 b FH(a)2442 1699 y FD(2)2470 1688 y FK(\))29 b(giv)n(es)339 1773 y(us)g FH(a)469 1784 y FD(1)516 1773 y FK(=)19 b FH(a)625 1784 y FD(2)653 1773 y FK(.)270 1925 y(Con)n(v)n(ersely)-6 b(,)32 b(let)e FH(f)38 b FK(b)r(e)31 b(a)g(p)r(oin)n(t)g(of)g FJ(C)t FK(.)45 b(W)-6 b(e)31 b(de\014ne)g(a)g(function)g(from)g FJ(A)g FK(to)g FJ(B)i FK(b)n(y)e(the)167 2010 y(form)n(ula:)766 2163 y(\()p FG(App)p FK(\))78 b FH(F)10 b FK(\()p FH(a)p FK(\))18 b(=)i FJ(f)p FH(\014)j FK(:)39 b FJ(9)p FH(a)1513 2174 y Fv(\016)1561 2163 y FJ(\032)20 b FH(a)f FK(\()p FH(a)1754 2174 y Fv(\016)1782 2163 y FH(;)12 b(\014)t FK(\))19 b FJ(2)h FH(f)8 b FJ(g)201 2351 y FK(i\))27 b FH(F)37 b FK(is)27 b(monotone:)36 b(immediate.)201 2485 y(ii\))44 b(If)h FH(a)32 b FK(=)556 2432 y Fo(S)615 2450 y Fv(")615 2505 y Fw(i)p Fv(2)p Fw(I)705 2485 y FH(a)741 2496 y Fw(i)761 2485 y FK(,)50 b(then)1009 2432 y Fo(S)1068 2450 y Fv(")1068 2505 y Fw(i)p Fv(2)p Fw(I)1158 2485 y FH(F)10 b FK(\()p FH(a)1276 2496 y Fw(i)1295 2485 y FK(\))32 b FJ(\032)g FH(F)10 b FK(\()p FH(a)p FK(\))44 b(b)n(y)h(monotonicit)n(y)-6 b(.)88 b(Con)n(v)n(ersely)-6 b(,)50 b(if)339 2570 y FH(\014)25 b FJ(2)d FH(F)10 b FK(\()p FH(a)p FK(\),)29 b(this)g(means)h(there)g(is)f(an)h FH(a)1422 2544 y Fv(0)1469 2570 y FK(\014nite,)g FH(a)1708 2544 y Fv(0)1746 2570 y FJ(\032)20 b FH(a)p FK(,)31 b(suc)n(h)g(that)f FH(\014)25 b FJ(2)c FH(F)10 b FK(\()p FH(a)2476 2544 y Fv(0)2492 2570 y FK(\);)31 b(but)339 2655 y(since)i FH(a)555 2629 y Fv(0)595 2655 y FJ(\032)674 2602 y Fo(S)732 2621 y Fv(")732 2675 y Fw(i)p Fv(2)p Fw(I)823 2655 y FH(a)859 2666 y Fw(i)879 2655 y FK(,)i(w)n(e)e(ha)n(v)n(e)h FH(a)1250 2629 y Fv(0)1291 2655 y FJ(\032)23 b FH(a)1405 2666 y Fw(k)1469 2655 y FK(for)34 b(some)f FH(k)j FK(\(that)d(is)g(wh)n (y)h FH(I)39 b FK(w)n(as)34 b(c)n(hosen)339 2740 y(directed!\))g(so)28 b FH(\014)c FJ(2)19 b FH(F)10 b FK(\()p FH(a)998 2751 y Fw(k)1028 2740 y FK(\))27 b(and)i(the)e(con)n(v)n(erse)h(inclusion)e (is)h(established.)201 2874 y(iii\))e(If)h FH(a)421 2885 y FD(1)464 2874 y FJ([)14 b FH(a)561 2885 y FD(2)609 2874 y FJ(2)19 b(A)p FK(,)27 b(then)g FH(F)10 b FK(\()p FH(a)1056 2885 y FD(1)1098 2874 y FJ(\\)k FH(a)1195 2885 y FD(2)1223 2874 y FK(\))19 b FJ(\032)h FH(F)10 b FK(\()p FH(a)1462 2885 y FD(1)1489 2874 y FK(\))k FJ(\\)g FH(F)c FK(\()p FH(a)1709 2885 y FD(2)1737 2874 y FK(\))26 b(b)n(y)i (monotonicit)n(y)-6 b(.)35 b(Con)n(v)n(ersely)-6 b(,)339 2959 y(if)58 b FH(\014)45 b FJ(2)d FH(F)10 b FK(\()p FH(a)729 2970 y FD(1)756 2959 y FK(\))24 b FJ(\\)h FH(F)10 b FK(\()p FH(a)997 2970 y FD(2)1024 2959 y FK(\),)66 b(this)58 b(means)h(that)g(\()p FH(a)1801 2933 y Fv(0)1801 2976 y FD(1)1829 2959 y FH(;)12 b(\014)t FK(\))p FH(;)g FK(\()p FH(a)2024 2933 y Fv(0)2024 2976 y FD(2)2051 2959 y FH(;)g(\014)t FK(\))41 b FJ(2)g FH(f)66 b FK(for)59 b(some)339 3044 y(appropriate)43 b FH(a)766 3018 y Fv(0)766 3061 y FD(1)824 3044 y FJ(\032)29 b FH(a)944 3055 y FD(1)1014 3044 y FK(and)44 b FH(a)1204 3018 y Fv(0)1204 3061 y FD(2)1261 3044 y FJ(\032)30 b FH(a)1382 3055 y FD(2)1410 3044 y FK(.)79 b(But)41 b(\()p FH(a)1726 3018 y Fv(0)1726 3061 y FD(1)1754 3044 y FH(;)12 b(\014)t FK(\))42 b(and)h(\()p FH(a)2113 3018 y Fv(0)2113 3061 y FD(2)2141 3044 y FH(;)12 b(\014)t FK(\))41 b(are)h(coheren)n(t)339 3129 y(and)29 b FH(a)514 3103 y Fv(0)514 3146 y FD(1)558 3129 y FJ([)15 b FH(a)656 3103 y Fv(0)656 3146 y FD(2)704 3129 y FJ(\032)k FH(a)814 3140 y FD(1)858 3129 y FJ([)d FH(a)957 3140 y FD(2)1004 3129 y FJ(2)k(A)p FK(,)28 b(so)g FH(a)1299 3103 y Fv(0)1299 3146 y FD(1)1347 3129 y FK(=)19 b FH(a)1456 3103 y Fv(0)1456 3146 y FD(2)1484 3129 y FK(,)28 b FH(a)1567 3103 y Fv(0)1567 3146 y FD(1)1615 3129 y FJ(\032)19 b FH(a)1725 3140 y FD(1)1769 3129 y FJ(\\)c FH(a)1867 3140 y FD(2)1923 3129 y FK(and)29 b FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(a)2309 3140 y FD(1)2351 3129 y FJ(\\)16 b FH(a)2450 3140 y FD(2)2478 3129 y FK(\).)201 3263 y(iv\))36 b(W)-6 b(e)36 b(nearly)h(forgot)g(to)g(sho)n(w)g(that)g FH(F)46 b FK(maps)37 b FJ(A)g FK(in)n(to)f FJ(B)r FK(:)53 b FH(F)10 b FK(\()p FH(a)p FK(\),)38 b(for)f FH(a)26 b FJ(2)g(A)p FK(,)39 b(is)d(a)339 3348 y(subset)h(of)g FJ(jB)r(j)p FK(,)i(of)e(whic)n(h)e(it)h(is)g(again)h(necessary)g(to)g (sho)n(w)g(coherence!)61 b(No)n(w,)39 b(if)339 3433 y FH(\014)382 3407 y Fv(0)399 3433 y FH(;)12 b(\014)473 3407 y Fv(00)522 3433 y FJ(2)20 b FH(F)10 b FK(\()p FH(a)p FK(\),)25 b(this)h(means)h(that)g(\()p FH(a)1347 3407 y Fv(0)1363 3433 y FH(;)12 b(\014)1437 3407 y Fv(0)1454 3433 y FK(\))p FH(;)g FK(\()p FH(a)1575 3407 y Fv(00)1604 3433 y FH(;)g(\014)1678 3407 y Fv(00)1708 3433 y FK(\))20 b FJ(2)f FH(f)34 b FK(for)27 b(appropriate)g FH(a)2409 3407 y Fv(0)2426 3433 y FH(;)12 b(a)2493 3407 y Fv(00)2542 3433 y FJ(\032)20 b FH(a)p FK(;)339 3518 y(but)33 b(then)g FH(a)678 3492 y Fv(0)711 3518 y FJ([)17 b FH(a)811 3492 y Fv(00)864 3518 y FJ(\032)23 b FH(a)g FJ(2)g(A)p FK(,)34 b(so,)h(as)e(\()p FH(a)1452 3492 y Fv(0)1468 3518 y FH(;)12 b(\014)1542 3492 y Fv(0)1558 3518 y FK(\))32 b(and)i(\()p FH(a)1824 3492 y Fv(00)1854 3518 y FH(;)12 b(\014)1928 3492 y Fv(00)1958 3518 y FK(\))32 b(are)g(coheren)n(t,)i FH(\014)2492 3492 y Fv(0)2531 3496 y FH(_)2531 3539 y(^)2623 3518 y(\014)2666 3492 y Fv(00)339 3603 y FK(\(mo)r(d)24 b FJ(B)r FK(\).)270 3724 y(Finally)-6 b(,)27 b(it)g(is)g(easy)h(to)g(c) n(hec)n(k)f(that)h(these)g(constructions)f(are)h(m)n(utually)f(in)n(v)n (erse.)108 b Fu(\003)270 3840 y FK(In)28 b(fact,)g(the)g(same)f (application)g(form)n(ula)h(o)r(ccurs)g(in)f(Scott's)h(domain)g(theory) g([)p FG(?)q FK(],)g(but)167 3925 y(the)f(corresp)r(onding)i(notion)f (of)g(\\trace")g(is)f(more)g(complicated.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 64 67 bop 167 167 a FK(64)1205 b Fz(CHAPTER)27 b(8.)63 b(COHERENCE)26 b(SP)-6 b(A)n(CES)167 404 y Fy(8.5.3)95 b(The)27 b(Berry)h(order)167 536 y FK(Being)h(a)h(coherence)f(space,)i FJ(A)17 b(!)f(B)32 b FK(is)d(naturally)h(ordered)g(b)n(y)g(inclusion.) 41 b(The)29 b(bijection)167 621 y(b)r(et)n(w)n(een)38 b FJ(A)19 b(!)g(B)41 b FK(and)e(the)f(stable)g(functions)h(from)f FJ(A)h FK(to)g FJ(B)h FK(then)f(induces)f(an)h(order)167 707 y(relation:)601 885 y FH(F)29 b FJ(\024)730 896 y FD(B)787 885 y FH(G)435 b FK(i\013)e FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))19 b FJ(\032)h(T)-6 b FH(r)r FK(\()p FH(G)p FK(\))167 1063 y(In)28 b(fact)f FJ(\024)453 1074 y FD(B)491 1063 y FK(,)h(the)g FM(Berry)g(or)l(der)p FK(,)g(is)f(giv)n(en)h(b)n(y:)386 1242 y FH(F)g FJ(\024)514 1253 y FD(B)572 1242 y FH(G)219 b FK(i\013)f FJ(8)p FH(a)1199 1216 y Fv(0)1215 1242 y FH(;)12 b(a)19 b FJ(2)h(A)g FK(\()p FH(a)1507 1216 y Fv(0)1543 1242 y FJ(\032)f FH(a)h FJ(\))g FH(F)10 b FK(\()p FH(a)1881 1216 y Fv(0)1897 1242 y FK(\))19 b(=)g FH(F)10 b FK(\()p FH(a)p FK(\))15 b FJ(\\)g FH(G)p FK(\()p FH(a)2355 1216 y Fv(0)2372 1242 y FK(\)\))167 1463 y FG(Pro)r(of)32 b FK(If)g FH(F)g FJ(\024)601 1474 y FD(B)662 1463 y FH(G)g FK(then)h FH(F)10 b FK(\()p FH(a)p FK(\))21 b FJ(\032)i FH(G)p FK(\()p FH(a)p FK(\))32 b(for)h(all)d FH(a)j FK(\(tak)n(e)f FH(a)23 b FK(=)f FH(a)1979 1437 y Fv(0)1996 1463 y FK(\).)49 b(Let)31 b(\()p FH(a;)12 b(\014)t FK(\))23 b FJ(2)f(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\);)167 1548 y(then)26 b FH(\014)d FJ(2)d FH(F)10 b FK(\()p FH(a)p FK(\))18 b FJ(\032)i FH(G)p FK(\()p FH(a)p FK(\).)35 b(W)-6 b(e)25 b(seek)g(to)h(sho)n(w)h (that)f(\()p FH(a;)12 b(\014)t FK(\))19 b FJ(2)g(T)-6 b FH(r)r FK(\()p FH(G)p FK(\).)36 b(Let)25 b FH(a)2215 1522 y Fv(0)2251 1548 y FJ(\032)20 b FH(a)26 b FK(suc)n(h)g(that)167 1633 y FH(\014)d FJ(2)d FH(G)p FK(\()p FH(a)413 1608 y Fv(0)430 1633 y FK(\);)27 b(then)h FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(a)p FK(\))15 b FJ(\\)g FH(G)p FK(\()p FH(a)1133 1608 y Fv(0)1150 1633 y FK(\))20 b(=)f FH(F)10 b FK(\()p FH(a)1388 1608 y Fv(0)1404 1633 y FK(\),)27 b(whic)n(h)g(forces)h FH(a)1914 1608 y Fv(0)1950 1633 y FK(=)19 b FH(a)p FK(.)270 1762 y(Con)n(v)n(ersely)-6 b(,)31 b(if)e FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))21 b FJ(\032)g(T)-6 b FH(r)r FK(\()p FH(G)p FK(\),)32 b(it)d(is)g(easy)h (to)h(see)e(that)h FH(F)10 b FK(\()p FH(a)p FK(\))20 b FJ(\032)h FH(G)p FK(\()p FH(a)p FK(\))31 b(for)f(all)e FH(a)p FK(.)43 b(In)167 1847 y(particular)26 b(if)g FH(a)592 1821 y Fv(0)628 1847 y FJ(\032)20 b FH(a)p FK(,)27 b(then)g FH(F)10 b FK(\()p FH(a)1064 1821 y Fv(0)1080 1847 y FK(\))19 b FJ(\032)g FH(F)10 b FK(\()p FH(a)p FK(\))k FJ(\\)g FH(G)p FK(\()p FH(a)1537 1821 y Fv(0)1554 1847 y FK(\).)35 b(No)n(w,)27 b(if)g FH(\014)c FJ(2)c FH(F)10 b FK(\()p FH(a)p FK(\))k FJ(\\)h FH(G)p FK(\()p FH(a)2349 1821 y Fv(0)2365 1847 y FK(\),)27 b(one)h(can)167 1932 y(\014nd)h FH(a)346 1943 y Fv(\016)393 1932 y FJ(\032)20 b FH(a)p FK(,)27 b FH(a)586 1907 y Fv(0)586 1950 y(\016)634 1932 y FJ(\032)19 b FH(a)744 1907 y Fv(0)789 1932 y FK(suc)n(h)28 b(that)908 2110 y(\()p FH(a)971 2121 y Fv(\016)998 2110 y FH(;)12 b(\014)t FK(\))20 b FJ(2)f(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))19 b FJ(\032)h(T)-6 b FH(r)r FK(\()p FH(G)p FK(\))20 b FJ(3)g FK(\()p FH(a)1776 2085 y Fv(0)1776 2128 y(\016)1803 2110 y FH(;)12 b(\014)t FK(\))167 2289 y(so)33 b(\()p FH(a)324 2300 y Fv(\016)351 2289 y FH(;)12 b(\014)t FK(\))32 b(and)h(\()p FH(a)690 2263 y Fv(0)690 2306 y(\016)718 2289 y FH(;)12 b(\014)t FK(\))31 b(are)h(coheren)n(t,)h (and)g(since)e FH(a)1638 2300 y Fv(\016)1683 2289 y FJ([)17 b FH(a)1783 2263 y Fv(0)1783 2306 y(\016)1833 2289 y FJ(\032)23 b FH(a)g FJ(2)f(A)p FK(,)34 b(w)n(e)d(ha)n(v)n(e)i FH(a)2462 2300 y Fv(\016)2513 2289 y FK(=)22 b FH(a)2625 2263 y Fv(0)2625 2306 y(\016)2653 2289 y FK(,)167 2374 y(and)29 b FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(a)553 2348 y Fv(0)553 2391 y(\016)580 2374 y FK(\))19 b(=)g FH(F)10 b FK(\()p FH(a)817 2385 y Fv(\016)844 2374 y FK(\))20 b FJ(\032)f FH(F)10 b FK(\()p FH(a)1083 2348 y Fv(0)1099 2374 y FK(\).)1472 b Fu(\003)270 2552 y FK(As)35 b(an)h(example,)h(it)d(is)g(easy)i(to)g(see)e(\(using)i(one)f(of)h(the) f(c)n(haracterisations)g(of)g FJ(\024)2607 2563 y FD(B)2645 2552 y FK(\))167 2637 y(that)28 b FH(F)366 2648 y FD(3)414 2637 y FJ(6\024)469 2648 y FD(B)527 2637 y FH(F)572 2648 y FD(1)627 2637 y FK(\(see)f FG(??)q FK(\))h(although)h FH(F)1237 2648 y FD(3)1265 2637 y FK(\()p FH(a;)12 b(b)p FK(\))20 b FJ(\032)f FH(F)1554 2648 y FD(1)1582 2637 y FK(\()p FH(a;)12 b(b)p FK(\))28 b(for)g(all)f FH(a;)12 b(b)20 b FJ(2)g(B)-10 b FM(o)l(ol)8 b FK(.)37 b(The)27 b(reader)167 2723 y(is)g(also)h(in)n(vited)e(to)i(sho)n(w)h(that)f(the) f(iden)n(tit)n(y)g(is)f(maximal.)270 2901 y(The)35 b(Berry)f(order)g (sa)n(ys)i(that)f(ev)l(aluation)g(preserv)n(es)f(the)g FM(pul)t(lb)l(ack)f FK(\()p FM(cf.)56 b FK(the)34 b(one)h(in)167 2986 y(section)27 b FG(??)q FK(\))1332 3083 y(\()p FH(G;)12 b(a)p FK(\))1006 3400 y(\()p FH(G;)g(a)1154 3374 y Fv(0)1171 3400 y FK(\))455 b(\()p FH(F)r(;)12 b(a)p FK(\))1328 3717 y(\()p FH(F)r(;)g(a)1469 3692 y Fv(0)1485 3717 y FK(\))1186 3299 y Fs(\000)1244 3240 y(\000)1277 3207 y(\000)-59 b(\022)1595 3299 y(@)1536 3240 y(@)1503 3207 y(@)g(I)1277 3616 y(@)1219 3558 y(@)1186 3525 y(@)g(I)1503 3616 y(\000)1562 3558 y(\000)1595 3525 y(\000)g(\022)167 3840 y FK(for)26 b FH(a)311 3814 y Fv(0)348 3840 y FJ(\032)19 b FH(a)26 b FK(in)g(\()p FJ(A)13 b(!)h(B)r FK(\))f(&)g FJ(A)p FK(,)27 b(so)f(this)g(is)f(exactly)h(the)f(order)h(relation)f(w) n(e)h(need)g(on)h FJ(A)13 b(!)h(B)167 3925 y FK(to)28 b(mak)n(e)g(ev)l(aluation)g(stable.)p eop PStoPSsaved restore %%Page: (68,69) 35 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 65 68 bop 167 167 a Fz(8.5.)64 b(THE)27 b(FUNCTION-SP)-6 b(A)n(CE)1461 b FK(65)167 404 y Fy(8.5.4)95 b(P)m(artial)29 b(functions)167 535 y FK(Let)43 b(us)g(see)g(ho)n(w)h(this)e (construction)i(w)n(orks)g(b)n(y)f(calculating)f FJ(I)-7 b FM(nt)28 b FJ(!)20 b(I)-7 b FM(nt)7 b FK(.)82 b(W)-6 b(e)43 b(ha)n(v)n(e)167 620 y FJ(I)-7 b FM(nt)267 631 y Fm(\014n)350 620 y FJ(')20 b FK(I)-12 b(N)15 b FJ([)h(f)p Fn(?)p FJ(g)27 b FK(and)i FJ(jI)-7 b FM(nt)7 b FJ(j)19 b FK(=)g(I)-12 b(N,)28 b(so)g FJ(jI)-7 b FM(nt)22 b FJ(!)17 b(I)-7 b FM(nt)7 b FJ(j)19 b(')g FK(\(I)-12 b(N)15 b FJ([)h(f)p Fn(?)p FJ(g)p FK(\))g FJ(\002)f FK(I)-12 b(N)28 b(where)201 782 y(i\))f(\()p FH(n;)12 b(m)p FK(\))481 759 y FH(_)481 802 y(^)569 782 y FK(\()p FH(n)637 756 y Fv(0)654 782 y FH(;)g(m)745 756 y Fv(0)761 782 y FK(\))28 b(if)f FH(n)19 b FK(=)h FH(n)1059 756 y Fv(0)1095 782 y FJ(\))g FH(m)g FK(=)f FH(m)1398 756 y Fv(0)201 925 y FK(ii\))26 b(\()p Fn(?)p FH(;)12 b(m)p FK(\))513 903 y FH(_)513 946 y(^)602 925 y FK(\()p Fn(?)p FH(;)g(m)p FK(\))167 1087 y(with)44 b(incoherence)g(otherwise.)86 b(This)44 b(is)g(the)h FM(dir)l(e)l(ct)h(sum)f FK(\(see)f(section)g FG(??)q FK(\))h(of)g(the)167 1172 y(coherence)23 b(space)h(whic)n(h)f (represen)n(ts)g(partial)g(functions)h(with)e(the)i(space)g(whic)n(h)f (represen)n(ts)167 1257 y(the)j(constan)n(ts)h(\\b)n(y)h(v)n(o)r (cation".)36 b(Let)26 b(us)g(ignore)g(the)g(latter)f(part)h(and)i (concen)n(trate)d(on)i(the)167 1342 y(space)h FJ(P)-6 b(F)34 b FK(de\014ned)28 b(on)h(the)e(w)n(eb)h(I)-12 b(N)15 b FJ(\002)g FK(I)-12 b(N)28 b(b)n(y)g(condition)g(\(i\).)270 1468 y(What)39 b(is)f(the)g(order)g(relation)g(on)h FJ(P)-6 b(F)6 b FK(?)67 b(W)-6 b(ell)37 b FH(f)d FJ(2)28 b(P)-6 b(F)45 b FK(is)37 b(a)i(set)f(of)h(pairs)f(\()p FH(n;)12 b(m)p FK(\))167 1553 y(suc)n(h)38 b(that)h(if)e(\()p FH(n;)12 b(m)p FK(\))p FH(;)g FK(\()p FH(n;)g(m)956 1528 y Fv(0)972 1553 y FK(\))27 b FJ(2)g FH(f)45 b FK(then)38 b FH(m)27 b FK(=)f FH(m)1578 1528 y Fv(0)1595 1553 y FK(,)41 b(whic)n(h)c(is)g(just)h(the)f(usual)i(\\graph")167 1639 y(represen)n(tation)29 b(of)g(a)g(partial)g(function.)39 b(Since)28 b(the)h(Berry)f(order)h(corresp)r(onds)h(simply)e(to)167 1724 y(con)n(tainmen)n(t,)f(it)g(is)g(the)g(usual)h(extension)g(order)g (on)g(partial)f(functions.)270 1850 y(In)40 b(the)e(Berry)h(order,)i (the)e(partial)f(functions)1632 1831 y Fo(e)1619 1850 y FH(f)47 b FK(and)40 b(the)e(constan)n(ts)j(b)n(y)e(v)n(o)r(cation)178 1935 y(_)-30 b FH(n)34 b FK(are)g(incomparable.)53 b(Ho)n(w)n(ev)n(er) 33 b FM(p)l(ointwise)i FK(w)n(e)e(ha)n(v)n(e)1736 1916 y Fo(e)1724 1935 y FH(f)e(<)1874 1920 y FK(_)1867 1935 y(0)j(for)g(an)n(y)h(partial)e(function)167 2020 y(whic)n(h)h(tak)n(es) h(no)g(other)f(v)l(alue)h(than)g(zero,)h(of)f(whic)n(h)f(there)g(are)g (in\014nitely)f(man)n(y)-6 b(.)57 b(One)167 2105 y(adv)l(an)n(tage)30 b(of)d(our)h(seman)n(tics)e(is)g(that)i(it)e(a)n(v)n(oids)i(this)e (phenomenon)i(of)g FM(c)l(omp)l(act)2403 2080 y FD(5)2459 2105 y FK(ob)t(jects)167 2190 y(with)f(in\014nitely)f(man)n(y)i(ob)t (jects)g(b)r(elo)n(w)f(them.)270 2275 y(Another)37 b(consequence)f(of)h (the)e(Berry)h(order)g(arises)g(at)g(an)h(ev)n(en)f(simpler)e(t)n(yp)r (e:)53 b(in)167 2361 y(the)40 b(function-space)h FJ(S)-6 b FM(gl)25 b FJ(!)20 b(S)-6 b FM(gl)6 b FK(,)44 b(where)c FJ(S)-6 b FM(gl)46 b FK(is)40 b(the)g(coherence)g(space)h(with)f(just)h (one)167 2446 y(tok)n(en)30 b(\(section)f FG(??)p FK(\).)41 b(In)30 b(the)f(p)r(oin)n(t)n(wise)f(\(Scott\))h(order,)h(the)f(iden)n (tit)n(y)f(function)i(is)f(b)r(elo)n(w)167 2531 y(the)e(constan)n(t)h (\\b)n(y)h(v)n(o)r(cation")f FJ(f\017)q(g)p FK(,)g(whilst)d(in)i(the)g (Berry)g(order)g(they)g(are)h(incomparable.)167 2616 y(This)e(means)h(that)g(in)f(the)g(stable)g(seman)n(tics,)g(unlik)n(e)g (the)h(Scott)f(seman)n(tics,)g(it)g(is)g(p)r(ossible)167 2701 y(for)k(a)g(test)g(program)g(to)g(succeed)f(on)i(the)e(iden)n(tit) n(y)g(\(whic)n(h)g(reads)h(its)f(input\))h(but)g(fail)e(on)167 2786 y(the)f(constan)n(t)i(\(whic)n(h)e(do)r(es)h(not\).)p 167 3711 1003 3 v 246 3763 a FC(5)273 3784 y FB(The)35 b(notion)f(of)h(compactness)h(in)e(top)r(ology)g(is)h(purely)f (order-theoretic:)48 b(if)34 b Fx(a)21 b Fl(\024)2288 3740 y Fh(S)2337 3754 y Fk(")2374 3784 y Fx(I)39 b FB(for)d(some)167 3854 y FA(dir)m(e)m(cte)m(d)c FB(set)g Fx(I)37 b FB(then)31 b Fx(a)19 b Fl(\024)g Fx(b)32 b FB(for)g(some)h Fx(b)19 b Fl(2)g Fx(I)5 b FB(.)47 b(Besides)31 b(Scott's)h(domain)g(theory)-5 b(,)33 b(this)e(also)h(arises)g(in)167 3925 y(ring)27 b(theory)g(as)h(No)r(etherianness)f(and)g(in)f(univ)n(ersal)h(algebra)g (as)i(\014nite)d(presen)n(tabilit)n(y)-5 b(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 66 69 bop 167 875 a FF(Chapter)28 b(9)167 1169 y(Denotational)f(Seman) -5 b(tics)28 b(of)g(T)167 1489 y FK(The)40 b(constructions)g(of)h(c)n (hapter)f FG(??)h FK(pro)n(vide)f(a)g(nice)f(denotational)i(seman)n (tics)e(of)h(the)167 1574 y(systems)28 b(w)n(e)f(ha)n(v)n(e)h(already)g (considered.)167 1811 y FE(9.1)114 b(Simple)27 b(t)m(yp)s(ed)i (calculus)167 1967 y FK(W)-6 b(e)27 b(prop)r(ose)i(here)e(to)h(in)n (terpret)f(the)g(simple)f(t)n(yp)r(ed)i(calculus,)f(based)h(on)h FJ(!)f FK(and)h FJ(\002)p FK(.)35 b(The)167 2052 y(essen)n(tial)26 b(idea)i(is)e(that:)270 2216 y FJ(\017)34 b FH(\025)p FK(-abstraction)29 b(turns)f(a)g(function)g(\()p FH(x)19 b FJ(7!)h FH(t)p FK([)p FH(x)p FK(]\))28 b(in)n(to)f(an)i(ob)t(ject;) 270 2361 y FJ(\017)34 b FK(application)27 b(asso)r(ciates)h(to)g(an)g (ob)t(ject)g FH(t)f FK(of)i(t)n(yp)r(e)e FH(U)7 b FJ(!)q FH(V)43 b FK(a)28 b(function)g FH(u)20 b FJ(7!)g FH(t)12 b(u)p FK(.)270 2525 y(In)52 b(other)g(w)n(ords,)58 b(application)51 b(and)i FH(\025)p FK(-abstraction)f(are)f(t)n(w)n(o)h(m)n(utually)f(in) n(v)n(erse)167 2610 y(op)r(erations)28 b(whic)n(h)f(iden)n(tify)g(ob)t (jects)g(of)h(t)n(yp)r(e)g FH(U)7 b FJ(!)q FH(V)43 b FK(and)29 b(functions)f(from)f FH(U)35 b FK(to)28 b FH(V)15 b FK(.)270 2738 y(So)29 b(w)n(e)e(shall)g(in)n(terpret)f(them)h(as)h (follo)n(ws:)270 2901 y FJ(\017)34 b FH(\025)p FK(-abstraction)f(b)n(y) g(the)e(op)r(eration)i(whic)n(h)e(maps)h(a)g(stable)g(function)g(from)g FJ(A)g FK(to)g FJ(B)339 2987 y FK(to)c(its)f(trace,)g(a)h(p)r(oin)n(t)g (of)g FJ(A)16 b(!)g(B)r FK(;)270 3132 y FJ(\017)34 b FK(application)29 b(b)n(y)i(the)e(op)r(eration)h(whic)n(h)f(maps)h(a)g (p)r(oin)n(t)g(of)g FJ(A)16 b(!)h(B)32 b FK(to)e(the)f(function)339 3217 y(of)g(whic)n(h)d(it)h(is)g(the)g(trace.)167 3423 y Fy(9.1.1)95 b(T)m(yp)s(es)167 3555 y FK(Supp)r(ose)34 b(w)n(e)d(ha)n(v)n(e)j(\014xed)f(for)f(eac)n(h)g(atomic)g(t)n(yp)r(e)g FH(S)1622 3566 y Fw(i)1675 3555 y FK(a)g(coherence)g(space)g([)-12 b([)q FH(S)2327 3566 y Fw(i)2347 3555 y FK(])g(])q(;)34 b(then)f(w)n(e)167 3640 y(de\014ne)28 b([)-12 b([)p FH(T)10 b FK(])-12 b(])29 b(for)f(eac)n(h)f(t)n(yp)r(e)h FH(T)38 b FK(b)n(y:)574 3816 y([)-12 b([)q FH(U)7 b FJ(\002)p FH(V)16 b FK(])-12 b(])20 b(=)f([)-12 b([)p FH(U)7 b FK(])-12 b(])17 b(&)e([)-12 b([)q FH(V)15 b FK(])-12 b(])408 b([)-12 b([)q FH(U)7 b FJ(!)p FH(V)16 b FK(])-12 b(])20 b(=)f([)-12 b([)q FH(U)7 b FK(])-12 b(])16 b FJ(!)g FK([)-12 b([)q FH(V)16 b FK(])-12 b(])1385 4101 y(66)p eop PStoPSsaved restore %%Page: (70,71) 36 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 67 70 bop 167 167 a Fz(9.1.)64 b(SIMPLE)28 b(TYPED)f(CALCULUS)1319 b FK(67)167 404 y Fy(9.1.2)95 b(T)-8 b(erms)167 538 y FK(If)25 b FH(t)p FK([)p FH(x)321 549 y FD(1)349 538 y FH(;)12 b(:)g(:)g(:)g(;)g(x)543 549 y Fw(n)576 538 y FK(])25 b(is)g(a)h(term)e(of)h(t)n(yp)r(e)h FH(T)35 b FK(dep)r(ending)25 b(on)h(free)f(v)l(ariables)g FH(x)2125 549 y Fw(i)2170 538 y FK(of)h(t)n(yp)r(e)f FH(S)2450 549 y Fw(i)2495 538 y FK(\(some)167 623 y(of)30 b(the)e FH(x)415 634 y Fw(i)464 623 y FK(ma)n(y)i(not)f(actually)g(o)r(ccur)g (in)f FH(t)p FK(\),)h(w)n(e)g(asso)r(ciate)g(to)g(it)f(a)i(stable)e (function)i([)-12 b([)p FH(t)p FK(])g(])30 b(of)167 708 y FH(n)e FK(argumen)n(ts)g(from)f([)-12 b([)q FH(S)812 719 y FD(1)840 708 y FK(])g(])q FH(;)12 b(:)g(:)g(:)f(;)h FK([)-12 b([)q FH(S)1090 719 y Fw(n)1124 708 y FK(])g(])28 b(to)g([)-12 b([)p FH(T)10 b FK(])-12 b(])q(:)251 876 y(1.)35 b FH(t)p FK([)p FH(x)422 887 y FD(1)451 876 y FH(;)12 b(:)g(:)g(:)f(;)h(x)644 887 y Fw(n)677 876 y FK(])23 b(=)f FH(x)834 887 y Fw(i)855 876 y FK(:)43 b(then)32 b([)-12 b([)q FH(t)p FK(])g(]\()p FH(a)1224 887 y FD(1)1252 876 y FH(;)12 b(:)g(:)g(:)g(;)g(a)1443 887 y Fw(n)1476 876 y FK(\))23 b(=)f FH(a)1638 887 y Fw(i)1658 876 y FK(;)34 b(the)e(stabilit)n(y)e(of)i(this)g(function)g(is)339 962 y(immediate.)251 1110 y(2.)j FH(t)20 b FK(=)f FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(;)29 b(w)n(e)f(ha)n(v)n(e)g(at)g(our)h(disp)r (osal)f(functions)g([)-12 b([)p FH(u)p FK(])g(])29 b(and)g([)-12 b([)q FH(v)s FK(])g(])28 b(from)f([)-12 b([)q FH(S)2334 1121 y FD(1)2362 1110 y FK(])g(])q FH(;)12 b(:)g(:)g(:)f(;)h FK([)-12 b([)q FH(S)2612 1121 y Fw(n)2646 1110 y FK(])g(])339 1195 y(to)29 b([)-12 b([)p FH(U)7 b FK(])-12 b(])29 b(and)g([)-12 b([)q FH(V)15 b FK(])-12 b(])29 b(resp)r(ectiv)n(ely)-6 b(.)35 b(Consider)28 b(the)f(stable)h(binary)h(function)f FJ(P)-18 b FM(air)8 b FK(,)28 b(from)339 1280 y([)-12 b([)q FH(U)7 b FK(])-12 b(])q FH(;)12 b FK([)-12 b([)p FH(V)16 b FK(])-12 b(])28 b(to)g([)-12 b([)p FH(U)7 b FK(])-12 b(])17 b(&)e([)-12 b([)q FH(V)15 b FK(])-12 b(])q(,)28 b(de\014ned)g(b)n(y:)1046 1493 y FJ(P)-18 b FM(air)8 b FK(\()p FH(a;)k(b)p FK(\))19 b(=)h FJ(f)p FK(1)p FJ(g)c(\002)g FH(a)g FJ([)f(f)p FK(2)p FJ(g)i(\002)e FH(b)339 1707 y FK(W)-6 b(e)28 b(put)f([)-12 b([)q FH(t)p FK(])g(])q(\()p FH(a)735 1718 y FD(1)762 1707 y FH(;)12 b(:)g(:)g(:)g(;)g(a)953 1718 y Fw(n)986 1707 y FK(\))20 b(=)f FJ(P)-18 b FM(air)8 b FK(\([)-12 b([)q FH(u)p FK(])g(]\()p FH(a)1412 1718 y FD(1)1440 1707 y FH(;)12 b(:)g(:)g(:)g(;)g(a)1631 1718 y Fw(n)1664 1707 y FK(\))p FH(;)g FK([)-12 b([)q FH(v)s FK(])g(]\()p FH(b)1867 1718 y FD(1)1895 1707 y FH(;)12 b(:)g(:)g(:)g(;)g(b)2079 1718 y Fw(n)2112 1707 y FK(\)\);)27 b(this)g(function)h(is)339 1792 y(still)e(stable.)251 1940 y(3.)35 b FH(t)21 b FK(=)g FH(\031)502 1915 y FD(1)530 1940 y FH(w)32 b FK(or)e FH(t)21 b FK(=)g FH(\031)865 1915 y FD(2)892 1940 y FH(w)r FK(.)43 b(Here)28 b(again)j(w)n(e)f(comp) r(ose)g(with)e(one)j(of)f(the)g(follo)n(wing)f(t)n(w)n(o)339 2025 y(stable)f(functions:)624 2239 y(\005)676 2213 y FD(1)703 2239 y FK(\()p FH(c)p FK(\))19 b(=)h FJ(f)p FH(\013)g FK(:)39 b(\(1)p FH(;)12 b(\013)p FK(\))20 b FJ(2)f FH(c)p FJ(g)285 b FK(\005)1688 2213 y FD(2)1715 2239 y FK(\()p FH(c)p FK(\))19 b(=)g FJ(f)p FH(\014)24 b FK(:)39 b(\(2)p FH(;)12 b(\014)t FK(\))20 b FJ(2)f FH(c)p FJ(g)251 2484 y FK(4.)35 b FH(t)24 b FK(=)f FH(\025x:)12 b(v)s FK(;)36 b(b)n(y)d(h)n(yp)r(othesis)h(w)n(e)f(already)g(ha)n(v)n (e)h(a)f(\()p FH(n)18 b FK(+)e(1\)-ary)34 b(stable)f(function)g([)-12 b([)q FH(v)s FK(])g(])339 2569 y(from)29 b([)-12 b([)534 2570 y FH(S)p 538 2590 34 3 v 581 2569 a FK(])g(])q FH(;)12 b FK([)-12 b([)p FH(U)7 b FK(])-12 b(])29 b(to)g([)-12 b([)q FH(V)15 b FK(])-12 b(])q(;)29 b(in)f(particular,)g(for)1561 2570 y FH(a)p 1565 2590 23 3 v 1626 2569 a FK(\014xed,)i(the)e (function)h FH(b)20 b FJ(7!)h FK([)-12 b([)q FH(v)s FK(])g(]\()2474 2570 y FH(a)p 2478 2590 V -1 x(;)12 b(b)p FK(\))29 b(is)339 2654 y(stable)f(from)f([)-12 b([)q FH(U)7 b FK(])-12 b(])28 b(to)g([)-12 b([)p FH(V)16 b FK(])-12 b(])28 b(and)h(so)f(one)g (can)g(de\014ne)g([)-12 b([)q FH(t)p FK(])g(]\()1870 2655 y FH(a)p 1874 2675 V -1 x FK(\))20 b(=)f FJ(T)-6 b FH(r)r FK(\()p FH(b)20 b FJ(7!)g FK([)-12 b([)q FH(v)s FK(])g(]\()2373 2655 y FH(a)p 2377 2675 V -1 x(;)12 b(b)p FK(\)\).)339 2815 y(Chec)n(king)38 b(that)f([)-12 b([)q FH(t)p FK(])g(])38 b(is)e(stable)h(is)g(a)h(b)r(oring)g(but)f(straigh)n (tforw)n(ard)i(exercise.)63 b(F)-6 b(or)339 2900 y(example,)35 b(in)f(the)g(case)g(where)f FH(n)25 b FK(=)f(1,)36 b(w)n(e)e(ha)n(v)n (e)h(to)f(sho)n(w)h(that)g(if)e FH(F)43 b FK(is)34 b(a)g(stable)339 2986 y(function)28 b(from)f FJ(A)16 b FK(&)g FJ(B)29 b FK(to)f FJ(C)t FK(,)g(it)f(induces)g(a)h(stable)f(function)h FH(G)g FK(from)f FJ(A)h FK(to)g FJ(B)18 b(!)e(C)t FK(,)339 3071 y(b)n(y)1053 3284 y FH(G)p FK(\()p FH(a)p FK(\))k(=)f FJ(T)-6 b FH(r)r FK(\()p FH(b)21 b FJ(7!)f FH(F)10 b FK(\()p FJ(P)-18 b FM(air)7 b FK(\()p FH(a;)12 b(b)p FK(\)\)\))339 3498 y(Then)28 b FH(G)g FK(itself)e(has)i(a)g(trace,)g (for)g(whic)n(h)e(w)n(e)i(shall)f(just)h(giv)n(e)f(the)g(form)n(ula:) 818 3711 y FJ(T)-6 b FH(r)r FK(\()p FH(G)p FK(\))21 b(=)e FJ(f)p FK(\()p FH(a;)12 b FK(\()p FH(b;)g(\015)t FK(\)\))19 b(:)39 b(\()p FJ(P)-18 b FM(air)8 b FK(\()p FH(a;)k(b)p FK(\))p FH(;)g(\015)t FK(\))19 b FJ(2)h(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))p FJ(g)339 3925 y FK(It)28 b(is)f(not)h(a)g (pro)r(of,)h(but)f(it)e(should)j(b)r(e)e(enough)i(to)f(con)n(vince)g (us!)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 68 71 bop 167 167 a FK(68)730 b Fz(CHAPTER)26 b(9.)63 b(DENOT)-6 b(A)g(TIONAL)26 b(SEMANTICS)h(OF)g(T)251 404 y FK(5.)35 b FH(t)20 b FK(=)f FH(w)14 b(u)25 b FK(with)f FH(w)j FK(of)e(t)n(yp)r(e)g FH(U)7 b FJ(!)p FH(V)16 b FK(,)25 b FH(u)g FK(of)g(t)n(yp)r(e)g FH(U)7 b FK(;)26 b(w)n(e)e(de\014ne)h(the)g(function)g FJ(A)p FM(pp)k FK(from)339 490 y([)-12 b([)q FH(U)7 b FJ(!)q FH(V)15 b FK(])-12 b(])q FH(;)12 b FK([)-12 b([)p FH(U)7 b FK(])-12 b(])29 b(to)e([)-12 b([)q FH(V)16 b FK(])-12 b(])28 b(b)n(y:)919 669 y FJ(A)p FM(pp)5 b FK(\()p FH(f)t(;)12 b(a)p FK(\))19 b(=)h FJ(f)p FH(\014)j FK(:)39 b FJ(9)p FH(a)1532 680 y Fv(\016)1580 669 y FJ(\032)20 b FH(a)f FK(\()p FH(a)1773 680 y Fv(\016)1801 669 y FH(;)12 b(\014)t FK(\))19 b FJ(2)h FH(f)8 b FJ(g)339 848 y FK(It)26 b(is)g(immediate)d(that)k FJ(A)p FM(pp)k FK(is)26 b(stable;)g(so)h(w)n(e)f(de\014ne)h([)-12 b([)p FH(t)p FK(])g(])q(\()1936 849 y FH(s)p 1940 869 19 3 v -1 x FK(\))19 b(=)h FJ(A)p FM(pp)5 b FK(\([)-12 b([)p FH(w)r FK(])g(])q(\()2377 849 y FH(s)p 2381 869 V -1 x FK(\))p FH(;)12 b FK([)-12 b([)p FH(u)p FK(])g(])q(\()2586 849 y FH(s)p 2590 869 V -1 x FK(\)\))270 973 y(As)37 b(an)g(exercise,)g(one)g(can)g(calculate)e(the)i(traces)f(of)h FJ(P)-18 b FM(air)8 b FK(,)39 b(\005)2038 947 y FD(1)2066 973 y FK(,)g(\005)2176 947 y FD(2)2203 973 y FK(,)g FJ(A)p FM(pp)j FK(and)37 b(the)167 1058 y(function)28 b(in)f FG(??)h FK(whic)n(h)f(tak)n(es)h FH(F)37 b FK(to)28 b FH(G)p FK(.)167 1288 y FE(9.2)114 b(Prop)s(erties)27 b(of)h(the)g(in)m(terpretation)167 1443 y FK(Essen)n(tially)-6 b(,)32 b(as)h(w)n(e)f(ha)n(v)n(e)h(said,)g(con)n(v)n(ersion)g(b)r (ecomes)e(denotational)i(equalit)n(y:)44 b(if)31 b FH(t)23 b Fu( )g FH(u)167 1528 y FK(then)28 b([)-12 b([)p FH(t)p FK(])g(])20 b(=)g([)-12 b([)p FH(u)p FK(])g(])q(.)35 b(T)-6 b(o)28 b(sho)n(w)h(this,)e(w)n(e)g(use:)354 1683 y(\005)406 1657 y FD(1)434 1683 y FK(\()p FJ(P)-18 b FM(air)8 b FK(\()p FH(a;)k(b)p FK(\)\))19 b(=)h FH(a)187 b FK(\005)1130 1657 y FD(2)1158 1683 y FK(\()p FJ(P)-18 b FM(air)8 b FK(\()p FH(a;)k(b)p FK(\)\))19 b(=)g FH(b)188 b FJ(A)p FM(pp)5 b FK(\()p FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))p FH(;)i(a)p FK(\))19 b(=)g FH(F)10 b FK(\()p FH(a)p FK(\))167 1837 y(The)43 b(last)g(form)n(ula)g(is)g(to)h(b)r(e)f (used)h(in)f(conjunction)h(with)e(a)i(substitution)f(prop)r(ert)n(y:) 167 1922 y(consider)27 b FH(v)s FK([)495 1923 y FH(x)p 499 1943 26 3 v -1 x(;)12 b(u)p FK([)623 1923 y FH(x)p 627 1943 V 663 1922 a FK(])p FH(=y)s FK(];)28 b(one)g(can)g(asso)r (ciate)f(to)h(this)f(t)n(w)n(o)h(stable)f(functions:)270 2047 y FJ(\017)34 b FK(b)n(y)29 b(calculating)d(the)h(in)n (terpretation)g(of)h(this)f(term;)270 2181 y FJ(\017)34 b FK(b)n(y)c(forming)g(the)f(\()p FH(n)16 b FK(+)f(1\)-ary)31 b(function)e([)-12 b([)q FH(v)s FK(])g(]\()1585 2182 y FH(a)p 1589 2202 23 3 v -1 x(;)12 b(b)p FK(\),)30 b(the)f FH(n)p FK(-ary)h(function)g([)-12 b([)p FH(u)p FK(])g(])q(\()2469 2182 y FH(a)p 2473 2202 V -1 x FK(\))29 b(and)339 2266 y(then)f([)-12 b([)q FH(v)s FK(])g(]\()617 2267 y FH(a)p 621 2287 V -1 x(;)12 b FK([)-12 b([)q FH(u)p FK(])g(]\()803 2267 y FH(a)p 807 2287 V -1 x FK(\)\).)167 2391 y(The)28 b(t)n(w)n(o)g(functions)g(so)g(obtained)h(are)f(equal,)g(as)g(can)g(b)r (e)g(sho)n(wn)h(without)f(di\016cult)n(y)f(\(but)167 2476 y(what)h(a)g(b)r(ore!\))36 b(b)n(y)28 b(induction)f(on)h FH(v)s FK(.)270 2593 y(This)g(prop)r(ert)n(y)g(is)f(used)h(th)n(us)g (\(omitting)e(the)i(auxiliary)f(v)l(ariables\):)501 2748 y([)-12 b([)q(\()p FH(\025x:)12 b(v)s FK(\))g FH(u)p FK(])-12 b(])20 b(=)f FJ(A)p FM(pp)5 b FK(\()p FJ(T)-6 b FH(r)r FK(\()p FH(a)20 b FJ(7!)g FK([)-12 b([)p FH(v)s FK(])g(])q(\()p FH(a)p FK(\)\))p FH(;)12 b FK([)-12 b([)p FH(u)p FK(])g(])q(\))19 b(=)g([)-12 b([)q FH(v)s FK(])g(]\([)g([)q FH(u)p FK(])g(])q(\))19 b(=)g([)-12 b([)q FH(v)s FK([)p FH(u=x)p FK(]])g(])270 2934 y(In)32 b(fact,)h(the)e(secondary)i (equations,)g(whic)n(h)e(w)n(e)g(k)n(eep)h(meeting)e(but)i(ha)n(v)n(e)g (not)g(tak)n(en)167 3019 y(seriously)-6 b(,)27 b(are)h(also)g (satis\014ed:)544 3174 y FJ(P)-18 b FM(air)8 b FK(\(\005)747 3148 y FD(1)775 3174 y FK(\()p FH(c)p FK(\))p FH(;)k FK(\005)942 3148 y FD(2)969 3174 y FK(\()p FH(c)p FK(\)\))18 b(=)i FH(c)376 b FJ(T)-6 b FH(r)r FK(\()p FH(a)21 b FJ(7!)f(A)p FM(pp)5 b FK(\()p FH(f)t(;)12 b(a)p FK(\)\))19 b(=)g FH(f)270 3360 y FK(Categorically)-6 b(,)40 b(what)f(w)n(e)f(ha)n(v)n(e) h(sho)n(wn)g(is)f(that)g(&)g(and)h FJ(!)g FK(are)f(the)g(pro)r(duct)h (and)167 3445 y(exp)r(onen)n(tial)d(for)h(a)g FM(Cartesian)g(close)l(d) g(c)l(ate)l(gory)g FK(whose)g(ob)t(jects)f(are)h(coherence)f(spaces)167 3530 y(and)f(whose)g(morphisms)f(are)g(stable)g(maps.)56 b(Ho)n(w)n(ev)n(er,)36 b(w)n(e)e(ha)n(v)n(e)h(forgotten)g(one)g(thing:) 167 3615 y(comp)r(osition!)g(But)27 b(it)g(is)g(easy)h(to)g(sho)n(w)h (that)f(the)f(trace)g(of)h FH(G)16 b FJ(\016)g FH(F)37 b FK(is)310 3770 y FJ(f)p FK(\()p FH(a)408 3781 y FD(1)452 3770 y FJ([)15 b FH(:::)i FJ([)e FH(a)686 3781 y Fw(k)717 3770 y FH(;)d(\015)t FK(\))18 b(:)40 b(\()p FJ(f)p FH(\014)993 3781 y FD(1)1021 3770 y FH(;)12 b(:::;)g(\014)1179 3781 y Fw(k)1209 3770 y FJ(g)p FH(;)g(\015)t FK(\))19 b FJ(2)h(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))p FH(;)31 b FK(\()p FH(a)1715 3781 y FD(1)1743 3770 y FH(;)12 b(\014)1813 3781 y FD(1)1840 3770 y FK(\))p FH(;)g(:::;)g FK(\()p FH(a)2049 3781 y Fw(k)2080 3770 y FH(;)g(\014)2150 3781 y Fw(k)2180 3770 y FK(\))19 b FJ(2)g(T)-6 b FH(r)r FK(\()p FH(G)p FK(\))p FJ(g)167 3925 y FK(where)27 b FH(F)37 b FK(and)28 b FH(G)g FK(are)g(stable)f(functions)h(from)f FJ(A)h FK(to)g FJ(B)i FK(and)f(from)e FJ(B)j FK(to)e FJ(C)k FK(resp)r(ectiv)n(ely)-6 b(.)p eop PStoPSsaved restore %%Page: (72,73) 37 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 69 72 bop 167 167 a Fz(9.3.)64 b(G)404 149 y(\177)391 167 y(ODEL'S)28 b(SYSTEM)1642 b FK(69)167 404 y FE(9.3)114 b(G\177)-57 b(odel's)27 b(system)167 580 y Fy(9.3.1)95 b(Bo)s(oleans)167 710 y FK(W)-6 b(e)27 b(shall)g(in)n(terpret)f(the)i (t)n(yp)r(e)f Fq(Bo)r(ol)h FK(b)n(y)g FJ(B)-10 b FM(o)l(ol)9 b FK(:)689 892 y([)-12 b([)q Fq(T)p FK(])g(])20 b(=)f FJ(T)958 852 y FD(def)966 892 y FK(=)26 b FJ(f)p FG(t)p FJ(g)523 b FK([)-12 b([)p Fq(F)p FK(])g(])21 b(=)e FJ(F)1932 852 y FD(def)1940 892 y FK(=)27 b FJ(f)p FG(f)7 b FJ(g)270 1059 y Fq(D)12 b FH(u)g(v)i(t)28 b FK(is)f(in)n(terpreted)g(using)h(a)h (ternary)f(stable)f(function)h FJ(D)j FK(from)c FJ(A)p FK(,)i FJ(A)p FK(,)f FJ(B)-10 b FM(o)l(ol)37 b FK(to)28 b FJ(A)p FK(,)167 1144 y(de\014ned)g(b)n(y)444 1312 y FJ(D)r FK(\()p FH(a;)12 b(b;)g Fn(?)p FK(\))20 b(=)f Fn(?)277 b FJ(D)r FK(\()p FH(a;)12 b(b;)g FJ(f)p FG(t)p FJ(g)p FK(\))20 b(=)g FH(a)277 b FJ(D)r FK(\()p FH(a;)12 b(b;)g FJ(f)p FG(f)7 b FJ(g)p FK(\))21 b(=)e FH(b)167 1479 y FK(and)29 b(so)f(w)n(e)f(put)h([)-12 b([)q Fq(D)12 b FH(u)g(v)i(t)p FK(])-12 b(])20 b(=)f FJ(D)r FK(\([)-12 b([)q FH(u)p FK(])g(])p FH(;)12 b FK([)-12 b([)q FH(v)s FK(])g(])p FH(;)12 b FK([)-12 b([)q FH(t)p FK(])g(]\).)270 1647 y(In)39 b(particular,)g(the)f(fact)g(that)g(terms)f(of)h(G\177)-34 b(odel's)38 b(system)g(can)g(b)r(e)g(in)n(terpreted)e(b)n(y)167 1732 y(stable)27 b(functions)g(mak)n(es)g(it)f(imp)r(ossible)f(to)j (de\014ne)f FM(p)l(ar)l(al)t(lel)f(or)p FK(.)36 b(Indeed,)27 b(if)g(the)f(equations)516 1900 y FH(t)12 b FJ(h)p Fq(T)p FH(;)g(x)p FJ(i)21 b Fu( )f Fq(T)349 b FH(t)12 b FJ(h)p FH(x;)g Fq(T)p FJ(i)20 b Fu( )g Fq(T)350 b FH(t)12 b FJ(h)p Fq(F)p FH(;)g Fq(F)p FJ(i)20 b Fu( )g Fq(F)167 2067 y FK(had)29 b(a)f(solution)f(in)g FG(T)p FK(,)h(w)n(e)f(w)n(ould)h (ha)n(v)n(e)468 2235 y([)-12 b([)q FH(t)p FK(])g(]\()p FJ(T)18 b FH(;)12 b Fn(?)p FK(\))19 b(=)g FJ(T)320 b FK([)-12 b([)p FH(t)p FK(])g(])q(\()p Fn(?)p FH(;)12 b FJ(T)17 b FK(\))j(=)f FJ(T)319 b FK([)-12 b([)q FH(t)p FK(])g(]\()p FJ(F)7 b FH(;)12 b FJ(F)7 b FK(\))19 b(=)g FJ(F)167 2402 y FK(whic)n(h)27 b(corresp)r(onds)i(to)f(the)f (non-stable)h(function)g(called)e FH(F)1822 2413 y FD(0)1877 2402 y FK(in)h FG(??)q FK(.)167 2605 y Fy(9.3.2)95 b(In)m(tegers)167 2736 y FK(The)27 b(ob)n(vious)h(idea)f(for)g(in)n(terpreting)f Fq(Int)h FK(is)f(the)h(coherence)f(space)i FJ(I)-7 b FM(nt)34 b FK(in)n(tro)r(duced)27 b(in)f(the)167 2821 y(previous)i(c)n(hapter:)343 3002 y([)-12 b([)q Fq(O)p FK(])g(])20 b(=)f FJ(O)618 2962 y FD(def)625 3002 y FK(=)27 b FJ(f)p FK(0)p FJ(g)177 b FK([)-12 b([)q Fq(S)12 b FH(t)p FK(])-12 b(])20 b(=)f FJ(S)5 b FK(\([)-12 b([)p FH(t)p FK(])g(])q(\))27 b(with)g FJ(S)5 b FK(\()p Fn(?)p FK(\))19 b(=)g Fn(?)p FH(;)31 b FJ(S)5 b FK(\()p FJ(f)p FH(n)p FJ(g)p FK(\))20 b(=)f FJ(f)p FH(n)d FK(+)g(1)p FJ(g)270 3169 y FK(This)34 b(in)n(terpretation)f(w)n(orks)j(only)e FM(by)h(values)p FK(;)i(indeed,)f(it)d(is)h(easy)h(to)g(\014nd)g FH(u)g FK(and)g FH(v)167 3255 y FK(suc)n(h)28 b(that)723 3422 y Fq(R)12 b FH(u)g(v)j Fq(O)k Fu( )h Fq(T)557 b(R)12 b FH(u)g(v)j FK(\()p Fq(S)d FH(x)p FK(\))19 b Fu( )h Fq(F)167 3590 y FK(If)28 b FH(F)36 b FK(is)27 b(the)h(function)f(whic)n (h)g(in)n(terprets)g FH(x)19 b FJ(7!)h Fq(R)12 b FH(u)g(v)j(x)p FK(,)28 b(this)f(forces)720 3757 y FH(F)10 b FK(\()p FJ(O)r FK(\))18 b(=)i FJ(f)p FG(t)p FJ(g)553 b FH(F)10 b FK(\()p FJ(S)5 b FK(\()p Fn(?)p FK(\)\))18 b(=)h FJ(f)p FG(f)7 b FJ(g)167 3925 y FK(but)28 b FJ(S)5 b FK(\()p Fn(?)p FK(\))19 b(=)g Fn(?)h FJ(\032)f(O)r FK(,)28 b(con)n(tradiction.) p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 70 73 bop 167 167 a FK(70)730 b Fz(CHAPTER)26 b(9.)63 b(DENOT)-6 b(A)g(TIONAL)26 b(SEMANTICS)h(OF)g(T)270 404 y FK(What)i(is)e(wrong)i(with)e FJ(I)-7 b FM(nt)7 b FK(?)35 b(If)28 b(w)n(e)f(apply)i FJ(S)k FK(to)28 b Fn(?)f FK(\(empt)n(y)h (information\),)f(w)n(e)h(obtain)167 490 y Fn(?)h FK(again,)j(whereas)d (w)n(e)g(kno)n(w)i(something)f(more,)f(namely)h(that)g(w)n(e)f(ha)n(v)n (e)i(a)f FM(suc)l(c)l(essor)g FK(|)167 575 y(a)e(piece)e(of)i (information)f(whic)n(h)g(ma)n(y)h(w)n(ell)e(b)r(e)h(su\016cien)n(t)h (for)g(a)g(recursion)f(step.)270 722 y(Therefore,)37 b(w)n(e)d(m)n(ust)h(revise)f(our)i(in)n(terpretation,)f(adding)h(0)1996 697 y FD(+)2073 722 y FK(for)g(the)f(information)167 807 y(\\b)r(eing)h(a)h(successor",)i FM(i.e.)d FK(something)g FH(>)25 b FK(0,)38 b(and)g(more)d(generally)-6 b(,)38 b FH(p)2170 782 y FD(+)2247 807 y FK(for)e(something)167 892 y(greater)27 b(than)i FH(p)p FK(.)35 b(Let)27 b(us)h(de\014ne)1057 867 y FD(1)1113 892 y FJ(I)-7 b FM(nt)1213 867 y FD(+)1282 892 y FK(b)n(y)29 b FJ(jI)-7 b FM(nt)1502 867 y FD(+)1544 892 y FJ(j)19 b FK(=)h FJ(f)p FK(0)p FH(;)12 b FK(0)1791 867 y FD(+)1833 892 y FH(;)g FK(1)p FH(;)g FK(1)1963 867 y FD(+)2006 892 y FH(;)g(:)g(:)g(:)p FJ(g)27 b FK(with:)402 1108 y FH(p)456 1086 y(_)456 1129 y(^)544 1108 y(q)j FK(i\013)d FH(p)19 b FK(=)g FH(q)237 b(p)1122 1083 y FD(+)1183 1086 y FH(_)1183 1129 y(^)1271 1108 y(q)30 b FK(i\013)d FH(p)19 b(<)g(q)237 b(p)1849 1083 y FD(+)1910 1086 y FH(_)1910 1129 y(^)1999 1108 y(q)2033 1083 y FD(+)2101 1108 y FK(for)28 b(all)e FH(p;)12 b(q)270 1379 y FK(T)-6 b(o)28 b(see)e(ho)n(w)i(it)e(all)f(w)n(orks)j(out,)g(let)d(us)j(lo)r (ok)f(for)g(the)g(maximal)e(p)r(oin)n(ts.)36 b(If)27 b FH(a)19 b FJ(2)h(I)-7 b FM(nt)2557 1354 y FD(+)2626 1379 y FK(is)167 1464 y(maximal,)26 b(either:)270 1654 y FJ(\017)34 b FK(some)g FH(p)24 b FJ(2)g FH(a)p FK(;)38 b(then)c FH(a)h FK(con)n(tains)f(no)h(other)g FH(q)s FK(,)g(nor)f(do)r(es)h(it)e(con)n(tain)i(an)n(y)g FH(q)2463 1629 y FD(+)2538 1654 y FK(with)339 1753 y FH(p)20 b FJ(\024)f FH(q)s FK(.)34 b(So)27 b FH(a)19 b FJ(\032)k Fo(e)-42 b FH(p)838 1713 y FD(def)846 1753 y FK(=)26 b FJ(f)p FK(0)995 1727 y FD(+)1038 1753 y FH(;)12 b(:)g(:)g(:)f(;)h FK(\()p FH(p)j FJ(\000)h FK(1\))1401 1727 y FD(+)1443 1753 y FH(;)c(p)o FJ(g)p FK(;)27 b(but)g(this)e(set)h(is)f(coheren)n (t,)h(and)h(as)g FH(a)f FK(is)339 1838 y(maximal)h(it)f(m)n(ust)i(b)r (e)f(equal)h(to)j Fo(e)-42 b FH(p)o FK(.)270 2013 y FJ(\017)34 b FH(a)f FK(con)n(tains)f(no)h FH(p)p FK(;)h(then)e FH(a)23 b FJ(\032)g Fo(f)-70 b FJ(1)1276 1974 y FD(def)1283 2013 y FK(=)30 b FJ(f)p FK(0)1436 1988 y FD(+)1479 2013 y FH(;)12 b FK(1)1544 1988 y FD(+)1586 2013 y FH(;)g FK(2)1651 1988 y FD(+)1693 2013 y FH(;)g(:)g(:)g(:)p FJ(g)32 b FK(whic)n(h)f(is)h(coheren)n(t,)h(so)g FH(a)f FK(is)339 2098 y(equal)c(to)g(this)f(in\014nite)f(set.)270 2288 y(The)i(in)n(terpretation)e(is)h(as)h(follo)n(ws:)393 2504 y FJ(O)21 b FK(=)e FJ(f)p FK(0)p FJ(g)227 b(S)5 b FK(\()p FH(a)p FK(\))19 b(=)g FJ(f)p FK(0)1173 2478 y FD(+)1216 2504 y FJ(g)d([)f(f)p FH(i)h FK(+)f(1)20 b(:)39 b FH(i)20 b FJ(2)f FH(a)p FJ(g)d([)g(f)p FK(\()p FH(i)f FK(+)g(1\))2076 2478 y FD(+)2138 2504 y FK(:)39 b FH(i)2220 2478 y FD(+)2281 2504 y FJ(2)20 b FH(a)p FJ(g)167 2720 y FK(In)28 b(particular)e(the)i(n)n(umeral)p 975 2681 35 3 v 27 w FH(p)19 b FK(=)g Fq(S)1140 2694 y Fw(p)1180 2720 y Fq(O)28 b FK(will)c(b)r(e)k(in)n(terpreted)e(b)n(y) 32 b Fo(e)-43 b FH(p)p FK(.)270 2867 y(It)33 b(remains)f(to)h(in)n (terpret)e(recursion:)45 b(giv)n(en)33 b(a)g(coherence)f(space)h FJ(A)p FK(,)h(a)g(p)r(oin)n(t)e FH(o)24 b FJ(2)f(A)167 2952 y FK(and)31 b(a)g(stable)e(function)h FH(F)40 b FK(from)30 b FJ(A)p FH(;)12 b FJ(I)-7 b FM(nt)1298 2927 y FD(+)1370 2952 y FK(to)30 b FJ(A)p FK(,)h(w)n(e)e(shall)h(construct)g (a)g(stable)g(function)167 3038 y FH(G)e FK(from)f FJ(I)-7 b FM(nt)517 3012 y FD(+)586 3038 y FK(to)28 b FJ(A)g FK(whic)n(h)f(satis\014es:)386 3253 y FH(G)p FK(\()p FJ(O)r FK(\))20 b(=)f FH(o)219 b(G)p FK(\()p FJ(S)5 b FK(\()p FH(a)p FK(\)\))20 b(=)f FH(F)10 b FK(\()p FH(G)p FK(\()p FH(a)p FK(\))p FH(;)i(a)p FK(\))218 b FH(G)p FK(\()p FH(a)p FK(\))20 b(=)f Fn(?)28 b FK(if)e(0)p FH(;)12 b FK(0)2260 3228 y FD(+)2331 3253 y FH(=)-42 b FJ(2)19 b FH(a)270 3469 y(G)35 b FK(is)e(actually)g(w)n(ell-de\014ned)g(on)h (the)g(\014nite)f(p)r(oin)n(ts)h(of)h FJ(I)-7 b FM(nt)1932 3444 y FD(+)1974 3469 y FK(;)37 b(it)c(is)g(easily)g(sho)n(wn)i(to)167 3554 y(b)r(e)c(monotone)h(and)g(hence)e(extends)h(to)g(a)h(con)n(tin)n (uous,)h(and)f(indeed)e(stable,)h(function)g(on)167 3639 y(in\014nite)26 b(p)r(oin)n(ts.)36 b(In)28 b(particular,)f FH(G)p FK(\()p Fo(f)-70 b FJ(1)p FK(\))20 b(=)1348 3586 y Fo(S)1407 3605 y Fv(")1434 3639 y FJ(f)p FH(G)p FK(\()p FJ(S)1598 3614 y Fw(n)1632 3639 y FK(\()p Fn(?)p FK(\)\))f(:)39 b FH(n)20 b FJ(2)f FK(I)-12 b(N)p FJ(g)p FK(.)p 167 3719 1003 3 v 246 3763 a FC(1)273 3784 y FB(These)32 b FA(lazy)g(natur)m(al) h(numb)m(ers)j FB(are)d(rather)e(more)h(complicated)f(than)g(the)g (usual)g(ones,)i(whic)n(h)e(do)167 3854 y(not)h(form)g(a)h(coherence)f (space)g(but)f(a)h(dI-domain)f(\(section)g Ft(??)p FB(\).)48 b(The)32 b(di\013erence)f(is)h(that)f(w)n(e)i(admit)167 3925 y(the)27 b(tok)n(en)h(1)473 3903 y FC(+)540 3925 y FB(in)e(the)h(absence)h(of)g(0)1053 3903 y FC(+)1092 3925 y FB(,)g(although)f(it)f(is)h(di\016cult)f(to)h(see)h(what)g(this) f(migh)n(t)g(mean.)p eop PStoPSsaved restore %%Page: (74,75) 38 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 71 74 bop 167 167 a Fz(9.3.)64 b(G)404 149 y(\177)391 167 y(ODEL'S)28 b(SYSTEM)1642 b FK(71)270 404 y(In)28 b(fact,)g(if)f FH(a)625 379 y Fv(0)661 404 y FJ(\032)19 b FH(a)28 b FK(is)f(the)h(largest)f(subset)h(of)g(the)f(form)270 566 y FJ(\017)38 b Fo(e)-43 b FH(p)20 b FK(=)f FJ(f)p FK(0)536 540 y FD(+)578 566 y FH(;)12 b(:)g(:)g(:)g(;)g FK(\()p FH(p)j FJ(\000)g FK(1\))941 540 y FD(+)983 566 y FH(;)d(p)p FJ(g)20 b FK(=)f FJ(S)1225 540 y Fw(p)1253 566 y FJ(O)r FK(,)28 b(or)270 727 y FJ(\017)k FK(\027)-50 b FH(p)394 688 y FD(def)401 727 y FK(=)27 b FJ(f)p FK(0)551 702 y FD(+)593 727 y FH(;)12 b FK(1)658 702 y FD(+)701 727 y FH(;)g(:::;)g FK(\()p FH(p)j FJ(\000)g FK(1\))1028 702 y FD(+)1070 727 y FJ(g)20 b FK(=)f FJ(S)1246 702 y Fw(p)1274 727 y Fn(?)167 889 y FK(then)30 b FH(G)p FK(\()p FH(a)448 863 y Fv(0)465 889 y FK(\))20 b(=)h FH(G)p FK(\()p FH(a)p FK(\))30 b(\(assuming)g FH(F)38 b FK(has)31 b(this)e(prop)r(ert)n(y\),)i(so)f(\(b)n(y)g(induction\))f (no)h(term)f(of)167 974 y FG(T)f FK(in)n(v)n(olv)n(es)f FH(p)h FK(or)f FH(p)699 948 y FD(+)768 974 y FK(in)g(its)g(seman)n (tics)g(without)g FJ(f)p FK(0)1602 948 y FD(+)1645 974 y FH(;)12 b(:)g(:)g(:)f FK(\()p FH(p)k FJ(\000)h FK(1\))1977 948 y FD(+)2019 974 y FJ(g)28 b FK(as)g(w)n(ell.)270 1147 y(As)k(an)g(exercise,)e(one)i(can)g(try)f(to)h(calculate)e (directly)f(a)j(stable)f(function)g(from)g FJ(I)-7 b FM(nt)2630 1121 y FD(+)167 1232 y FK(to)28 b FJ(I)-7 b FM(nt)356 1206 y FD(+)425 1232 y FK(whic)n(h)27 b(represen)n(ts)g (the)h(predecessor.)167 1436 y Fy(9.3.3)95 b(In\014nit)m(y)28 b(and)f(\014xed)h(p)s(oin)m(t)167 1567 y FK(What)d(is)g(the)g(r^)-34 b(ole)24 b(of)h(the)g(ob)t(ject)g Fo(f)-70 b FJ(1)p FK(?)34 b(W)-6 b(e)25 b(see)f(that)i(it)e(is)g(a)i(\014xed)f(p)r(oin)n(t)g(of)h (the)f(successor:)167 1652 y FJ(S)5 b FK(\()p Fo(f)-70 b FJ(1)p FK(\))20 b(=)h Fo(f)-70 b FJ(1)p FK(.)39 b(One)29 b(could)f(try)h(to)g(add)h(it)e(to)h(the)g(syn)n(tax)h(of)g FG(T)p FK(,)f(with)f(the)g FM(nonc)l(onver)l(gent)167 1737 y FK(rewriting)e(rule)g FJ(1)20 b Fu( )g Fq(S)12 b FJ(1)p FK(.)36 b(W)-6 b(e)27 b(see,)h(b)n(y)g(using)g(the)f (iterator,)g(that)1076 1910 y Fq(It)11 b FH(u)h(v)j FJ(1)20 b Fu( )g FH(v)15 b FK(\()p Fq(It)c FH(u)h(v)i FJ(1)p FK(\))167 2083 y(and)29 b(so)f FJ(1)p FK(,)g(com)n(bined)f(with)g (recursion,)g(giv)n(es)h(us)g(access)f(to)h(the)f FM(\014xe)l(d)h(p)l (oint)p FK(,)g Fq(Y)r FK(.)270 2210 y(In)i(the)f(denotational)g(seman)n (tics,)g(the)g(tok)n(en)h FH(\013)f FK(o)r(ccurs)g(in)g(the)g(in)n (terpretation)f(of)h Fq(Y)r FH(f)167 2295 y FK(whenev)n(er)35 b FJ(h)p FH(a;)12 b(\013)p FJ(i)37 b FK(o)r(ccurs)f(in)f(the)g(trace)g (of)h(\(the)f(in)n(terpretation)g(of)5 b(\))36 b FH(f)43 b FK(and)36 b(the)g(clique)167 2380 y FH(a)k FK(o)r(ccurs)h(in)e(the)h (in)n(terpretation)f(of)i Fq(Y)r FH(f)8 b FK(.)72 b(Hardly)40 b(surprisingly)-6 b(,)43 b(this)c(is)h(a)g(recursiv)n(e)167 2465 y(de\014nition,)32 b(and)g(it)f(is)f(obtained)i(b)n(y)g(rep)r (eatedly)f(applying)h FH(f)38 b FK(to)32 b Fn(?)p FK(.)46 b(The)31 b(tok)n(ens)h(of)g(the)167 2550 y(in)n(terpretation)26 b(of)i Fq(Y)h FK(itself)d(can)i(therefore)f(b)r(e)g(describ)r(ed)g(in)g (terms)g(of)h(\014nite)f(trees.)270 2723 y(It)39 b(is)f(not)h(our)g (purp)r(ose)h(here)e(to)g(discuss)h(the)f(programming)h(applications)f (of)h(the)167 2808 y(\014xed)e(p)r(oin)n(t)f(\(general)g(recursion\),)i (an)f(idea)f(whic)n(h)f(is)h(curren)n(tly)f(rather)h(alien)f(to)i(t)n (yp)r(e)167 2893 y(systems,)j(although)e(the)f(denotational)h(seman)n (tics)e(accommo)r(dates)h(it)g(v)n(ery)g(w)n(ell.)62 b(But)167 2978 y(fundamen)n(tally)-6 b(,)28 b(what)g(do)r(es)g(this)f (mean?)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 72 75 bop 167 874 a FF(Chapter)28 b(10)167 1168 y(Sums)g(in)f(Natural)g (Deduction)167 1487 y FK(This)k(c)n(hapter)i(giv)n(es)f(a)g(brief)f (description)g(of)i(those)f(parts)h(of)f(natural)h(deduction)f(whose) 167 1573 y(b)r(eha)n(viour)i(is)f(not)h(so)g(prett)n(y)-6 b(,)35 b(although)g(they)e(sho)n(w)i(precisely)c(the)i(features)g(whic) n(h)g(are)167 1658 y(most)26 b(t)n(ypical)e(of)j(in)n(tuitionism.)32 b(F)-6 b(or)26 b(this)f(fragmen)n(t,)i(our)f(syn)n(tactic)f(metho)r(ds) h(are)f(frankly)167 1743 y(inadequate,)i(and)g(only)g(a)f(complete)e (recasting)i(of)g(the)g(ideas)g(could)g(allo)n(w)f(us)i(to)f(progress.) 167 1828 y(In)j(terms)g(of)g(syn)n(tax,)j(there)d(are)g(three)f (connectors)i(to)f(put)h(bac)n(k:)40 b FJ(:)12 b FK(,)29 b FJ(_)h FK(and)g FJ(9)p FK(.)40 b(F)-6 b(or)30 b FJ(:)12 b FK(,)167 1913 y(it)27 b(is)g(common)g(to)h(add)h(a)f(sym)n(b)r(ol)f FJ(?)g FK(\(absurdit)n(y\))h(and)g(in)n(terp)r(et)f FJ(:)p FH(A)g FK(as)h FH(A)19 b FJ(\))h(?)p FK(.)270 2036 y(The)28 b(rules)f(are:)427 2237 y FJ(\001)427 2274 y(\001)427 2312 y(\001)411 2370 y FH(A)p 344 2414 186 4 v 551 2430 a FJ(_)p FK(1)p FJ(I)344 2491 y FH(A)15 b FJ(_)h FH(B)936 2237 y FJ(\001)936 2274 y(\001)936 2312 y(\001)917 2370 y FH(B)p 853 2414 V 1059 2430 a FJ(_)p FK(2)p FJ(I)853 2491 y FH(A)f FJ(_)g FH(B)1444 2272 y FJ(\001)1444 2310 y(\001)1444 2348 y(\001)1361 2405 y FH(A)g FJ(_)h FH(B)1694 2213 y FK([)p FH(A)p FK(])1729 2272 y FJ(\001)1729 2310 y(\001)1729 2348 y(\001)1712 2405 y FH(C)1931 2213 y FK([)p FH(B)t FK(])1969 2272 y FJ(\001)1969 2310 y(\001)1969 2348 y(\001)1951 2405 y FH(C)p 1361 2450 645 4 v 2026 2465 a FJ(_E)1656 2526 y FH(C)2311 2236 y FJ(\001)2311 2274 y(\001)2311 2312 y(\001)2294 2370 y(?)p 2294 2415 55 4 v 2369 2431 a(?E)2294 2491 y FH(C)822 2761 y FJ(\001)822 2799 y(\001)822 2837 y(\001)734 2899 y FH(A)p FK([)p FH(a=\030)s FK(])p 734 2944 195 4 v 949 2960 a FJ(9I)754 3020 y(9)p FH(\030)s(:)c(A)1667 2805 y FJ(\001)1667 2843 y(\001)1667 2881 y(\001)1599 2939 y(9)p FH(\030)s(:)g(A)1902 2747 y FK([)p FH(A)p FK(])1937 2806 y FJ(\001)1937 2844 y(\001)1937 2881 y(\001)1920 2939 y FH(C)p 1599 2983 375 4 v 1995 2999 a FJ(9E)1759 3060 y FH(C)167 3196 y FK(The)31 b(v)l(ariable)h FH(\030)j FK(m)n(ust)c(no)i(longer)e(b)r(e)h (free)f(in)g(the)g(h)n(yp)r(otheses)i(or)f(the)g(conclusion)f(after)167 3281 y(use)d(of)g(the)f(rule)g FJ(9E)6 b FK(.)36 b(There)27 b(is,)g(of)h(course,)g(no)g(rule)f FJ(?I)5 b FK(.)167 3514 y FE(10.1)114 b(Defects)28 b(of)g(the)g(system)167 3669 y FK(The)41 b(in)n(tro)r(duction)f(rules)g(\(t)n(w)n(o)h(for)h FJ(_)p FK(,)i(none)e(for)f FJ(?)f FK(and)i(one)f(for)h FJ(9)p FK(\))f(are)f(excellen)n(t!)167 3754 y(Moreo)n(v)n(er,)24 b(if)e(y)n(ou)i(men)n(tally)e(turn)h(them)e(upside-do)n(wn,)k(y)n(ou)f (will)c(\014nd)k(the)e(same)h(structure)167 3840 y(as)32 b FJ(^)p FK(1)p FJ(E)6 b FK(,)34 b FJ(^)o FK(2)p FJ(E)6 b FK(,)34 b FJ(8E)j FK(\(in)31 b(linear)f(logic,)h(there)g(is)g(only)g (one)h(rule)f(in)f(eac)n(h)i(case,)h(since)d(they)167 3925 y FM(ar)l(e)e FK(actually)f(turned)h(o)n(v)n(er\).)1385 4101 y(72)p eop PStoPSsaved restore %%Page: (76,77) 39 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 73 76 bop 167 167 a Fz(10.2.)65 b(ST)-6 b(AND)n(ARD)26 b(CONVERSIONS)1299 b FK(73)270 404 y(The)32 b(elimination)d(rules)i (are)h(v)n(ery)g(bad.)49 b(What)33 b(is)e(catastrophic)h(ab)r(out)h (them)e(is)g(the)167 490 y(parasitic)f(presence)h(of)g(a)h(form)n(ula)f FH(C)37 b FK(whic)n(h)30 b(has)i(no)g(structural)f(link)f(with)g(the)h (form)n(ula)167 575 y(whic)n(h)d(is)f(eliminated.)34 b FH(C)g FK(pla)n(ys)29 b(the)f(r^)-34 b(ole)27 b(of)i(a)g(con)n(text,) f(and)i(the)e(writing)e(of)j(these)f(rules)167 660 y(is)f(a)h (concession)g(to)g(sequen)n(t)g(calculus.)270 909 y(In)j(fact,)g(the)g (adoption)g(of)g(these)g(rules)e(\(and)j(let)d(us)i(rep)r(eat)f(that)h (there)e(is)h(curren)n(tly)167 994 y(no)d(alternativ)n(e\))d(con)n (tradicts)i(the)g(idea)f(that)i(natural)f(deductions)g(are)g(the)g (\\real)g(ob)t(jects")167 1079 y(b)r(ehind)42 b(the)h(pro)r(ofs.)81 b(Indeed,)47 b(w)n(e)42 b(cannot)h(decen)n(tly)f(w)n(ork)h(with)e(the)i (full)e(fragmen)n(t)167 1164 y(without)27 b(iden)n(tifying)g FM(a)h(priori)35 b FK(di\013eren)n(t)27 b(deductions,)h(for)g(example:) 456 1459 y FJ(\001)456 1497 y(\001)456 1535 y(\001)373 1592 y FH(A)15 b FJ(_)h FH(B)706 1400 y FK([)p FH(A)p FK(])741 1459 y FJ(\001)741 1497 y(\001)741 1535 y(\001)724 1592 y FH(C)943 1400 y FK([)p FH(B)t FK(])980 1459 y FJ(\001)980 1497 y(\001)980 1535 y(\001)963 1592 y FH(C)p 373 1637 645 4 v 1038 1653 a FJ(_E)668 1713 y FH(C)p 665 1758 60 4 v 745 1774 a Fq(r)665 1835 y FH(D)1334 1540 y FK(and)1734 1580 y FJ(\001)1734 1618 y(\001)1734 1656 y(\001)1651 1713 y FH(A)f FJ(_)h FH(B)1984 1400 y FK([)p FH(A)p FK(])2019 1459 y FJ(\001)2019 1497 y(\001)2019 1535 y(\001)2002 1592 y FH(C)p 2000 1637 V 2079 1653 a Fq(r)2000 1713 y FH(D)2251 1400 y FK([)p FH(B)t FK(])2288 1459 y FJ(\001)2288 1497 y(\001)2288 1535 y(\001)2271 1592 y FH(C)p 2269 1637 V 2348 1653 a Fq(r)2269 1713 y FH(D)p 1651 1758 677 4 v 2348 1774 a FJ(_E)1960 1835 y FH(D)270 2053 y FK(F)-6 b(ortunately)g(,)27 b(this)e(kind)h(of)g (iden)n(ti\014cation)e(can)i(b)r(e)g(written)e(in)h(an)h(asymmetrical)d (form)167 2138 y(as)28 b(a)h(\\comm)n(uting)e(con)n(v)n(ersion",)i (satisfying)f(Ch)n(urc)n(h-Rosser)g(and)h(strong)g(normalisation.)167 2224 y(Nev)n(ertheless,)59 b(ev)n(en)54 b(though)h(the)f(damage)h(is)e (limited,)k(the)d(need)f(to)i(add)f(these)167 2309 y(supplemen)n(tary) 25 b(rules)f(rev)n(eals)h(an)h(inadequacy)g(of)f(the)g(syn)n(tax.)36 b(The)25 b(true)g(deductions)g(are)167 2394 y(nothing)j(more)g(than)g (equiv)l(alence)f(classes)g(of)h(deductions)g(mo)r(dulo)f(comm)n (utation)h(rules.)270 2558 y(What)h(w)n(e)e(w)n(ould)g(lik)n(e)f(to)i (write)e(in)h(the)h(case)f(of)h FJ(_E)34 b FK(for)28 b(example,)f(is)1302 2790 y FH(A)16 b FJ(_)f FH(B)p 1302 2834 186 4 v 1302 2911 a(A)78 b(B)167 3130 y FK(with)24 b(t)n(w)n(o)h(conclusions.)34 b(Later,)26 b(these)e(t)n(w)n(o)h (conclusions)g(w)n(ould)f(ha)n(v)n(e)i(to)f(b)r(e)g(brough)n(t)h(bac)n (k)167 3215 y(together)35 b(in)n(to)f(one.)57 b(But)35 b(w)n(e)f(ha)n(v)n(e)h(no)h(w)n(a)n(y)f(of)h(bringing)e(them)g(bac)n(k) i(together,)g(apart)167 3300 y(from)25 b(writing)e FJ(_E)31 b FK(as)26 b(w)n(e)e(did,)h(whic)n(h)g(forces)f(us)i(to)f(c)n(ho)r(ose) g(the)g(momen)n(t)f(of)h(reuni\014cation.)167 3385 y(The)30 b(comm)n(utation)g(rules)g(express)h(the)f(fact)g(that)h(this)f(momen)n (t)g(can)h(fundamen)n(tally)f(b)r(e)167 3470 y(p)r(ostp)r(oned.)167 3751 y FE(10.2)114 b(Standard)30 b(con)m(v)m(ersions)167 3925 y FK(These)d(are)h(redexes)f(of)h(t)n(yp)r(e)g(in)n(tro)r (duction/elimination:)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 74 77 bop 167 167 a FK(74)782 b Fz(CHAPTER)26 b(10.)64 b(SUMS)28 b(IN)f(NA)-6 b(TURAL)26 b(DEDUCTION)636 375 y FJ(\001)636 413 y(\001)636 451 y(\001)620 508 y FH(A)p 553 553 186 4 v 759 569 a FJ(_)p FK(1)p FJ(I)553 629 y FH(A)15 b FJ(_)h FH(B)1032 438 y FK([)p FH(A)p FK(])1067 496 y FJ(\001)1067 534 y(\001)1067 572 y(\001)1049 629 y FH(C)1269 438 y FK([)p FH(B)t FK(])1306 496 y FJ(\001)1306 534 y(\001)1306 572 y(\001)1289 629 y FH(C)p 553 674 791 4 v 1364 690 a FJ(_E)921 751 y FH(C)1591 491 y FK(con)n(v)n(erts)28 b(to)2082 409 y FJ(\001)2082 447 y(\001)2082 485 y(\001)2066 542 y FH(A)2082 583 y FJ(\001)2082 621 y(\001)2082 659 y(\001)2065 716 y FH(C)636 877 y FJ(\001)636 915 y(\001)636 953 y(\001)618 1010 y FH(B)p 553 1054 186 4 v 759 1070 a FJ(_)p FK(2)p FJ(I)553 1131 y FH(A)15 b FJ(_)h FH(B)1032 939 y FK([)p FH(A)p FK(])1067 998 y FJ(\001)1067 1036 y(\001)1067 1074 y(\001)1049 1131 y FH(C)1269 939 y FK([)p FH(B)t FK(])1306 998 y FJ(\001)1306 1036 y(\001)1306 1074 y(\001)1289 1131 y FH(C)p 553 1176 791 4 v 1364 1192 a FJ(_E)921 1252 y FH(C)1591 993 y FK(con)n(v)n(erts)28 b(to)2083 911 y FJ(\001)2083 949 y(\001)2083 987 y(\001)2065 1044 y FH(B)2083 1085 y FJ(\001)2083 1123 y(\001)2083 1161 y(\001)2065 1218 y FH(C)921 1378 y FJ(\001)921 1416 y(\001)921 1454 y(\001)834 1516 y FH(A)p FK([)p FH(a=\030)s FK(])p 834 1561 195 4 v 1049 1577 a FJ(9I)853 1637 y(9)p FH(\030)s(:)12 b(A)1279 1446 y FK([)p FH(A)p FK(])1314 1504 y FJ(\001)1314 1542 y(\001)1314 1580 y(\001)1297 1637 y FH(C)p 853 1682 498 4 v 1372 1698 a FJ(9E)1075 1759 y FH(C)1591 1497 y FK(con)n(v)n(erts)28 b(to)2152 1404 y FJ(\001)2152 1442 y(\001)2152 1480 y(\001)2065 1542 y FH(A)p FK([)p FH(a=\030)s FK(])2152 1600 y FJ(\001)2152 1638 y(\001)2152 1676 y(\001)2134 1733 y FH(C)270 1929 y FK(Note)39 b(that,)k(since)38 b(there)g(is)h(no)h(in)n(tro)r(duction) e(rule)g(for)i FJ(?)p FK(,)h(there)d(is)g(no)i(standard)167 2014 y(con)n(v)n(ersion)28 b(for)g(this)f(sym)n(b)r(ol.)270 2136 y(Let)34 b(us)h(just)g(think)f(for)g(a)h(momen)n(t)e(ab)r(out)j (the)e(structure)g(of)g(redexes:)49 b(on)35 b(the)f(one)167 2221 y(hand)g(there)e(is)g(an)h(in)n(tro)r(duction,)h(on)f(the)g(other) f(an)i(elimination,)d(and)j(the)e(elimination)167 2306 y(follo)n(ws)g(the)g(in)n(tro)r(duction.)50 b(But)32 b(there)g(are)h(some)f(eliminations)e(\()p FJ(\))p FK(,)k FJ(_)p FK(,)g FJ(9)p FK(\))e(with)g(more)167 2392 y(premises)g(and)j(w) n(e)e(only)h(consider)g(as)g(redexes)g(the)f(case)h(where)f(the)g(in)n (tro)r(duction)h(ends)167 2477 y(in)k(the)g FM(princip)l(al)46 b FK(premise)37 b(of)i(the)f(elimination,)h(namely)e(the)i(one)f(whic)n (h)g(carries)f(the)167 2562 y(eliminated)25 b(sym)n(b)r(ol.)35 b(F)-6 b(or)28 b(example)935 2713 y([)p FH(A)p FK(])970 2772 y FJ(\001)970 2810 y(\001)970 2848 y(\001)952 2905 y FH(B)p 871 2950 218 4 v 1109 2966 a FJ(\))q(I)871 3026 y FH(A)20 b FJ(\))g FH(B)1578 2889 y FJ(\001)1578 2926 y(\001)1578 2964 y(\001)1371 3026 y FK(\()p FH(A)f FJ(\))h FH(B)t FK(\))f FJ(\))h FH(C)p 871 3071 934 4 v 1826 3087 a FJ(\))q(E)1311 3148 y FH(C)167 3282 y FK(is)44 b(not)g(considered)g (as)h(a)g(redex.)85 b(This)43 b(is)h(fortunate,)49 b(as)c(w)n(e)f(w)n (ould)g(ha)n(v)n(e)i(trouble)167 3367 y(con)n(v)n(erting)28 b(it!)167 3600 y FE(10.3)114 b(The)28 b(need)h(for)e(extra)h(con)m(v)m (ersions)167 3754 y FK(T)-6 b(o)40 b(understand)h(ho)n(w)g(w)n(e)e(are) g(naturally)h(led)f(to)h(in)n(tro)r(ducing)f(extra)h(con)n(v)n (ersions,)j(let)167 3840 y(us)38 b(examine)g(the)f(pro)r(of)i(of)g(the) f FM(Subformula)g(Pr)l(op)l(erty)h FK(in)e(the)h(case)g(of)g(the)g(\()p FJ(^)p FH(;)12 b FJ(\))p FH(;)g FJ(8)p FK(\))167 3925 y(fragmen)n(t)28 b(in)f(suc)n(h)h(a)g(w)n(a)n(y)h(as)f(to)g(see)f(the)g (obstacles)h(to)g(generalising)e(it.)p eop PStoPSsaved restore %%Page: (78,79) 40 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 75 78 bop 167 167 a Fz(10.3.)65 b(THE)27 b(NEED)f(F)n(OR)i(EXTRA)e (CONVERSIONS)863 b FK(75)167 404 y Fy(10.3.1)94 b(Subform)m(ula)27 b(Prop)s(ert)m(y)167 548 y FG(Theorem)g FK(Let)g FH(\016)j FK(b)r(e)d(a)i(normal)e(deduction)g(in)h(the)f(\()p FJ(^)19 b(\))h(8)p FK(\))27 b(fragmen)n(t.)35 b(Then)201 745 y(i\))27 b(ev)n(ery)h(form)n(ula)f(in)g FH(\016)j FK(is)d(a)h(subform)n (ula)g(of)g(a)h(conclusion)e(or)h(a)g(h)n(yp)r(othesis)g(of)g FH(\016)s FK(;)201 910 y(ii\))38 b(if)i FH(\016)i FK(ends)e(in)f(an)i (elimination,)f(it)f(has)i(a)f FM(princip)l(al)g(br)l(anch)p FK(,)k FM(i.e.)c FK(a)g(sequence)g(of)339 995 y(form)n(ulae)28 b FH(A)680 1006 y FD(0)707 995 y FH(;)12 b(A)790 1006 y FD(1)818 995 y FH(;)g(:)g(:)g(:)f(;)h(A)1024 1006 y Fw(n)1085 995 y FK(suc)n(h)28 b(that:)421 1187 y FJ(\017)35 b FH(A)543 1198 y FD(0)598 1187 y FK(is)27 b(an)i(\(undisc)n(harged\))f (h)n(yp)r(othesis;)421 1310 y FJ(\017)35 b FH(A)543 1321 y Fw(n)604 1310 y FK(is)27 b(the)g(conclusion;)421 1433 y FJ(\017)35 b FH(A)543 1444 y Fw(i)590 1433 y FK(is)26 b(the)h(principal)e(premise)h(of)h(an)h(elimination)c(of)k(whic)n(h)e (the)h(conclusion)g(is)491 1519 y FH(A)543 1530 y Fw(i)p FD(+1)654 1519 y FK(\(for)h FH(i)19 b FK(=)g(0)p FH(;)12 b(:)g(:)g(:)g(;)g(n)k FJ(\000)f FK(1\).)339 1710 y(In)28 b(particular)f FH(A)805 1721 y Fw(n)865 1710 y FK(is)g(a)h(subform)n (ula)h(of)f FH(A)1498 1721 y FD(0)1525 1710 y FK(.)167 2038 y FG(Pro)r(of)g FK(W)-6 b(e)27 b(ha)n(v)n(e)i(three)e(cases)g(to)h (consider:)251 2235 y(1.)35 b(If)28 b FH(\016)i FK(consists)d(of)i(a)f (h)n(yp)r(othesis,)g(there)f(is)g(nothing)h(to)g(do.)251 2400 y(2.)35 b(If)28 b FH(\016)i FK(ends)e(in)f(an)h(in)n(tro)r (duction,)g(for)g(example)1343 2640 y FH(A)78 b(B)p 1343 2685 186 4 v 1550 2700 a FJ(^I)1343 2761 y FH(A)16 b FJ(^)f FH(B)339 2988 y FK(then)28 b(it)f(su\016ces)h(to)g(apply)g(the)f (induction)g(h)n(yp)r(othesis)i(ab)r(o)n(v)n(e)g FH(A)e FK(and)i FH(B)t FK(.)251 3153 y(3.)35 b(If)28 b FH(\016)i FK(ends)e(in)f(an)h(elimination,)d(for)j(example)1251 3393 y FH(A)19 b FJ(\))h FH(B)83 b(A)p 1251 3438 348 4 v 1619 3453 a FJ(\)E)1397 3514 y FH(B)339 3741 y FK(it)38 b(is)f(not)i(p)r(ossible)f(that)h(the)f(pro)r(of)h(ab)r(o)n(v)n(e)h (the)e(principal)e(premise)h(ends)i(in)e(an)339 3826 y(in)n(tro)r(duction,)27 b(so)h(it)e(ends)h(in)g(an)h(elimination)c (and)k(has)g(a)f(principal)f(branc)n(h,)i(whic)n(h)339 3911 y(can)g(b)r(e)g(extended)g(to)g(a)g(principal)e(branc)n(h)i(of)g FH(\016)s FK(.)939 b Fu(\003)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 76 79 bop 167 167 a FK(76)782 b Fz(CHAPTER)26 b(10.)64 b(SUMS)28 b(IN)f(NA)-6 b(TURAL)26 b(DEDUCTION)167 404 y Fy(10.3.2)94 b(Extension)28 b(to)f(the)h(full)g(fragmen)m(t)167 535 y FK(F)-6 b(or)28 b(the)f(full)f(calculus,)h(w)n(e)g(come)f (against)j(an)f(enormous)g(di\016cult)n(y:)35 b(it)26 b(is)h(no)h(longer)g(true)167 620 y(that)f(the)f(conclusion)h(of)g(an)g (elimination)d(is)i(a)h(subform)n(ula)g(of)g(its)f(principal)f (premise:)33 b(the)167 705 y(\\)p FH(C)5 b FK(")28 b(of)e(the)g(three)g (elimination)d(rules)j(has)h(nothing)g(to)f(do)h(with)f(the)g (eliminated)d(form)n(ula.)167 790 y(So)32 b(w)n(e)f(are)h(led)f(to)g (restricting)f(the)h(notion)h(of)g(principal)e(branc)n(h)j(to)f(those)g (eliminations)167 875 y(whic)n(h)g(are)h(w)n(ell-b)r(eha)n(v)n(ed)e(\() p FJ(^)p FK(1)p FJ(E)6 b FK(,)35 b FJ(^)p FK(2)p FJ(E)6 b FK(,)35 b FJ(\)E)k FK(and)34 b FJ(8E)6 b FK(\))32 b(and)i(w)n(e)e (can)h(try)g(to)g(extend)g(our)167 961 y(theorem.)46 b(Of)31 b(course)h(it)e(will)f(b)r(e)i(necessary)h(to)g(restrict)d (part)j(\(ii\))e(to)i(the)f(case)g(where)g FH(\016)167 1046 y FK(ends)d(in)f(a)h(\\go)r(o)r(d")i(elimination.)270 1161 y(The)g(theorem)f(is)g(pro)n(v)n(ed)i(as)f(b)r(efore)g(in)f(the)h (case)g(of)g(in)n(tro)r(ductions,)g(but)g(the)g(case)g(of)167 1246 y(eliminations)25 b(is)i(more)g(complex:)270 1363 y FJ(\017)34 b FK(If)g FH(\016)h FK(ends)f(in)f(a)h(go)r(o)r(d)h (elimination,)d(lo)r(ok)i(at)f(its)g(principal)f(premise)f FH(A)p FK(:)47 b(w)n(e)33 b(shall)339 1448 y(b)r(e)c(em)n(barrassed)h (in)e(the)h(case)g(where)f FH(A)h FK(is)f(the)h(conclusion)g(of)g(a)h (bad)g(elimination.)339 1533 y(Otherwise)c(w)n(e)h(conclude)g(the)h (existence)e(of)i(a)g(principal)e(branc)n(h.)270 1666 y FJ(\017)34 b FK(If)23 b FH(\016)j FK(ends)d(in)g(a)g(bad)i (elimination,)c(lo)r(ok)j(again)g(at)f(its)f(principal)g(premise)f FH(A)p FK(:)33 b(it)22 b(is)h(not)339 1751 y(the)29 b(conclusion)g(of)h (an)g(in)n(tro)r(duction.)39 b(If)29 b FH(A)g FK(is)f(a)i(h)n(yp)r (othesis)g(or)f(the)g(conclusion)g(of)339 1836 y(a)d(go)r(o)r(d)h (elimination,)c(it)i(is)f(a)i(subform)n(ula)g(of)g(a)g(h)n(yp)r (othesis,)h(and)f(the)f(result)g(follo)n(ws)339 1921 y(easily)-6 b(.)35 b(There)27 b(still)e(remains)i(the)g(case)h(where)f FH(A)g FK(comes)g(from)g(a)h(bad)h(elimination.)270 2038 y(T)-6 b(o)36 b(sum)g(up,)i(it)d(w)n(ould)g(b)r(e)h(necessary)g(to)f (get)h(rid)f(of)h(con\014gurations)h(formed)e(from)167 2123 y(a)i(succession)f(of)h(t)n(w)n(o)g(rules:)52 b(a)37 b(bad)h(elimination)33 b(of)k(whic)n(h)f(the)g(conclusion)h FH(C)42 b FK(is)35 b(the)167 2208 y(principal)24 b(premise)g(of)i(an)g (elimination,)d(go)r(o)r(d)k(or)f(bad.)36 b(Once)24 b(w)n(e)h(ha)n(v)n (e)i(done)f(this,)g(w)n(e)f(can)167 2293 y(reco)n(v)n(er)31 b(the)f(Subform)n(ula)i(Prop)r(ert)n(y)-6 b(.)46 b(A)30 b(quic)n(k)h(calculation)f(sho)n(ws)i(that)f(the)g(n)n(um)n(b)r(er)g (of)167 2378 y(con\014gurations)h(is)d(3)17 b FJ(\002)f FK(7)21 b(=)g(21)31 b(and)g(there)e(is)g(no)i(question)f(of)h (considering)e(them)g(one)h(b)n(y)167 2463 y(one.)35 b(In)27 b(an)n(y)g(case,)f(the)g(remo)n(v)l(al)g(of)g(these)g (con\014gurations)i(is)d(certainly)g(necessary)-6 b(,)27 b(as)f(the)167 2548 y(follo)n(wing)h(example)g(sho)n(ws:)815 2808 y FH(A)16 b FJ(_)f FH(A)1110 2687 y FK([)p FH(A)p FK(])78 b([)p FH(A)p FK(])p 1110 2731 259 4 v 1389 2747 a FJ(^I)1148 2808 y FH(A)16 b FJ(^)f FH(A)1627 2687 y FK([)p FH(A)p FK(])78 b([)p FH(A)p FK(])p 1627 2731 V 1906 2747 a FJ(^I)1665 2808 y FH(A)15 b FJ(^)h FH(A)p 815 2853 1032 4 v 1867 2868 a FJ(_E)1167 2923 y FH(A)g FJ(^)f FH(A)p 1167 2967 182 4 v 1370 2983 a FJ(^)p FK(1)p FJ(E)1232 3044 y FH(A)167 3164 y FK(whic)n(h)27 b(do)r(es)h(not)g (satisfy)g(the)g(Subform)n(ula)g(Prop)r(ert)n(y)-6 b(.)167 3394 y FE(10.4)114 b(Comm)m(uting)27 b(con)m(v)m(ersions)167 3612 y FK(In)35 b(what)g(follo)n(ws,)708 3578 y FH(C)841 3531 y FK(.)841 3555 y(.)841 3578 y(.)p 708 3623 152 4 v 881 3639 a Fq(r)755 3700 y FH(D)940 3612 y FK(denotes)g(an)h (elimination)c(of)j(the)g(principal)e(premise)g FH(C)5 b FK(,)37 b(the)167 3754 y(conclusion)27 b(is)h FH(D)i FK(and)e(the)g(ellipsis)d(represen)n(ts)i(some)h(p)r(ossible)f (secondary)i(premises)d(with)167 3840 y(the)33 b(corresp)r(onding)h (deductions.)53 b(This)33 b(sym)n(b)r(olic)f(notation)j(co)n(v)n(ers)e (the)g(sev)n(en)h(cases)g(of)167 3925 y(elimination.)p eop PStoPSsaved restore %%Page: (80,81) 41 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 77 80 bop 167 167 a Fz(10.4.)65 b(COMMUTING)26 b(CONVERSIONS)1229 b FK(77)251 404 y(1.)35 b(comm)n(utation)28 b(of)g FJ(?E)6 b FK(:)717 603 y FJ(\001)717 641 y(\001)717 679 y(\001)699 737 y(?)p 699 782 55 4 v 775 798 a(?E)700 858 y FH(C)986 812 y FK(.)986 835 y(.)986 858 y(.)p 700 903 306 4 v 1026 919 a Fq(r)823 980 y FH(D)1410 720 y FK(con)n(v)n(erts)28 b(to)2126 664 y FJ(\001)2126 702 y(\001)2126 740 y(\001)2109 798 y(?)p 2106 843 60 4 v 2186 858 a(?E)2106 919 y FH(D)251 1339 y FK(2.)35 b(comm)n(utation)28 b(of)g FJ(_E)6 b FK(:)427 1608 y FJ(\001)427 1646 y(\001)427 1684 y(\001)344 1741 y FH(A)15 b FJ(_)h FH(B)677 1550 y FK([)p FH(A)p FK(])712 1608 y FJ(\001)712 1646 y(\001)712 1684 y(\001)695 1741 y FH(C)914 1550 y FK([)p FH(B)t FK(])951 1608 y FJ(\001)951 1646 y(\001)951 1684 y(\001)934 1741 y FH(C)p 344 1786 645 4 v 1009 1802 a FJ(_E)639 1862 y FH(C)1212 1816 y FK(.)1212 1839 y(.)1212 1862 y(.)p 639 1907 593 4 v 1252 1923 a Fq(r)906 1984 y FH(D)1281 1689 y FK(con)n(v)n(erts)28 b(to)1705 1729 y FJ(\001)1705 1767 y(\001)1705 1805 y(\001)1622 1862 y FH(A)15 b FJ(_)h FH(B)1955 1550 y FK([)p FH(A)p FK(])1990 1608 y FJ(\001)1990 1646 y(\001)1990 1684 y(\001)1973 1741 y FH(C)2158 1694 y FK(.)2158 1718 y(.)2158 1741 y(.)p 1973 1786 205 4 v 2197 1802 a Fq(r)2045 1862 y FH(D)2369 1550 y FK([)p FH(B)t FK(])2406 1608 y FJ(\001)2406 1646 y(\001)2406 1684 y(\001)2389 1741 y FH(C)2576 1694 y FK(.)2576 1718 y(.)2576 1741 y(.)p 2389 1786 207 4 v 2616 1802 a Fq(r)2462 1862 y FH(D)p 1622 1907 901 4 v 2542 1923 a FJ(_E)2042 1984 y FH(D)251 2343 y FK(3.)35 b(comm)n(utation)28 b(of)g FJ(9E)6 b FK(:)593 2611 y FJ(\001)593 2649 y(\001)593 2687 y(\001)525 2745 y(9)p FH(\030)s(:)12 b(A)828 2554 y FK([)p FH(A)p FK(])863 2612 y FJ(\001)863 2650 y(\001)863 2688 y(\001)846 2745 y FH(C)p 525 2790 375 4 v 921 2806 a FJ(9E)686 2866 y FH(C)1116 2820 y FK(.)1116 2843 y(.)1116 2866 y(.)p 686 2911 450 4 v 1156 2927 a Fq(r)881 2988 y FH(D)1367 2693 y FK(con)n(v)n(erts)28 b(to)1957 2733 y FJ(\001)1957 2771 y(\001)1957 2808 y(\001)1889 2866 y(9)p FH(\030)s(:)12 b(A)2191 2554 y FK([)p FH(A)p FK(])2227 2612 y FJ(\001)2227 2650 y(\001)2227 2688 y(\001)2209 2745 y FH(C)2394 2698 y FK(.)2394 2722 y(.)2394 2745 y(.)p 2209 2790 205 4 v 2434 2806 a Fq(r)2282 2866 y FH(D)p 1889 2911 452 4 v 2362 2927 a FJ(9E)2085 2988 y FH(D)270 3280 y FG(Example)53 b FK(The)28 b(most)f(complicated)f(situation)h(is:)447 3584 y FJ(\001)447 3622 y(\001)447 3660 y(\001)364 3717 y FH(A)15 b FJ(_)h FH(B)748 3526 y FK([)p FH(A)p FK(])783 3584 y FJ(\001)783 3622 y(\001)783 3660 y(\001)697 3717 y FH(C)21 b FJ(_)16 b FH(D)1085 3526 y FK([)p FH(B)t FK(])1122 3584 y FJ(\001)1122 3622 y(\001)1122 3660 y(\001)1036 3717 y FH(C)21 b FJ(_)16 b FH(D)p 364 3762 865 4 v 1249 3778 a FJ(_E)700 3839 y FH(C)21 b FJ(_)16 b FH(D)1487 3647 y FK([)p FH(C)5 b FK(])1523 3706 y FJ(\001)1523 3743 y(\001)1523 3781 y(\001)1505 3839 y FH(E)1726 3647 y FK([)p FH(D)r FK(])1765 3706 y FJ(\001)1765 3743 y(\001)1765 3781 y(\001)1748 3839 y FH(E)p 700 3883 1103 4 v 1823 3899 a FJ(_E)1224 3960 y FH(E)2111 3665 y FK(con)n(v)n(erts)28 b(to)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 78 81 bop 167 167 a FK(78)782 b Fz(CHAPTER)26 b(10.)64 b(SUMS)28 b(IN)f(NA)-6 b(TURAL)26 b(DEDUCTION)482 567 y FJ(\001)482 605 y(\001)482 643 y(\001)399 700 y FH(A)15 b FJ(_)h FH(B)783 387 y FK([)p FH(A)p FK(])818 445 y FJ(\001)818 483 y(\001)818 521 y(\001)732 578 y FH(C)21 b FJ(_)16 b FH(D)1071 387 y FK([)p FH(C)5 b FK(])1108 445 y FJ(\001)1108 483 y(\001)1108 521 y(\001)1090 578 y FH(E)1311 387 y FK([)p FH(D)r FK(])1350 445 y FJ(\001)1350 483 y(\001)1350 521 y(\001)1332 578 y FH(E)p 732 623 656 4 v 1408 639 a FJ(_E)1032 700 y FH(E)1695 387 y FK([)p FH(B)t FK(])1732 445 y FJ(\001)1732 483 y(\001)1732 521 y(\001)1646 578 y FH(C)21 b FJ(_)16 b FH(D)1985 387 y FK([)p FH(C)5 b FK(])2022 445 y FJ(\001)2022 483 y(\001)2022 521 y(\001)2004 578 y FH(E)2225 387 y FK([)p FH(D)r FK(])2264 445 y FJ(\001)2264 483 y(\001)2264 521 y(\001)2246 578 y FH(E)p 1646 623 V 2322 639 a FJ(_E)1946 700 y FH(E)p 399 745 1603 4 v 2022 760 a FJ(_E)1173 821 y FH(E)167 1010 y FK(W)-6 b(e)31 b(see)g(in)g(particular)f(that)i(the)f(general)g (case)h(\(with)e(an)i(unsp)r(eci\014ed)g(elimination)c Fq(r)q FK(\))k(is)167 1095 y(more)27 b(in)n(telligible)c(than)28 b(its)f(21)i(sp)r(ecialisations.)167 1355 y FE(10.5)114 b(Prop)s(erties)28 b(of)f(con)m(v)m(ersion)167 1520 y FK(First)34 b(of)h(all,)h(the)e(normal)h(form,)i(if)d(it)f(exists,)k (is)d(unique:)50 b(that)35 b(follo)n(ws)f(again)i(from)f(a)167 1605 y(Ch)n(urc)n(h-Rosser)c(prop)r(ert)n(y)-6 b(.)46 b(The)30 b(result)g(remains)f(true)i(in)f(this)g(case,)h(since)f(the)h (con\015icts)167 1690 y(of)d(the)g(kind)950 1867 y FJ(\001)950 1905 y(\001)950 1943 y(\001)934 2000 y FH(A)p 867 2045 186 4 v 1073 2061 a FJ(_)p FK(1)p FJ(I)867 2121 y FH(A)15 b FJ(_)g FH(B)1345 1930 y FK([)p FH(A)p FK(])1381 1988 y FJ(\001)1381 2026 y(\001)1381 2064 y(\001)1363 2121 y FH(C)1583 1930 y FK([)p FH(B)t FK(])1620 1988 y FJ(\001)1620 2026 y(\001)1620 2064 y(\001)1603 2121 y FH(C)p 867 2166 791 4 v 1678 2182 a FJ(_E)1235 2243 y FH(C)1881 2196 y FK(.)1881 2219 y(.)1881 2243 y(.)p 1235 2287 666 4 v 1921 2303 a Fq(r)1538 2364 y FH(D)167 2548 y FK(whic)n(h)27 b(con)n(v)n(erts)h(in)f(t)n(w)n(o)h(di\013eren)n(t)f(w)n(a)n(ys,)h (namely)401 2811 y([)p FH(A)p FK(])436 2870 y FJ(\001)436 2908 y(\001)436 2946 y(\001)419 3003 y FH(C)604 2956 y FK(.)604 2979 y(.)604 3003 y(.)p 419 3048 205 4 v 643 3064 a Fq(r)491 3124 y FH(D)902 2890 y FK(and)1330 2809 y FJ(\001)1330 2847 y(\001)1330 2885 y(\001)1314 2942 y FH(A)p 1246 2987 186 4 v 1453 3003 a FJ(_)p FK(1)p FJ(I)1246 3064 y FH(A)16 b FJ(_)f FH(B)1725 2751 y FK([)p FH(A)p FK(])1761 2809 y FJ(\001)1761 2847 y(\001)1761 2885 y(\001)1743 2942 y FH(C)1928 2895 y FK(.)1928 2919 y(.)1928 2942 y(.)p 1743 2987 205 4 v 1968 3003 a Fq(r)1816 3064 y FH(D)2140 2751 y FK([)p FH(B)t FK(])2177 2809 y FJ(\001)2177 2847 y(\001)2177 2885 y(\001)2159 2942 y FH(C)2347 2895 y FK(.)2347 2919 y(.)2347 2942 y(.)p 2159 2987 207 4 v 2386 3003 a Fq(r)2233 3064 y FH(D)p 1246 3108 1046 4 v 2313 3124 a FJ(_E)1740 3185 y FH(D)167 3369 y FK(are)28 b(easily)e(resolv)n(ed,)i(b)r(ecause)f(the)h(second)g (deduction)g(con)n(v)n(erts)g(to)g(the)f(\014rst.)270 3584 y(It)i(is)f(p)r(ossible)h(to)g(extend)g(the)g(results)f(obtained)i (for)f(the)g(\()p FJ(^)p FH(;)12 b FJ(\))p FH(;)g FJ(8)p FK(\))28 b(fragmen)n(t)h(to)g(the)167 3669 y(full)22 b(calculus,)i(at)f(the)h(price)e(of)i(b)r(oring)g(complications.)32 b([)p FG(?)q FK(])23 b(giv)n(es)h(all)e(the)i(tec)n(hnical)d(details) 167 3754 y(for)28 b(doing)g(this.)35 b(The)27 b(abstract)h(prop)r (erties)f(of)h(reducibilit)n(y)d(for)j(this)f(case)g(are)h(in)f([)p FG(?)p FK(],)h(and)167 3840 y(there)g(are)h(no)h(real)e(problems)h (when)g(w)n(e)g(extend)g(this)f(to)i(existen)n(tial)d(quan)n (ti\014cation)j(o)n(v)n(er)167 3925 y(t)n(yp)r(es.)p eop PStoPSsaved restore %%Page: (82,83) 42 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 79 82 bop 167 167 a Fz(10.6.)65 b(THE)27 b(ASSOCIA)-6 b(TED)26 b(FUNCTIONAL)g(CALCULUS)695 b FK(79)270 404 y(Ha)n(ving)37 b(said)f(this,)i(w)n(e)e(shall)f(giv)n(e)h(no)h(pro)r (of,)j(b)r(ecause)c(the)g(theoretical)e(in)n(terest)h(is)167 490 y(limited.)d(One)27 b(tends)h(to)g(think)f(that)h(natural)g (deduction)g(should)g(b)r(e)f(mo)r(di\014ed)g(to)h(correct)167 575 y(suc)n(h)h(atro)r(cities:)34 b(if)27 b(a)i(connector)f(has)h(suc)n (h)g(bad)g(rules,)f(one)g(ignores)g(it)f(\(a)i(v)n(ery)f(common)167 660 y(attitude\))j(or)i(one)f(tries)f(to)h(c)n(hange)h(the)f(v)n(ery)g (spirit)f(of)i(natural)f(deduction)g(in)g(order)g(to)167 745 y(b)r(e)f(able)f(to)i(in)n(tegrate)e(it)g(harmoniously)h(with)g (the)f(others.)46 b(It)31 b(do)r(es)g(not)h(seem)e(that)h(the)167 830 y(\()p FJ(?)p FH(;)12 b FJ(_)p FH(;)g FJ(9)p FK(\))26 b(fragmen)n(t)i(of)g(the)f(calculus)g(is)g(etc)n(hed)g(on)h(tablets)f (of)h(stone.)270 1002 y(Moreo)n(v)n(er,)34 b(the)d(extensions)h(are)g (long)g(and)g(di\016cult,)g(and)g(for)g(all)f(that)h(y)n(ou)h(will)c (not)167 1088 y(learn)21 b(an)n(ything)j(new)d(apart)i(from)f(tec)n (hnical)e(v)l(ariations)j(on)f(reducibilit)n(y)-6 b(.)31 b(So)23 b(it)e(will)e(su\016ce)167 1173 y(to)35 b(kno)n(w)h(that)g(the) f(strong)h(normalisation)e(theorem)h(also)g(holds)g(in)g(this)f(case.) 58 b(In)35 b(the)167 1258 y(unlik)n(ely)g(ev)n(en)n(t)h(that)g(y)n(ou)i (w)n(an)n(t)e(to)h(see)e(the)h(pro)r(of,)k(y)n(ou)d(ma)n(y)g(consult)f (the)g(references)167 1343 y(ab)r(o)n(v)n(e.)167 1633 y FE(10.6)114 b(The)28 b(asso)s(ciated)h(functional)g(calculus)167 1812 y FK(Returning)g(to)h(the)f(idea)g(of)h(Heyting,)f(it)g(is)g(p)r (ossible)f(to)i(understand)h(the)e(Curry-Ho)n(w)n(ard)167 1897 y(isomorphism)46 b(in)h(the)g(case)g(of)h FJ(?)e FK(and)i FJ(_)f FK(\(the)g(case)g(of)h FJ(9)f FK(will)d(receiv)n(e)i (no)i(more)167 1982 y(consideration)27 b(than)i(did)e(that)h(of)h FJ(8)p FK(\).)167 2241 y Fy(10.6.1)94 b(Empt)m(y)28 b(t)m(yp)s(e)g (\(corresp)s(onding)d(to)i Fg(?)p Fy(\))167 2395 y Fq(Emp)d FK(is)g(considered)g(to)h(b)r(e)f(the)h(empt)n(y)f(t)n(yp)r(e.)34 b(F)-6 b(or)25 b(this)f(reason,)j(there)c(will)f(b)r(e)i(a)h(canonical) 167 2480 y(function)i FH(")473 2491 y Fw(U)542 2480 y FK(from)g Fq(Emp)f FK(to)i(an)n(y)g(t)n(yp)r(e)f FH(U)7 b FK(:)35 b(if)26 b FH(t)h FK(is)f(of)h(t)n(yp)r(e)g Fq(Emp)p FK(,)h(them)e FH(")2179 2491 y Fw(U)2232 2480 y FH(t)h FK(is)f(of)i(t)n(yp)r(e)f FH(U)7 b FK(.)167 2565 y(The)27 b(comm)n(utation)h(for)f FH(")879 2576 y Fw(U)949 2565 y FK(is)g(set)g(out)h(in)g(\014v)n(e)g(cases:)1213 2894 y FH(\031)1255 2868 y FD(1)1282 2894 y FK(\()p FH(")1341 2905 y Fw(U)5 b Fv(\002)p Fw(V)1474 2894 y FH(t)p FK(\))58 b Fu( )h FH(")1745 2905 y Fw(U)1799 2894 y FH(t)1213 2979 y(\031)1255 2953 y FD(2)1282 2979 y FK(\()p FH(")1341 2990 y Fw(U)5 b Fv(\002)p Fw(V)1474 2979 y FH(t)p FK(\))58 b Fu( )h FH(")1745 2990 y Fw(V)1800 2979 y FH(t)1220 3149 y FK(\()p FH(")1279 3160 y Fw(U)5 b Fv(!)p Fw(V)1423 3149 y FH(t)p FK(\))12 b FH(u)58 b Fu( )h FH(")1745 3160 y Fw(V)1800 3149 y FH(t)1219 3319 y(")1251 3330 y Fw(U)1305 3319 y FK(\()p FH(")1364 3330 y Fp(Emp)1474 3319 y FH(t)p FK(\))f Fu( )h FH(")1745 3330 y Fw(U)1799 3319 y FH(t)986 3490 y(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b FK(\()p FH(")1349 3501 y Fw(R)p FD(+)p Fw(S)1474 3490 y FH(t)p FK(\))58 b Fu( )h FH(")1745 3501 y Fw(U)1799 3490 y FH(t)167 3754 y FK(In)41 b(the)f(last)g(case)h(\()p FH(\016)31 b(x:)12 b(u)29 b(y)s(:)12 b(v)31 b(t)40 b FK(is)g(in)n(tro)r(duced)g(b) r(elo)n(w\))g FH(U)48 b FK(is)40 b(the)g(common)h(t)n(yp)r(e)g(of)167 3840 y FH(u)g FK(and)h FH(v)s FK(.)74 b(It)40 b(is)g(easy)h(to)g(see)f (that)h FH(")1306 3851 y Fw(U)1389 3840 y FK(corresp)r(onds)h(exactly)e (to)h FJ(?E)46 b FK(and)41 b(the)g(\014v)n(e)167 3925 y(con)n(v)n(ersions)28 b(ab)r(o)n(v)n(e)h(to)f(the)g(\014v)n(e)g(comm)n (utations)f(of)h FJ(?)p FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 80 83 bop 167 167 a FK(80)782 b Fz(CHAPTER)26 b(10.)64 b(SUMS)28 b(IN)f(NA)-6 b(TURAL)26 b(DEDUCTION)167 404 y Fy(10.6.2)94 b(Sum)27 b(t)m(yp)s(e)h(\(corresp)s(onding)d(to)i Fg(_)p Fy(\))167 535 y FK(F)-6 b(or)28 b FH(U)23 b FK(+)15 b FH(V)h FK(,)28 b(w)n(e)f(ha)n(v)n(e)h(the)g(follo)n(wing)e(sc)n (hemes:)251 659 y(1.)35 b(If)28 b FH(u)g FK(is)f(of)h(t)n(yp)r(e)g FH(U)7 b FK(,)28 b(then)f FH(\023)1083 634 y FD(1)1112 659 y FH(u)g FK(is)g(of)h(t)n(yp)r(e)g FH(U)23 b FK(+)15 b FH(V)h FK(.)251 794 y(2.)35 b(If)28 b FH(v)i FK(is)d(of)i(t)n(yp)r(e) e FH(V)16 b FK(,)28 b(then)f FH(\023)1081 768 y FD(2)1110 794 y FH(v)j FK(is)d(of)h(t)n(yp)r(e)g FH(U)23 b FK(+)15 b FH(V)h FK(.)251 928 y(3.)35 b(If)c FH(x)p FK(,)h FH(y)g FK(are)f(v)l(ariables)f(of)h(resp)r(ectiv)n(e)e(t)n(yp)r(es)i FH(R)q FK(,)h FH(S)t FK(,)g(and)g FH(u)p FK(,)f FH(v)s FK(,)h FH(t)e FK(are)h(of)g(resp)r(ectiv)n(e)339 1013 y(t)n(yp)r(es)d FH(U)7 b FK(,)28 b FH(U)7 b FK(,)28 b FH(R)17 b FK(+)e FH(S)t FK(,)29 b(then)1327 1163 y FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)22 b(t)339 1313 y FK(is)30 b(a)g(term)f(of)i(t)n(yp)r(e)f FH(U)7 b FK(.)43 b(F)-6 b(urthermore,)31 b(the)e(o)r(ccurrences)h(of)g FH(x)h FK(in)e FH(u)i FK(are)f(b)r(ound)h(b)n(y)339 1398 y(this)i (construction,)i(as)g(are)e(those)h(of)g FH(y)i FK(in)d FH(v)s FK(.)52 b(This)33 b(corresp)r(onds)i(to)f(the)f FM(p)l(attern)339 1483 y(matching)1001 1633 y Fq(match)20 b FH(t)f Fq(with)g(inl)10 b FH(x)20 b FJ(!)g FH(u)g FJ(j)f Fq(inr)13 b FH(y)22 b FJ(!)e FH(v)339 1782 y FK(in)27 b(a)i(functional)e(programming)h(language)h(lik)n(e)d Fr(CAML)p FK(.)270 1907 y(Ob)n(viously)i(the)f FH(\023)746 1881 y FD(1)774 1907 y FK(,)g FH(\023)844 1881 y FD(2)900 1907 y FK(and)h FH(\016)h FK(sc)n(hemes)e(in)n(terpret)e FJ(_)p FK(1)p FJ(I)5 b FK(,)28 b FJ(_)p FK(2)p FJ(I)34 b FK(and)28 b FJ(_E)6 b FK(.)35 b(The)27 b(standard)167 1992 y(con)n(v)n(ersions)h(are:)504 2117 y FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b FK(\()p FH(\023)859 2091 y FD(1)887 2117 y FH(r)r FK(\))f Fu( )g FH(u)p FK([)p FH(r)r(=x)p FK(])338 b FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b FK(\()p FH(\023)1933 2091 y FD(2)1961 2117 y FH(s)p FK(\))f Fu( )g FH(v)s FK([)p FH(s=y)s FK(])270 2271 y(The)28 b(comm)n(uting)f(con)n(v)n(ersions)h(are)662 2479 y FH(\031)704 2450 y FD(1)731 2479 y FK(\()p FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b(t)p FK(\))59 b Fu( )g FH(\016)21 b(x:)12 b FK(\()p FH(\031)1493 2450 y FD(1)1521 2479 y FH(u)p FK(\))19 b FH(y)s(:)12 b FK(\()p FH(\031)1743 2450 y FD(1)1770 2479 y FH(v)s FK(\))19 b FH(t)463 b(U)27 b FK(=)19 b FH(V)d FJ(\002)o FH(W)662 2564 y(\031)704 2535 y FD(2)731 2564 y FK(\()p FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b(t)p FK(\))59 b Fu( )g FH(\016)21 b(x:)12 b FK(\()p FH(\031)1493 2535 y FD(2)1521 2564 y FH(u)p FK(\))19 b FH(y)s(:)12 b FK(\()p FH(\031)1743 2535 y FD(2)1770 2564 y FH(v)s FK(\))19 b FH(t)463 b(U)27 b FK(=)19 b FH(V)d FJ(\002)o FH(W)668 2679 y FK(\()p FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b(t)p FK(\))12 b FH(w)61 b Fu( )e FH(\016)21 b(x:)12 b FK(\()p FH(u)g(w)r FK(\))20 b FH(y)s(:)12 b FK(\()p FH(v)h(w)r FK(\))20 b FH(t)460 b(U)27 b FK(=)19 b FH(V)d FJ(!)p FH(W)630 2793 y(")662 2804 y Fw(W)731 2793 y FK(\()p FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b(t)p FK(\))59 b Fu( )g FK(\()p FH(\016)21 b(x:)12 b FK(\()p FH(")1510 2804 y Fw(W)1579 2793 y FH(u)p FK(\))20 b FH(y)s(:)12 b FK(\()p FH(")1792 2804 y Fw(W)1860 2793 y FH(v)s FK(\))19 b FH(t)p FK(\))400 b FH(U)27 b FK(=)19 b Fq(Emp)361 2908 y FH(\016)j(x)453 2879 y Fv(0)470 2908 y FH(:)12 b(u)540 2879 y Fv(0)576 2908 y FH(y)613 2879 y Fv(0)628 2908 y FH(:)g(v)695 2879 y Fv(0)731 2908 y FK(\()p FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b(t)p FK(\))59 b Fu( )g FH(\016)21 b(x:)12 b FK(\()p FH(\016)22 b(x)1543 2879 y Fv(0)1560 2908 y FH(:)12 b(u)1630 2879 y Fv(0)1666 2908 y FH(y)1703 2879 y Fv(0)1719 2908 y FH(:)g(v)1786 2879 y Fv(0)1821 2908 y FH(u)p FK(\))20 b FH(y)s(:)12 b FK(\()p FH(\016)21 b(x)2093 2879 y Fv(0)2109 2908 y FH(:)12 b(u)2179 2879 y Fv(0)2215 2908 y FH(y)2252 2879 y Fv(0)2268 2908 y FH(:)g(v)2335 2879 y Fv(0)2371 2908 y FH(v)s FK(\))19 b FH(t)2310 2993 y(U)27 b FK(=)19 b FH(V)31 b FK(+)15 b FH(W)167 3116 y FK(whic)n(h)27 b(corresp)r(ond)h(exactly)g(to)g(the)f(rules)g(of)h(natural)g (deduction.)167 3315 y Fy(10.6.3)94 b(Additional)28 b(con)m(v)m (ersions)167 3446 y FK(Let)f(us)h(note)g(for)g(the)f(record)h(the)f (analogues)i(of)f FJ(h)p FH(\031)1589 3420 y FD(1)1617 3446 y FH(t;)12 b(\031)1715 3420 y FD(2)1743 3446 y FH(t)p FJ(i)20 b Fu( )g FH(t)27 b FK(and)i FH(\025x:)12 b(t)g(x)20 b Fu( )g FH(t)p FK(:)667 3600 y FH(")699 3611 y Fp(Emp)809 3600 y FH(t)g Fu( )g FH(t)500 b(\016)22 b(x:)12 b FK(\()p FH(\023)1643 3574 y FD(1)1671 3600 y FH(x)p FK(\))19 b FH(y)s(:)12 b FK(\()p FH(\023)1875 3574 y FD(2)1903 3600 y FH(y)s FK(\))18 b FH(t)i Fu( )g FH(t)167 3754 y FK(Clearly)32 b(the)h(terms)g(on)h(b)r(oth)h(sides)e(of)h(the)f(\\)p Fu( )p FK(")i(are)f(denotationally)f(equal.)53 b(Ho)n(w)n(ev)n(er)167 3840 y(the)28 b(direction)f(in)i(whic)n(h)f(the)g(con)n(v)n(ersion)h (should)h(w)n(ork)f(is)f(not)h(v)n(ery)g(clear:)36 b(the)29 b(opp)r(osite)167 3925 y(one)f(is)f(in)g(fact)h(m)n(uc)n(h)f(more)g (natural.)p eop PStoPSsaved restore %%Page: (84,85) 43 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 81 84 bop 167 874 a FF(Chapter)28 b(11)167 1168 y(System)f(F)167 1488 y FK(System)36 b FG(F)h FK([)p FG(?)p FK(])g(arises)f(as)h(an)g (extension)g(of)g(the)f(simple)f(t)n(yp)r(ed)i(calculus,)g(obtained)g (b)n(y)167 1573 y(adding)26 b(an)f(op)r(eration)g(of)h(abstraction)f (on)g(t)n(yp)r(es.)35 b(This)24 b(op)r(eration)i(is)e(extremely)e(p)r (o)n(w)n(erful)167 1659 y(and)29 b(in)e(particular)g(all)g(the)g(usual) h(data-t)n(yp)r(es)i(\(in)n(tegers,)d(lists,)f FM(etc.)p FK(\))35 b(are)28 b(de\014nable.)36 b(The)167 1744 y(system)23 b(w)n(as)i(in)n(tro)r(duced)e(in)h(the)f(con)n(text)h(of)g(pro)r(of)h (theory)f([)p FG(?)q FK(],)h(but)f(it)e(w)n(as)j(indep)r(enden)n(tly) 167 1829 y(disco)n(v)n(ered)i(in)g(computer)h(science)d([)p FG(?)q FK(].)270 1956 y(The)41 b(most)f(primitiv)n(e)d(v)n(ersion)k(of) g(the)f(system)g(is)g(set)g(out)h(here:)61 b(it)39 b(is)h(based)h(on) 167 2041 y(implication)25 b(and)k(univ)n(ersal)e(quan)n(ti\014cation.) 37 b(W)-6 b(e)28 b(shall)f(con)n(ten)n(t)h(ourselv)n(es)g(with)f (de\014ning)167 2126 y(the)g(system)h(and)g(giving)g(some)f (illustrations)f(of)i(its)f(expressiv)n(e)g(p)r(o)n(w)n(er.)167 2363 y FE(11.1)114 b(The)28 b(calculus)167 2518 y FM(T)-5 b(yp)l(es)49 b FK(are)f(de\014ned)g(starting)g(from)f FM(typ)l(e)i(variables)e FH(X)r(;)12 b(Y)t(;)g(Z)q(;)g(:)g(:)g(:)48 b FK(b)n(y)h(means)e(of)i(t)n(w)n(o)167 2603 y(op)r(erations:)251 2766 y(1.)35 b(if)27 b FH(U)35 b FK(and)29 b FH(V)43 b FK(are)27 b(t)n(yp)r(es,)i(then)e FH(U)7 b FJ(!)q FH(V)43 b FK(is)27 b(a)h(t)n(yp)r(e.)251 2910 y(2.)35 b(if)27 b FH(V)43 b FK(is)27 b(a)h(t)n(yp)r(e,)g(and)h FH(X)k FK(a)28 b(t)n(yp)r(e)g(v)l(ariable,)g(then)f(\005)p FH(X)r(:)12 b(V)43 b FK(is)27 b(a)h(t)n(yp)r(e.)167 3073 y(There)f(are)g(\014v)n(e) h(sc)n(hemes)f(for)h(forming)g FM(terms)6 b FK(:)251 3236 y(1.)35 b FM(variables:)k FH(x)700 3210 y Fw(T)739 3236 y FH(;)12 b(y)807 3210 y Fw(T)845 3236 y FH(;)g(z)911 3210 y Fw(T)950 3236 y FH(;)g(:)g(:)g(:)28 b FK(of)g(t)n(yp)r(e)g FH(T)10 b FK(,)251 3380 y(2.)35 b FM(applic)l(ation:)41 b FH(tu)27 b FK(of)h(t)n(yp)r(e)g FH(V)16 b FK(,)27 b(where)g FH(t)h FK(is)f(of)h(t)n(yp)r(e)g FH(U)7 b FJ(!)p FH(V)43 b FK(and)29 b FH(u)f FK(is)f(of)h(t)n(yp)r(e)g FH(U)7 b FK(,)251 3525 y(3.)35 b FH(\025)p FM(-abstr)l(action:)k FH(\025x)871 3499 y Fw(U)914 3525 y FH(:)12 b(v)29 b FK(of)d(t)n(yp)r(e)h FH(U)7 b FJ(!)q FH(V)15 b FK(,)27 b(where)e FH(x)1714 3499 y Fw(U)1783 3525 y FK(is)g(a)i(v)l(ariable)f (of)h(t)n(yp)r(e)f FH(U)34 b FK(and)27 b FH(v)339 3610 y FK(is)g(of)i(t)n(yp)r(e)e FH(V)16 b FK(,)251 3754 y(4.)35 b FM(universal)g(abstr)l(action:)57 b FK(if)34 b FH(v)39 b FK(is)c(a)h(term)f(of)h(t)n(yp)r(e)g FH(V)16 b FK(,)38 b(then)d(w)n(e)h(can)g(form)g(\003)p FH(X)r(:)12 b(v)339 3840 y FK(of)33 b(t)n(yp)r(e)f(\005)p FH(X)r(:)12 b(V)j FK(,)33 b(so)g(long)g(as)f(the)g(v)l(ariable)g FH(X)37 b FK(is)32 b(not)g(free)g(in)f(the)h(t)n(yp)r(e)g(of)g(a)h(free)339 3925 y(v)l(ariable)28 b(of)g FH(v)s FK(.)1385 4101 y(81)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 82 85 bop 167 167 a FK(82)1550 b Fz(CHAPTER)26 b(11.)64 b(SYSTEM)28 b(F)251 404 y FK(5.)35 b FM(universal)g(applic)l(ation)41 b FK(\(sometimes)33 b(called)h FM(extr)l(action)p FK(\):)50 b(if)35 b FH(t)g FK(is)f(a)i(term)e(of)i(t)n(yp)r(e)339 490 y(\005)p FH(X)r(:)12 b(V)43 b FK(and)29 b FH(U)35 b FK(is)27 b(a)h(t)n(yp)r(e,)g(then)f FH(t)12 b(U)35 b FK(is)27 b(a)h(term)e(of)i(t)n(yp)r(e)g FH(V)15 b FK([)p FH(U)t(=X)6 b FK(].)270 663 y(As)27 b(w)n(ell)d(as)j(the)f(usual)h FM(c)l(onversions)f FK(for)h(application/)p FH(\025)p FK(-abstraction,)g(there)e(is)h(one)h(for)167 748 y(the)g(other)h(pair) f(of)i(sc)n(hemes:)1094 921 y(\(\003)p FH(X)r(:)12 b(v)s FK(\))g FH(U)25 b Fu( )20 b FH(v)s FK([)p FH(U)t(=X)6 b FK(])167 1135 y FG(Con)n(v)n(en)n(tion)53 b FK(W)-6 b(e)27 b(shall)g(write)f FH(U)1132 1146 y FD(1)1160 1135 y FJ(!)p FH(U)1277 1146 y FD(2)1305 1135 y FJ(!)12 b FH(:)g(:)g(:)g(U)1527 1146 y Fw(n)1560 1135 y FJ(!)p FH(V)k FK(,)28 b(without)f(paren)n(theses,)h(for)1005 1308 y FH(U)1052 1319 y FD(1)1080 1308 y FJ(!)q FK(\()p FH(U)1225 1319 y FD(2)1252 1308 y FJ(!)12 b FH(:)g(:)g(:)g FK(\()p FH(U)1501 1319 y Fw(n)1534 1308 y FJ(!)p FH(V)k FK(\))c FH(:)g(:)g(:)o FK(\))167 1482 y(and)29 b(similarly)-6 b(,)25 b FH(f)19 b(u)698 1493 y FD(1)738 1482 y FH(u)777 1493 y FD(2)817 1482 y FH(:)12 b(:)g(:)f(u)948 1493 y Fw(n)1009 1482 y FK(for)28 b(\()p FH(:)12 b(:)g(:)g FK(\(\()p FH(f)19 b(u)1385 1493 y FD(1)1413 1482 y FK(\))12 b FH(u)1491 1493 y FD(2)1519 1482 y FK(\))g FH(:)g(:)g(:)o FK(\))g FH(u)1716 1493 y Fw(n)1749 1482 y FK(.)167 1717 y FE(11.2)114 b(Commen)m(ts)167 1872 y FK(First)32 b(let)g(us)h(illustrate)e(the)i (restriction)e(on)i(v)l(ariables)g(in)g(univ)n(ersal)f(abstraction:)47 b(if)33 b(w)n(e)167 1957 y(could)g(form)g(\003)p FH(X)r(:)12 b(x)711 1931 y Fw(X)758 1957 y FK(,)35 b(what)e(w)n(ould)g(then)g(b)r (e)g(the)g(t)n(yp)r(e)g(of)h(the)e(free)g(v)l(ariable)h FH(x)g FK(in)g(this)167 2042 y(expression?)55 b(On)34 b(the)f(other)i(hand,)i(w)n(e)d FM(c)l(an)39 b FK(form)34 b(\003)p FH(X)r(:)12 b(\025x)1860 2016 y Fw(X)1908 2042 y FH(:)g(x)1978 2016 y Fw(X)2060 2042 y FK(of)34 b(t)n(yp)r(e)g(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)g FK(,)167 2127 y(whic)n(h)27 b(is)g(the)g(iden)n(tit)n(y)g(of)h(an)n(y)h(t)n(yp)r(e.)270 2300 y(The)e(na)-8 b(\177)-27 b(\020v)n(e)29 b(in)n(terpretation)d(of)i (the)f(\\\005")h(t)n(yp)r(e)f(is)g(that)g(an)h(ob)t(ject)f(of)h(t)n(yp) r(e)g(\005)p FH(X)r(:)12 b(V)42 b FK(is)27 b(a)167 2385 y(function)h(whic)n(h,)f(to)h(ev)n(ery)f(t)n(yp)r(e)h FH(U)7 b FK(,)28 b(asso)r(ciates)g(an)g(ob)t(ject)g(of)g(t)n(yp)r(e)g FH(V)15 b FK([)p FH(U)t(=X)6 b FK(].)270 2511 y(This)28 b(in)n(terpretation)f(runs)i(up)g(against)g(a)g(problem)e(of)i FM(size)5 b FK(:)37 b(in)28 b(order)g(to)h(understand)167 2597 y(\005)p FH(X)r(:)12 b(V)j FK(,)42 b(it)37 b(is)h(necessary)h(to)g (kno)n(w)h FM(al)t(l)45 b FK(the)38 b FH(V)16 b FK([)p FH(U)t(=X)6 b FK(].)68 b(But)39 b(among)h(all)d(the)i FH(V)15 b FK([)p FH(U)t(=X)6 b FK(])167 2682 y(there)38 b(are)h(some)f(whic)n(h)g(are)h(\(in)f(general\))g(more)g(complex)g (than)h(the)g(t)n(yp)r(e)g(whic)n(h)f(w)n(e)167 2767 y(seek)33 b(to)h(mo)r(del,)g(for)g(example)f FH(V)16 b FK([\005)p FH(X)r(:)c(V)j(=X)6 b FK(].)54 b(So)34 b(there)f(is)g(a)h (circularit)n(y)d(in)i(the)g(na)-8 b(\177)-27 b(\020v)n(e)167 2852 y(in)n(terpretation,)28 b(and)h(one)h(can)f(exp)r(ect)f(the)g(w)n (orst)h(to)g(happ)r(en.)40 b(In)28 b(fact)h(it)f(all)f(w)n(orks)i(out,) 167 2937 y(but)i(the)f(system)g(is)g(extremely)e(sensitiv)n(e)i(to)g (mo)r(di\014cations)g(whic)n(h)g(are)h(not)g(of)g(a)g(logical)167 3022 y(nature.)270 3148 y(W)-6 b(e)30 b(can)h(nev)n(ertheless)d(mak)n (e)i(\(a)h(bit\))e(more)g(precise)f(the)i(idea)g(of)g(a)h(function)f (de\014ned)167 3233 y(on)39 b FM(al)t(l)44 b FK(t)n(yp)r(es:)56 b(in)37 b(some)h(sense,)i(a)e(function)g(of)h(univ)n(ersal)e(t)n(yp)r (e)h(m)n(ust)g(b)r(e)f(\\uniform",)167 3319 y FM(i.e.)32 b FK(do)h(the)e(same)h(thing)g(on)h(all)d(t)n(yp)r(es.)49 b FH(\025)p FK(-abstraction)32 b(accommo)r(dates)g(a)h(certain)d(dose) 167 3404 y(of)37 b(non-uniformit)n(y)-6 b(,)39 b(for)e(example)e(w)n(e) h(can)h(de\014ne)g(a)g(function)f(b)n(y)h(cases)g(\(if)e(.)11 b(.)g(.)75 b(then)167 3489 y(.)11 b(.)g(.)76 b(else\).)62 b(Suc)n(h)38 b(a)f(kind)h(of)f(de\014nition)g(is)f(inconceiv)l(able)g (for)h(univ)n(ersal)f(abstraction:)167 3574 y(the)f(v)l(alues)h(tak)n (en)h(b)n(y)f(an)g(ob)t(ject)g(of)g(univ)n(ersal)f(t)n(yp)r(e)h(on)g (di\013eren)n(ts)f(t)n(yp)r(es)h(ha)n(v)n(e)g(to)g(b)r(e)167 3659 y(essen)n(tially)h(\\the)h(same")h(\(see)f FG(??)q FK(\).)68 b(It)38 b(still)e(remains)h(to)i(mak)n(e)g(this)f(v)l(ague)h (in)n(tuition)167 3744 y(precise)26 b(b)n(y)i(appropriate)h(seman)n (tic)d(considerations.)p eop PStoPSsaved restore %%Page: (86,87) 44 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 83 86 bop 167 167 a Fz(11.3.)65 b(REPRESENT)-6 b(A)g(TION)25 b(OF)j(SIMPLE)g(TYPES)903 b FK(83)167 404 y FE(11.3)114 b(Represen)m(tation)29 b(of)f(simple)e(t)m(yp)s(es)167 564 y FK(A)k(large)g(part)h(of)g(the)f(in)n(terest)f(in)h FG(F)h FK(is)f(in)g(the)g(p)r(ossibilit)n(y)f(of)i(de\014ning)g (commonly)f(used)167 649 y(t)n(yp)r(es)e(in)f(it;)g(w)n(e)g(shall)g (dev)n(ote)h(the)f(rest)g(of)h(the)g(c)n(hapter)g(to)f(this.)167 864 y Fy(11.3.1)94 b(Bo)s(oleans)167 999 y FK(W)-6 b(e)27 b(de\014ne)h Fq(Bo)r(ol)g FK(\(not)g(the)f(one)h(of)g(system)g FG(T)p FK(\))f(as)h(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)g FJ(!)p FH(X)34 b FK(with)567 1208 y Fq(T)633 1169 y FD(def)641 1208 y FK(=)27 b(\003)p FH(X)r(:)12 b(\025x)939 1183 y Fw(X)986 1208 y FH(:)g(\025y)1094 1183 y Fw(X)1141 1208 y FH(:)g(x)400 b Fq(F)1670 1169 y FD(def)1677 1208 y FK(=)27 b(\003)p FH(X)r(:)12 b(\025x)1975 1183 y Fw(X)2023 1208 y FH(:)g(\025y)2131 1183 y Fw(X)2178 1208 y FH(:)g(y)167 1400 y FK(and)29 b(if)e FH(u;)12 b(v)s(;)g(t)27 b FK(are)g(of)i(resp)r (ectiv)n(e)d(t)n(yp)r(es)i FH(U;)12 b(U;)g Fq(Bo)r(ol)26 b FK(w)n(e)h(de\014ne)h Fq(D)12 b FH(u)g(v)i(t)27 b FK(of)h(t)n(yp)r(e) g FH(U)35 b FK(b)n(y)1165 1605 y Fq(D)12 b FH(u)g(v)i(t)1369 1566 y FD(def)1377 1605 y FK(=)26 b FH(t)12 b(U)19 b(u)12 b(v)270 1844 y FK(Let)28 b(us)g(calculate)e Fq(D)12 b FH(u)g(v)i Fq(T)27 b FK(and)i Fq(D)12 b FH(u)g(v)i Fq(F)p FK(:)854 2063 y Fq(D)e FH(u)g(v)i Fq(T)67 b FK(=)g(\(\003)p FH(X)r(:)12 b(\025x)1493 2037 y Fw(X)1541 2063 y FH(:)g(\025y)1649 2037 y Fw(X)1696 2063 y FH(:)g(x)p FK(\))g FH(U)18 b(u)12 b(v)1120 2148 y Fu( )59 b FK(\()p FH(\025x)1355 2122 y Fw(U)1397 2148 y FH(:)12 b(\025y)1505 2122 y Fw(U)1546 2148 y FH(:)g(x)p FK(\))g FH(u)g(v)1120 2233 y Fu( )59 b FK(\()p FH(\025y)1353 2207 y Fw(U)1394 2233 y FH(:)12 b(u)p FK(\))g FH(v)1120 2318 y Fu( )59 b FH(u)862 2488 y Fq(D)12 b FH(u)g(v)i Fq(F)67 b FK(=)g(\(\003)p FH(X)r(:)12 b(\025x)1493 2463 y Fw(X)1541 2488 y FH(:)g(\025y)1649 2463 y Fw(X)1696 2488 y FH(:)g(y)s FK(\))g FH(U)17 b(u)12 b(v)1120 2573 y Fu( )59 b FK(\()p FH(\025x)1355 2548 y Fw(U)1397 2573 y FH(:)12 b(\025y)1505 2548 y Fw(U)1546 2573 y FH(:)g(y)s FK(\))g FH(u)g(v)1120 2659 y Fu( )59 b FK(\()p FH(\025y)1353 2633 y Fw(U)1394 2659 y FH(:)12 b(y)1462 2633 y Fw(U)1503 2659 y FK(\))g FH(v)1120 2744 y Fu( )59 b FH(v)167 3047 y Fy(11.3.2)94 b(Pro)s(duct)27 b(of)g(t)m(yp)s(es)167 3198 y FK(W)-6 b(e)27 b(de\014ne)h FH(U)7 b FJ(\002)p FH(V)678 3159 y FD(def)686 3198 y FK(=)27 b(\005)p FH(X)r(:)12 b FK(\()p FH(U)7 b FJ(!)p FH(V)15 b FJ(!)q FH(X)6 b FK(\))p FJ(!)p FH(X)33 b FK(with)965 3407 y FJ(h)p FH(u;)12 b(v)s FJ(i)1146 3368 y FD(def)1153 3407 y FK(=)27 b(\003)p FH(X)r(:)12 b(\025x)1451 3382 y Fw(U)5 b Fv(!)p Fw(V)11 b Fv(!)p Fw(X)1678 3407 y FH(:)h(x)g(u)g(v) 270 3599 y FK(The)28 b(pro)t(jections)f(are)h(de\014ned)g(as)g(follo)n (ws:)527 3804 y FH(\031)569 3778 y FD(1)596 3804 y FH(t)641 3764 y FD(def)648 3804 y FK(=)f FH(t)12 b(U)19 b FK(\()p FH(\025x)938 3778 y Fw(U)980 3804 y FH(:)12 b(\025y)1088 3778 y Fw(V)1130 3804 y FH(:)g(x)p FK(\))359 b FH(\031)1628 3778 y FD(2)1656 3804 y FH(t)1700 3764 y FD(def)1708 3804 y FK(=)27 b FH(t)12 b(V)27 b FK(\()p FH(\025x)1999 3778 y Fw(U)2041 3804 y FH(:)12 b(\025y)2149 3778 y Fw(V)2191 3804 y FH(:)g(y)s FK(\))p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 84 87 bop 167 167 a FK(84)1550 b Fz(CHAPTER)26 b(11.)64 b(SYSTEM)28 b(F)270 404 y FK(Let)g(us)g(calculate)e FH(\031)826 379 y FD(1)853 404 y FJ(h)p FH(u;)12 b(v)s FJ(i)29 b FK(and)f FH(\031)1222 379 y FD(2)1250 404 y FJ(h)p FH(u;)12 b(v)s FJ(i)p FK(:)607 567 y FH(\031)649 542 y FD(1)676 567 y FJ(h)p FH(u;)g(v)s FJ(i)68 b FK(=)f(\(\003)p FH(X)r(:)12 b(\025x)1269 542 y Fw(U)5 b Fv(!)o Fw(V)12 b Fv(!)o Fw(X)1495 567 y FH(:)g(x)g(u)g(v)s FK(\))g FH(U)18 b FK(\()p FH(\025x)1874 542 y Fw(U)1916 567 y FH(:)12 b(\025y)2024 542 y Fw(V)2067 567 y FH(:)g(x)p FK(\))896 653 y Fu( )59 b FK(\()p FH(\025x)1131 627 y Fw(U)5 b Fv(!)p Fw(V)11 b Fv(!)p Fw(U)1351 653 y FH(:)h(x)g(u)g(v)s FK(\))g(\()p FH(\025x)1665 627 y Fw(U)1707 653 y FH(:)g(\025y)1815 627 y Fw(V)1857 653 y FH(:)g(x)p FK(\))896 738 y Fu( )59 b FK(\()p FH(\025x)1131 712 y Fw(U)1173 738 y FH(:)12 b(\025y)1281 712 y Fw(V)1323 738 y FH(:)g(x)p FK(\))g FH(u)g(v)896 823 y Fu( )59 b FK(\()p FH(\025y)1129 797 y Fw(V)1171 823 y FH(:)12 b(u)p FK(\))g FH(v)896 908 y Fu( )59 b FH(u)607 1078 y(\031)649 1053 y FD(2)676 1078 y FJ(h)p FH(u;)12 b(v)s FJ(i)68 b FK(=)f(\(\003)p FH(X)r(:)12 b(\025x)1269 1053 y Fw(U)5 b Fv(!)o Fw(V)12 b Fv(!)o Fw(X)1495 1078 y FH(:)g(x)g(u)g(v)s FK(\))g FH(V)27 b FK(\()p FH(\025x)1876 1053 y Fw(U)1918 1078 y FH(:)12 b(\025y)2026 1053 y Fw(V)2068 1078 y FH(:)g(y)2136 1053 y Fw(V)2178 1078 y FK(\))896 1163 y Fu( )59 b FK(\()p FH(\025x)1131 1138 y Fw(U)5 b Fv(!)p Fw(V)11 b Fv(!)p Fw(V)1353 1163 y FH(:)h(x)g(u)g(v)s FK(\))g(\()p FH(\025x)1667 1138 y Fw(U)1708 1163 y FH(:)g(\025y)1816 1138 y Fw(V)1858 1163 y FH(:)g(y)s FK(\))896 1248 y Fu( )59 b FK(\()p FH(\025x)1131 1223 y Fw(U)1173 1248 y FH(:)12 b(\025y)1281 1223 y Fw(V)1323 1248 y FH(:)g(y)s FK(\))g FH(u)g(v)896 1333 y Fu( )59 b FK(\()p FH(\025y)1129 1308 y Fw(V)1171 1333 y FH(:)12 b(y)s FK(\))g FH(v)896 1419 y Fu( )59 b FH(v)270 1624 y FK(Note)39 b(that)g FJ(h)p FH(\031)687 1599 y FD(1)715 1624 y FH(t;)12 b(\031)813 1599 y FD(2)840 1624 y FH(t)p FJ(i)28 b Fu( )g FH(t)38 b FK(do)r(es)h(not)h(hold,)i(ev) n(en)c(if)g(w)n(e)g(allo)n(w)g FH(\025x)2223 1599 y Fw(U)2265 1624 y FH(:)12 b(t)g(x)28 b Fu( )f FH(t)39 b FK(and)167 1710 y(\003)p FH(X)r(:)12 b(t)g(X)25 b Fu( )20 b FH(t)p FK(.)167 1912 y Fy(11.3.3)94 b(Empt)m(y)28 b(t)m(yp)s(e)167 2059 y FK(W)-6 b(e)27 b(can)h(de\014ne)g Fq(Emp)776 2019 y FD(def)783 2059 y FK(=)f(\005)p FH(X)r(:)12 b(X)33 b FK(with)27 b FH(")1290 2070 y Fw(U)1344 2059 y FH(t)1388 2019 y FD(def)1396 2059 y FK(=)f FH(t)12 b(U)7 b FK(.)167 2261 y Fy(11.3.4)94 b(Sum)27 b(t)m(yp)s(e)167 2408 y FK(If)h FH(U;)12 b(V)42 b FK(are)28 b(t)n(yp)r(es,)g(w)n(e)f(can)h (de\014ne)g FH(U)23 b FK(+)15 b FH(V)1382 2368 y FD(def)1390 2408 y FK(=)26 b(\005)p FH(X)r(:)12 b FK(\()p FH(U)7 b FJ(!)p FH(X)f FK(\))p FJ(!)p FK(\()p FH(V)16 b FJ(!)p FH(X)6 b FK(\))p FJ(!)p FH(X)g FK(.)270 2530 y(If)28 b FH(u;)12 b(v)31 b FK(are)c(of)h(t)n(yp)r(es)g FH(U;)12 b(V)43 b FK(w)n(e)27 b(de\014ne)h FH(\023)1362 2504 y FD(1)1390 2530 y FH(u)g FK(and)h FH(\023)1620 2504 y FD(2)1648 2530 y FH(v)h FK(of)e(t)n(yp)r(e)g FH(U)23 b FK(+)15 b FH(V)43 b FK(b)n(y)383 2708 y FH(\023)407 2683 y FD(1)436 2708 y FH(u)495 2669 y FD(def)502 2708 y FK(=)27 b(\003)p FH(X)r(:)12 b(\025x)800 2683 y Fw(U)5 b Fv(!)p Fw(X)936 2708 y FH(:)12 b(\025y)1044 2683 y Fw(V)f Fv(!)p Fw(X)1181 2708 y FH(:)h(x)g(u)217 b(\023)1543 2683 y FD(2)1571 2708 y FH(v)1627 2669 y FD(def)1634 2708 y FK(=)27 b(\003)p FH(X)r(:)12 b(\025x)1932 2683 y Fw(U)5 b Fv(!)p Fw(X)2068 2708 y FH(:)12 b(\025y)2176 2683 y Fw(V)f Fv(!)p Fw(X)2313 2708 y FH(:)h(y)i(v)270 2873 y FK(If)26 b FH(u;)12 b(v)s(;)g(t)26 b FK(are)g(of)g(resp)r(ectiv) n(e)f(t)n(yp)r(es)h FH(U;)12 b(U;)g(R)h FK(+)g FH(S)t FK(,)27 b(w)n(e)e(de\014ne)i FH(\016)21 b(x:)12 b(u)20 b(y)s(:)12 b(v)22 b(t)k FK(of)g(t)n(yp)r(e)g FH(U)33 b FK(b)n(y)888 3052 y FH(\016)21 b(x:)12 b(u)20 b(y)s(:)12 b(v)22 b(t)1236 3013 y FD(def)1244 3052 y FK(=)27 b FH(t)12 b(U)18 b FK(\()p FH(\025x)1533 3027 y Fw(U)1575 3052 y FH(:)12 b(u)p FK(\))g(\()p FH(\025y)1788 3027 y Fw(V)1830 3052 y FH(:)g(v)s FK(\))270 3254 y(Let)28 b(us)g(calculate)e FH(\016)21 b(x:)12 b(u)20 b(y)s(:)12 b(v)22 b FK(\()p FH(\023)1139 3229 y FD(1)1167 3254 y FH(r)r FK(\):)428 3417 y FH(\016)g(x:)12 b(u)20 b(y)s(:)12 b(v)21 b FK(\()p FH(\023)783 3392 y FD(1)811 3417 y FH(r)r FK(\))67 b(=)g(\(\003)p FH(X)r(:)12 b(\025x)1303 3392 y Fw(R)p Fv(!)o Fw(X)1438 3417 y FH(:)g(\025y)1546 3392 y Fw(S)s Fv(!)o Fw(X)1676 3417 y FH(:)g(x)g(r)r FK(\))g FH(U)18 b FK(\()p FH(\025x)2001 3392 y Fw(R)2042 3417 y FH(:)12 b(u)p FK(\))g(\()p FH(\025y)2255 3392 y Fw(S)2290 3417 y FH(:)g(v)s FK(\))930 3502 y Fu( )59 b FK(\()p FH(\025x)1165 3477 y Fw(R)p Fv(!)p Fw(U)1294 3502 y FH(:)12 b(\025y)1402 3477 y Fw(S)s Fv(!)p Fw(U)1526 3502 y FH(:)g(x)g(r)r FK(\))g(\()p FH(\025x)1786 3477 y Fw(R)1827 3502 y FH(:)g(u)p FK(\))g(\()p FH(\025y)2040 3477 y Fw(S)2075 3502 y FH(:)g(v)s FK(\))930 3587 y Fu( )59 b FK(\()p FH(\025y)1163 3562 y Fw(S)s Fv(!)o Fw(U)1287 3587 y FH(:)12 b FK(\()p FH(\025x)1424 3562 y Fw(R)1464 3587 y FH(:)g(u)p FK(\))g FH(r)r FK(\))g(\()p FH(\025y)1749 3562 y Fw(S)1784 3587 y FH(:)g(v)s FK(\))930 3672 y Fu( )59 b FK(\()p FH(\025x)1165 3647 y Fw(R)1206 3672 y FH(:)12 b(u)p FK(\))g FH(r)930 3758 y Fu( )59 b FH(u)p FK([)p FH(r)r(=x)p FK(])167 3925 y(and)29 b(similarly)24 b FH(\016)e(x:)12 b(u)20 b(y)s(:)12 b(v)21 b FK(\()p FH(\023)947 3899 y FD(2)976 3925 y FH(s)p FK(\))e Fu( )h FH(v)s FK([)p FH(s=y)s FK(].)p eop PStoPSsaved restore %%Page: (88,89) 45 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 85 88 bop 167 167 a Fz(11.4.)65 b(REPRESENT)-6 b(A)g(TION)25 b(OF)j(A)f(FREE)g(STR)n(UCTURE)693 b FK(85)270 404 y(On)44 b(the)f(other)g(hand,)49 b(the)43 b(translation)g(do)r(es)h(not)g(in)n (terpret)d(the)i(comm)n(uting)g(or)167 490 y(secondary)31 b(con)n(v)n(ersions)g(asso)r(ciated)g(with)e(the)h(sum)g(t)n(yp)r(e;)h (the)f(same)g(remark)g(applies)f(to)167 575 y(the)d(t)n(yp)r(e)h Fq(Emp)g FK(and)g(also)g(to)g(the)g(t)n(yp)r(e)f Fq(Bo)r(ol)h FK(whic)n(h)f(has)h(a)h(sum)e(structure)g(and)i(for)f(whic)n(h)167 660 y(it)g(is)g(p)r(ossible)g(to)g(write)f(comm)n(utation)h(rules.)167 862 y Fy(11.3.5)94 b(Existen)m(tial)30 b(t)m(yp)s(e)167 993 y FK(If)e FH(V)43 b FK(is)27 b(a)h(t)n(yp)r(e)f(and)i FH(X)34 b FK(a)28 b(t)n(yp)r(e)f(v)l(ariable,)h(then)f(one)h(can)h (de\014ne)913 1172 y(\006)p FH(X)r(:)12 b(V)1128 1132 y FD(def)1135 1172 y FK(=)27 b(\005)p FH(Y)t(:)12 b FK(\(\005)p FH(X)r(:)g FK(\()p FH(V)i FJ(!)q FH(Y)h FK(\)\))p FJ(!)p FH(Y)270 1337 y FK(If)34 b FH(U)41 b FK(is)33 b(a)h(t)n(yp)r(e)f(and)i FH(v)i FK(a)d(term)e(of)i(t)n(yp)r(e)g FH(V)15 b FK([)p FH(U)t(=X)6 b FK(],)36 b(then)d(w)n(e)g(de\014ne)h FJ(h)p FH(U;)12 b(v)s FJ(i)34 b FK(of)g(t)n(yp)r(e)167 1422 y(\006)p FH(X)r(:)12 b(V)43 b FK(b)n(y)958 1601 y FJ(h)p FH(U;)12 b(v)s FJ(i)1145 1561 y FD(def)1153 1601 y FK(=)27 b(\003)p FH(Y)t(:)12 b(\025x)1436 1575 y FD(\005)p Fw(X)q(:)c(V)j Fv(!)p Fw(Y)1670 1601 y FH(:)h(x)g(U)19 b(v)270 1804 y FK(Corresp)r(onding)38 b(to)e(the)g(in)n(tro)r(duction)g(of)g(\006,)i (there)e(is)f(an)i(elimination:)50 b(if)35 b FH(w)j FK(is)e(of)167 1889 y(t)n(yp)r(e)c FH(W)41 b FK(and)32 b FH(t)f FK(of)h(t)n(yp)r(e)g (\006)p FH(X)r(:)12 b(V)j FK(,)32 b FH(X)37 b FK(is)31 b(a)h(t)n(yp)r(e)f(v)l(ariable,)h FH(x)g FK(a)g(v)l(ariable)f(of)h(t)n (yp)r(e)f FH(V)47 b FK(and)167 1974 y(the)28 b(only)g(free)f(o)r (ccurrences)g(of)h FH(X)34 b FK(in)27 b(the)h(t)n(yp)r(e)g(of)h(a)f (free)f(v)l(ariable)h(of)g FH(w)i FK(are)e(in)f(the)h(t)n(yp)r(e)167 2059 y(of)j FH(x)p FK(,)i(one)e(can)g(form)g FJ(r)p FH(X)r(:)12 b(x:)g(w)24 b(t)31 b FK(of)g(t)n(yp)r(e)g FH(W)41 b FK(\(the)30 b(o)r(ccurrences)g(of)i FH(X)37 b FK(and)32 b FH(x)f FK(in)f FH(w)j FK(are)167 2144 y(b)r(ound)c(b)n(y)g(this)e (construction\):)935 2327 y FJ(r)p FH(X)r(:)12 b(x:)g(w)22 b(t)1269 2287 y FD(def)1277 2327 y FK(=)k FH(t)12 b(W)21 b FK(\(\003)p FH(X)r(:)12 b(\025x)1724 2301 y Fw(V)1768 2327 y FH(:)g(w)r FK(\))270 2529 y(Let)28 b(us)g(calculate)e(\()p FJ(r)p FH(X)r(:)12 b(x:)g(w)21 b FK(\))12 b FJ(h)p FH(U;)g(v)s FJ(i)p FK(:)466 2693 y(\()p FJ(r)p FH(X)r(:)g(x:)g(w)22 b FK(\))12 b FJ(h)p FH(U;)g(v)s FJ(i)66 b FK(=)h(\(\003)p FH(Y)t(:)12 b(\025x)1406 2667 y FD(\005)p Fw(X)q(:)d(V)i Fv(!)p Fw(Y)1640 2693 y FH(:)h(x)g(U)19 b(v)s FK(\))12 b FH(W)21 b FK(\(\003)p FH(X)r(:)12 b(\025x)2193 2667 y Fw(V)2236 2693 y FH(:)g(w)r FK(\))1048 2778 y Fu( )59 b FK(\()p FH(\025x)1283 2752 y FD(\005)p Fw(X)q(:)9 b(V)i Fv(!)p Fw(W)1532 2778 y FH(:)h(x)g(U)19 b(v)s FK(\))12 b(\(\003)p FH(X)r(:)g(\025x)1999 2752 y Fw(V)2041 2778 y FH(:)g(w)r FK(\))1048 2863 y Fu( )59 b FK(\(\003)p FH(X)r(:)12 b(\025x)1421 2837 y Fw(V)1464 2863 y FH(:)g(w)r FK(\))g FH(U)19 b(v)1048 2949 y Fu( )59 b FK(\()p FH(\025x)1283 2924 y Fw(V)12 b FD([)p Fw(U)r(=X)t FD(])1460 2949 y FH(:)g(w)r FK([)p FH(U)t(=X)6 b FK(]\))12 b FH(v)1048 3036 y Fu( )59 b FH(w)r FK([)p FH(U)t(=X)6 b FK(][)p FH(v)s(=x)1542 3010 y Fw(V)12 b FD([)p Fw(U)r(=X)t FD(])1719 3036 y FK(])167 3196 y(This)29 b(giv)n(es)g(a)g(con)n(v)n(ersion)h (rule)e(whic)n(h)g(w)n(as)i(for)g(example)e(in)g(the)h(original)f(v)n (ersion)i(of)f(the)167 3281 y(system.)167 3514 y FE(11.4)114 b(Represen)m(tation)29 b(of)f(a)g(free)f(structure)167 3669 y FK(W)-6 b(e)38 b(ha)n(v)n(e)g(translated)g(some)g(simple)d(t)n (yp)r(es;)44 b(w)n(e)37 b(shall)g(con)n(tin)n(ue)h(with)f(some)g (inductiv)n(e)167 3754 y(t)n(yp)r(es:)i(in)n(tegers,)28 b(trees,)h(lists,)f FM(etc.)39 b FK(Undoubtedly)30 b(the)f(p)r (ossibilities)d(are)j(endless)f(and)j(w)n(e)167 3840 y(shall)c(giv)n(e)f(the)h(general)g(solution)g(to)h(this)e(kind)i(of)g (question)f(b)r(efore)g(sp)r(ecialising)e(to)j(more)167 3925 y(concrete)f(situations.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 86 89 bop 167 167 a FK(86)1550 b Fz(CHAPTER)26 b(11.)64 b(SYSTEM)28 b(F)167 404 y Fy(11.4.1)94 b(F)-8 b(ree)28 b(structure)167 540 y FK(Let)f(\002)g(b)r(e)h(a)g(collection)d(of)j (formal)f(expressions)h(generated)g(b)n(y)270 715 y FJ(\017)34 b FK(some)28 b(atoms)g FH(c)755 726 y FD(1)782 715 y FH(;)12 b(:)g(:)g(:)g(;)g(c)967 726 y Fw(k)1024 715 y FK(to)28 b(start)g(o\013)g(with;)270 868 y FJ(\017)34 b FK(some)g(functions)f(whic)n(h)g(allo)n(w)f(us)i(to)g(build)e(new)h (\002-terms)f(from)i(old.)52 b(The)33 b(most)339 953 y(simple)24 b(case)h(is)f(that)i(of)g(unary)g(functions)g(from)f(\002)g (to)g(\002,)h(but)f(w)n(e)g(can)h(also)f(imagine)339 1038 y(functions)j(of)g(sev)n(eral)f(argumen)n(ts)h(from)f(\002)p FH(;)12 b FK(\002)p FH(;)g(:)g(:)g(:)f(;)h FK(\002)27 b(to)g(\002.)35 b(These)27 b(functions)h(then)339 1123 y(ha)n(v)n(e)39 b(t)n(yp)r(es)e(\002)p FJ(!)q FK(\002)p FJ(!)11 b FH(:)h(:)g(:)g FJ(!)p FK(\002)p FJ(!)q FK(\002.)64 b(Including)37 b(the)g(0-ary)h(case)g(\(constan)n(ts\),)j(w)n(e)339 1208 y(then)28 b(ha)n(v)n(e)h(functions)f(of)g FH(n)g FK(argumen)n(ts,)g(with)f(p)r(ossibly)g FH(n)20 b FK(=)f(0.)270 1383 y(\002)30 b(ma)n(y)h(also)f(mak)n(e)g(use)g(of)h(auxiliary)e(t)n (yp)r(es)i(in)e(its)g(constructions;)j(for)f(example)e(one)167 1468 y(migh)n(t)j(em)n(b)r(ed)g(a)h(t)n(yp)r(e)f FH(U)40 b FK(in)n(to)32 b(\002,)i(whic)n(h)e(will)d(giv)n(e)k(a)g(function)f (from)h FH(U)39 b FK(to)33 b(\002.)50 b(There)167 1553 y(could)27 b(b)r(e)f(ev)n(en)h(more)f(complex)g(situations.)35 b(T)-6 b(ak)n(e)28 b(for)f(example)f(the)g(case)h(of)g(lists)e(formed) 167 1639 y(from)32 b(ob)t(jects)g(of)g(t)n(yp)r(e)g FH(U)7 b FK(.)48 b(W)-6 b(e)32 b(ha)n(v)n(e)h(a)f(constan)n(t)h(\(the)f(empt)n (y)f(list\))f(and)j(w)n(e)f(can)g(build)167 1724 y(lists)h(b)n(y)i(the) f(follo)n(wing)g(op)r(eration:)50 b(if)33 b FH(u)i FK(is)f(an)h(ob)t (ject)f(of)h(t)n(yp)r(e)g FH(U)42 b FK(and)35 b FH(t)f FK(a)h(list,)g(then)167 1809 y Fq(cons)13 b FH(u)f(t)27 b FK(is)g(a)h(list.)34 b(W)-6 b(e)27 b(ha)n(v)n(e)i(here)e(a)h (function)g(from)f FH(U;)12 b FK(\002)27 b(to)h(\002.)270 1945 y(But)h(there)f(are)h(ev)n(en)g(more)f(dramatic)g(p)r (ossibilities.)36 b(T)-6 b(ak)n(e)29 b(the)g(case)f(of)i(w)n (ell-founded)167 2030 y(trees)i(with)g(branc)n(hing)i(t)n(yp)r(e)g FH(U)7 b FK(.)51 b(Suc)n(h)34 b(a)g(structure)e(is)h(a)g(leaf)f(or)i (is)e(comp)r(osed)i(from)f(a)167 2115 y FH(U)7 b FK(-indexed)27 b(family)e(of)i(trees:)34 b(so,)28 b(in)e(this)h(case,)g(w)n(e)f(ha)n (v)n(e)h(to)g(consider)g(a)g(function)g(of)g(t)n(yp)r(e)167 2201 y(\()p FH(U)7 b FJ(!)p FK(\002\))p FJ(!)p FK(\002.)270 2394 y(No)n(w)35 b(let)e(us)i(turn)g(to)f(the)h(general)f(case.)56 b(The)34 b(structure)g(\002)g(will)e(b)r(e)i(describ)r(ed)f(b)n(y)167 2479 y(means)25 b(of)g(a)g(\014nite)f(n)n(um)n(b)r(er)h(of)g(functions) g(\()p FM(c)l(onstructors)p FK(\))g FH(f)1808 2490 y FD(1)1836 2479 y FH(;)12 b(:)g(:)g(:)f(;)h(f)2024 2490 y Fw(n)2082 2479 y FK(resp)r(ectiv)n(ely)23 b(of)i(t)n(yp)r(e)167 2564 y FH(S)209 2575 y FD(1)237 2564 y FH(;)12 b(:)g(:)g(:)g(;)g(S)434 2575 y Fw(n)467 2564 y FK(.)36 b(The)27 b(t)n(yp)r(e)h FH(S)870 2575 y Fw(i)918 2564 y FK(m)n(ust)f(itself)f(b)r(e)h(of)i(the) e(particular)g(form)1030 2758 y FH(S)1072 2769 y Fw(i)1112 2758 y FK(=)19 b FH(T)1235 2733 y Fw(i)1225 2776 y FD(1)1255 2758 y FJ(!)p FH(T)1375 2733 y Fw(i)1365 2776 y FD(2)1395 2758 y FJ(!)12 b FH(:)g(:)g(:)g(T)1620 2733 y Fw(i)1610 2776 y(k)1636 2783 y Ff(i)1658 2758 y FJ(!)p FK(\002)167 2952 y(with)27 b(\002)g(o)r(ccurring)g(only)h(p)r(ositiv)n(ely)e(\(in)h (the)h(sense)f(of)h FG(??)q FK(\))g(in)f(the)g FH(T)2078 2926 y Fw(i)2068 2969 y(j)2098 2952 y FK(.)270 3088 y(W)-6 b(e)32 b(shall)f(implicitly)c(require)k(that)h(\002)f(b)r(e)h(the)f (free)g(structure)g(generated)h(b)n(y)h(the)e FH(f)2633 3099 y Fw(i)2653 3088 y FK(,)167 3173 y(whic)n(h)36 b(is)h(to)g(sa)n(y) h(that)g(ev)n(ery)f(elemen)n(t)e(of)i(\002)g(is)f(represen)n(ted)g(in)h (a)g FM(unique)42 b FK(w)n(a)n(y)c(b)n(y)g(a)167 3259 y(succession)27 b(of)i(applications)e(of)h(the)f FH(f)1210 3270 y Fw(i)1230 3259 y FK(.)270 3452 y(F)-6 b(or)29 b(this)d(purp)r(ose,)j(w)n(e)e(replace)f(\002)i(b)n(y)g(a)g(v)l (ariable)f FH(X)33 b FK(\(w)n(e)27 b(shall)g(con)n(tin)n(ue)g(to)h (write)e FH(S)2652 3463 y Fw(i)167 3537 y FK(for)i FH(S)319 3548 y Fw(i)339 3537 y FK([)p FH(X=)p FK(\002]\))g(and)h(w)n(e)e(in)n (tro)r(duce:)966 3731 y FH(T)j FK(=)19 b(\005)p FH(X)r(:)12 b(S)1293 3742 y FD(1)1321 3731 y FJ(!)p FH(S)1433 3742 y FD(2)1462 3731 y FJ(!)g FH(:)g(:)g(:)f(S)1678 3742 y Fw(n)1712 3731 y FJ(!)q FH(X)167 3925 y FK(W)-6 b(e)27 b(shall)g(see)g(that)h FH(T)38 b FK(has)29 b(a)f(go)r(o)r(d)h(claim)c (to)j(represen)n(t)f(\002.)p eop PStoPSsaved restore %%Page: (90,91) 46 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 87 90 bop 167 167 a Fz(11.4.)65 b(REPRESENT)-6 b(A)g(TION)25 b(OF)j(A)f(FREE)g(STR)n(UCTURE)693 b FK(87)167 404 y Fy(11.4.2)94 b(Represen)m(tation)28 b(of)f(the)h(constructors)167 553 y FK(W)-6 b(e)37 b(ha)n(v)n(e)h(to)g(\014nd)g(an)g(ob)t(ject)f FH(f)1091 564 y Fw(i)1148 553 y FK(for)h(eac)n(h)f(t)n(yp)r(e)h FH(S)1649 564 y Fw(i)1669 553 y FK([)p FH(T)8 b(=X)e FK(].)65 b(In)38 b(other)f(w)n(ords,)j(w)n(e)d(are)167 639 y(lo)r(oking)29 b(for)h(a)f(function)h FH(f)900 650 y Fw(i)949 639 y FK(whic)n(h)e(tak)n(es)i FH(k)1371 650 y Fw(i)1420 639 y FK(argumen)n(ts)f(of)h(t)n(yp)r(es)f FH(T)2084 613 y Fw(i)2074 656 y(j)2104 639 y FK([)p FH(T)8 b(=X)e FK(])30 b(and)g(returns)167 724 y(a)e(v)l(alue)g(of)g(t)n(yp)r (e)g FH(T)10 b FK(.)270 886 y(Let)38 b FH(x)448 897 y FD(1)476 886 y FH(;)12 b(:)g(:)g(:)g(;)g(x)670 897 y Fw(k)696 904 y Ff(i)756 886 y FK(b)r(e)38 b(the)g(argumen)n(ts)h(of)g FH(f)1478 897 y Fw(i)1498 886 y FK(.)68 b(As)38 b FH(X)44 b FK(o)r(ccurs)38 b FM(p)l(ositively)45 b FK(in)38 b FH(T)2496 861 y Fw(i)2486 904 y(j)2516 886 y FK(,)j(the)167 971 y(canonical)27 b(function)h FH(h)789 982 y Fw(i)836 971 y FK(of)g(t)n(yp)r(e)g FH(T)10 b FJ(!)q FH(X)33 b FK(de\014ned)28 b(b)n(y)414 1218 y FH(h)454 1229 y Fw(i)485 1218 y FH(x)20 b FK(=)f FH(x)12 b(X)17 b(y)779 1187 y Fw(S)809 1194 y Fi(1)776 1235 y FD(1)848 1218 y FH(:)12 b(:)g(:)g(y)978 1192 y Fw(S)1008 1198 y Ff(n)975 1235 y Fw(n)1287 1218 y FK(\(where)27 b FH(X)r(;)12 b(y)1642 1229 y FD(1)1669 1218 y FH(;)g(:)g(:)g(:)f(;)h(y)1857 1229 y Fw(n)1918 1218 y FK(are)27 b(parameters\))167 1464 y(induces)34 b(a)h(function)g FH(T)825 1438 y Fw(i)815 1481 y(j)845 1464 y FK([)p FH(h)904 1475 y Fw(i)923 1464 y FK(])g(from)f FH(T)1201 1438 y Fw(i)1191 1481 y(j)1221 1464 y FK([)p FH(T)8 b(=X)e FK(])35 b(to)g FH(T)1585 1438 y Fw(i)1575 1481 y(j)1640 1464 y FK(dep)r(ending)g(on)g FH(X)r(;)12 b(y)2214 1475 y FD(1)2241 1464 y FH(;)g(:)g(:)g(:)g(;)g(y) 2430 1475 y Fw(n)2463 1464 y FK(.)56 b(This)167 1549 y(function)25 b(could)g(b)r(e)g(de\014ned)g(formally)-6 b(,)25 b(but)g(w)n(e)g(shall)f(see)g(it)g(m)n(uc)n(h)h(b)r(etter)f (with)g(examples.)270 1711 y(Finally)j(w)n(e)g(put)h FH(t)772 1722 y Fw(j)817 1711 y FK(=)19 b FH(T)940 1686 y Fw(i)930 1729 y(j)960 1711 y FK([)p FH(h)1019 1722 y Fw(i)1039 1711 y FK(])12 b FH(x)1109 1722 y Fw(j)1163 1711 y FK(for)28 b FH(j)23 b FK(=)c(1)p FH(;)12 b(:)g(:)g(:)g(;)g(k) 1623 1722 y Fw(i)1670 1711 y FK(and)29 b(w)n(e)e(de\014ne)761 1968 y FH(f)795 1979 y Fw(i)827 1968 y FH(x)866 1979 y FD(1)906 1968 y FH(:)12 b(:)g(:)f(x)1037 1979 y Fw(k)1063 1986 y Ff(i)1105 1968 y FK(=)19 b(\003)p FH(X)r(:)12 b(\025y)1393 1937 y Fw(S)1423 1944 y Fi(1)1390 1985 y FD(1)1450 1968 y FH(:)23 b(:)12 b(:)g(:)g(\025y)1662 1942 y Fw(S)1692 1948 y Ff(n)1659 1985 y Fw(n)1725 1968 y FH(:)g(y)1790 1979 y Fw(i)1821 1968 y FH(t)1846 1979 y FD(1)1885 1968 y FH(:)g(:)g(:)g(t)2003 1979 y Fw(k)2029 1986 y Ff(i)167 2364 y Fy(11.4.3)94 b(Induction)167 2513 y FK(The)41 b(question)g(of)h(kno)n(wing)g(whether)e(the)h(only)g(ob)t (jects)g(of)h(t)n(yp)r(e)f FH(T)51 b FK(whic)n(h)40 b(one)i(can)167 2598 y(construct)f(are)f(indeed)h(those)g(generated)g(from)f(the)h FH(f)1738 2609 y Fw(i)1798 2598 y FK(is)g(hard;)48 b(the)40 b(answ)n(er)i(is)e FM(yes)p FK(,)167 2683 y(almost!)35 b(W)-6 b(e)27 b(shall)g(come)g(bac)n(k)i(to)f(this)f(in)g FG(??)q FK(.)270 2846 y(A)34 b(preliminary)d(indication)h(of)i(this)f (fact)h(is)f(the)g(p)r(ossibilit)n(y)f(of)i(de\014ning)g(a)g(function) 167 2931 y(b)n(y)29 b(induction)e(on)i(the)f(construction)f(of)i(\002.) 36 b(W)-6 b(e)28 b(start)g(o\013)g(with)f(a)i(t)n(yp)r(e)f FH(U)35 b FK(and)29 b(functions)167 3016 y FH(g)200 3027 y FD(1)228 3016 y FH(;)12 b(:)g(:)g(:)g(;)g(g)416 3027 y Fw(n)475 3016 y FK(of)27 b(t)n(yp)r(es)f FH(S)784 3027 y Fw(i)805 3016 y FK([)p FH(U)t(=X)6 b FK(])26 b(\()p FH(i)19 b FK(=)g(1)p FH(;)12 b(:)g(:)g(:)g(;)g(n)p FK(\).)35 b(W)-6 b(e)26 b(w)n(ould)g(lik)n(e)f(to)h(de\014ne)h(a)f(function)h FH(h)f FK(of)167 3101 y(t)n(yp)r(e)i FH(T)10 b FJ(!)p FH(U)35 b FK(satisfying:)347 3347 y FH(h)12 b FK(\()p FH(f)460 3358 y Fw(i)491 3347 y FH(x)530 3358 y FD(1)569 3347 y FH(:)g(:)g(:)g(x)701 3358 y Fw(k)727 3365 y Ff(i)749 3347 y FK(\))19 b(=)g FH(g)901 3358 y Fw(i)933 3347 y FH(u)972 3358 y FD(1)1012 3347 y FH(:)12 b(:)g(:)g(u)1144 3358 y Fw(k)1170 3365 y Ff(i)1371 3347 y FK(where)27 b FH(u)1614 3358 y Fw(j)1659 3347 y FK(=)20 b FH(T)1783 3322 y Fw(i)1773 3365 y(j)1803 3347 y FK([)p FH(h)p FK(])12 b FH(x)1932 3358 y Fw(j)1985 3347 y FK(for)28 b FH(j)23 b FK(=)c(1)p FH(;)12 b(:)g(:)g(:)g(;)g(k)2445 3358 y Fw(i)167 3594 y FK(F)-6 b(or)28 b(this)f(w)n(e)g(put)h FH(h)12 b(x)20 b FK(=)f FH(x)12 b(U)19 b(g)1005 3605 y FD(1)1044 3594 y FH(:)12 b(:)g(:)g(g)1170 3605 y Fw(n)1231 3594 y FK(and)29 b(the)e(previous)h(equation)g(is)f(clearly)f (satis\014ed.)270 3840 y(This)33 b(represen)n(tation)g(of)h(inductiv)n (e)e(t)n(yp)r(es)h(w)n(as)h(inspired)e(b)n(y)i(a)g(1970)h(man)n (uscript)e(of)167 3925 y(Martin-L\177)-34 b(of.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 88 91 bop 167 167 a FK(88)1550 b Fz(CHAPTER)26 b(11.)64 b(SYSTEM)28 b(F)167 404 y FE(11.5)114 b(Represen)m(tation)29 b(of)f(inductiv)m(e)g(t)m(yp)s(es)167 559 y FK(All)d(the)h (de\014nitions)g(giv)n(en)h(in)f FG(??)h FK(\(except)f(the)g(existen)n (tial)e(t)n(yp)r(e\))j(are)f(particular)g(cases)h(of)167 644 y(what)h(w)n(e)f(describ)r(e)f(in)h FG(??)q FK(:)36 b(they)28 b(do)g(not)g(come)f(out)h(of)g(a)g(hat.)251 791 y(1.)35 b(The)28 b FM(b)l(o)l(ole)l(an)35 b FK(t)n(yp)r(e)28 b(has)i(t)n(w)n(o)e(constan)n(ts,)i(whic)n(h)e(will)d(then)j(giv)n(e)h FH(f)2171 802 y FD(1)2227 791 y FK(and)g FH(f)2400 802 y FD(2)2456 791 y FK(of)g(t)n(yp)r(e)339 876 y(b)r(o)r(olean:)49 b(so)35 b FH(S)778 887 y FD(1)830 876 y FK(=)24 b FH(S)950 887 y FD(2)1002 876 y FK(=)g FH(X)40 b FK(and)35 b Fq(Bo)r(ol)24 b FK(=)f(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)g FJ(!)p FH(X)g FK(.)54 b(It)34 b(is)f(easy)i(to)f(sho)n(w)339 962 y(that)k Fq(T)f FK(and)h Fq(F)f FK(are)f(indeed)h(the)f(0-ary)i (functions)g(de\014ned)f(in)f FG(??)i FK(and)g(that)f(the)339 1047 y(induction)28 b(op)r(eration)g(is)f(nothing)h(other)g(than)g Fq(D)p FK(.)251 1187 y(2.)35 b(The)e FM(pr)l(o)l(duct)41 b FK(t)n(yp)r(e)33 b(has)h(a)f(function)g FH(f)1429 1198 y FD(1)1490 1187 y FK(of)g(t)n(w)n(o)g(argumen)n(ts,)i(one)f(of)f(t)n (yp)r(e)g FH(U)40 b FK(and)339 1272 y(one)29 b(of)g(t)n(yp)r(e)g FH(V)16 b FK(.)38 b(So)29 b(w)n(e)f(ha)n(v)n(e)i FH(S)1244 1283 y FD(1)1292 1272 y FK(=)20 b FH(U)7 b FJ(!)q FH(V)15 b FJ(!)q FH(X)6 b FK(,)29 b(whic)n(h)e(explains)i(the)f(translation.) 339 1357 y(The)33 b(pairing)g(function)h(\014ts)f(in)g(w)n(ell)e(with)h (the)h(general)g(case)g(of)h FG(??)q FK(,)g(but)g(the)f(t)n(w)n(o)339 1442 y(pro)t(jections)c(go)h(outside)f(this)f(treatmen)n(t:)37 b(they)29 b(are)g(in)g(fact)g(more)f(easy)i(to)f(handle)339 1527 y(than)g(the)e(indirect)f(sc)n(heme)g(resulting)h(from)g(a)h(mec)n (hanical)e(application)h(of)i FG(??)p FK(.)251 1667 y(3.)35 b(The)d FM(sum)38 b FK(t)n(yp)r(e)32 b(has)h(t)n(w)n(o)f(functions)h (\(the)e(canonical)h(injections\),)g(so)g FH(S)2357 1678 y FD(1)2408 1667 y FK(=)23 b FH(U)7 b FJ(!)p FH(X)339 1753 y FK(and)37 b FH(S)528 1764 y FD(2)582 1753 y FK(=)25 b FH(V)16 b FJ(!)p FH(X)6 b FK(.)60 b(The)35 b(in)n(terpretation)g(of)h FG(??)h FK(matc)n(hes)e(faithfully)g(the)h(general)339 1838 y(sc)n(heme.)251 1978 y(4.)f(The)41 b FM(empty)47 b FK(t)n(yp)r(e)41 b(has)h(nothing,)j(so)c FH(n)29 b FK(=)f(0.)75 b(The)41 b(function)f FH(")2193 1989 y Fw(U)2276 1978 y FK(is)g(indeed)g(its)339 2063 y(induction)28 b(op)r(erator.)270 2210 y(Let)g(us)g(no)n(w)g(turn)g(to)g(some)f(more)g(complex)g (examples.)167 2412 y Fy(11.5.1)94 b(In)m(tegers)167 2543 y FK(The)36 b(in)n(teger)f(t)n(yp)r(e)h(has)h(t)n(w)n(o)g (functions:)53 b Fq(O)36 b FK(of)g(t)n(yp)r(e)h(in)n(teger)e(and)i Fq(S)g FK(from)f(in)n(tegers)f(to)167 2628 y(in)n(tegers,)27 b(whic)n(h)g(giv)n(es)g FH(S)863 2639 y FD(1)911 2628 y FK(=)20 b FH(X)33 b FK(and)c FH(S)1256 2639 y FD(2)1303 2628 y FK(=)20 b FH(X)6 b FJ(!)p FH(X)g FK(,)27 b(so)983 2807 y Fq(Int)1082 2768 y FD(def)1090 2807 y FK(=)f(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FK(\()p FH(X)g FJ(!)p FH(X)g FK(\))p FJ(!)p FH(X)270 2973 y FK(In)28 b(the)g(t)n(yp)r(e)f Fq(Int)p FK(,)h(the)g(in)n(teger)e FH(n)i FK(will)d(b)r(e)i(represen)n (ted)g(b)n(y)p 763 3100 42 3 v 763 3139 a FH(n)20 b FK(=)f(\003)p FH(X)r(:)12 b(\025x)1114 3114 y Fw(X)1162 3139 y FH(:)g(\025y)1270 3114 y Fw(X)t Fv(!)o Fw(X)1411 3139 y FH(:)27 b(y)14 b FK(\()p FH(y)f FK(\()p FH(y)h(:)e(:)g(:)g FK(\()p FH(y)1457 3183 y Fo(|)p 1489 3183 114 9 v 114 w({z)p 1667 3183 V 114 w(})1454 3243 y Fx(n)28 b FB(o)r(ccurrences)1836 3139 y FH(x)p FK(\))12 b FH(:)g(:)g(:)p FK(\)\))270 3423 y(By)28 b(in)n(terc)n(hanging)g FH(S)859 3434 y FD(1)915 3423 y FK(and)h FH(S)1096 3434 y FD(2)1124 3423 y FK(,)f(one)g(could)f (represen)n(t)g Fq(Int)h FK(b)n(y)g(the)g(v)l(arian)n(t)1050 3589 y(\005)p FH(X)r(:)12 b FK(\()p FH(X)6 b FJ(!)p FH(X)g FK(\))p FJ(!)p FK(\()p FH(X)g FJ(!)p FH(X)g FK(\))167 3754 y(whic)n(h)35 b(giv)n(es)g(essen)n(tially)f(the)h(same)g(thing.)59 b(In)35 b(this)g(case,)i(the)e(in)n(terpretation)f(of)i FH(n)g FK(is)167 3840 y(immediate:)f(it)28 b(is)g(the)h(function)f (whic)n(h)h(to)g(an)n(y)h(t)n(yp)r(e)f FH(U)36 b FK(and)30 b(function)f FH(f)36 b FK(of)29 b(t)n(yp)r(e)g FH(U)7 b FJ(!)q FH(U)167 3925 y FK(asso)r(ciates)28 b(the)f(function)h FH(f)929 3899 y Fw(n)962 3925 y FK(,)f FM(i.e.)h FH(f)35 b FK(iterated)27 b FH(n)g FK(times.)p eop PStoPSsaved restore %%Page: (92,93) 47 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 89 92 bop 167 167 a Fz(11.5.)65 b(REPRESENT)-6 b(A)g(TION)25 b(OF)j(INDUCTIVE)d(TYPES)763 b FK(89)270 404 y(Let)28 b(us)g(write)e(the)h(basic)g(functions:)402 583 y Fq(O)473 543 y FD(def)481 583 y FK(=)f(\003)p FH(X)r(:)12 b(\025x)778 557 y Fw(X)826 583 y FH(:)g(\025y)934 557 y Fw(X)t Fv(!)o Fw(X)1076 583 y FH(:)g(x)235 b Fq(S)12 b FH(t)1476 543 y FD(def)1483 583 y FK(=)27 b(\003)p FH(X)r(:)12 b(\025x)1781 557 y Fw(X)1829 583 y FH(:)g(\025y)1937 557 y Fw(X)t Fv(!)o Fw(X)2078 583 y FH(:)g(y)i FK(\()p FH(t)e(X)17 b(x)12 b(y)s FK(\))167 761 y(Of)27 b(course,)h(w)n(e)f(ha)n(v)n(e)i Fq(O)19 b FK(=)p 918 707 35 3 v 20 w(0)28 b(and)g Fq(S)p 1168 722 42 3 v 12 w FH(n)20 b Fu( )p 1319 707 130 3 v 20 w FH(n)p FK(+1.)270 889 y(As)25 b(to)g(the)f(induction)g(op)r (erator,)i(it)e(is)f(in)h(fact)h(the)f FM(iter)l(ator)33 b Fq(It)p FK(,)25 b(whic)n(h)f(tak)n(es)h(an)g(ob)t(ject)167 974 y(of)j(t)n(yp)r(e)g FH(U)7 b FK(,)28 b(a)g(function)g(of)g(t)n(yp)r (e)g FH(U)7 b FJ(!)p FH(U)35 b FK(and)29 b(returns)e(a)h(result)f(of)h (t)n(yp)r(e)g FH(U)7 b FK(:)737 1189 y Fq(It)k FH(u)h(f)20 b(t)67 b FK(=)f FH(t)12 b(U)19 b(u)12 b(f)711 1360 y Fq(It)f FH(u)h(f)20 b Fq(O)67 b FK(=)f(\(\003)p FH(X)r(:)12 b(\025x)1353 1334 y Fw(X)1401 1360 y FH(:)g(\025y)1509 1334 y Fw(X)t Fv(!)o Fw(X)1651 1360 y FH(:)g(x)p FK(\))g FH(U)18 b(u)12 b(f)980 1445 y Fu( )59 b FK(\()p FH(\025x)1215 1419 y Fw(U)1257 1445 y FH(:)12 b(\025y)1365 1419 y Fw(U)5 b Fv(!)o Fw(U)1495 1445 y FH(:)12 b(x)p FK(\))g FH(u)g(f)980 1530 y Fu( )59 b FK(\()p FH(\025y)1213 1504 y Fw(U)5 b Fv(!)o Fw(U)1343 1530 y FH(:)12 b(u)p FK(\))g FH(f)980 1615 y Fu( )59 b FH(u)633 1785 y Fq(It)12 b FH(u)g(f)19 b FK(\()p Fq(S)12 b FH(t)p FK(\))67 b(=)f(\(\003)p FH(X)r(:)12 b(\025x)1353 1760 y Fw(X)1401 1785 y FH(:)g(\025y)1509 1760 y Fw(X)t Fv(!)o Fw(X)1651 1785 y FH(:)g(y)h FK(\()p FH(t)f(X)17 b(x)12 b(y)s FK(\)\))g FH(U)18 b(u)12 b(f)980 1870 y Fu( )59 b FK(\()p FH(\025x)1215 1845 y Fw(U)1257 1870 y FH(:)12 b(\025y)1365 1845 y Fw(U)5 b Fv(!)o Fw(U)1495 1870 y FH(:)12 b(y)i FK(\()p FH(t)e(U)18 b(x)12 b(y)s FK(\)\))g FH(u)g(f)980 1955 y Fu( )59 b FK(\()p FH(\025y)1213 1930 y Fw(U)5 b Fv(!)o Fw(U)1343 1955 y FH(:)12 b(y)i FK(\()p FH(t)e(U)18 b(u)12 b(y)s FK(\)\))g FH(f)980 2040 y Fu( )59 b FH(f)20 b FK(\()p FH(t)12 b(U)18 b(u)12 b(f)c FK(\))989 2126 y(=)66 b FH(f)20 b FK(\()p Fq(It)11 b FH(u)h(f)19 b(t)p FK(\))270 2352 y(It)28 b(is)f(not)h(true)f(that)h Fq(It)12 b FH(u)g(f)p 1015 2298 V 19 w(n)p FK(+1)20 b Fu( )g FH(f)f FK(\()p Fq(It)11 b FH(u)h(f)p 1493 2313 42 3 v 19 w(n)q FK(\),)27 b(but)h(b)r(oth)h(terms)d(reduce)h(to)1101 2530 y FH(f)19 b FK(\()p FH(f)g FK(\()p FH(f)g(:)12 b(:)g(:)g FK(\()p FH(f)1101 2574 y Fo(|)p 1133 2574 124 9 v 124 w({z)p 1321 2574 V 124 w(})1071 2641 y Fx(n)p FB(+1)28 b(o)r(ccurrences)1528 2530 y FH(u)p FK(\))12 b FH(:)g(:)g(:)p FK(\)\))167 2811 y(so)28 b(at)g(least)f Fq(It)11 b FH(u)h(f)p 670 2758 130 3 v 19 w(n)p FK(+1)20 b FJ(\030)g FH(f)f FK(\()p Fq(It)11 b FH(u)h(f)p 1133 2773 42 3 v 19 w(n)p FK(\))28 b(,)f(where)g(\\)p FJ(\030)p FK(")h(is)f(the)g(equiv)l(alence) g(closure)g(of)h(\\)p Fu( )p FK(".)167 2897 y(In)23 b(fact,)g(\\)p Fu( )p FK(")h(satis\014es)f(the)f(Ch)n(urc)n(h-Rosser)h(prop)r(ert)n(y) -6 b(,)25 b(so)e(that)g(t)n(w)n(o)g(terms)e(are)i(equiv)l(alen)n(t)167 2982 y(i\013)k(they)h(reduce)f(to)h(a)g(common)f(one.)270 3110 y(While)35 b(w)n(e)i(are)f(on)i(the)e(sub)t(ject,)j(let)d(us)h (sho)n(w)h(ho)n(w)f FM(r)l(e)l(cursion)h FK(can)f(b)r(e)f(de\014ned)i (in)167 3195 y(terms)28 b(of)i FM(iter)l(ation)p FK(.)41 b(Let)29 b FH(u)h FK(b)r(e)f(of)h(t)n(yp)r(e)f FH(U)7 b FK(,)30 b FH(f)37 b FK(of)30 b(t)n(yp)r(e)f FH(U)7 b FJ(!)q Fq(Int)p FJ(!)p FH(U)g FK(.)41 b(W)-6 b(e)29 b(construct)h FH(g)i FK(of)167 3281 y(t)n(yp)r(e)c FH(U)7 b FJ(\002)p Fq(Int)p FJ(!)p FH(U)g FJ(\002)p Fq(Int)28 b FK(b)n(y)900 3459 y FH(g)22 b FK(=)e FH(\025x)1108 3433 y Fw(U)5 b Fv(\002)p Fp(Int)1246 3459 y FH(:)12 b FJ(h)p FH(f)20 b FK(\()p FH(\031)1427 3433 y FD(1)1454 3459 y FH(x)p FK(\))12 b(\()p FH(\031)1601 3433 y FD(2)1628 3459 y FH(x)p FK(\))p FH(;)g Fq(S)g FH(\031)1817 3433 y FD(2)1845 3459 y FH(x)p FJ(i)167 3637 y FK(In)28 b(particular,)f FH(g)14 b FJ(h)p FH(u;)p 744 3598 V 12 w(n)q FJ(i)20 b Fu( )g FJ(h)p FH(f)f(u)p 1054 3598 V 12 w(n;)p 1126 3583 130 3 v 12 w(n)p FK(+1)q FJ(i)p FK(.)35 b(So)29 b(if)e Fq(It)11 b FJ(h)p FH(u;)p 1658 3583 35 3 v 12 w FK(0)q FJ(i)h FH(g)p 1779 3598 42 3 v 14 w(n)20 b FJ(\030)f(h)p FH(t)1966 3648 y Fw(n)2000 3637 y FH(;)p 2031 3598 V 12 w(n)p FJ(i)28 b FK(then:)550 3815 y Fq(It)11 b FJ(h)p FH(u;)p 702 3761 35 3 v 12 w FK(0)q FJ(i)h FH(g)p 823 3761 130 3 v 14 w(n)p FK(+1)20 b FJ(\030)g FH(g)14 b FK(\()p Fq(It)d FJ(h)p FH(u;)p 1273 3761 35 3 v 12 w FK(0)q FJ(i)h FH(g)p 1395 3776 42 3 v 15 w(n)p FK(\))19 b FJ(\030)h FH(g)14 b FJ(h)p FH(t)1656 3826 y Fw(n)1689 3815 y FH(;)p 1720 3776 V 12 w(n)p FJ(i)20 b(\030)g(h)p FH(f)f(t)1988 3826 y Fw(n)p 2033 3776 V 2033 3815 a FH(n;)p 2105 3761 130 3 v 12 w(n)p FK(+1)q FJ(i)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 90 93 bop 167 167 a FK(90)1550 b Fz(CHAPTER)26 b(11.)64 b(SYSTEM)28 b(F)270 413 y FK(Finally)-6 b(,)27 b(consider)g Fq(R)12 b FH(u)g(f)20 b(t)1001 374 y FD(def)1009 413 y FK(=)27 b FH(\031)1132 388 y FD(1)1159 413 y FK(\()p Fq(It)11 b FJ(h)p FH(u;)p 1338 359 35 3 v 12 w FK(0)q FJ(i)h FH(g)j(t)p FK(\).)35 b(W)-6 b(e)27 b(ha)n(v)n(e:)635 586 y Fq(R)12 b FH(u)g(f)p 796 532 V 20 w FK(0)20 b FJ(\030)f FH(u)468 b Fq(R)12 b FH(u)g(f)p 1592 532 130 3 v 20 w(n)p FK(+1)20 b FJ(\030)f FH(f)g FK(\()p Fq(R)12 b FH(u)g(f)p 2055 547 42 3 v 19 w(n)q FK(\))p 2136 547 V 12 w FH(n)270 759 y FK(The)33 b(second)h(equation)g(for)g(recursion)e(is)h (satis\014ed)g(b)n(y)i(v)l(alues)e(only)-6 b(,)36 b FM(i.e.)d FK(for)h(eac)n(h)f FH(n)167 844 y FK(separately)-6 b(.)67 b(W)-6 b(e)37 b(mak)n(e)h(no)h(secret)e(of)h(the)g(fact)g(that)g(this)f (is)h(a)g(defect)f(of)i(system)e FG(F)p FK(.)167 929 y(Indeed,)28 b(if)f(w)n(e)g(program)h(the)g(predecessor)f(function)747 1102 y Fq(p)n(red)12 b(O)20 b FK(=)f Fq(O)579 b(p)n(red)13 b FK(\()p Fq(S)f FH(x)p FK(\))20 b(=)f FH(x)167 1274 y FK(the)40 b(second)h(equation)g(will)c(only)k(b)r(e)f(satis\014ed)h (for)f FH(x)h FK(of)f(the)h(form)p 2166 1236 V 40 w FH(n)p FK(,)i(whic)n(h)d(means)167 1359 y(that)32 b(the)g(program)h(decomp)r (oses)f(the)g(argumen)n(t)g FH(x)h FK(completely)c(in)n(to)j Fq(S)12 b(S)g(S)g FH(:)g(:)g(:)g Fq(S)g(O)p FK(,)33 b(then)167 1445 y(reconstructs)43 b(it)f(lea)n(ving)i(out)g(the)f(last)g(sym)n(b)r (ol)g Fq(S)p FK(.)83 b(Of)43 b(course)h(it)e(w)n(ould)h(b)r(e)h(more) 167 1530 y(economical)26 b(to)i(remo)n(v)n(e)f(the)h(\014rst)f (instead!)167 1734 y Fy(11.5.2)94 b(Lists)167 1864 y FH(U)29 b FK(b)r(eing)22 b(a)g(t)n(yp)r(e,)h(w)n(e)f(w)n(an)n(t)g(to)h (form)e(the)h(t)n(yp)r(e)g Fq(List)12 b FH(U)7 b FK(,)23 b(whose)f(ob)t(jects)g(are)g(\014nite)f(sequences)167 1949 y(\()p FH(u)233 1960 y FD(1)261 1949 y FH(;)12 b(:)g(:)g(:)g(;)g (u)455 1960 y Fw(n)488 1949 y FK(\))27 b(of)h(t)n(yp)r(e)g FH(U)7 b FK(.)36 b(W)-6 b(e)27 b(ha)n(v)n(e)i(t)n(w)n(o)f(functions:) 270 2110 y FJ(\017)34 b FK(the)28 b(sequence)f(\(\))g(of)i(t)n(yp)r(e)e Fq(List)12 b FH(U)7 b FK(,)28 b(and)h(hence)e FH(S)1672 2121 y FD(1)1720 2110 y FK(=)19 b FH(X)6 b FK(;)270 2254 y FJ(\017)34 b FK(the)28 b(function)g(whic)n(h)f(maps)i(an)f(ob)t(ject) g FH(u)g FK(of)g(t)n(yp)r(e)g FH(U)35 b FK(and)29 b(a)g(sequence)e(\()p FH(u)2390 2265 y FD(1)2418 2254 y FH(;)12 b(:)g(:)g(:)g(;)g(u)2612 2265 y Fw(n)2645 2254 y FK(\))339 2339 y(to)28 b(\()p FH(u;)12 b(u)564 2350 y FD(1)592 2339 y FH(;)g(:)g(:)g(:)g(;)g(u)786 2350 y Fw(n)819 2339 y FK(\).)36 b(So)28 b FH(S)1043 2350 y FD(2)1091 2339 y FK(=)19 b FH(U)7 b FJ(!)q FH(X)f FJ(!)p FH(X)g FK(.)270 2499 y(Mec)n(hanically)27 b(applying)h(the)f (general)g(sc)n(heme,)g(w)n(e)g(get)757 2727 y Fq(List)11 b FH(U)986 2687 y FD(def)994 2727 y FK(=)66 b(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FK(\()p FH(U)h FJ(!)p FH(X)f FJ(!)p FH(X)g FK(\))p FJ(!)p FH(X)860 2916 y Fq(nil)986 2877 y FD(def)994 2916 y FK(=)66 b(\003)p FH(X)r(:)12 b(\025x)1331 2891 y Fw(X)1379 2916 y FH(:)g(\025y)1487 2891 y Fw(U)5 b Fv(!)o Fw(X)t Fv(!)o Fw(X)1717 2916 y FH(:)12 b(x)713 3021 y Fq(cons)h FH(u)f(t)986 2982 y FD(def)994 3021 y FK(=)66 b(\003)p FH(X)r(:)12 b(\025x)1331 2995 y Fw(X)1379 3021 y FH(:)g(\025y)1487 2995 y Fw(U)5 b Fv(!)o Fw(X)t Fv(!)o Fw(X)1717 3021 y FH(:)12 b(y)i(u)e FK(\()p FH(t)g(X)17 b(x)12 b(y)s FK(\))167 3234 y(So)28 b(the)g(sequence)f(\()p FH(u)747 3245 y FD(1)775 3234 y FH(;)12 b(:)g(:)g(:)g(;)g(u)969 3245 y Fw(n)1002 3234 y FK(\))28 b(is)e(represen)n(ted)h(b)n(y)730 3406 y(\003)p FH(X)r(:)12 b(\025x)947 3381 y Fw(X)995 3406 y FH(:)g(\025y)1103 3381 y Fw(U)5 b Fv(!)o Fw(X)t Fv(!)o Fw(X)1333 3406 y FH(:)12 b(y)i(u)1451 3417 y FD(1)1491 3406 y FK(\()p FH(y)f(u)1604 3417 y FD(2)1644 3406 y FH(:)f(:)g(:)g FK(\()p FH(y)i(u)1851 3417 y Fw(n)1896 3406 y FH(x)p FK(\))e FH(:)g(:)g(:)p FK(\))167 3579 y(whic)n(h)27 b(w)n(e)g (recognise,)g(replacing)g FH(y)j FK(b)n(y)e Fq(cons)h FK(and)f FH(x)g FK(b)n(y)g Fq(nil)o FK(,)g(as)897 3752 y Fq(cons)12 b FH(u)1074 3763 y FD(1)1114 3752 y FK(\()p Fq(cons)h FH(u)1319 3763 y FD(2)1358 3752 y FH(:)f(:)g(:)g FK(\()p Fq(cons)h FH(u)1656 3763 y Fw(n)1701 3752 y Fq(nil)o FK(\))f FH(:)g(:)g(:)o FK(\))167 3925 y(This)27 b(last)g(term)g(could)g (b)r(e)h(obtained)g(b)n(y)g(reducing)f(\()p FH(u)1659 3936 y FD(1)1687 3925 y FH(;)12 b(:)g(:)g(:)g(;)g(u)1881 3936 y Fw(n)1914 3925 y FK(\))g(\()p Fq(List)f FH(U)c FK(\))12 b Fq(nil)f(cons)q FK(.)p eop PStoPSsaved restore %%Page: (94,95) 48 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 91 94 bop 167 167 a Fz(11.5.)65 b(REPRESENT)-6 b(A)g(TION)25 b(OF)j(INDUCTIVE)d(TYPES)763 b FK(91)270 404 y(The)25 b(b)r(eha)n(viour)g(of)g(lists)f(is)g(v)n(ery)g(similar)e(to)j(that)g (of)h(in)n(tegers.)33 b(W)-6 b(e)24 b(ha)n(v)n(e)i(in)e(particular)167 490 y(an)i(iteration)f(on)h(lists:)33 b(if)25 b FH(W)35 b FK(is)25 b(a)h(t)n(yp)r(e,)g FH(w)i FK(is)d(of)h(t)n(yp)r(e)g FH(W)10 b FK(,)25 b FH(f)33 b FK(is)25 b(of)h(t)n(yp)r(e)g FH(U)7 b FJ(!)q FH(W)j FJ(!)p FH(W)g FK(,)26 b(one)167 575 y(can)i(de\014ne)g(for)g FH(t)f FK(of)h(t)n(yp)r(e)g Fq(List)12 b FH(U)35 b FK(the)27 b(term)f Fq(It)12 b FH(w)i(f)19 b(t)27 b FK(of)i(t)n(yp)r(e)e FH(W)38 b FK(b)n(y)1140 753 y Fq(It)11 b FH(w)j(f)19 b(t)1356 714 y FD(def)1363 753 y FK(=)27 b FH(t)12 b(W)21 b(w)14 b(f)167 918 y FK(whic)n(h)27 b(satis\014es)558 1083 y Fq(It)12 b FH(w)i(f)19 b Fq(nil)f Fu( )i FH(w)394 b Fq(It)11 b FH(w)j(f)19 b FK(\()p Fq(cons)13 b FH(u)f(t)p FK(\))19 b Fu( )h FH(f)f(u)12 b FK(\()p Fq(It)f FH(w)j(f)20 b(t)p FK(\))167 1285 y FG(Examples)270 1430 y FJ(\017)34 b Fq(It)12 b(nil)e(cons)j FH(t)20 b Fu( )g FH(t)27 b FK(for)h(all)e FH(t)i FK(of)g(the)f(form)h(\()p FH(u)1503 1441 y FD(1)1531 1430 y FH(;)12 b(:)g(:)g(:)f(;)h(u)1724 1441 y Fw(n)1758 1430 y FK(\).)270 1570 y FJ(\017)34 b FK(If)i FH(W)g FK(=)25 b Fq(List)12 b FH(V)51 b FK(where)36 b FH(V)51 b FK(is)36 b(another)h(t)n(yp)r(e,)h(and)f FH(f)c FK(=)26 b FH(\025x)2024 1545 y Fw(U)2066 1570 y FH(:)12 b(\025y)2174 1545 y Fp(List)d Fw(W)2315 1570 y FH(:)j Fq(cons)g FK(\()p FH(g)i(x)p FK(\))e FH(y)339 1655 y FK(where)27 b FH(g)j FK(is)d(of)h(t)n(yp)r(e)g FH(U)7 b FJ(!)q FH(V)15 b FK(,)28 b(it)f(is)g(easy)h(to)g(see)f(that) 948 1848 y Fq(It)11 b(nil)g FH(f)19 b FK(\()p FH(u)1202 1859 y FD(1)1230 1848 y FH(;)12 b(:)g(:)g(:)g(;)g(u)1424 1859 y Fw(n)1457 1848 y FK(\))20 b Fu( )g FK(\()p FH(g)14 b(u)1707 1859 y FD(1)1735 1848 y FH(;)e(:)g(:)g(:)f(;)h(g)j(u)1976 1859 y Fw(n)2009 1848 y FK(\))270 2110 y(Using)28 b(a)g(pro)r(duct)g(t) n(yp)r(e,)g(w)n(e)f(can)h(obtain)g(a)h(recursion)e(op)r(erator)h(\(b)n (y)g(v)l(alues\):)822 2273 y Fq(R)12 b FH(v)j(f)k Fq(nil)58 b FJ(\030)g FH(v)542 2358 y Fq(R)12 b FH(v)j(f)k FK(\()p FH(u)765 2369 y FD(1)793 2358 y FH(;)12 b(:)g(:)g(:)g(;)g(u)987 2369 y Fw(n)1020 2358 y FK(\))59 b FJ(\030)f FH(f)20 b(u)1312 2369 y FD(1)1351 2358 y FK(\()p FH(u)1417 2369 y FD(2)1445 2358 y FH(;)12 b(:)g(:)g(:)g(;)g(u)1639 2369 y Fw(n)1672 2358 y FK(\))g(\()p Fq(R)g FH(v)i(f)20 b FK(\()p FH(u)1961 2369 y FD(2)1989 2358 y FH(;)12 b(:)g(:)g(:)f(;)h(u) 2182 2369 y Fw(n)2216 2358 y FK(\)\))167 2518 y(with)27 b FH(v)k FK(of)d(t)n(yp)r(e)g FH(V)44 b FK(and)29 b FH(f)35 b FK(of)29 b(t)n(yp)r(e)f FH(U)7 b FJ(!)q Fq(List)k FH(U)c FJ(!)q FH(V)15 b FJ(!)q FH(V)g FK(.)37 b(This)27 b(enables)h(us)g(to)g (de\014ne,)h(for)167 2603 y(example,)35 b(the)e(truncation)h(of)g(a)h (list)d(b)n(y)i(remo)n(v)l(al)g(of)g(its)f(\014rst)h(elemen)n(t)e(\(if) h(an)n(y\),)j(in)d(an)167 2688 y(analogous)d(w)n(a)n(y)e(to)g(the)g (predecessor:)724 2853 y Fq(tail)10 b(nil)18 b FK(=)i Fq(nil)555 b(tail)o FK(\()p Fq(cons)12 b FH(u)g(t)p FK(\))20 b(=)f FH(t)167 3018 y FK(where)27 b(the)g(second)h(equation)h(is)e (only)h(satis\014ed)f(for)h FH(t)g FK(of)g(the)f(form)h(\()p FH(u)2110 3029 y FD(1)2138 3018 y FH(;)12 b(:)g(:)g(:)f(;)h(u)2331 3029 y Fw(n)2365 3018 y FK(\).)270 3140 y(As)28 b(an)g(exercise,)e (de\014ne)i(b)n(y)g(iteration:)270 3285 y FJ(\017)34 b FM(c)l(onc)l(atenation)5 b FK(:)36 b(\()p FH(u)877 3296 y FD(1)905 3285 y FH(;)12 b(:)g(:)g(:)g(;)g(u)1099 3296 y Fw(n)1132 3285 y FK(\))19 b(@)h(\()p FH(v)1312 3296 y FD(1)1340 3285 y FH(;)12 b(:)g(:)g(:)f(;)h(v)1527 3296 y Fw(m)1575 3285 y FK(\))19 b(=)g(\()p FH(u)1760 3296 y FD(1)1788 3285 y FH(;)12 b(:)g(:)g(:)g(;)g(u)1982 3296 y Fw(n)2015 3285 y FH(;)g(v)2079 3296 y FD(1)2107 3285 y FH(;)g(:)g(:)g(:)g(;)g(v)2295 3296 y Fw(m)2342 3285 y FK(\))270 3425 y FJ(\017)34 b FM(r)l(eversal)7 b FK(:)36 b Fq(reverse)11 b FK(\()p FH(u)906 3436 y FD(1)934 3425 y FH(;)h(:)g(:)g(:)g(;)g(u)1128 3436 y Fw(n)1161 3425 y FK(\))20 b(=)f(\()p FH(u)1347 3436 y Fw(n)1380 3425 y FH(;)12 b(:)g(:)g(:)g(;)g(u)1574 3436 y FD(1)1602 3425 y FK(\))270 3607 y Fq(List)g FH(U)35 b FK(dep)r(ends)28 b(on)g FH(U)7 b FK(,)28 b(but)g(the)f(de\014nition)g(w)n(e)g(ha)n(v)n (e)h(giv)n(en)g(is)f(in)g(fact)g(uniform)g(in)g(it,)167 3692 y(so)h(w)n(e)f(can)h(de\014ne)638 3814 y Fq(Nil)57 b FK(=)i(\003)p FH(X)r(:)12 b Fq(nil)n FK([)p FH(X)6 b FK(])118 b(of)28 b(t)n(yp)r(e)g(\005)p FH(X)r(:)12 b Fq(List)f FH(X)578 3899 y Fq(Cons)60 b FK(=)f(\003)p FH(X)r(:)12 b Fq(cons)p FK([)p FH(X)6 b FK(])59 b(of)28 b(t)n(yp)r(e)g(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p Fq(List)11 b FH(X)6 b FJ(!)q Fq(List)11 b FH(X)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 92 95 bop 167 167 a FK(92)1550 b Fz(CHAPTER)26 b(11.)64 b(SYSTEM)28 b(F)167 404 y Fy(11.5.3)94 b(Binary)28 b(trees)167 535 y FK(W)-6 b(e)27 b(are)h(in)n(terested)e(in)h(\014nite)g(binary)h (trees.)35 b(F)-6 b(or)28 b(this,)f(w)n(e)g(ha)n(v)n(e)i(t)n(w)n(o)f (functions:)270 695 y FJ(\017)34 b FK(the)28 b(tree)e(consisting)i (only)g(of)g(its)f(ro)r(ot,)h(so)g FH(S)1571 706 y FD(1)1619 695 y FK(=)19 b FH(X)6 b FK(;)270 838 y FJ(\017)34 b FK(the)28 b(construction)f(of)i(a)f(tree)e(from)i(t)n(w)n(o)f(trees,)g (so)i FH(S)1773 849 y FD(2)1821 838 y FK(=)19 b FH(X)6 b FJ(!)p FH(X)g FJ(!)p FH(X)g FK(.)632 1098 y Fq(Bintree)898 1059 y FD(def)905 1098 y FK(=)66 b(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FK(\()p FH(X)g FJ(!)p FH(X)g FJ(!)p FH(X)g FK(\))p FJ(!)p FH(X)771 1288 y Fq(nil)898 1249 y FD(def)905 1288 y FK(=)66 b(\003)p FH(X)r(:)12 b(\025x)1242 1262 y Fw(X)1290 1288 y FH(:)g(\025y)1398 1262 y Fw(X)t Fv(!)o Fw(X)t Fv(!)p Fw(X)1634 1288 y FH(:)g(x)558 1393 y Fq(couple)f FH(u)h(v)898 1353 y FD(def)905 1393 y FK(=)66 b(\003)p FH(X)r(:)12 b(\025x)1242 1367 y Fw(X)1290 1393 y FH(:)g(\025y)1398 1367 y Fw(X)t Fv(!)o Fw(X)t Fv(!)p Fw(X)1634 1393 y FH(:)g(y)i FK(\()p FH(u)e(X)17 b(x)12 b(y)s FK(\))g(\()p FH(v)h(X)18 b(x)12 b(y)s FK(\))270 1631 y(Iteration)25 b(on)h(trees)f(is)f(then)h (de\014ned)h(b)n(y)g Fq(It)12 b FH(w)i(f)19 b(t)1608 1592 y FD(def)1616 1631 y FK(=)27 b FH(t)12 b(W)21 b(w)14 b(f)33 b FK(when)25 b FH(W)35 b FK(is)24 b(a)i(t)n(yp)r(e,)g FH(w)i FK(of)167 1716 y(t)n(yp)r(e)g FH(W)10 b FK(,)27 b FH(f)35 b FK(of)28 b(t)n(yp)r(e)g FH(W)10 b FJ(!)p FH(W)g FJ(!)p FH(W)38 b FK(and)28 b FH(t)g FK(of)g(t)n(yp)r(e)g Fq(Bintree)o FK(.)35 b(It)28 b(satis\014es:)457 1888 y Fq(It)12 b FH(w)i(f)19 b Fq(nil)f Fu( )i FH(w)293 b Fq(It)11 b FH(w)j(f)19 b FK(\()p Fq(couple)12 b FH(u)g(v)s FK(\))19 b Fu( )h FH(f)f FK(\()p Fq(It)11 b FH(w)j(f)19 b(u)p FK(\))12 b(\()p Fq(It)f FH(w)j(f)20 b(v)s FK(\))167 2179 y Fy(11.5.4)94 b(T)-8 b(rees)28 b(of)f(branc)m(hing)h(t)m(yp)s(e)g Fe(U)167 2310 y FK(There)f(are)g(t)n(w)n(o)h(functions:)270 2470 y FJ(\017)34 b FK(the)28 b(tree)e(consisting)i(only)g(of)g(its)f (ro)r(ot,)h(so)g FH(S)1571 2481 y FD(1)1619 2470 y FK(=)19 b FH(X)6 b FK(;)270 2613 y FJ(\017)34 b FK(the)21 b(construction)f(of)i (a)f(tree)e(from)i(a)g(family)e(\()p FH(t)1591 2624 y Fw(u)1623 2613 y FK(\))1650 2624 y Fw(u)p Fv(2)p Fw(U)1774 2613 y FK(of)i(trees,)g(so)h FH(S)2158 2624 y FD(2)2205 2613 y FK(=)e(\()p FH(U)7 b FJ(!)p FH(X)f FK(\))p FJ(!)p FH(X)g FK(.)647 2877 y Fq(T)-6 b(ree)12 b FH(U)898 2838 y FD(def)906 2877 y FK(=)65 b(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FK(\(\()p FH(U)h FJ(!)p FH(X)f FK(\))p FJ(!)q FH(X)g FK(\))p FJ(!)p FH(X)771 3067 y Fq(nil)898 3028 y FD(def)906 3067 y FK(=)65 b(\003)p FH(X)r(:)12 b(\025x)1242 3041 y Fw(X)1290 3067 y FH(:)g(\025y)1398 3041 y FD(\()p Fw(U)5 b Fv(!)p Fw(X)t FD(\))p Fv(!)p Fw(X)1667 3067 y FH(:)12 b(x)602 3172 y Fq(collect)e FH(f)898 3132 y FD(def)906 3172 y FK(=)65 b(\003)p FH(X)r(:)12 b(\025x)1242 3146 y Fw(X)1290 3172 y FH(:)g(\025y)1398 3146 y FD(\()p Fw(U)5 b Fv(!)p Fw(X)t FD(\))p Fv(!)p Fw(X)1667 3172 y FH(:)12 b(y)i FK(\()p FH(\025z)1848 3146 y Fw(U)1890 3172 y FH(:)e(f)19 b(z)c(X)i(x)12 b(y)s FK(\))270 3369 y(The)31 b(\(trans\014nite\))f(iteration)f(is)h(de\014ned)h(b)n(y)g Fq(It)12 b FH(w)i(h)e(t)1739 3330 y FD(def)1747 3369 y FK(=)29 b FH(t)12 b(W)21 b(w)14 b(h)30 b FK(when)h FH(W)40 b FK(is)30 b(a)h(t)n(yp)r(e,)167 3454 y FH(w)f FK(of)e(t)n(yp)r(e)g FH(W)10 b FK(,)27 b FH(f)35 b FK(of)28 b(t)n(yp)r(e)g(\()p FH(U)7 b FJ(!)q FH(W)j FK(\))p FJ(!)p FH(W)37 b FK(and)29 b FH(t)e FK(of)h(t)n(yp)r(e)g Fq(Bintree)o FK(.)35 b(It)28 b(satis\014es:)479 3627 y Fq(It)11 b FH(w)j(h)e Fq(nil)18 b Fu( )i FH(w)314 b Fq(It)12 b FH(w)i(h)e FK(\()p Fq(collect)d FH(f)f FK(\))19 b Fu( )h FH(h)12 b FK(\()p FH(\025x)1918 3601 y Fw(U)1959 3627 y FH(:)g Fq(It)f FH(w)j(h)e FK(\()p FH(f)19 b(x)p FK(\)\))270 3840 y(Notice)h(that)i Fq(Bintree)e FK(could)h(b)r(e)g(treated)g(as)h (the)f(t)n(yp)r(e)h(of)f(trees)g(with)f(b)r(o)r(olean)i(branc)n(hing) 167 3925 y(t)n(yp)r(e,)28 b(without)f(substan)n(tial)h(alteration.)p eop PStoPSsaved restore %%Page: (96,97) 49 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 93 96 bop 167 167 a Fz(11.6.)65 b(THE)27 b(CURR)-6 b(Y-HO)n(W)e(ARD)25 b(ISOMORPHISM)924 b FK(93)270 404 y(Just)30 b(as)f(w)n(e)f(can)h (abstract)h(on)f FH(U)36 b FK(in)28 b Fq(List)11 b FH(U)c FK(,)30 b(the)e(same)g(thing)h(is)f(p)r(ossible)g(with)g(trees.)167 490 y(This)21 b(p)r(oten)n(tial)f(for)h(abstraction)h(sho)n(ws)g(up)g (the)f(mo)r(dularit)n(y)f(of)i FG(F)f FK(v)n(ery)g(w)n(ell:)30 b(for)22 b(example,)167 575 y(one)37 b(can)f(de\014ne)h(the)f(mo)r (dule)f Fq(Collect)24 b FK(=)h(\003)p FH(X)r(:)12 b Fq(collect)n FK([)p FH(X)6 b FK(],)38 b(whic)n(h)e(can)g(subsequen)n(tly)h(b)r(e)167 660 y(used)i(b)n(y)h(sp)r(ecifying)e(the)h(t)n(yp)r(e)g FH(X)6 b FK(.)69 b(Of)39 b(course,)j(w)n(e)c(see)h(the)f(v)l(alue)h(of) h(this)e(in)h(more)167 745 y(complicated)21 b(cases:)34 b(w)n(e)22 b(only)i(write)d(the)i(program)h(once,)g(but)g(it)e(can)h(b) r(e)g(applied)g(\(plugged)167 830 y(in)n(to)k(other)h(mo)r(dules\))f (in)g(a)h(great)g(v)l(ariet)n(y)g(of)g(situations.)167 1065 y FE(11.6)114 b(The)28 b(Curry-Ho)m(w)m(ard)h(Isomorphism)167 1220 y FK(The)24 b(t)n(yp)r(es)g(in)f FG(F)h FK(are)g(nothing)h(other)f (than)g(prop)r(ositions)h(quan)n(ti\014ed)g(at)f(the)g FM(se)l(c)l(ond)g(or)l(der)p FK(,)167 1305 y(and)31 b(the)f (isomorphism)f(w)n(e)h(ha)n(v)n(e)h(already)f(established)g(for)g(the)g (arro)n(w)h(extends)f(to)g(these)167 1390 y(quan)n(ti\014ers:)845 1548 y FJ(\001)845 1586 y(\001)845 1624 y(\001)829 1681 y FH(A)p 764 1726 181 4 v 965 1742 a FJ(8)1005 1716 y FD(2)1032 1742 y FJ(I)764 1802 y(8)p FH(X)r(:)12 b(A)1785 1539 y FJ(\001)1785 1577 y(\001)1785 1615 y(\001)1704 1673 y(8)p FH(X)r(:)g(A)p 1673 1718 244 4 v 1937 1733 a FJ(8)1977 1708 y FD(2)2004 1733 y FJ(E)1673 1794 y FH(A)p FK([)p FH(B)t(=X)6 b FK(])167 1954 y(whic)n(h)27 b(corresp)r(ond)h(exactly)g(to)g(univ)n(ersal)f(abstraction)h(and)h (application.)270 2081 y(If)38 b FH(t)f FK(of)g(t)n(yp)r(e)h FH(A)e FK(represen)n(ts)h(the)g(part)h(of)f(the)g(deduction)g(ab)r(o)n (v)n(e)i FJ(8)2209 2055 y FD(2)2236 2081 y FJ(I)5 b FK(,)40 b(then)e(\003)p FH(X)r(:)12 b(t)167 2166 y FK(represen)n(ts)39 b(the)g(whole)g(deduction.)71 b(The)40 b(usual)g(restriction)d(on)j(v)l (ariables)g(in)f(natural)167 2251 y(deduction)26 b(\()p FH(X)32 b FK(not)27 b(free)f(in)f(the)i(h)n(yp)r(otheses\))g(corresp)r (onds)h(exactly)-6 b(,)26 b(as)h(w)n(e)f(can)h(see)f(here,)167 2336 y(to)i(the)f(restriction)f(on)i(the)g(formation)f(of)h(univ)n (ersal)g(abstraction.)270 2462 y(Lik)n(ewise,)40 b FJ(8)625 2437 y FD(2)652 2462 y FJ(E)45 b FK(corresp)r(onds)39 b(to)g(an)g(application)f(to)g(t)n(yp)r(e)h FH(B)t FK(.)67 b(T)-6 b(o)39 b(b)r(e)f(completely)167 2547 y(precise,)32 b(in)h(the)f(case)h(where)e FH(X)39 b FK(do)r(es)33 b(not)g(app)r(ear)h (in)e FH(A)p FK(,)i(one)f(should)g(sp)r(ecify)f(what)h FH(B)167 2632 y FK(has)c(b)r(een)e(substituted.)270 2806 y(The)e(con)n(v)n(ersion)h(rule)e(\(\003)p FH(X)r(:)12 b(v)s FK(\))g FH(U)26 b Fu( )20 b FH(v)s FK([)p FH(U)t(=X)6 b FK(])25 b(corresp)r(onds)h(exactly)f(to)g(what)h(w)n(e)f(w)n(an)n(t) 167 2891 y(for)j(natural)g(deduction:)660 3026 y FJ(\001)660 3063 y(\001)660 3101 y(\001)644 3159 y FH(A)p 579 3203 181 4 v 781 3219 a FJ(8)821 3194 y FD(2)848 3219 y FJ(I)579 3280 y(8)p FH(X)r(:)12 b(A)p 548 3325 244 4 v 812 3341 a FJ(8)852 3315 y FD(2)879 3341 y FJ(E)548 3401 y FH(A)p FK([)p FH(B)t(=X)6 b FK(])1303 3150 y(con)n(v)n(erts)28 b(to)2132 3145 y FJ(\001)2132 3182 y(\001)2132 3220 y(\001)2020 3282 y FH(A)p FK([)p FH(B)t(=X)6 b FK(])p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 94 97 bop 167 874 a FF(Chapter)28 b(12)167 1168 y(Coherence)g(Seman)-5 b(tics)28 b(of)g(the)f(Sum)167 1487 y FK(Here)i(w)n(e)h(consider)g(the) h(denotational)g(seman)n(tics)e(of)i Fq(Emp)g FK(and)g(+)f(\(corresp)r (onding)i(to)e FJ(?)167 1573 y FK(and)f FJ(_)p FK(\))e(in)n(tro)r (duced)h(in)f(c)n(hapter)g FG(??)q FK(.)270 1746 y Fq(Emp)i FK(is)g(naturally)g(in)n(terpreted)e(as)j(the)f(coherence)f(space)h FJ(E)-17 b FM(mp)34 b FK(whose)c(w)n(eb)f(is)f(empt)n(y)-6 b(,)167 1831 y(and)29 b(the)e(in)n(terpretation)f(of)j FH(")988 1842 y Fw(U)1069 1831 y FK(follo)n(ws)e(immediately)1673 1805 y FD(1)1697 1831 y FK(.)270 2004 y(The)k(sum,)i(on)f(the)e(other)i (hand,)h(p)r(oses)f(some)f(delicate)e(problems.)46 b(When)31 b FJ(A)g FK(and)i FJ(B)167 2089 y FK(are)i(t)n(w)n(o)h(coherence)e (spaces,)k(there)d(is)f(just)i(one)g(ob)n(vious)h(notion)e(of)h(sum,)i (namely)c(the)167 2174 y FM(dir)l(e)l(ct)25 b(sum)31 b FK(in)n(tro)r(duced)24 b(b)r(elo)n(w.)34 b(Unfortunately)-6 b(,)26 b(the)e FH(\016)j FK(sc)n(heme)d(is)g(not)h(in)n(terpreted.)33 b(This)167 2259 y(ob)t(jection)27 b(also)h(holds)g(for)g(other)g(kinds) g(of)g(seman)n(tics,)f(for)h(example)f(Scott)g(domains.)270 2385 y(After)39 b(examining)f(and)i(rejecting)e(a)i(certain)e(n)n(um)n (b)r(er)h(of)g(fudged)h(alternativ)n(es,)i(w)n(e)167 2471 y(are)c(led)g(bac)n(k)h(to)g(the)f(original)f(solution,)k(whic)n (h)d(w)n(ould)h(w)n(ork)f(with)g FM(line)l(ar)46 b FK(functions)167 2556 y(\()p FM(i.e.)28 b FK(preserving)f(unions\),)h(and)h(w)n(e)e (arriv)n(e)g(at)h(a)g(represen)n(tation)f(of)h(the)g(sum)f(t)n(yp)r(e)h (as:)1291 2729 y(!)p FJ(A)16 b(\010)g FK(!)p FJ(B)167 2902 y FK(It)23 b(is)f(this)g(decomp)r(osition)h(whic)n(h)f(is)h(the)f (origin)h(of)g(linear)f(logic:)32 b(the)23 b(op)r(erations)g FJ(\010)g FK(\(direct)167 2987 y(sum\))k(and)i(!)16 b (\(linearisation\))26 b(are)h(in)g(fact)h(logical)e(op)r(erations)i(in) f(their)g(o)n(wn)h(righ)n(t.)p 167 3578 1003 3 v 246 3622 a FC(1)273 3643 y FB(The)g(reader)g(familiar)e(with)h(category)i (theory)f(should)f(notice)g(that)g Fd(Emp)g FB(is)h FA(not)34 b FB(an)28 b(initial)d(ob)s(ject.)167 3713 y(This)h(is)g(to)h(b)r(e)e (exp)r(ected)h(in)f(an)n(y)i(reasonable)g(category)g(of)g(domains,)f(b) r(ecause)g(there)g(can)h(b)r(e)f(no)g(initial)167 3784 y(ob)s(ject)33 b(in)f(a)h(non-degenerate)f(Cartesian)g(closed)h (category)h(where)e(ev)n(ery)i(ob)s(ject)f(is)f(inhabited)e(\(as)j(it) 167 3854 y(will)f(b)r(e)h(if)g(there)h(are)g(\014xp)r(oin)n(ts\).)52 b(With)33 b(linear)f(logic,)j(the)f(problem)e(v)m(anishes)h(b)r(ecause) h(w)n(e)h(do)e(not)167 3925 y(require)27 b(a)h FA(Cartesian)f FB(closed)h(category)-5 b(.)1385 4101 y FK(94)p eop PStoPSsaved restore %%Page: (98,99) 50 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 95 98 bop 167 167 a Fz(12.1.)65 b(DIRECT)26 b(SUM)1776 b FK(95)167 404 y FE(12.1)114 b(Direct)27 b(sum)167 560 y FK(The)50 b(problem)f(with)h(sum)g(t)n(yp)r(es)h(arises)e(from)h(the) h(imp)r(ossibilit)n(y)c(of)k(de\014ning)f(the)167 645 y(in)n(terpretation)26 b(b)n(y)j(means)e(of)i(the)e(direct)f(sum:)743 863 y FJ(jA)15 b(\010)g(B)s(j)k FK(=)g FJ(jAj)c FK(+)h FJ(jB)r(j)j FK(=)g FJ(f)p FK(1)p FJ(g)d(\002)g(jAj)f([)g(f)p FK(2)p FJ(g)i(\002)e(jB)r(j)631 1109 y FK(\(1)p FH(;)d(\013)p FK(\))813 1087 y FH(_)813 1129 y(^)902 1109 y FK(\(1)p FH(;)g(\013)1038 1083 y Fv(0)1055 1109 y FK(\))47 b(\(mo)r(d)23 b FJ(A)16 b(\010)g(B)r FK(\))86 b(if)27 b FH(\013)1747 1087 y(_)1747 1129 y(^)1835 1109 y(\013)1879 1083 y Fv(0)1943 1109 y FK(\(mo)r(d)d FJ(A)p FK(\))632 1279 y(\(2)p FH(;)12 b(\014)t FK(\))813 1257 y FH(_)813 1300 y(^)902 1279 y FK(\(2)p FH(;)g(\014)1037 1253 y Fv(0)1053 1279 y FK(\))47 b(\(mo)r(d)24 b FJ(A)16 b(\010)f(B)r FK(\))88 b(if)27 b FH(\014)1745 1257 y(_)1745 1300 y(^)1834 1279 y(\014)1877 1253 y Fv(0)1940 1279 y FK(\(mo)r(d)d FJ(B)r FK(\))167 1431 y(with)j(incoherence)f(otherwise.)270 1559 y(Domain-theoretically) -6 b(,)37 b(this)e(amoun)n(ts)j(to)f(taking)g(the)f(disjoin)n(t)g (union)h(with)e(the)h Fn(?)167 1644 y FK(elemen)n(t)25 b(iden)n(ti\014ed,)i(so)h(it)f(is)g(sometimes)e(called)h(an)j FM(amalgamate)l(d)g(sum)p FK(.)270 1820 y(If)g(w)n(e)g(de\014ne)g(the)f (\(stable\))g(functions)h FJ(I)-7 b FM(nj)1446 1793 y FD(1)1503 1820 y FK(from)28 b FJ(A)h FK(to)g FJ(A)17 b(\010)e(B)32 b FK(and)e FJ(I)-7 b FM(nj)2308 1793 y FD(2)2365 1820 y FK(from)29 b FJ(B)i FK(to)167 1905 y FJ(A)16 b(\010)f(B)30 b FK(b)n(y)638 2081 y FJ(I)-7 b FM(nj)740 2054 y FD(1)767 2081 y FK(\()p FH(a)p FK(\))20 b(=)f FJ(f)p FK(1)p FJ(g)e(\002)e FH(a)471 b FJ(I)-7 b FM(nj)1750 2054 y FD(2)1778 2081 y FK(\()p FH(b)p FK(\))19 b(=)g FJ(f)p FK(2)p FJ(g)e(\002)e FH(b)167 2257 y FK(ev)n(ery)27 b(ob)t(ject)f(of)h(the)g(coherence)e(space)i FJ(A)15 b(\010)f(B)29 b FK(can)e(b)r(e)f(written)f FJ(I)-7 b FM(nj)2064 2230 y FD(1)2092 2257 y FK(\()p FH(a)p FK(\))26 b(for)h(some)g FH(a)19 b FJ(2)h(A)167 2342 y FK(or)33 b FJ(I)-7 b FM(nj)363 2315 y FD(2)391 2342 y FK(\()p FH(b)p FK(\))32 b(for)h(some)g FH(b)24 b FJ(2)f(B)r FK(.)51 b(This)32 b(expression)h(is)f(unique,)i(except)f(in)f(the)g(case)h(of)g (the)167 2427 y(empt)n(y)26 b(set:)34 b Fn(?)19 b FK(=)h FJ(I)-7 b FM(nj)768 2400 y FD(1)796 2427 y Fn(?)20 b FK(=)f FJ(I)-7 b FM(nj)1046 2400 y FD(2)1073 2427 y Fn(?)p FK(.)35 b(This)26 b(non-uniqueness)h(of)g(the)e(decomp)r(osition)h(mak) n(es)167 2512 y(it)h(imp)r(ossible)e(to)j(de\014ne)g(a)g(function)g (casewise)616 2689 y FH(H)5 b FK(\()p FJ(I)-7 b FM(nj)807 2662 y FD(1)835 2689 y FK(\()p FH(a)p FK(\)\))19 b(=)g FH(F)10 b FK(\()p FH(a)p FK(\))448 b FH(H)5 b FK(\()p FJ(I)-7 b FM(nj)1828 2662 y FD(2)1856 2689 y FK(\()p FH(b)p FK(\)\))19 b(=)h FH(G)p FK(\()p FH(b)p FK(\))167 2865 y(from)31 b(t)n(w)n(o)h(stable)e(functions)i FH(F)40 b FK(from)31 b FJ(A)h FK(to)f FJ(C)36 b FK(and)c FH(G)g FK(from)f FJ(B)i FK(to)f FJ(C)t FK(.)46 b(Indeed)31 b(this)g(fails)167 2950 y(for)d(the)f(argumen)n(t)h Fn(?)p FK(,)g(since)e FH(F)10 b FK(\()p Fn(?)p FK(\))27 b(has)h(no)h(reason)f(to)g(b)r(e)g (equal)f(to)h FH(G)p FK(\()p Fn(?)p FK(\).)167 3187 y FE(12.2)114 b(Lifted)28 b(sum)167 3343 y FK(A)k(\014rst)f(solution)h (is)f(giv)n(en)h(b)n(y)h(adding)g(t)n(w)n(o)f FM(tags)g FK(1)g(and)h(2)f(to)g FJ(jA)16 b(\010)f(B)s(j)31 b FK(to)h(form)g FJ(A)17 b(q)g(B)r FK(:)167 3428 y(1)26 b(is)g(coheren)n(t)f(with)g(the) h(\(1)p FH(;)12 b(\013)p FK(\))26 b(but)g(not)h(with)e(the)g(\(2)p FH(;)12 b(\014)t FK(\))26 b(and)h(lik)n(ewise)c(2)k(with)e(the)g(\(2)p FH(;)12 b(\014)t FK(\))167 3513 y(but)28 b(not)g(with)f(the)g(\(1)p FH(;)12 b(\013)p FK(\).)270 3640 y(W)-6 b(e)28 b(can)g(then)g (de\014ne:)553 3817 y FJ(q)606 3787 y FD(1)634 3817 y FK(\()p FH(a)p FK(\))20 b(=)f FJ(f)p FK(1)p FJ(g)d([)g(I)-7 b FM(nj)1102 3789 y FD(1)1130 3817 y FK(\()p FH(a)p FK(\))386 b FJ(q)1659 3787 y FD(2)1687 3817 y FK(\()p FH(b)p FK(\))19 b(=)g FJ(f)p FK(2)p FJ(g)e([)e(I)-7 b FM(nj)2147 3789 y FD(2)2175 3817 y FK(\()p FH(b)p FK(\))p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 96 99 bop 167 167 a FK(96)537 b Fz(CHAPTER)27 b(12.)64 b(COHERENCE)25 b(SEMANTICS)j(OF)f(THE)g(SUM)270 404 y FK(No)n(w,)h(from)g FH(F)37 b FK(and)28 b FH(G)p FK(,)g(the)g(casewise) e(de\014nition)h(is)g(p)r(ossible:)648 597 y FH(H)5 b FK(\()p FJ(q)791 567 y FD(1)818 597 y FK(\()p FH(a)p FK(\)\))20 b(=)f FH(F)10 b FK(\()p FH(a)p FK(\))480 b FH(H)5 b FK(\()p FJ(q)1795 567 y FD(2)1823 597 y FK(\()p FH(b)p FK(\)\))20 b(=)f FH(G)p FK(\()p FH(b)p FK(\))1025 789 y FH(H)5 b FK(\()p FH(c)p FK(\))19 b(=)h Fn(?)78 b FK(if)26 b FH(c)16 b FJ(\\)f(f)p FK(1)p FH(;)d FK(2)q FJ(g)20 b FK(=)f Fn(?)167 981 y FK(In)33 b(other)g(w)n(ords,)j(in)c (order)h(to)h(kno)n(w)g(whether)e FH(\015)27 b FJ(2)c FH(H)5 b FK(\()p FH(c)p FK(\),)35 b(w)n(e)d(lo)r(ok)i(inside)e FH(c)g FK(for)i(a)f(tag)167 1066 y(1)26 b(or)h(2,)g(then)f(if)f(w)n(e)h (\014nd)h(one)f(\(sa)n(y)h(1\),)g(w)n(e)e(write)f FH(c)c FK(=)f FJ(q)1711 1036 y FD(1)1739 1066 y FK(\()p FH(a)p FK(\))25 b(and)j(ask)f(whether)e FH(\015)e FJ(2)d FH(G)p FK(\()p FH(a)p FK(\).)270 1202 y(This)28 b(solution)f(in)n(terprets)f (the)i(standard)h(con)n(v)n(ersion)f(sc)n(hemes:)504 1394 y FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b FK(\()p FH(\023)859 1368 y FD(1)887 1394 y FH(r)r FK(\))f Fu( )g FH(u)p FK([)p FH(r)r(=x)p FK(])338 b FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b FK(\()p FH(\023)1933 1368 y FD(2)1961 1394 y FH(s)p FK(\))f Fu( )g FH(v)s FK([)p FH(s=y)s FK(])167 1586 y(Ho)n(w)n(ev)n(er)27 b(the)h(in)n (terpretation)e FH(H)33 b FK(of)28 b(the)g(term)e FH(\016)c(x:)12 b FK(\()p FH(\023)1656 1560 y FD(1)1684 1586 y FH(x)p FK(\))20 b FH(y)s(:)12 b FK(\()p FH(\023)1889 1560 y FD(2)1916 1586 y FH(y)s FK(\))18 b FH(z)s FK(,)28 b(whic)n(h)f(is)g (de\014ned)h(b)n(y)631 1778 y FH(H)5 b FK(\()p FJ(q)773 1749 y FD(1)801 1778 y FK(\()p FH(a)p FK(\)\))19 b(=)g FJ(q)1063 1749 y FD(1)1091 1778 y FK(\()p FH(a)p FK(\))464 b FH(H)5 b FK(\()p FJ(q)1787 1749 y FD(2)1815 1778 y FK(\()p FH(b)p FK(\)\))19 b(=)g FJ(q)2070 1749 y FD(2)2098 1778 y FK(\()p FH(b)p FK(\))1025 1970 y FH(H)5 b FK(\()p FH(c)p FK(\))19 b(=)h Fn(?)78 b FK(if)26 b FH(c)16 b FJ(\\)f(f)p FK(1)p FH(;)d FK(2)q FJ(g)20 b FK(=)f Fn(?)167 2163 y FK(do)r(es)32 b(not)g(alw)n(a)n(ys)h(satisfy)f FH(H)5 b FK(\()p FH(c)p FK(\))22 b(=)g FH(c)p FK(.)48 b(In)31 b(fact)h(this)f(equation)h(is)f(satis\014ed)h(only)g(for)g FH(c)g FK(of)167 2248 y(the)27 b(form)h FJ(q)511 2218 y FD(1)539 2248 y FK(\()p FH(a)p FK(\),)f FJ(q)728 2218 y FD(2)756 2248 y FK(\()p FH(b)p FK(\))g(or)h Fn(?)p FK(.)270 2383 y(On)36 b(the)g(other)g(hand,)k(the)c(comm)n(uting)f(con) n(v)n(ersions)i(do)g(hold:)53 b(let)34 b FH(t)26 b FJ(7!)g Fq(E)12 b FH(t)35 b FK(b)r(e)h(an)167 2468 y(elimination)31 b(of)j(the)g(form)f FH(\031)972 2443 y FD(1)1000 2468 y FH(t)p FK(,)i(or)f FH(\031)1216 2443 y FD(2)1244 2468 y FH(t)p FK(,)h(or)f FH(t)12 b(w)r FK(,)36 b(or)e FH(")1688 2479 y Fw(U)1742 2468 y FH(t)p FK(,)h(or)f FH(\016)26 b(x)2012 2443 y Fv(0)2029 2468 y FH(:)12 b(u)2099 2443 y Fv(0)2139 2468 y FH(y)2176 2443 y Fv(0)2192 2468 y FH(:)g(v)2259 2443 y Fv(0)2299 2468 y FH(t)p FK(.)54 b(W)-6 b(e)34 b(w)n(an)n(t)167 2554 y(to)28 b(c)n(hec)n(k)f(that)i Fq(E)12 b FK(\()p FH(\016)21 b(x:)12 b(u)20 b(y)s(:)12 b(v)22 b(t)p FK(\))27 b(and)i FH(\016)22 b(x:)12 b FK(\()p Fq(E)g FH(u)p FK(\))19 b FH(y)s(:)12 b FK(\()p Fq(E)g FH(v)s FK(\))18 b FH(t)28 b FK(ha)n(v)n(e)g(the)g(same)f(in)n (terpretation.)167 2639 y(In)33 b(the)f(case)g(where)f(\(seman)n (tically\))f FH(t)j FK(is)e FJ(q)1401 2609 y FD(1)1429 2639 y FH(a)p FK(,)j(the)e(t)n(w)n(o)h(expressions)f(giv)n(e)g([)-12 b([)q Fq(E)12 b FH(u)p FK(])-12 b(])q(\()p FH(a)p FK(\).)49 b(In)167 2724 y(the)37 b(case)f(where)g FH(c)18 b FJ(\\)h(f)p FK(1)p FH(;)12 b FK(2)q FJ(g)26 b FK(=)g Fn(?)p FK(,)39 b(w)n(e)d(get)h(on)h(the)e(one)h(hand)i FH(E)t FK(\()p Fn(?)p FK(\))d(where)g FH(E)41 b FK(is)36 b(the)167 2809 y(stable)26 b(function)h(corresp)r(onding)h(to)f Fq(E)p FK(,)g(and)h(on)g(the)e(other)h Fn(?)p FK(;)g(but)g(it)f(is)g(easy)h (to)g(see)g(that)167 2894 y FH(E)t FK(\()p Fn(?)p FK(\))19 b(=)g Fn(?)28 b FK(\()p FH(E)j FK(is)c FM(strict)p FK(\))h(in)f(all)f (the)h(cases)h(in)f(question.)270 3030 y(Ha)n(ving)35 b(said)g(this,)g(the)f(presence)f(of)i(an)g(equation)g(\(ho)n(w)n(ev)n (er)f(minor\))f(whic)n(h)h(is)g(not)167 3115 y(in)n(terpreted)d(means)i (w)n(e)g(m)n(ust)f(reject)g(the)g(seman)n(tics.)51 b(Ev)n(en)33 b(if)f(w)n(e)g(are)h(unsure)g(ho)n(w)h(to)167 3200 y(use)28 b(it,)e(the)i(equation)1076 3392 y FH(\016)22 b(x:)12 b FK(\()p FH(\023)1250 3367 y FD(1)1278 3392 y FH(x)p FK(\))20 b FH(y)s(:)12 b FK(\()p FH(\023)1483 3367 y FD(2)1510 3392 y FH(y)s FK(\))19 b FH(t)g FK(=)g FH(t)167 3584 y FK(pla)n(ys)26 b(a)f(part)h(in)f(the)g(implicit)c(symmetries)i (of)i(the)g(disjunction.)35 b(Once)24 b(again,)j(w)n(e)d(are)i(not)167 3669 y(lo)r(oking)33 b(for)h(a)f(mo)r(del)g(at)g(an)n(y)h(price,)g(but) f(for)g(a)h(con)n(vincing)f(one.)52 b(F)-6 b(or)34 b(that,)h(ev)n(en)e (the)167 3754 y(secondary)24 b(connectors)f(\(suc)n(h)g(as)g FJ(_)p FK(\))f(and)i(the)e(marginal)g(equations)h(are)g(precious,)g(b)r (ecause)167 3840 y(they)k(sho)n(w)g(up)g(some)g(p)r(oin)n(ts)g(of)g (discord)f(b)r(et)n(w)n(een)g(syn)n(tax)j(and)e(seman)n(tics.)34 b(By)27 b(trying)g(to)167 3925 y(analyse)h(this)f(discord,)h(one)g(can) g(hop)r(e)g(to)g(\014nd)h(some)e(prop)r(erties)g(hidden)h(in)f(the)g (syn)n(tax.)p eop PStoPSsaved restore %%Page: (100,101) 51 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 97 100 bop 167 167 a Fz(12.2.)65 b(LIFTED)27 b(SUM)1788 b FK(97)167 404 y Fy(12.2.1)94 b(dI-domains)167 536 y FK(There)29 b(is)g(a)h(simple)d(solution,)j(but)g(it)f(requires)g(the)g (abandonmen)n(t)j(of)e(coherence)e(spaces:)167 621 y(let)39 b(us)h(simply)e(sa)n(y)k(that)e(in)f FJ(A)20 b(q)f(B)r FK(,)43 b(w)n(e)c(only)i(consider)e(suc)n(h)i(ob)t(jects)f(as)g FJ(q)2436 592 y FD(1)2464 621 y FH(a)p FK(,)j FJ(q)2615 592 y FD(2)2643 621 y FH(b)167 706 y FK(and)32 b Fn(?)p FK(.)46 b(As)31 b(a)h(result)e(of)i(what)f(has)i(gone)f(b)r(efore,)g (ev)n(erything)f(will)e(w)n(ork)i(prop)r(erly)-6 b(,)33 b(but)167 792 y(the)28 b(structure)f(so)i(obtained)f(is)f(no)i(longer)f (a)g(coherence)g(space:)36 b(indeed,)27 b(if)h FH(\013)20 b FJ(2)f(jAj)p FK(,)28 b(then)167 877 y FJ(q)220 847 y FD(1)248 877 y FH(\013)20 b FK(=)f FJ(f)p FK(1)p FH(;)12 b FK(\(1)p FH(;)g(\013)p FK(\))q FJ(g)28 b FK(app)r(ears)g(in)f FJ(A)16 b(q)g(B)r FK(,)28 b(but)g(not)g(its)f(subset)h FJ(f)p FK(\(1)p FH(;)12 b(\013)p FK(\))q FJ(g)p FK(.)270 1005 y(In)33 b(fact,)g(w)n(e)e(see)h(that)g(it)f(is)g(necessary)h(to)h (add)g(to)f(the)g(idea)f(of)i FM(c)l(oher)l(enc)l(e)k FK(a)32 b FM(p)l(artial)167 1090 y(or)l(der)g(r)l(elation)5 b FK(,)33 b(here)e(1)23 b FH(<)f FK(\(1)p FH(;)12 b(\013)p FK(\),)32 b(2)23 b FH(<)f FK(\(2)p FH(;)12 b(\014)t FK(\).)47 b(W)-6 b(e)31 b(are)g(in)n(terested)f(in)h(coheren)n(t)g(subsets)167 1175 y(of)h(the)f(space)g(whic)n(h)g(are)g FM(downwar)l(ds-close)l(d)7 b FK(:)43 b(if)31 b FH(\013)1612 1150 y Fv(0)1650 1175 y FH(<)22 b(\013)h FJ(2)f FH(a)p FK(,)32 b(then)f FH(\013)2158 1150 y Fv(0)2197 1175 y FJ(2)22 b FH(a)p FK(.)47 b(According)167 1260 y(to)28 b([)p FG(?)p FK(],)g(the)f(tok)n(ens)i(should)f(b)r(e)f (regarded)h(as)g(\\ev)n(en)n(ts",)h(where)e(coherence)g(sp)r(eci\014es) f(when)167 1346 y(t)n(w)n(o)k(ev)n(en)n(ts)h FM(may)37 b FK(co-exist)30 b(and)h(the)f(partial)f(order)h FH(\013)1668 1320 y Fv(0)1706 1346 y FH(<)21 b(\013)31 b FK(sa)n(ys)g(that)g(if)e (the)h(ev)n(en)n(t)g FH(\013)h FK(is)167 1431 y(presen)n(t)d(then)g (the)f(ev)n(en)n(t)h FH(\013)928 1405 y Fv(0)973 1431 y FM(must)34 b FK(also)29 b(b)r(e)e(presen)n(t.)36 b(This)28 b(is)f(called)f(an)j FM(event)d(structur)l(e)p FK(;)167 1516 y([)p FG(?)q FK(])h(c)n(haracterises)g(the)g(resulting)g(spaces,)h (whic)n(h)f(are)h(exactly)f([)p FG(?)p FK(]'s)h(original)f FM(dI-domains)p FK(.)270 1644 y(As)35 b(an)g(example,)g(one)f(can)h (re-de\014ne)f(the)g FM(lazy)h(natur)l(al)f(numb)l(ers)p FK(,)i FJ(I)-7 b FM(nt)2288 1619 y FD(+)2330 1644 y FK(,)36 b(whic)n(h)e(w)n(e)167 1729 y(met)27 b(in)h(section)f FG(??)q FK(.)38 b(Clearly)26 b(w)n(e)i(w)n(an)n(t)h FH(p)1323 1704 y FD(+)1384 1729 y FH(<)20 b(q)30 b FK(and)g FH(p)1694 1704 y FD(+)1755 1729 y FH(<)20 b(q)1863 1704 y FD(+)1932 1729 y FK(for)29 b FH(p)19 b(<)h(q)s FK(;)28 b(one)g(ma)n(y)h(then)167 1814 y(sho)n(w)34 b(that)f(the)g(p)r(oin)n(ts)h(of)f(the)g(corresp)r (onding)h(dI-domain)g FJ(I)-7 b FM(nt)1966 1789 y Fw(<)2041 1814 y FK(are)33 b(just)g(the)j Fo(e)-42 b FH(p)p FK(,)31 b(\027)-49 b FH(p)p FK(,)34 b Fn(?)167 1900 y FK(and)29 b Fo(f)-70 b FJ(1)p FK(.)36 b(The)27 b(three)g(spaces)h(satisfy)g(the)f FM(domain)i(e)l(quations)330 2077 y FJ(I)-7 b FM(nt)27 b FJ(')19 b(S)-6 b FM(gl)21 b FJ(\010)16 b(I)-7 b FM(nt)163 b FJ(I)-7 b FM(nt)1060 2052 y FD(+)1121 2077 y FJ(')19 b(S)-6 b FM(gl)22 b FJ(\010)15 b FK(\()p FJ(S)-6 b FM(gl)21 b FK(&)16 b FJ(I)-7 b FM(nt)1679 2052 y FD(+)1721 2077 y FK(\))156 b FJ(I)-7 b FM(nt)2004 2052 y Fw(<)2065 2077 y FJ(')20 b(E)-17 b FM(mp)20 b FJ(q)c(I)-7 b FM(nt)2440 2052 y Fw(<)167 2255 y FK(where)30 b FJ(S)-6 b FM(gl)36 b FK(is)30 b(the)g(coherence)f(space)i(with)f(just)g(one)h(tok)n(en)g (\(section)f FG(??)q FK(\).)44 b(This)29 b(ma)n(y)i(b)r(e)167 2340 y(used)d(as)g(an)h(alternativ)n(e)d(w)n(a)n(y)j(of)f(de\014ning)g (inductiv)n(e)e(data)j(t)n(yp)r(es.)270 2469 y(The)h(damage)h(caused)f (b)n(y)h(this)e(in)n(terpretation)g(is)g(limited,)f(b)r(ecause)i(one)g (can)g(require)167 2554 y(that)21 b(for)h(all)e FH(\013)f FJ(2)h(jAj)p FK(,)i(the)f(set)f(of)i FH(\013)1122 2528 y Fv(0)1158 2554 y FH(<)d(\013)j FK(b)r(e)e(\014nite,)i(whic)n(h)f (ensures)g(that)g(the)g(do)n(wn-closure)167 2639 y(of)29 b(a)h(\014nite)e(set)g(is)g(alw)n(a)n(ys)i(\014nite,)e(and)i(so)f(w)n (e)g(are)g(sa)n(v)n(ed)h(from)e(one)h(of)h(our)f(ob)t(jections)g(to)167 2724 y(Scott)f(domains.)270 2902 y(Seman)n(tically)-6 b(,)34 b(there)f(is)g(nothing)i(else)e(to)h(quarrel)f(with)g(ab)r(out)i (this)e(in)n(terpretation,)167 2987 y(whic)n(h)28 b(accoun)n(ts)i(for)g (all)d(reasonable)j(constructions.)40 b(But)29 b(on)h(the)e(other)h (hand,)i(it)d(forces)167 3072 y(us)44 b(to)g(lea)n(v)n(e)g(the)f(class) h(of)g(coherence)f(spaces,)49 b(and)44 b(uses)h(an)f(order)g(relation)f (whic)n(h)167 3157 y(compromises)27 b(the)g(conceptual)g(simplicit)n(y) d(of)29 b(the)e(system.)270 3286 y(This)j(leads)g(us)h(to)g(lo)r(ok)f (for)h(something)f(else,)g(whic)n(h)g(do)r(es)h(preserv)n(e)e(this)h (class.)43 b(The)167 3371 y(price)c(will)f(b)r(e)i(a)h(more)f (complicated)f(in)n(terpretation)g(of)i(the)f(sum)h(\(although)g(w)n(e) f(are)167 3456 y(basically)26 b(only)h(in)n(terested)e(in)h(the)g(sum)h (as)g(a)g(test)f(for)h(our)g(seman)n(tic)e(ideas\))i(but)g(w)n(e)f (shall)167 3541 y(b)r(e)h(rew)n(arded)h(with)f(a)h(no)n(v)n(el)g(idea:) 35 b FM(line)l(arity)p FK(.)270 3669 y(The)29 b(in)n(terpretation)e(w)n (e)g(shall)h(giv)n(e)g(is)g(manifestly)f(not)i(asso)r(ciativ)n(e.)37 b(It)28 b(is)g(in)n(teresting)167 3754 y(to)44 b(remark)g(that)g(Winsk) n(el's)f(in)n(terpretation)g(is)g(not)i(either:)66 b(indeed,)48 b(if)43 b FJ(A)p FH(;)12 b FJ(B)r FH(;)g FJ(C)48 b FK(are)167 3840 y(coherence)23 b(spaces)i(considered)f(as)g(ev)n(en)n(t)h (structures)e(\(with)g(a)i(trivial)d(order)i(relation\))f(then)167 3925 y(\()p FJ(A)16 b(q)f(B)r FK(\))h FJ(q)g(C)31 b FK(and)e FJ(A)16 b(q)f FK(\()p FJ(B)j(q)e(C)t FK(\))27 b(are)h(not)g(the)f (same:)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 98 101 bop 167 167 a FK(98)537 b Fz(CHAPTER)27 b(12.)64 b(COHERENCE)25 b(SEMANTICS)j(OF)f(THE)g(SUM)276 435 y FK(\(1)p FH(;)12 b FK(\(1)p FH(;)g(\013)p FK(\)\))53 b(\(1)p FH(;)12 b FK(\(2)p FH(;)g(\014)t FK(\)\))341 686 y(\(1)p FH(;)g FK(1\))181 b(\(1)p FH(;)12 b FK(2\))178 b(\(2)p FH(;)12 b(\015)t FK(\))567 941 y(1)467 b(2)p 416 585 3 84 v 750 585 V 1084 835 V 492 835 a Fs(@)468 810 y(@)635 835 y(\000)659 810 y(\000)651 1103 y FK(\()p FJ(A)16 b(q)f(B)r FK(\))h FJ(q)g(C)2283 435 y FK(\(2)p FH(;)c FK(\(2)p FH(;)g(\015)t FK(\)\))-614 b(\(2)p FH(;)12 b FK(\(1)p FH(;)g(\014)t FK(\)\))2345 686 y(\(2)p FH(;)g FK(2\))-487 b(\(2)p FH(;)12 b FK(1\))-492 b(\(1)p FH(;)12 b(\013)p FK(\))2237 941 y(2)-535 b(1)p 2420 585 V 2086 585 V 1752 835 V 2288 835 a Fs(\000)2313 810 y(\000)2146 835 y(@)2121 810 y(@)1820 1103 y FJ(A)16 b(q)g FK(\()p FJ(B)i(q)d(C)t FK(\))167 1412 y FE(12.3)114 b(Linearit)m(y)167 1571 y FK(W)-6 b(e)32 b(ha)n(v)n(e)h(already)f(remark)n(ed)g(that)g (the)g(op)r(eration)g FH(t)23 b FJ(7!)g FH(t)12 b(u)31 b FK(is)h(strict,)f FM(i.e.)h FK(preserv)n(es)g Fn(?)p FK(.)167 1656 y(Better)c(than)i(this)f(it)g(is)g FM(line)l(ar)p FK(.)40 b(Let)29 b(us)h(lo)r(ok)g(no)n(w)g(at)g(what)g(that)g(can)g (mean.)41 b(Let)29 b FH(E)k FK(b)r(e)167 1741 y(the)27 b(function)h(from)g FJ(A)15 b(!)i(B)30 b FK(to)d FJ(B)j FK(de\014ned)f(b)n(y)699 1927 y FH(E)t FK(\()p FH(f)8 b FK(\))19 b(=)g FH(f)8 b FK(\()p FH(a)p FK(\))78 b(where)27 b FH(a)h FK(is)f(a)h(giv)n(en)f(ob)t(ject)h(of)g FJ(A)p FK(.)270 2159 y(Let)35 b(us)h(w)n(ork)g(out)f FJ(T)-6 b FH(r)r FK(\()p FH(E)t FK(\):)51 b(w)n(e)35 b(ha)n(v)n(e)h(to)g (\014nd)g(all)e(the)h FH(\014)28 b FJ(2)d FH(E)t FK(\()p FH(f)8 b FK(\))35 b(with)f FH(f)43 b FK(minimal.)167 2244 y(No)n(w)31 b FH(\014)26 b FJ(2)c FH(E)t FK(\()p FH(f)8 b FK(\))22 b(=)f FH(f)8 b FK(\()p FH(a)p FK(\))31 b(i\013)f(there)h(exists)f(some)h FH(a)1567 2255 y Fv(\016)1618 2244 y FJ(\032)21 b FH(a)32 b FK(suc)n(h)g(that)f(\()p FH(a)2146 2255 y Fv(\016)2174 2244 y FH(;)12 b(\014)t FK(\))22 b FJ(2)g FH(f)8 b FK(.)45 b(So)32 b(the)167 2330 y(minimal)c FH(f)39 b FK(are)31 b(the)h(singletons)f FJ(f)p FK(\()p FH(a)1192 2341 y Fv(\016)1220 2330 y FH(;)12 b(\014)t FK(\))o FJ(g)32 b FK(with)e FH(a)1588 2341 y Fv(\016)1638 2330 y FJ(\032)22 b FH(a)p FK(,)33 b FH(a)1839 2341 y Fv(\016)1898 2330 y FK(\014nite,)f(and)g(the)f(ob)t(jects)h(of) 167 2415 y FJ(T)-6 b FH(r)r FK(\()p FH(E)t FK(\))28 b(are)g(of)g(the)f (form)701 2601 y(\()p FJ(f)p FK(\()p FH(a)826 2612 y Fv(\016)854 2601 y FH(;)12 b(\014)t FK(\))p FJ(g)p FH(;)24 b(\014)t FK(\))77 b(with)27 b FH(\014)d FJ(2)19 b(jB)r(j)p FK(,)27 b FH(a)1641 2612 y Fv(\016)1689 2601 y FJ(\032)19 b FH(a)p FK(,)28 b FH(a)1882 2612 y Fv(\016)1938 2601 y FK(\014nite.)270 2833 y(A)34 b(stable)f(function)h FH(F)43 b FK(from)34 b FJ(A)g FK(to)g FJ(B)j FK(is)c FM(line)l(ar)g FK(precisely)f(when)i FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))34 b(consists)g(of)167 2918 y(pairs)28 b(\()p FJ(f)p FH(\013)p FJ(g)p FH(;)12 b(\014)t FK(\))27 b(with)g FH(\013)20 b FJ(2)f(jAj)27 b FK(and)i FH(\014)23 b FJ(2)d(jB)r(j)p FK(.)167 3131 y Fy(12.3.1)94 b(Characterisation)28 b(in)g(terms)e(of)h(preserv)-5 b(ation)167 3265 y FK(Let)27 b(us)h(lo)r(ok)g(at)g(some)g(of)g(the)f(prop)r(erties)g(of)h(linear)e (functions.)201 3435 y(i\))51 b FH(F)10 b FK(\()p Fn(?)p FK(\))35 b(=)h Fn(?)p FK(.)105 b(Indeed,)58 b(to)51 b(ha)n(v)n(e)h FH(\014)41 b FJ(2)36 b FH(F)10 b FK(\()p Fn(?)p FK(\),)56 b(w)n(e)50 b(need)i FH(a)2101 3446 y Fv(\016)2165 3435 y FJ(\032)36 b Fn(?)51 b FK(suc)n(h)h(that)339 3520 y(\()p FH(a)402 3531 y Fv(\016)430 3520 y FH(;)12 b(\014)t FK(\))19 b FJ(2)h(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\);)27 b(but)h FH(a)1004 3531 y Fv(\016)1052 3520 y FK(=)19 b Fn(?)28 b FK(and)g(so)h(cannot)f(b)r(e)g(a)g(singleton.)201 3669 y(ii\))81 b(If)i FH(a)514 3680 y FD(1)573 3669 y FJ([)31 b FH(a)687 3680 y FD(2)774 3669 y FJ(2)58 b(A)p FK(,)97 b(then)82 b FH(F)10 b FK(\()p FH(a)1385 3680 y FD(1)1444 3669 y FJ([)31 b FH(a)1558 3680 y FD(2)1586 3669 y FK(\))58 b(=)g FH(F)10 b FK(\()p FH(a)1901 3680 y FD(1)1928 3669 y FK(\))31 b FJ([)h FH(F)10 b FK(\()p FH(a)2183 3680 y FD(2)2210 3669 y FK(\).)200 b(Clearly)339 3754 y FH(F)10 b FK(\()p FH(a)457 3765 y FD(1)485 3754 y FK(\))19 b FJ([)h FH(F)10 b FK(\()p FH(a)716 3765 y FD(2)743 3754 y FK(\))30 b FJ(\032)g FH(F)10 b FK(\()p FH(a)1003 3765 y FD(1)1050 3754 y FJ([)20 b FH(a)1153 3765 y FD(2)1181 3754 y FK(\).)81 b(Con)n(v)n(ersely)-6 b(,)47 b(if)41 b FH(\014)34 b FJ(2)d FH(F)10 b FK(\()p FH(a)2045 3765 y FD(1)2092 3754 y FJ([)20 b FH(a)2195 3765 y FD(2)2223 3754 y FK(\),)46 b(that)d(means)339 3840 y(there)27 b(is)g(some)g FH(a)807 3814 y Fv(0)843 3840 y FJ(\032)19 b FH(a)953 3851 y FD(1)996 3840 y FJ([)c FH(a)1094 3851 y FD(2)1150 3840 y FK(suc)n(h)28 b(that)f(\()p FH(a)1526 3814 y Fv(0)1543 3840 y FH(;)12 b(\014)t FK(\))19 b FJ(2)g(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\);)27 b(but)h FH(a)2116 3814 y Fv(0)2160 3840 y FK(is)f(a)g(singleton,)g(so)339 3925 y FH(a)375 3899 y Fv(0)412 3925 y FJ(\032)19 b FH(a)522 3936 y FD(1)550 3925 y FK(,)28 b(in)f(whic)n(h)g(case)g FH(\014)d FJ(2)19 b FH(F)10 b FK(\()p FH(a)1281 3936 y FD(1)1308 3925 y FK(\),)28 b(or)g FH(a)1507 3899 y Fv(0)1543 3925 y FJ(\032)20 b FH(a)1654 3936 y FD(2)1682 3925 y FK(,)27 b(in)g(whic)n(h)g(case)h FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(a)2413 3936 y FD(2)2440 3925 y FK(\).)p eop PStoPSsaved restore %%Page: (102,103) 52 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 99 102 bop 167 167 a Fz(12.3.)65 b(LINEARITY)1834 b FK(99)270 404 y(These)39 b(prop)r(erties)f(c)n(haracterise)f(the)i(stable)f (functions)h(whic)n(h)f(are)h(linear;)k(indeed,)167 490 y(if)27 b FH(\014)c FJ(2)d FH(F)10 b FK(\()p FH(a)p FK(\))26 b(with)h FH(a)h FK(minimal,)d FH(a)j FK(m)n(ust)f(b)r(e)h(a)g (singleton:)201 652 y(i\))f FH(F)10 b FK(\()p Fn(?)p FK(\))18 b(=)h Fn(?)p FK(,)28 b(so)g FH(a)20 b FJ(6)p FK(=)f Fn(?)p FK(.)201 797 y(ii\))27 b(if)h FH(a)21 b FK(=)f FH(a)531 771 y Fv(0)564 797 y FJ([)15 b FH(a)662 771 y Fv(00)693 797 y FK(,)29 b(then)g FH(F)10 b FK(\()p FH(a)p FK(\))19 b(=)h FH(F)10 b FK(\()p FH(a)1260 771 y Fv(0)1276 797 y FK(\))16 b FJ([)g FH(F)10 b FK(\()p FH(a)1500 771 y Fv(00)1529 797 y FK(\),)29 b(so)g FH(\014)24 b FJ(2)d FH(F)10 b FK(\()p FH(a)1943 771 y Fv(0)1958 797 y FK(\))29 b(or)g FH(\014)24 b FJ(2)d FH(F)10 b FK(\()p FH(a)2353 771 y Fv(00)2382 797 y FK(\);)29 b(so,)h(if)e FH(a)339 882 y FK(is)d(not)h(a)f(singleton,)h(w)n(e)e(can)i(\014nd)g(a) g(decomp)r(osition)e FH(a)c FK(=)f FH(a)1962 856 y Fv(0)1991 882 y FJ([)12 b FH(a)2086 856 y Fv(00)2141 882 y FK(whic)n(h)24 b(con)n(tradicts)339 967 y(the)k(minimalit)n(y)c(of)k FH(a)p FK(.)270 1171 y(Prop)r(erties)f(\(i\))f(and)j(\(ii\))c(com)n (bine)i(with)g(preserv)l(ation)h(of)g(\014ltered)e(unions)j(\()p FG(Lin)p FK(\):)731 1334 y(if)e FH(A)19 b FJ(\032)h(A)p FK(,)27 b(and)i(for)f(all)f FH(a)1433 1345 y FD(1)1461 1334 y FH(;)12 b(a)1528 1345 y FD(2)1575 1334 y FJ(2)20 b FH(A)p FK(,)27 b FH(a)1776 1345 y FD(1)1820 1334 y FJ([)15 b FH(a)1918 1345 y FD(2)1966 1334 y FJ(2)20 b(A)p FK(,)915 1419 y(then)27 b FH(F)10 b FK(\()1158 1367 y Fo(S)1228 1419 y FH(A)p FK(\))19 b(=)1399 1367 y Fo(S)1458 1419 y FJ(f)p FH(F)10 b FK(\()p FH(a)p FK(\))19 b(:)39 b FH(a)20 b FJ(2)f FH(A)p FJ(g)167 1582 y FK(Observ)n(e)34 b(that)g(this)f(condition)h(is)f(in)g(the)h(spirit)e(of)i(coherence)f (spaces,)j(whic)n(h)e(m)n(ust)f(b)r(e)167 1667 y(closed)h(under)h (pairwise-b)r(ounded)g(unions.)57 b(So)35 b(w)n(e)f(can)h(de\014ne)g FM(line)l(ar)g(stable)e(functions)167 1752 y FK(from)27 b FJ(A)h FK(to)g FJ(B)i FK(b)n(y)f(\()p FG(Lin)p FK(\))c(and)k(\()p FG(St)p FK(\):)702 1915 y(if)e FH(a)806 1926 y FD(1)850 1915 y FJ([)15 b FH(a)948 1926 y FD(2)996 1915 y FJ(2)k(A)28 b FK(then)g FH(F)10 b FK(\()p FH(a)1426 1926 y FD(1)1469 1915 y FJ(\\)15 b FH(a)1567 1926 y FD(2)1595 1915 y FK(\))20 b(=)f FH(F)10 b FK(\()p FH(a)1833 1926 y FD(1)1860 1915 y FK(\))16 b FJ(\\)f FH(F)10 b FK(\()p FH(a)2083 1926 y FD(2)2110 1915 y FK(\))167 2078 y(the)27 b(monotonicit)n(y)h(of)g FH(F)37 b FK(b)r(eing)27 b(a)h(consequence)g(of)g(\()p FG(Lin)p FK(\).)167 2283 y Fy(12.3.2)94 b(Linear)29 b(implication)167 2414 y FK(W)-6 b(e)37 b(stra)n(y)n(ed)h(from)f(the)h(trace)e(to)i(giv)n (e)f(a)h(c)n(haracterisation)f(in)f(terms)h(of)h(preserv)l(ation.)167 2499 y(Returning)25 b(to)h(it,)f(if)g(w)n(e)g(kno)n(w)h(that)g FH(F)35 b FK(is)25 b(linear,)f(w)n(e)h(can)h(discard)g(the)f(singleton) g(sym)n(b)r(ols)167 2585 y(in)i FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\):)933 2760 y FJ(T)-6 b FM(rlin)5 b FK(\()p FH(F)10 b FK(\))19 b(=)g FJ(f)p FK(\()p FH(\013;)12 b(\014)t FK(\))19 b(:)40 b FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(\013)p FK(\))p FJ(g)270 2935 y FK(The)29 b(set)g(of)g(all)f(the)h FJ(T)-6 b FM(rlin)5 b FK(\()p FH(F)10 b FK(\))28 b(as)h FH(F)39 b FK(v)l(aries)28 b(o)n(v)n(er)i(stable)e(linear)g(functions)h (from)g FJ(A)g FK(to)167 3020 y FJ(B)i FK(forms)e(a)h(coherence)e (space)h FJ(A)16 b Fu(\()g FJ(B)32 b FK(\()p FM(line)l(ar)c(implic)l (ation)p FK(\),)i(with)e FJ(jA)16 b Fu(\()g FJ(B)r(j)k FK(=)g FJ(jAj)c(\002)g(jB)r(j)167 3105 y FK(and)29 b(\()p FH(\013;)12 b(\014)t FK(\))497 3083 y FH(_)497 3125 y(^)586 3105 y FK(\()p FH(\013)657 3079 y Fv(0)673 3105 y FH(;)g(\014)747 3079 y Fv(0)763 3105 y FK(\))47 b(\(mo)r(d)24 b FJ(A)15 b Fu(\()h FJ(B)s FK(\))27 b(if)201 3267 y(i\))g FH(\013)339 3245 y(_)339 3288 y(^)427 3267 y(\013)471 3242 y Fv(0)535 3267 y FK(\(mo)r(d)d FJ(A)p FK(\))19 b FJ(\))h FH(\014)973 3245 y(_)973 3288 y(^)1061 3267 y(\014)1104 3242 y Fv(0)1168 3267 y FK(\(mo)r(d)j FJ(B)r FK(\))201 3412 y(ii\))j FH(\014)357 3390 y(^)357 3433 y(_)445 3412 y(\014)488 3386 y Fv(0)551 3412 y FK(\(mo)r(d)e FJ(B)r FK(\))c FJ(\))g FH(\013)983 3390 y(^)983 3433 y(_)1071 3412 y(\013)1115 3386 y Fv(0)1179 3412 y FK(\(mo)r(d)j FJ(A)p FK(\))167 3575 y(in)k(whic)n(h)g(w)n(e)g (in)n(tro)r(duce)g(the)h(abbreviation:)760 3750 y FH(\013)824 3728 y(^)824 3770 y(_)912 3750 y(\013)956 3724 y Fv(0)1020 3750 y FK(\(mo)r(d)c FJ(A)p FK(\))j(for)h FJ(:)p FK(\()p FH(\013)1561 3728 y(_)1561 3770 y(^)1650 3750 y(\013)1694 3724 y Fv(0)1710 3750 y FK(\))g(or)g FH(\013)19 b FK(=)h FH(\013)2035 3724 y Fv(0)167 3925 y FK(for)28 b FM(inc)l(oher)l(enc)l (e)p FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 100 103 bop 167 167 a FK(100)503 b Fz(CHAPTER)27 b(12.)64 b(COHERENCE)25 b(SEMANTICS)j(OF)f(THE)g(SUM)270 404 y FK(Immediately)61 b(w)n(e)i(can)h(see)e(the)h(essen)n(tial)f(prop)r (ert)n(y)i(of)g(linear)e(implication:)167 490 y FM(antisymmetry)p FK(.)83 b(If)42 b(w)n(e)h(de\014ne,)k(for)c(a)g(coherence)g(space)g FJ(A)p FK(,)k(the)42 b(space)i FJ(A)2391 464 y Fv(?)2475 490 y FK(\()p FM(line)l(ar)167 575 y(ne)l(gation)p FK(\))27 b(b)n(y)1243 775 y FJ(jA)1319 750 y Fv(?)1361 775 y FJ(j)19 b FK(=)g FJ(jAj)803 976 y FH(\013)867 954 y(_)867 997 y(^)955 976 y(\013)999 950 y Fv(0)1063 976 y FK(\(mo)r(d)24 b FJ(A)1302 950 y Fv(?)1344 976 y FK(\))78 b(i\013)f FH(\013)1650 954 y(^)1650 997 y(_)1739 976 y(\013)1783 950 y Fv(0)1846 976 y FK(\(mo)r(d)24 b FJ(A)p FK(\))167 1177 y(then)e(the)g(map)g(\()p FH(\013;)12 b(\014)t FK(\))19 b FJ(7!)h FK(\()p FH(\014)t(;)12 b(\013)p FK(\))22 b(is)f(an)i (isomorphism)e(from)h FJ(A)7 b Fu(\()g FJ(B)25 b FK(to)d FJ(B)2145 1151 y Fv(?)2194 1177 y Fu(\()7 b FJ(A)2335 1151 y Fv(?)2377 1177 y FK(.)34 b(In)22 b(other)167 1262 y(w)n(ords,)28 b(\()p FH(\013;)12 b(\014)t FK(\))580 1240 y FH(_)580 1282 y(^)668 1262 y FK(\()p FH(\013)739 1236 y Fv(0)756 1262 y FH(;)g(\014)830 1236 y Fv(0)846 1262 y FK(\))47 b(\(mo)r(d)23 b FJ(A)16 b Fu(\()g FJ(B)s FK(\))27 b(i\013)g(\()p FH(\014)t(;)12 b(\013)p FK(\))1649 1240 y FH(_)1649 1282 y(^)1738 1262 y FK(\()p FH(\014)1808 1236 y Fv(0)1824 1262 y FH(;)g(\013)1899 1236 y Fv(0)1916 1262 y FK(\))46 b(\(mo)r(d)24 b FJ(B)2220 1236 y Fv(?)2278 1262 y Fu(\()16 b FJ(A)2428 1236 y Fv(?)2469 1262 y FK(\).)270 1402 y(What)38 b(is)f(the)g(meaning)h(of)f(this?)64 b(A)37 b(stable)g(function)h(tak)n(es)g(an)g(input)f(of)h FJ(A)g FK(and)167 1487 y(returns)c(an)i(output)f(of)g FJ(B)r FK(.)57 b(When)35 b(the)f(function)g(is)g(linear,)h(this)f(pro)r(cess)h (can)g(b)r(e)f(seen)167 1572 y(dually)f(as)h(returning)f(an)i(input)e (of)h FJ(A)g FK(\()p FM(i.e.)f FK(an)h(output)h(of)f FJ(A)1917 1546 y Fv(?)1959 1572 y FK(\))f(from)g(an)h(output)h(of)f FJ(B)167 1657 y FK(\()p FM(i.e.)28 b FK(an)h(input)f(of)h FJ(B)739 1631 y Fv(?)781 1657 y FK(\).)38 b(So)29 b(the)f(linear)f (implication)e(in)n(tro)r(duces)j(a)h(symmetrical)c(form)k(of)167 1742 y(functional)h(dep)r(endence,)h(the)f(dualit)n(y)f(of)i(r^)-34 b(oles)30 b(of)g(the)g(argumen)n(t)h(and)g(the)f(result)f(b)r(eing)167 1827 y(expressed)c(b)n(y)h(the)e FM(line)l(ar)h(ne)l(gation)30 b FJ(A)20 b(7!)g(A)1395 1802 y Fv(?)1437 1827 y FK(.)34 b(This)25 b(is)f(analogous)j(to)e(transp)r(osition)h(\(not)167 1912 y(in)n(v)n(ersion\))h(in)g(Linear)g(Algebra.)270 2052 y(T)-6 b(o)35 b(mak)n(e)f(this)f(relev)l(an)n(t,)i(w)n(e)e(ha)n(v) n(e)i(to)f(sho)n(w)h(that)f(linearit)n(y)e(is)h(not)h(an)h(exceptional) 167 2137 y(phenomenon,)29 b(and)g(w)n(e)e(shall)g(b)r(e)g(able)g(to)h (symmetrise)e(the)h(functional)h(situations.)167 2389 y FE(12.4)114 b(Linearisation)167 2551 y FK(Let)27 b FJ(A)h FK(b)r(e)f(a)i(coherence)d(space.)36 b(W)-6 b(e)27 b(can)h(de\014ne)g(the)g(space)g(!)p FJ(A)g FK(\(\\of)g(course)g FJ(A)p FK("\))g(b)n(y)924 2751 y FJ(j)p FK(!)p FJ(Aj)19 b FK(=)g FJ(A)1187 2762 y Fm(\014n)1271 2751 y FK(=)g FJ(f)p FH(a)h FJ(2)f(A)h FK(:)39 b FH(a)28 b FK(\014nite)o FJ(g)917 2952 y FH(a)953 2963 y FD(1)1000 2930 y FH(_)1000 2973 y(^)1089 2952 y(a)1125 2963 y FD(2)1200 2952 y FK(\(mo)r(d)23 b(!)p FJ(A)q FK(\))78 b(i\013)27 b FH(a)1686 2963 y FD(1)1729 2952 y FJ([)16 b FH(a)1828 2963 y FD(2)1876 2952 y FJ(2)j(A)270 3153 y FK(The)28 b(basic)f(function)h(asso)r(ciated)g(with)f(!)p FJ(A)h FK(is)910 3353 y FH(a)19 b FJ(7!)h FK(!)q FH(a)f FK(=)h FJ(f)p FH(a)1275 3364 y Fv(\016)1322 3353 y FK(:)40 b FH(a)1417 3364 y Fv(\016)1464 3353 y FJ(\032)20 b FH(a)p FK(,)28 b FH(a)1658 3364 y Fv(\016)1713 3353 y FK(\014nite)p FJ(g)167 3554 y FK(from)f FJ(A)h FK(to)g(!)p FJ(A)p FK(.)36 b(This)27 b(function)h(is)f(stable,)g(but)h(far)g(from)g(b)r(eing)f (linear!)270 3754 y(The)f(in)n(teresting)f(p)r(oin)n(t)h(ab)r(out)i(!)p FJ(A)e FK(is)g(that)h FJ(A)13 b(!)h(B)29 b FK(is)d(equal)g(to)g(\(!)p FJ(A)p FK(\))14 b Fu(\()g FJ(B)28 b FK(as)f(one)g(can)167 3840 y(easily)34 b(sho)n(w.)58 b(In)34 b(other)h(w)n(ords,)j FM(pr)l(ovide)l(d)e(we)e(change)g(the)h(sour)l(c)l(e)g(sp)l(ac)l(e)p FK(,)j(ev)n(ery)c(stable)167 3925 y(function)28 b(is)f(linear!)p eop PStoPSsaved restore %%Page: (104,105) 53 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 101 104 bop 167 167 a Fz(12.4.)65 b(LINEARISA)-6 b(TION)1637 b FK(101)270 404 y(Let)28 b(us)g(mak)n(e)f(this)g(precise)g(b)n(y)h(in) n(tro)r(ducing)f(some)h(notation:)270 612 y FJ(\017)34 b FK(If)d FH(F)39 b FK(is)29 b(stable)h(from)g FJ(A)h FK(to)f FJ(B)r FK(,)i(w)n(e)d(de\014ne)i(a)f(linear)f(stable)h (function)g FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\))29 b(from)339 697 y(!)q FJ(A)e FK(to)h FJ(B)i FK(b)n(y)f FJ(T)-6 b FM(rlin)5 b FK(\()p FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\)\))18 b(=)i FJ(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\).)35 b(W)-6 b(e)27 b(ha)n(v)n(e:)1214 971 y FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\)\(!)o FH(a)p FK(\))20 b(=)f FH(F)10 b FK(\()p FH(a)p FK(\))339 1245 y(Indeed,)46 b(if)c FH(\014)33 b FJ(2)d FH(F)10 b FK(\()p FH(a)p FK(\),)45 b(then)d(for)h(some)f FH(a)1575 1256 y Fv(\016)1633 1245 y FJ(\032)29 b FH(a)p FK(,)46 b(w)n(e)c(ha)n(v)n(e)h(\()p FH(a)2180 1256 y Fv(\016)2208 1245 y FH(;)12 b(\014)t FK(\))29 b FJ(2)h(T)-6 b FH(r)r FK(\()p FH(F)10 b FK(\))29 b(=)339 1330 y FJ(T)-6 b FM(rlin)6 b FK(\()p FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\)\);)32 b(but)g FH(a)971 1341 y Fv(\016)1022 1330 y FJ(2)22 b FK(!)p FH(a)p FK(,)33 b(so)g FH(\014)26 b FJ(2)c(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\)\(!)o FH(a)p FK(\).)48 b(Similarly)-6 b(,)30 b(if)g FH(\014)d FJ(2)22 b(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\)\(!)o FH(a)p FK(\),)339 1415 y(w)n(e)28 b(see)f(that)h FH(\014)23 b FJ(2)d FH(F)10 b FK(\()p FH(a)p FK(\).)270 1588 y FJ(\017)34 b FK(If)28 b FH(G)f FK(is)g(linear)f(from)h(!)p FJ(A)g FK(to)h FJ(B)r FK(,)g(w)n(e)f (de\014ne)g(a)h(stable)f(function)g FJ(D)-10 b FM(elin)5 b FK(\()p FH(G)p FK(\))27 b(from)g FJ(A)h FK(to)339 1673 y FJ(B)i FK(b)n(y:)1185 1947 y FJ(D)-10 b FM(elin)5 b FK(\()p FH(G)p FK(\)\()p FH(a)p FK(\))20 b(=)f FH(G)p FK(\(!)p FH(a)p FK(\))270 2300 y(It)31 b(is)f(easy)i(to)f(see)f(that)i FJ(L)-12 b FM(in)35 b FK(and)d FJ(D)-10 b FM(elin)36 b FK(are)31 b(m)n(utually)f(in)n(v)n(erse)g(op)r(erations)2393 2274 y FD(2)2422 2300 y FK(,)i(and)g(in)167 2385 y(particular)27 b(the)g(equation)h FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\)\(!)o FH(a)p FK(\))20 b(=)f FH(F)10 b FK(\()p FH(a)p FK(\))26 b(c)n(haracterises)h FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\).)270 2546 y(W)-6 b(e)26 b(can)h(no)n(w)f(see) g(v)n(ery)g(w)n(ell)e(ho)n(w)j(the)f(rev)n(ersibilit)n(y)d(w)n(orks)k (for)f(ordinary)h(implication:)552 2788 y FJ(A)15 b(!)i(B)61 b FK(=)d(!)p FJ(A)16 b Fu(\()g FJ(B)61 b(')e(B)1383 2762 y Fv(?)1440 2788 y Fu(\()16 b FK(\(!)p FJ(A)p FK(\))1663 2753 y Fv(?)1764 2788 y FK(=)58 b FJ(B)1924 2762 y Fv(?)1982 2788 y Fu(\()16 b FK(?)o(\()p FJ(A)2191 2762 y Fv(?)2233 2788 y FK(\))1139 3047 y(where)27 b(?)p FJ(C)1436 3008 y FD(def)1444 3047 y FK(=)g(\(!\()p FJ(C)1639 3021 y Fv(?)1680 3047 y FK(\)\))1734 3007 y Fv(?)167 3289 y FK(In)34 b(other)f(w)n(ords)i(the)e(\(non-linear\))g(implication)e(is)i (rev)n(ersible,)g(but)h(this)f(requires)f(some)167 3374 y(complicated)26 b(constructions)i(whic)n(h)g(ha)n(v)n(e)h(no)f (connection)g(with)f(the)h(functional)f(in)n(tuition)167 3459 y(w)n(e)g(started)h(o\013)g(with.)270 3620 y(All)20 b(this)g(is)h(side-trac)n(king)f(us,)j(to)n(w)n(ards)f(linear)e(logic,) h(and)i(w)n(e)d(shall)h(stic)n(k)f(to)h(concluding)167 3705 y(the)27 b(in)n(terpretation)g(of)h(the)f(sum.)p 167 3790 1003 3 v 246 3833 a FC(2)273 3854 y FB(Categorically)-5 b(,)32 b(this)f(sa)n(ys)h(that)f(!)h(is)f(the)g(left)g(adjoin)n(t)g(to) h(the)f(forgetful)f(functor)h(from)h(coherence)167 3925 y(spaces)c(and)f FA(line)m(ar)34 b FB(maps)27 b(to)h(coherence)g (spaces)g(and)f FA(stable)32 b FB(maps.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 102 105 bop 167 167 a FK(102)503 b Fz(CHAPTER)27 b(12.)64 b(COHERENCE)25 b(SEMANTICS)j(OF)f(THE)g(SUM)167 404 y FE(12.5)114 b(Linearised)27 b(sum)167 559 y FK(W)-6 b(e)27 b(de\014ne)h FJ(A)16 b(q)g(B)22 b FK(=)d(!)p FJ(A)d(\010)f FK(!)p FJ(B)30 b FK(and)f(in)e(the)h(ob)n(vious)h(w)n(a)n(y:)693 731 y FJ(q)746 701 y FD(1)774 731 y FH(a)20 b FK(=)f FJ(f)p FK(1)p FJ(g)e(\002)e FK(!)p FH(a)527 b FJ(q)1729 701 y FD(2)1757 731 y FH(b)19 b FK(=)h FJ(f)p FK(2)p FJ(g)c(\002)g FK(!)p FH(b)270 902 y FK(Casewise)28 b(de\014nition)g(is) g(no)h(longer)g(a)g(problem:)36 b(if)28 b FH(F)38 b FK(is)28 b(stable)g(from)h FJ(A)f FK(to)h FJ(C)k FK(and)d FH(G)167 987 y FK(is)d(stable)g(from)h FJ(B)i FK(to)d FJ(C)t FK(,)h(de\014ne)g FH(H)33 b FK(from)28 b FJ(A)16 b(q)f(B)30 b FK(to)e FJ(C)k FK(b)n(y)479 1158 y FH(H)5 b FK(\()p FJ(f)p FK(1)p FJ(g)17 b(\002)e FH(A)p FK(\))k(=)g FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\)\()p FH(A)p FK(\))310 b FH(H)5 b FK(\()p FJ(f)p FK(2)p FJ(g)17 b(\002)f FH(B)t FK(\))j(=)g FJ(L)-12 b FM(in)5 b FK(\()p FH(G)p FK(\)\()p FH(B)t FK(\))167 1330 y(without)27 b(con\015ict)g(at)h Fn(?)p FK(,)g(since)e FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\))27 b(and)h FJ(L)-12 b FM(in)5 b FK(\()p FH(G)p FK(\))28 b(are)g(linear)e(and)i(so) h FH(H)5 b FK(\()p Fn(?)p FK(\))19 b(=)h Fn(?)p FK(.)270 1501 y(The)44 b(in)n(terpretation)e(is)h(not)h(particularly)e (economical)h(but)h(it)e(has)j(the)e(merit)f(of)167 1586 y(making)29 b(use)g(of)g(the)f(direct)f(sum,)i(and)h(not)f(an)n(y)h (less)e(in)n(telligible)c(considerations.)38 b(Ab)r(o)n(v)n(e)167 1671 y(all,)c(it)e(suggests)j(a)f(decomp)r(osition)f(of)h(the)g(sum)f (whic)n(h)g(sho)n(ws)i(up)f(the)f(more)g(primitiv)n(e)167 1756 y(op)r(erations:)h(\\!")26 b(whic)n(h)e(w)n(e)g(found)i(in)d(the)i (decomp)r(osition)e(of)i(the)f(arro)n(w,)i(and)g(\\)p FJ(\010)p FK(")f(whic)n(h)167 1841 y(is)i(the)g(truly)g(disjunctiv)n(e) g(part)h(of)g(the)g(sum.)270 2013 y(Let)g(us)g(c)n(hec)n(k)f(the)h (equations)g(w)n(e)f(w)n(an)n(t)h(to)g(in)n(terpret.)270 2138 y(If)23 b FH(F)10 b FK(,)23 b FH(G)f FK(and)i FH(a)f FK(are)f(the)g(in)n(terpretations)f(of)i FH(u)p FK([)p FH(x)p FK(],)i FH(v)s FK([)p FH(y)s FK(])d(and)h FH(r)r FK(,)h(then)e(the)g(in)n(terpretation)167 2223 y(of)41 b FH(\016)30 b(x:)12 b(u)29 b(y)s(:)12 b(v)30 b FK(\()p FH(\023)644 2197 y FD(1)672 2223 y FH(r)r FK(\))40 b(is)g FJ(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\)\(!)n FH(a)p FK(\),)44 b(whic)n(h)39 b(is)g(equal)i(to)f(the)g(in)n(terpretation)e FH(F)10 b FK(\()p FH(a)p FK(\))40 b(of)167 2308 y FH(u)p FK([)p FH(r)r(=x)p FK(].)d(Similarly)-6 b(,)25 b(w)n(e)i(shall)g(in)n (terpret)f(the)h(con)n(v)n(ersion)h FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)22 b FK(\()p FH(\023)2098 2283 y FD(2)2126 2308 y FH(s)p FK(\))e Fu( )g FH(v)s FK([)p FH(s=y)s FK(].)270 2433 y(No)n(w)32 b(w)n(e)e(shall)h(turn)g(to)g(the)g (equation)h FH(\016)24 b(x:)12 b FK(\()p FH(\023)1561 2408 y FD(1)1589 2433 y FH(x)p FK(\))22 b FH(y)s(:)12 b FK(\()p FH(\023)1796 2408 y FD(2)1823 2433 y FH(y)s FK(\))21 b FH(t)h FK(=)g FH(t)p FK(.)45 b(First,)32 b(w)n(e)e(see)h (that)167 2518 y FJ(L)-12 b FM(in)5 b FK(\()p FJ(q)349 2489 y FD(1)377 2518 y FK(\)\()p FH(A)p FK(\))18 b(=)h FJ(f)p FK(1)p FJ(g)t(\002)t FH(A)p FK(,)i(b)r(ecause)f(it)f(is)g(the)g (unique)h(linear)e(solution)i FH(F)29 b FK(of)20 b FH(F)10 b FK(\(!)o FH(a)p FK(\))20 b(=)f FJ(f)p FK(1)p FJ(g)t(\002)t FK(!)p FH(a)p FK(.)167 2604 y(In)27 b(particular,)g(if)f FH(t)h FK(is)g(in)n(terpreted)e(b)n(y)j FJ(f)p FK(1)p FJ(g)16 b(\002)f FH(A)p FK(,)27 b(then)g FH(\016)22 b(x:)12 b FK(\()p FH(\023)1873 2578 y FD(1)1901 2604 y FH(x)p FK(\))20 b FH(y)s(:)12 b FK(\()p FH(\023)2106 2578 y FD(2)2133 2604 y FH(y)s FK(\))18 b FH(t)27 b FK(is)g(in)n(terpreted)167 2689 y(b)n(y)40 b FJ(L)-12 b FM(in)5 b FK(\()p FJ(q)461 2659 y FD(1)489 2689 y FK(\)\()p FH(A)p FK(\))27 b(=)h FJ(f)p FK(1)p FJ(g)20 b(\002)f FH(A)p FK(,)42 b(and)f(similarly)-6 b(,)40 b(if)f FH(t)h FK(is)f(in)n(terpreted)f(b)n(y)i FJ(f)p FK(2)p FJ(g)20 b(\002)f FH(B)t FK(,)43 b(then)167 2774 y FH(\016)22 b(x:)12 b FK(\()p FH(\023)341 2748 y FD(1)369 2774 y FH(x)p FK(\))20 b FH(y)s(:)12 b FK(\()p FH(\023)574 2748 y FD(2)601 2774 y FH(y)s FK(\))18 b FH(t)28 b FK(is)f(in)n(terpreted)f(b)n(y)i FJ(L)-12 b FM(in)5 b FK(\()p FJ(q)1451 2744 y FD(2)1479 2774 y FK(\)\()p FH(B)t FK(\))19 b(=)g FJ(f)p FK(2)p FJ(g)d(\002)g FH(B)t FK(.)270 2899 y(Finally)-6 b(,)27 b(the)h(comm)n(uting)e(con)n(v)n (ersions)j(are)e(of)h(the)g(form)862 3070 y Fq(E)12 b FK(\()p FH(\016)22 b(x:)12 b(u)20 b(y)s(:)12 b(v)21 b(t)p FK(\))e Fu( )h FH(\016)i(x:)12 b FK(\()p Fq(E)g FH(u)p FK(\))19 b FH(y)s(:)12 b FK(\()p Fq(E)g FH(v)s FK(\))18 b FH(t)167 3242 y FK(where)27 b Fq(E)39 b FK(is)27 b(an)i(elimination.) j FM(In)27 b(every)h(c)l(ase)p FK(,)g(it)e(is)h(easy)i(to)f(see)f(that) h(the)f(corresp)r(onding)167 3327 y(function)33 b FH(E)k FK(is)32 b FM(line)l(ar)p FK(.)51 b(So)34 b(it)d(is)i(enough)h(to)f (pro)n(v)n(e)h(that,)g(if)e FH(E)37 b FK(is)c(linear,)f(the)h(function) 167 3412 y(de\014ned)25 b(casewise)f(from)h FH(E)15 b FJ(\016)c FH(F)35 b FK(and)26 b FH(E)16 b FJ(\016)11 b FH(G)26 b FK(is)e FH(E)16 b FJ(\016)11 b FH(H)5 b FK(,)27 b(where)d FH(H)30 b FK(is)24 b(de\014ned)i(casewise)d(from)167 3497 y FH(F)37 b FK(and)29 b FH(G)p FK(.)35 b(But)28 b(this)f(is)g(a)h(consequence)g(of)1028 3668 y FJ(L)-12 b FM(in)5 b FK(\()p FH(E)19 b FJ(\016)d FH(F)10 b FK(\))19 b(=)g FH(E)h FJ(\016)c(L)-12 b FM(in)5 b FK(\()p FH(F)10 b FK(\))167 3840 y(\(and)47 b(lik)n(ewise)d FJ(L)-12 b FM(in)5 b FK(\()p FH(E)24 b FJ(\016)e FH(G)p FK(\))33 b(=)f FH(E)25 b FJ(\016)c(L)-12 b FM(in)5 b FK(\()p FH(G)p FK(\)\))46 b(whic)n(h)g(follo)n(ws)f(immediately)e(from)j(the)167 3925 y(c)n(haracterisation)27 b(of)h FJ(L)-12 b FM(in)5 b FK(\()p FH(E)20 b FJ(\016)c FH(F)10 b FK(\).)p eop PStoPSsaved restore %%Page: (106,107) 54 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 103 106 bop 167 167 a Fz(12.6.)65 b(TENSOR)26 b(PR)n(ODUCT)g(AND)h (UNITS)1097 b FK(103)270 404 y(In)27 b(the)g(in)n(terpretation)e(of)i (the)g(comm)n(uting)e(con)n(v)n(ersions,)j(it)e(is)g(of)h(course)g (crucial)e(that)167 490 y(the)i(eliminations)e(b)r(e)j(linear.)270 663 y(The)g(direct)e(sum)h(is)g(the)h(dual)g(of)g(the)f(direct)f(pro)r (duct:)1080 836 y(\()p FJ(A)16 b FK(&)f FJ(B)r FK(\))1323 802 y Fv(?)1384 836 y FK(=)20 b FJ(A)1514 810 y Fv(?)1571 836 y FJ(\010)c(B)1690 810 y Fv(?)167 1009 y FK(It)30 b(is)g(of)h(course)g(more)f(in)n(teresting)f(to)i(w)n(ork)g(with)f FJ(\010)p FK(,)h(whic)n(h)f(has)i(a)f(simple)d(relationship)167 1094 y(with)f(&,)g(than)i(with)d FJ(q)p FK(,)i(whic)n(h)f(b)r(eha)n(v)n (es)h(quite)f(badly)-6 b(.)167 1329 y FE(12.6)114 b(T)-10 b(ensor)29 b(pro)s(duct)f(and)h(units)167 1484 y FK(The)h(direct)e(sum) i(forms)g(the)f(disjoin)n(t)h(union)g(of)g(the)g(w)n(ebs)g(of)g(t)n(w)n (o)g(coherence)f(spaces,)i(so)167 1569 y(what)d(is)f(the)g(meaning)h (of)g(the)f(graph)i(pro)r(duct?)270 1696 y(W)-6 b(e)28 b(de\014ne)g FJ(A)16 b(\012)f(B)30 b FK(to)e(b)r(e)g(the)g(coherence)e (space)i(whose)h(tok)n(ens)f(are)g(the)f(pairs)h FJ(h)p FH(\013;)12 b(\014)t FJ(i)p FK(,)167 1781 y(where)27 b FH(\013)20 b FJ(2)f(jAj)27 b FK(and)i FH(\014)23 b FJ(2)d(jB)r(j)p FK(,)27 b(with)g(the)g(coherence)g(relation)237 1954 y FJ(h)p FH(\013;)12 b(\014)t FJ(i)429 1932 y FH(_)429 1975 y(^)518 1954 y FJ(h)p FH(\013)589 1928 y Fv(0)606 1954 y FH(;)g(\014)680 1928 y Fv(0)696 1954 y FJ(i)47 b FK(\(mo)r(d)24 b FJ(A)16 b(\012)f(B)s FK(\))68 b(i\013)h FH(\013)1432 1932 y(_)1432 1975 y(^)1520 1954 y(\013)1564 1928 y Fv(0)1628 1954 y FK(\(mo)r(d)23 b FJ(A)p FK(\))28 b(and)h FH(\014)2122 1932 y(_)2122 1975 y(^)2211 1954 y(\014)2254 1928 y Fv(0)2317 1954 y FK(\(mo)r(d)24 b FJ(B)r FK(\))167 2127 y(This)g(is)h(called)e(the)h FM(tensor)h(pr)l(o)l (duct)p FK(.)36 b(The)24 b(dual)i(\(linear)d(negation\))i(of)h(the)e (tensor)h(pro)r(duct)167 2212 y(is)i(called)f(the)h FM(p)l(ar)36 b FK(or)28 b FM(tensor)g(sum)p FK(:)1079 2385 y(\()p FJ(A)16 b(\012)f(B)r FK(\))1324 2351 y Fv(?)1385 2385 y FK(=)k FJ(A)1514 2360 y Fv(?)1572 2385 y Fc(O)c FJ(B)1690 2360 y Fv(?)167 2558 y FK(Comparing)28 b(this)f(with)g(the)g FM(line)l(ar)h(implic)l(ation)g FK(w)n(e)f(ha)n(v)n(e)926 2738 y FJ(A)16 b Fu(\()g FJ(B)22 b FK(=)d FJ(A)1289 2713 y Fv(?)1346 2738 y Fc(O)d FJ(B)22 b FK(=)d(\()p FJ(A)d(\012)f(B)1775 2713 y Fv(?)1817 2738 y FK(\))1844 2699 y Fv(?)270 2999 y FK(Finally)-6 b(,)35 b(eac)n(h)f(of)g(the)g(four)g(asso)r(ciativ)n(e) g(binary)g(op)r(ertions)g FJ(\010)p FK(,)i(&,)f FJ(\012)e FK(and)i Fc(O)f FK(has)h(a)167 3085 y(unit,)d(resp)r(ectiv)n(ely)e (called)g FG(0)p FK(,)i FJ(>)p FK(,)f FG(1)g FK(and)i FJ(?)d FK(\(see)h(section)g FG(??)q FK(\).)47 b(Ho)n(w)n(ev)n(er)31 b(for)h(coherence)167 3170 y(spaces)c(they)g(coincide)e(in)h(pairs:)270 3331 y FJ(\017)34 b FG(0)20 b FK(=)f FJ(>)f FK(=)h FJ(E)-17 b FM(mp)5 b FK(,)28 b(where)f FJ(jE)-17 b FM(mp)t FJ(j)19 b FK(=)h Fn(?)270 3475 y FJ(\017)34 b FG(1)20 b FK(=)f FJ(?)f FK(=)h FJ(S)-6 b FM(gl)6 b FK(,)28 b(where)f FJ(jS)-6 b FM(gl)5 b FJ(j)19 b FK(=)g FJ(f\017)q(g)p FK(.)167 3636 y(Whic)n(h)40 b(of)h(these)g(is)f(the)g FM(terminal)h(obje)l(ct)47 b FK(for)41 b(coherence)f(spaces)h(and)h(stable)e(maps?)167 3721 y(F)-6 b(or)28 b(linear)d(maps?)35 b(Ho)n(w)27 b(do)h(these)f(t)n (yp)r(es)g(relate)f(to)h FM(absur)l(dity)34 b FK(and)28 b FM(tautolo)l(gy)34 b FK(in)27 b(natural)167 3806 y(deduction?)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 104 107 bop 167 878 a FF(Chapter)28 b(13)167 1175 y(Cut)f(Elimination)g (\(Hauptsatz\))167 1505 y FK(Gen)n(tzen's)32 b(theorem,)h(one)g(of)f (the)g(most)h(imp)r(ortan)n(t)e(in)h(logic,)h(is)e(not)i(v)n(ery)g(far) f(remo)n(v)n(ed)167 1590 y(from)26 b(normalisation)f(in)h(natural)g (deduction,)h(whic)n(h)e(is)h(to)g(a)h(large)e(exten)n(t)h(inspired)f (b)n(y)i(it.)167 1675 y(In)e(a)g(sligh)n(tly)f(mo)r(di\014ed)h(form,)g (it)f(is)g(at)h(the)g(ro)r(ot)g(of)h(languages)g(suc)n(h)g(as)f Fr(PROLOG)p FK(.)i(In)e(other)167 1760 y(w)n(ords,)j(it)f(is)g(a)g (result)g(whic)n(h)g(ev)n(ery)n(one)h(should)g(see)f(pro)n(v)n(ed)h(at) g(least)f(once.)35 b(Ho)n(w)n(ev)n(er)27 b(the)167 1845 y(pro)r(of)i(is)e(v)n(ery)i(delicate)c(and)k(\014ddly)-6 b(.)37 b(So)29 b(w)n(e)f(shall)f(b)r(egin)h(b)n(y)g(p)r(oin)n(ting)g (out)h(the)e(k)n(ey)i(cases)167 1930 y(whic)n(h)35 b(it)f(is)g(imp)r (ortan)n(t)h(to)h(understand.)59 b(Afterw)n(ards)35 b(w)n(e)g(shall)f (dev)n(elop)i(the)f(detailed)167 2015 y(pro)r(of,)29 b(whose)f(in)n(tricacies)d(are)i(less)g(in)n(teresting.)167 2264 y FE(13.1)114 b(The)28 b(k)m(ey)g(cases)167 2425 y FK(The)f(aim)g(is)g(to)h(eliminate)c(cuts)k(of)g(the)f(sp)r(ecial)g (form)1014 2611 y FH(A)p 1018 2631 39 3 v 1086 2610 a FJ(`)19 b FH(C)q(;)1229 2611 y(B)p 1233 2631 43 3 v 83 w(A)p 1368 2631 39 3 v -30 x Fv(0)1432 2610 y FH(;)12 b(C)25 b FJ(`)1600 2611 y FH(B)p 1603 2631 43 3 v 1656 2581 a Fv(0)p 1014 2655 658 4 v 1693 2671 a Fq(Cut)1147 2732 y FH(A)p 1151 2752 39 3 v -1 x(;)1230 2732 y(A)p 1233 2752 V 1281 2702 a Fv(0)1317 2731 y FJ(`)1380 2732 y FH(B)p 1384 2752 43 3 v 1436 2731 a(;)1467 2732 y(B)p 1470 2752 V 1523 2702 a Fv(0)167 2917 y FK(where)31 b(the)g(left)f (premise)f(is)i(a)h(righ)n(t)f(logical)e(rule)i(and)h(the)f(righ)n(t)g (premise)f(a)i(left)e(logical)167 3002 y(rule,)36 b(so)f(that)g(b)r (oth)h(in)n(tro)r(duce)e(the)h(main)f(sym)n(b)r(ol)h(of)g FH(C)5 b FK(.)57 b(These)35 b(cases)g(enligh)n(ten)e(the)167 3088 y(deep)28 b(symmetries)d(of)j(logical)e(rules,)h(whic)n(h)g(matc)n (h)h(eac)n(h)f(other)h(exactly)-6 b(.)251 3264 y(1.)35 b FJ(R^)28 b FK(and)g FJ(L)p FK(1)p FJ(^)712 3467 y FH(A)p 715 3486 39 3 v 783 3466 a FJ(`)20 b FH(C)q(;)927 3467 y(B)p 931 3486 43 3 v 82 w(A)p 1065 3486 39 3 v -30 x Fv(0)1149 3466 y FJ(`)g FH(D)r(;)1302 3467 y(B)p 1305 3486 43 3 v 1358 3437 a Fv(0)p 712 3511 663 4 v 1395 3526 a FJ(R^)736 3588 y FH(A)p 739 3608 39 3 v 787 3587 a(;)818 3588 y(A)p 822 3608 V -30 x Fv(0)906 3587 y FJ(`)g FH(C)h FJ(^)15 b FH(D)r(;)1191 3588 y(B)p 1195 3608 43 3 v 1247 3587 a(;)1278 3588 y(B)p 1282 3608 V 1334 3558 a Fv(0)1718 3467 y FH(A)p 1721 3486 39 3 v 1769 3437 a Fv(00)1799 3466 y FH(;)d(C)25 b FJ(`)1967 3467 y FH(B)p 1970 3486 43 3 v 2023 3437 a Fv(00)p 1649 3511 473 4 v 2142 3526 a FJ(L)p FK(1)p FJ(^)1649 3588 y FH(A)p 1652 3608 39 3 v -30 x Fv(00)1731 3587 y FH(;)12 b(C)20 b FJ(^)c FH(D)22 b FJ(`)2035 3588 y FH(B)p 2039 3608 43 3 v 2091 3558 a Fv(00)p 736 3632 1386 4 v 2142 3648 a Fq(Cut)1118 3709 y FH(A)p 1121 3729 39 3 v 1169 3708 a(;)1200 3709 y(A)p 1204 3729 V -30 x Fv(0)1268 3708 y FH(;)1299 3709 y(A)p 1303 3729 V -30 x Fv(00)1401 3708 y FJ(`)1463 3709 y FH(B)p 1467 3729 43 3 v 1519 3708 a(;)1550 3709 y(B)p 1554 3729 V 1606 3679 a Fv(0)1622 3708 y FH(;)1653 3709 y(B)p 1657 3729 V 1709 3679 a Fv(00)339 3925 y FK(is)27 b(replaced)g(b)n(y)1368 4101 y(104)p eop PStoPSsaved restore %%Page: (108,109) 55 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 105 108 bop 167 167 a Fz(13.1.)65 b(THE)27 b(KEY)f(CASES)1617 b FK(105)1087 390 y FH(A)p 1091 410 39 3 v 1158 389 a FJ(`)20 b FH(C)q(;)1302 390 y(B)p 1306 410 43 3 v 83 w(A)p 1440 410 39 3 v 1488 360 a Fv(00)1518 389 y FH(;)12 b(C)25 b FJ(`)1686 390 y FH(B)p 1689 410 43 3 v 1742 360 a Fv(00)p 1087 434 685 4 v 1792 450 a Fq(Cut)1220 511 y FH(A)p 1223 531 39 3 v -1 x(;)1303 511 y(A)p 1306 531 V 1354 481 a Fv(00)1404 510 y FJ(`)1466 511 y FH(B)p 1470 531 43 3 v 1522 510 a(;)1553 511 y(B)p 1557 531 V 1609 481 a Fv(00)1119 571 y FK(=)-17 b(=)h(=)g(=)g(=)f(=)h(=)g(=)g(=) g(=)g(=)g(=)g(=)g(=)g(=)g(=)1119 633 y FH(A)p 1122 652 39 3 v 1170 632 a(;)1201 633 y(A)p 1205 652 V -30 x Fv(0)1269 632 y FH(;)1300 633 y(A)p 1304 652 V -30 x Fv(00)1402 632 y FJ(`)1464 633 y FH(B)p 1468 652 43 3 v 1520 632 a(;)1551 633 y(B)p 1555 652 V 1607 603 a Fv(0)1623 632 y FH(;)1654 633 y(B)p 1658 652 V 1710 603 a Fv(00)339 841 y FK(where)32 b(the)f(double)i(bar)f(denotes)h(a)f(certain)f(n)n (um)n(b)r(er)h(of)g(structural)g(rules,)g(in)g(this)339 926 y(case)c(w)n(eak)n(ening)g(and)h(exc)n(hange.)251 1177 y(2.)35 b FJ(R^)28 b FK(and)g FJ(L)p FK(2)p FJ(^)712 1373 y FH(A)p 715 1393 39 3 v 783 1372 a FJ(`)20 b FH(C)q(;)927 1373 y(B)p 931 1393 43 3 v 82 w(A)p 1065 1393 39 3 v -30 x Fv(0)1149 1372 y FJ(`)g FH(D)r(;)1302 1373 y(B)p 1305 1393 43 3 v 1358 1343 a Fv(0)p 712 1417 663 4 v 1395 1433 a FJ(R^)736 1495 y FH(A)p 739 1514 39 3 v 787 1494 a(;)818 1495 y(A)p 822 1514 V -31 x Fv(0)906 1494 y FJ(`)g FH(C)h FJ(^)15 b FH(D)r(;)1191 1495 y(B)p 1195 1514 43 3 v 1247 1494 a(;)1278 1495 y(B)p 1282 1514 V 1334 1464 a Fv(0)1715 1373 y FH(A)p 1719 1393 39 3 v -30 x Fv(00)1797 1372 y FH(;)d(D)21 b FJ(`)1969 1373 y FH(B)p 1973 1393 43 3 v 2025 1343 a Fv(00)p 1649 1417 473 4 v 2142 1433 a FJ(L)p FK(2)p FJ(^)1649 1495 y FH(A)p 1652 1514 39 3 v -31 x Fv(00)1731 1494 y FH(;)12 b(C)20 b FJ(^)c FH(D)22 b FJ(`)2035 1495 y FH(B)p 2039 1514 43 3 v 2091 1464 a Fv(00)p 736 1538 1386 4 v 2142 1554 a Fq(Cut)1118 1616 y FH(A)p 1121 1636 39 3 v 1169 1615 a(;)1200 1616 y(A)p 1204 1636 V -30 x Fv(0)1268 1615 y FH(;)1299 1616 y(A)p 1303 1636 V -30 x Fv(00)1401 1615 y FJ(`)1463 1616 y FH(B)p 1467 1636 43 3 v 1519 1615 a(;)1550 1616 y(B)p 1554 1636 V 1606 1586 a Fv(0)1622 1615 y FH(;)1653 1616 y(B)p 1657 1636 V 1709 1586 a Fv(00)339 1824 y FK(is)27 b(replaced)g(similarly)e(b)n(y)1064 2033 y FH(A)p 1067 2053 39 3 v -30 x Fv(0)1152 2032 y FJ(`)19 b FH(D)r(;)1304 2033 y(B)p 1308 2053 43 3 v 1360 2003 a Fv(0)1455 2033 y FH(A)p 1459 2053 39 3 v -30 x Fv(00)1537 2032 y FH(;)12 b(D)21 b FJ(`)1709 2033 y FH(B)p 1713 2053 43 3 v 1765 2003 a Fv(00)p 1064 2077 731 4 v 1816 2093 a Fq(Cut)1203 2155 y FH(A)p 1207 2174 39 3 v -30 x Fv(0)1272 2154 y FH(;)1303 2155 y(A)p 1306 2174 V 1354 2125 a Fv(00)1404 2154 y FJ(`)1466 2155 y FH(B)p 1470 2174 43 3 v 1522 2125 a Fv(0)1539 2154 y FH(;)1570 2155 y(B)p 1573 2174 V 1626 2125 a Fv(00)1119 2214 y FK(=)-17 b(=)h(=)g(=)g(=)f(=)h(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)1119 2276 y FH(A)p 1122 2296 39 3 v 1170 2275 a(;)1201 2276 y(A)p 1205 2296 V -30 x Fv(0)1269 2275 y FH(;)1300 2276 y(A)p 1304 2296 V -30 x Fv(00)1402 2275 y FJ(`)1464 2276 y FH(B)p 1468 2296 43 3 v 1520 2275 a(;)1551 2276 y(B)p 1555 2296 V 1607 2246 a Fv(0)1623 2275 y FH(;)1654 2276 y(B)p 1658 2296 V 1710 2246 a Fv(00)251 2517 y FK(3.)35 b FJ(R)p FK(1)p FJ(_)28 b FK(and)h FJ(L_)781 2713 y FH(A)p 784 2732 39 3 v 852 2712 a FJ(`)19 b FH(C)q(;)995 2713 y(B)p 999 2732 43 3 v 710 2756 413 4 v 1143 2772 a FJ(R)p FK(1)p FJ(_)710 2834 y FH(A)p 713 2854 39 3 v 781 2833 a FJ(`)h FH(C)h FJ(_)15 b FH(D)r(;)1066 2834 y(B)p 1070 2854 43 3 v 1432 2713 a(A)p 1435 2732 39 3 v 1483 2683 a Fv(0)1500 2712 y FH(;)d(C)25 b FJ(`)1667 2713 y FH(B)p 1671 2732 43 3 v 1723 2683 a Fv(0)1818 2713 y FH(A)p 1821 2732 39 3 v -30 x Fv(00)1900 2712 y FH(;)12 b(D)21 b FJ(`)2072 2713 y FH(B)p 2075 2732 43 3 v 2128 2683 a Fv(00)p 1432 2756 727 4 v 2178 2772 a FJ(L_)1457 2834 y FH(A)p 1461 2854 39 3 v -30 x Fv(0)1525 2833 y FH(;)1556 2834 y(A)p 1560 2854 V -30 x Fv(00)1638 2833 y FH(;)12 b(C)21 b FJ(_)16 b FH(D)21 b FJ(`)1943 2834 y FH(B)p 1946 2854 43 3 v 1999 2804 a Fv(0)2015 2833 y FH(;)2046 2834 y(B)p 2050 2854 V 2102 2804 a Fv(00)p 710 2878 1423 4 v 2153 2894 a Fq(Cut)1110 2955 y FH(A)p 1114 2975 39 3 v -1 x(;)1193 2955 y(A)p 1196 2975 V -30 x Fv(0)1261 2954 y FH(;)1292 2955 y(A)p 1295 2975 V -30 x Fv(00)1393 2954 y FJ(`)1456 2955 y FH(B)p 1459 2975 43 3 v 1512 2954 a(;)1543 2955 y(B)p 1546 2975 V 1599 2925 a Fv(0)1615 2954 y FH(;)1646 2955 y(B)p 1649 2975 V 1702 2925 a Fv(00)339 3163 y FK(is)27 b(replaced)g(b)n(y)1101 3373 y FH(A)p 1104 3393 39 3 v 1172 3372 a FJ(`)20 b FH(C)q(;)1316 3373 y(B)p 1320 3393 43 3 v 82 w(A)p 1454 3393 39 3 v -30 x Fv(0)1518 3372 y FH(;)12 b(C)25 b FJ(`)1686 3373 y FH(B)p 1689 3393 43 3 v 1742 3343 a Fv(0)p 1101 3417 658 4 v 1779 3432 a Fq(Cut)1233 3494 y FH(A)p 1237 3514 39 3 v -1 x(;)1316 3494 y(A)p 1319 3514 V -30 x Fv(0)1404 3493 y FJ(`)1466 3494 y FH(B)p 1470 3514 43 3 v 1522 3493 a(;)1553 3494 y(B)p 1557 3514 V 1609 3464 a Fv(0)1119 3554 y FK(=)-17 b(=)h(=)g(=)g(=)f(=)h(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g (=)g(=)1119 3615 y FH(A)p 1122 3635 39 3 v 1170 3614 a(;)1201 3615 y(A)p 1205 3635 V -30 x Fv(0)1269 3614 y FH(;)1300 3615 y(A)p 1304 3635 V -30 x Fv(00)1402 3614 y FJ(`)1464 3615 y FH(B)p 1468 3635 43 3 v 1520 3614 a(;)1551 3615 y(B)p 1555 3635 V 1607 3585 a Fv(0)1623 3614 y FH(;)1654 3615 y(B)p 1658 3635 V 1710 3585 a Fv(00)339 3824 y FK(This)28 b(is)e(the)i(dual)g(of)g(case)f FG(??)q FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 106 109 bop 167 167 a FK(106)710 b Fz(CHAPTER)26 b(13.)64 b(CUT)27 b(ELIMINA)-6 b(TION)26 b(\(HA)n(UPTSA)-6 b(TZ\))251 404 y FK(4.)35 b FJ(R)p FK(2)p FJ(_)28 b FK(and)h FJ(L_)776 603 y FH(A)p 780 623 39 3 v 848 602 a FJ(`)19 b FH(D)r(;)1000 603 y(B)p 1004 623 43 3 v 710 647 413 4 v 1143 663 a FJ(R)p FK(2)p FJ(_)710 724 y FH(A)p 713 744 39 3 v 781 723 a FJ(`)h FH(C)h FJ(_)15 b FH(D)r(;)1066 724 y(B)p 1070 744 43 3 v 1432 603 a(A)p 1435 623 39 3 v 1483 573 a Fv(0)1500 602 y FH(;)d(C)25 b FJ(`)1667 603 y FH(B)p 1671 623 43 3 v 1723 573 a Fv(0)1818 603 y FH(A)p 1821 623 39 3 v -30 x Fv(00)1900 602 y FH(;)12 b(D)21 b FJ(`)2072 603 y FH(B)p 2075 623 43 3 v 2128 573 a Fv(00)p 1432 647 727 4 v 2178 663 a FJ(L_)1457 724 y FH(A)p 1461 744 39 3 v -30 x Fv(0)1525 723 y FH(;)1556 724 y(A)p 1560 744 V -30 x Fv(00)1638 723 y FH(;)12 b(C)21 b FJ(_)16 b FH(D)21 b FJ(`)1943 724 y FH(B)p 1946 744 43 3 v 1999 694 a Fv(0)2015 723 y FH(;)2046 724 y(B)p 2050 744 V 2102 694 a Fv(00)p 710 768 1423 4 v 2153 784 a Fq(Cut)1110 846 y FH(A)p 1114 865 39 3 v -1 x(;)1193 846 y(A)p 1196 865 V -30 x Fv(0)1261 845 y FH(;)1292 846 y(A)p 1295 865 V -30 x Fv(00)1393 845 y FJ(`)1456 846 y FH(B)p 1459 865 43 3 v 1512 845 a(;)1543 846 y(B)p 1546 865 V 1599 816 a Fv(0)1615 845 y FH(;)1646 846 y(B)p 1649 865 V 1702 816 a Fv(00)339 1057 y FK(is)27 b(replaced)g(b)n(y)1080 1269 y FH(A)p 1084 1289 39 3 v 1152 1268 a FJ(`)19 b FH(D)r(;)1304 1269 y(B)p 1308 1289 43 3 v 83 w(A)p 1442 1289 39 3 v 1490 1239 a Fv(00)1520 1268 y FH(;)12 b(D)22 b FJ(`)1693 1269 y FH(B)p 1696 1289 43 3 v 1748 1239 a Fv(00)p 1080 1313 699 4 v 1799 1329 a Fq(Cut)1220 1390 y FH(A)p 1223 1410 39 3 v -1 x(;)1303 1390 y(A)p 1306 1410 V 1354 1360 a Fv(00)1404 1389 y FJ(`)1466 1390 y FH(B)p 1470 1410 43 3 v 1522 1389 a(;)1553 1390 y(B)p 1557 1410 V 1609 1360 a Fv(00)1119 1450 y FK(=)-17 b(=)h(=)g(=)g(=)f(=) h(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)1119 1512 y FH(A)p 1122 1531 39 3 v 1170 1511 a(;)1201 1512 y(A)p 1205 1531 V -31 x Fv(0)1269 1511 y FH(;)1300 1512 y(A)p 1304 1531 V -31 x Fv(00)1402 1511 y FJ(`)1464 1512 y FH(B)p 1468 1531 43 3 v 1520 1511 a(;)1551 1512 y(B)p 1555 1531 V 1607 1481 a Fv(0)1623 1511 y FH(;)1654 1512 y(B)p 1658 1531 V 1710 1481 a Fv(00)339 1723 y FK(This)28 b(is)e(the)i(dual)g(of)g (case)f FG(??)q FK(.)251 2019 y(5.)35 b FJ(R:)28 b FK(and)g FJ(L:)1175 1898 y FH(A)p 1179 1918 39 3 v -1 x(;)12 b(C)25 b FJ(`)1394 1898 y FH(B)p 1398 1918 43 3 v 1154 1942 319 4 v 1493 1958 a FJ(R:)1154 2019 y FH(A)p 1157 2039 39 3 v 1225 2018 a FJ(`)19 b(:)p FH(C)q(;)1415 2019 y(B)p 1419 2039 43 3 v 1772 1898 a(A)p 1775 1918 39 3 v 1823 1868 a Fv(0)1860 1897 y FJ(`)g FH(C)q(;)2003 1898 y(B)p 2007 1918 43 3 v 2060 1868 a Fv(0)p 1746 1942 356 4 v 2122 1958 a FJ(L:)1746 2019 y FH(A)p 1750 2039 39 3 v -30 x Fv(0)1815 2018 y FH(;)12 b FJ(:)p FH(C)24 b FJ(`)2029 2019 y FH(B)p 2033 2039 43 3 v 2085 1989 a Fv(0)p 1154 2063 948 4 v 2122 2079 a Fq(Cut)1431 2141 y FH(A)p 1435 2160 39 3 v -1 x(;)1514 2141 y(A)p 1518 2160 V -30 x Fv(0)1602 2140 y FJ(`)1664 2141 y FH(B)p 1668 2160 43 3 v 1720 2140 a(;)1751 2141 y(B)p 1755 2160 V 1807 2111 a Fv(0)339 2455 y FK(is)j(replaced)g(b)n(y)1101 2667 y FH(A)p 1104 2687 39 3 v 1152 2637 a Fv(0)1188 2666 y FJ(`)20 b FH(C)q(;)1332 2667 y(B)p 1336 2687 43 3 v 1388 2637 a Fv(0)1483 2667 y FH(A)p 1487 2687 39 3 v -1 x(;)12 b(C)25 b FJ(`)1702 2667 y FH(B)p 1706 2687 43 3 v 1101 2711 658 4 v 1779 2727 a Fq(Cut)1233 2789 y FH(A)p 1237 2808 39 3 v -30 x Fv(0)1302 2788 y FH(;)1333 2789 y(A)p 1336 2808 V 1404 2788 a FJ(`)1466 2789 y FH(B)p 1470 2808 43 3 v 1522 2759 a Fv(0)1539 2788 y FH(;)1570 2789 y(B)p 1573 2808 V 1233 2848 a FK(=)-17 b(=)g(=)h(=)g(=)g(=)g(=)g (=)g(=)f(=)1233 2910 y FH(A)p 1237 2930 39 3 v -1 x(;)1316 2910 y(A)p 1319 2930 V -30 x Fv(0)1404 2909 y FJ(`)1466 2910 y FH(B)p 1470 2930 43 3 v 1522 2909 a(;)1553 2910 y(B)p 1557 2930 V 1609 2880 a Fv(0)339 3121 y FK(Note)28 b(the)f(switc)n(h.)251 3272 y(6.)35 b FJ(R\))28 b FK(and)h FJ(L\))729 3471 y FH(A)p 733 3491 39 3 v -1 x(;)12 b(C)25 b FJ(`)19 b FH(D)r(;)1038 3471 y(B)p 1042 3491 43 3 v 690 3515 444 4 v 1155 3531 a FJ(R\))690 3592 y FH(A)p 693 3612 39 3 v 761 3591 a FJ(`)h FH(C)25 b FJ(\))20 b FH(D)r(;)1078 3592 y(B)p 1081 3612 43 3 v 1432 3471 a(A)p 1435 3491 39 3 v -30 x Fv(0)1520 3470 y FJ(`)f FH(C)q(;)1663 3471 y(B)p 1667 3491 43 3 v 1720 3441 a Fv(0)1814 3471 y FH(A)p 1818 3491 39 3 v -30 x Fv(00)1896 3470 y FH(;)12 b(D)22 b FJ(`)2068 3471 y FH(B)p 2072 3491 43 3 v 2124 3441 a Fv(00)p 1432 3515 723 4 v 2175 3531 a FJ(L\))1440 3592 y FH(A)p 1443 3612 39 3 v -30 x Fv(0)1508 3591 y FH(;)1539 3592 y(A)p 1543 3612 V -30 x Fv(00)1621 3591 y FH(;)12 b(C)25 b FJ(\))20 b FH(D)h FJ(`)1957 3592 y FH(B)p 1960 3612 43 3 v 2013 3562 a Fv(0)2029 3591 y FH(;)2060 3592 y(B)p 2064 3612 V 2116 3562 a Fv(00)p 690 3636 1457 4 v 2167 3652 a Fq(Cut)1107 3714 y FH(A)p 1111 3733 39 3 v -1 x(;)1190 3714 y(A)p 1193 3733 V -30 x Fv(0)1258 3713 y FH(;)1289 3714 y(A)p 1292 3733 V -30 x Fv(00)1390 3713 y FJ(`)1453 3714 y FH(B)p 1456 3733 43 3 v 1509 3713 a(;)1540 3714 y(B)p 1543 3733 V 1596 3684 a Fv(0)1612 3713 y FH(;)1643 3714 y(B)p 1646 3733 V 1699 3684 a Fv(00)339 3925 y FK(is)27 b(replaced)g(b)n(y)p eop PStoPSsaved restore %%Page: (110,111) 56 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 107 110 bop 167 167 a Fz(13.1.)65 b(THE)27 b(KEY)f(CASES)1617 b FK(107)767 390 y FH(A)p 770 410 39 3 v 818 360 a Fv(0)855 389 y FJ(`)19 b FH(C)q(;)998 390 y(B)p 1002 410 43 3 v 1055 360 a Fv(0)1149 390 y FH(A)p 1153 410 39 3 v -1 x(;)12 b(C)25 b FJ(`)19 b FH(D)r(;)1458 390 y(B)p 1462 410 43 3 v 767 434 748 4 v 1535 450 a Fq(Cut)899 511 y FH(A)p 903 531 39 3 v -30 x Fv(0)968 510 y FH(;)999 511 y(A)p 1002 531 V 1070 510 a FJ(`)1132 511 y FH(B)p 1136 531 43 3 v 1188 481 a Fv(0)1205 510 y FH(;)12 b(D)r(;)1326 511 y(B)p 1329 531 V 899 571 a FK(=)-29 b(=)-16 b(=)g(=)g(=)g(=)g(=)g (=)g(=)g(=)g(=)g(=)-30 b(=)899 633 y FH(A)p 903 652 39 3 v -1 x(;)982 633 y(A)p 986 652 V -30 x Fv(0)1070 632 y FJ(`)19 b FH(D)r(;)1222 633 y(B)p 1226 652 43 3 v 1278 632 a(;)1309 633 y(B)p 1313 652 V 1365 603 a Fv(0)1752 633 y FH(A)p 1756 652 39 3 v -30 x Fv(00)1834 632 y FH(;)12 b(D)22 b FJ(`)2006 633 y FH(B)p 2010 652 43 3 v 2062 603 a Fv(00)p 899 677 1193 4 v 2113 692 a Fq(Cut)1185 754 y FH(A)p 1189 774 39 3 v -1 x(;)1268 754 y(A)p 1271 774 V 1319 724 a Fv(0)1336 753 y FH(;)1367 754 y(A)p 1370 774 V 1418 724 a Fv(00)1468 753 y FJ(`)1531 754 y FH(B)p 1534 774 43 3 v 1586 753 a(;)1617 754 y(B)p 1621 774 V 1673 724 a Fv(0)1690 753 y FH(;)1721 754 y(B)p 1724 774 V 1777 724 a Fv(00)339 980 y FK(So)29 b(the)e(problem)g(is)g (solv)n(ed)h(b)n(y)g FM(two)k FK(cuts.)251 1253 y(7.)j FJ(R8)27 b FK(and)i FJ(L8)943 1467 y FH(A)p 947 1486 39 3 v 1015 1466 a FJ(`)19 b FH(C)q(;)1158 1467 y(B)p 1162 1486 43 3 v 892 1510 375 4 v 1287 1526 a FJ(R8)892 1588 y FH(A)p 895 1608 39 3 v 963 1587 a FJ(`)h(8)p FH(\030)s(:)12 b(C)q(;)1211 1588 y(B)p 1214 1608 43 3 v 1533 1467 a(A)p 1537 1486 39 3 v -30 x Fv(0)1601 1466 y FH(;)g(C)5 b FK([)p FH(a=\030)s FK(])22 b FJ(`)1911 1467 y FH(B)p 1915 1486 43 3 v 1967 1437 a Fv(0)p 1533 1510 451 4 v 2005 1526 a FJ(L8)1553 1588 y FH(A)p 1556 1608 39 3 v 1604 1558 a Fv(0)1621 1587 y FH(;)12 b FJ(8)p FH(\030)s(:)g(C)24 b FJ(`)1892 1588 y FH(B)p 1895 1608 43 3 v 1948 1558 a Fv(0)p 892 1632 1073 4 v 1985 1648 a Fq(Cut)1232 1709 y FH(A)p 1235 1729 39 3 v -1 x(;)1315 1709 y(A)p 1318 1729 V 1366 1679 a Fv(0)1402 1708 y FJ(`)1465 1709 y FH(B)p 1468 1729 43 3 v 1521 1708 a(;)1552 1709 y(B)p 1555 1729 V 1608 1679 a Fv(0)339 1935 y FK(is)j(replaced)g(b)n(y)956 2163 y FH(A)p 960 2182 39 3 v 1027 2162 a FJ(`)20 b FH(C)5 b FK([)p FH(a=\030)s FK(])p FH(;)1316 2163 y(B)p 1321 2182 43 3 v 84 w(A)p 1456 2182 39 3 v -30 x Fv(0)1520 2162 y FH(;)12 b(C)5 b FK([)p FH(a=\030)s FK(])22 b FJ(`)1830 2163 y FH(B)p 1834 2182 43 3 v 1886 2133 a Fv(0)p 956 2207 947 4 v 1923 2222 a Fq(Cut)1233 2284 y FH(A)p 1237 2304 39 3 v -1 x(;)1316 2284 y(A)p 1319 2304 V -30 x Fv(0)1404 2283 y FJ(`)1466 2284 y FH(B)p 1470 2304 43 3 v 1522 2283 a(;)1553 2284 y(B)p 1557 2304 V 1609 2254 a Fv(0)339 2510 y FK(where)27 b FH(a)h FK(is)f(substituted)h(for)f FH(\030)32 b FK(throughout)d(the)f(left-hand)f(sub-pro)r(of.)251 2668 y(8.)35 b FJ(R9)28 b FK(and)h FJ(L9)881 2881 y FH(A)p 885 2901 39 3 v 953 2880 a FJ(`)19 b FH(C)5 b FK([)p FH(a=\030)s FK(])p FH(;)1241 2881 y(B)p 1247 2901 43 3 v 881 2925 418 4 v 1320 2941 a FJ(R9)903 3003 y FH(A)p 906 3022 39 3 v 974 3002 a FJ(`)20 b(9)p FH(\030)s(:)12 b(C)q(;)1221 3003 y(B)p 1225 3022 43 3 v 1618 2881 a(A)p 1621 2901 39 3 v 1669 2851 a Fv(0)1686 2880 y FH(;)g(C)25 b FJ(`)1853 2881 y FH(B)p 1857 2901 43 3 v 1909 2851 a Fv(0)p 1566 2925 412 4 v 1998 2941 a FJ(L9)1566 3003 y FH(A)p 1569 3022 39 3 v -31 x Fv(0)1634 3002 y FH(;)12 b FJ(9)p FH(\030)s(:)g(C)25 b FJ(`)1905 3003 y FH(B)p 1909 3022 43 3 v 1961 2972 a Fv(0)p 903 3046 1075 4 v 1998 3062 a Fq(Cut)1244 3124 y FH(A)p 1248 3144 39 3 v -1 x(;)1327 3124 y(A)p 1330 3144 V 1378 3094 a Fv(0)1414 3123 y FJ(`)1477 3124 y FH(B)p 1481 3144 43 3 v 1533 3123 a(;)1564 3124 y(B)p 1567 3144 V 1620 3094 a Fv(0)339 3350 y FK(is)i(replaced)g(b)n(y)956 3577 y FH(A)p 960 3597 39 3 v 1027 3576 a FJ(`)20 b FH(C)5 b FK([)p FH(a=\030)s FK(])p FH(;)1316 3577 y(B)p 1321 3597 43 3 v 84 w(A)p 1456 3597 39 3 v -30 x Fv(0)1520 3576 y FH(;)12 b(C)5 b FK([)p FH(a=\030)s FK(])22 b FJ(`)1830 3577 y FH(B)p 1834 3597 43 3 v 1886 3547 a Fv(0)p 956 3621 947 4 v 1923 3637 a Fq(Cut)1233 3699 y FH(A)p 1237 3718 39 3 v -1 x(;)1316 3699 y(A)p 1319 3718 V -30 x Fv(0)1404 3698 y FJ(`)1466 3699 y FH(B)p 1470 3718 43 3 v 1522 3698 a(;)1553 3699 y(B)p 1557 3718 V 1609 3669 a Fv(0)339 3925 y FK(This)28 b(is)e(the)i(dual)g(of)g(case)f FG(??)q FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 108 111 bop 167 167 a FK(108)710 b Fz(CHAPTER)26 b(13.)64 b(CUT)27 b(ELIMINA)-6 b(TION)26 b(\(HA)n(UPTSA)-6 b(TZ\))167 404 y FE(13.2)114 b(The)28 b(principal)g(lemma)167 571 y FK(The)f FM(de)l(gr)l(e)l(e)34 b FH(@)t FK(\()p FH(A)p FK(\))27 b(of)h(a)g FM(formula)34 b FK(is)26 b(de\014ned)j(b)n(y:)270 764 y FJ(\017)34 b FH(@)t FK(\()p FH(A)p FK(\))20 b(=)f(1)28 b(for)g FH(A)f FK(atomic)270 927 y FJ(\017)34 b FH(@)t FK(\()p FH(A)16 b FJ(^)f FH(B)t FK(\))20 b(=)f FH(@)t FK(\()p FH(A)c FJ(_)h FH(B)t FK(\))j(=)h FH(@)t FK(\()p FH(A)f FJ(\))h FH(B)t FK(\))f(=)g(max)q(\()p FH(@)t FK(\()p FH(A)p FK(\))p FH(;)12 b(@)t FK(\()p FH(B)t FK(\)\))i(+)i(1)270 1090 y FJ(\017)34 b FH(@)t FK(\()p FJ(:)p FH(A)p FK(\))20 b(=)f FH(@)t FK(\()p FJ(8)p FH(\030)s(:)12 b(A)p FK(\))18 b(=)i FH(@)t FK(\()p FJ(9)p FH(\030)s(:)12 b(A)p FK(\))19 b(=)h FH(@)t FK(\()p FH(A)p FK(\))15 b(+)g(1)270 1283 y(so)29 b(that)f FH(@)t FK(\()p FH(A)p FK([)p FH(a=\030)s FK(]\))20 b(=)g FH(@)t FK(\()p FH(A)p FK(\).)270 1433 y(The)32 b FM(de)l(gr)l(e)l(e)38 b FK(of)33 b(a)f FM(cut)g(rule)37 b FK(is)31 b(de\014ned)i(to)f(b)r(e)g(the)g(degree)f(of)i(the)f(form)n (ula)g(whic)n(h)f(it)167 1518 y(eliminates.)45 b(The)32 b(k)n(ey)g(cases)g(considered)f(ab)r(o)n(v)n(e)i(replace)e(a)h(cut)g(b) n(y)g(one)h(or)f(t)n(w)n(o)g(cuts)g(of)167 1603 y(lo)n(w)n(er)27 b(degree.)270 1752 y(The)c FM(de)l(gr)l(e)l(e)29 b FH(d)p FK(\()p FH(\031)s FK(\))22 b(of)h(a)h FM(pr)l(o)l(of)39 b FK(is)23 b(the)f(sup)i(of)f(the)g(degrees)g(of)g(its)f(cut)h(rules,)g (so)h FH(d)p FK(\()p FH(\031)s FK(\))18 b(=)i(0)167 1838 y(i\013)27 b FH(\031)j FK(is)d(cut-free.)270 1987 y(The)32 b FM(height)38 b FH(h)p FK(\()p FH(\031)s FK(\))30 b(of)i(a)g FM(pr)l(o)l(of)48 b FK(is)31 b(that)h(of)f(its)g(asso)r(ciated)h(tree:) 42 b(if)30 b FH(\031)35 b FK(ends)c(in)g(a)h(rule)167 2072 y(whose)23 b(premises)f(are)g(pro)n(v)n(ed)i(b)n(y)g FH(\031)1124 2083 y FD(1)1152 2072 y FH(;)12 b(:)g(:)g(:)g(;)g(\031) 1346 2083 y Fw(n)1402 2072 y FK(\()p FH(n)19 b FK(=)g(0)p FH(;)12 b FK(1)24 b(or)f(2\))g(then)g FH(h)p FK(\()p FH(\031)s FK(\))c(=)g(sup)q(\()p FH(h)p FK(\()p FH(\031)2475 2083 y Fw(i)2494 2072 y FK(\)\))8 b(+)g(1.)270 2292 y(The)22 b(principal)f(lemma)f(sa)n(ys)k(that)e(the)g(\014nal)h(cut)f(rule)f (can)h(b)r(e)g(eliminated.)31 b(Its)22 b(complex)167 2377 y(form)n(ulation)27 b(tak)n(es)h(accoun)n(t)h(of)f(the)f (structural)g(rules)g(whic)n(h)g(in)n(terfere)f(with)g(cuts.)167 2597 y FG(Notation)79 b FK(If)642 2598 y FH(A)p 646 2618 39 3 v 735 2597 a FK(is)40 b(a)h(sequence)f(of)h(form)n(ulae,)j(then) 1795 2598 y FH(A)p 1798 2618 V 1854 2597 a FJ(\000)19 b FH(C)46 b FK(denotes)2290 2598 y FH(A)p 2294 2618 V 2382 2597 a FK(where)40 b(an)167 2682 y FM(arbitr)l(ary)35 b FK(n)n(um)n(b)r(er)28 b(of)g(o)r(ccurrences)e(of)j(the)e(form)n(ula)g FH(C)33 b FK(ha)n(v)n(e)c(b)r(een)e(deleted.)167 2902 y FG(Lemma)22 b FK(Let)j FH(C)30 b FK(b)r(e)25 b(a)g(form)n(ula)g(of)h (degree)e FH(d)p FK(,)i(and)g FH(\031)s(;)12 b(\031)1690 2877 y Fv(0)1731 2902 y FK(pro)r(ofs)26 b(of)2040 2903 y FH(A)p 2043 2923 V 2111 2902 a FJ(`)2174 2903 y FH(B)p 2177 2923 43 3 v 2274 2902 a FK(and)2430 2903 y FH(A)p 2433 2923 39 3 v -29 x Fv(0)2518 2902 y FJ(`)2580 2903 y FH(B)p 2584 2923 43 3 v 2636 2874 a Fv(0)167 2988 y FK(of)h(degrees)e(less)h(than)g FH(d)p FK(.)35 b(Then)26 b(w)n(e)g(can)g(mak)n(e)g(a)h(pro)r(of)1694 2962 y FD(1)1749 2988 y FH($)h FK(of)1935 2989 y FH(A)p 1938 3008 39 3 v 1986 2988 a(;)2017 2989 y(A)p 2021 3008 V -30 x Fv(0)2087 2988 y FJ(\000)13 b FH(C)25 b FJ(`)2292 2989 y FH(B)p 2295 3008 43 3 v 2349 2988 a FJ(\000)13 b FH(C)q(;)2498 2989 y(B)p 2502 3008 V 2555 2959 a Fv(0)2617 2988 y FK(of)167 3073 y(degree)27 b(less)g(than)h FH(d)p FK(.)167 3293 y FG(Pro)r(of)42 b FH($)h FK(is)e(constructed)g(b)n(y)i(induction)e(on) h FH(h)p FK(\()p FH(\031)s FK(\))18 b(+)i FH(h)p FK(\()p FH(\031)1870 3267 y Fv(0)1885 3293 y FK(\),)45 b(but)d(unfortunately)h (not)167 3378 y(symmetrically)25 b(in)j FH(\031)j FK(and)f FH(\031)955 3352 y Fv(0)971 3378 y FK(:)37 b(at)28 b(some)g(stages)i (preference)d(is)g(giv)n(en)i(to)f FH(\031)s FK(,)h(or)g(to)f FH(\031)2497 3352 y Fv(0)2513 3378 y FK(,)h(and)167 3463 y FH($)g FK(is)e(irrev)n(ersibly)f(a\013ected)h(b)n(y)h(this)g(c)n (hoice.)270 3612 y(T)-6 b(o)41 b(simplify)c(matters,)42 b(w)n(e)d(shall)g(supp)r(ose)i(that)f(in)1793 3613 y FH(A)p 1797 3633 39 3 v -29 x Fv(0)1868 3612 y FJ(\000)19 b FH(C)45 b FK(and)2187 3613 y FH(B)p 2190 3633 43 3 v 2250 3612 a FJ(\000)19 b FH(C)45 b FK(w)n(e)39 b(ha)n(v)n(e)167 3698 y(remo)n(v)n(ed)24 b FM(al)t(l)31 b FK(the)24 b(o)r(ccurrences)g (of)h FH(C)5 b FK(.)34 b(This)24 b(allo)n(ws)g(us)h(to)g(a)n(v)n(oid)g (length)n(y)g(circumlo)r(cutions)167 3783 y(without)i(making)h(an)n(y)h (essen)n(tial)d(di\013erence)g(to)i(the)g(pro)r(of.)p 167 3860 1003 3 v 246 3903 a FC(1)273 3925 y Fx($)g FB(is)g(a)f(v)m (arian)n(t)h(of)f Fx(\031)r FB(,)i(not)e(of)h Fx(!)r FB(.)p eop PStoPSsaved restore %%Page: (112,113) 57 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 109 112 bop 167 167 a Fz(13.2.)65 b(THE)27 b(PRINCIP)-6 b(AL)26 b(LEMMA)1341 b FK(109)270 404 y(The)30 b(last)g(rule)f Fq(r)j FK(of)e FH(\031)j FK(has)e(premises)1353 405 y FH(A)p 1357 425 39 3 v 23 x Fw(i)1446 404 y FJ(`)1511 405 y FH(B)p 1514 425 43 3 v 1567 428 a Fw(i)1638 404 y FK(pro)n(v)n(ed)g(b)n(y)g FH(\031)2011 415 y Fw(i)2031 404 y FK(,)g(and)g(the)f(last)g(rule)f Fq(r)2655 379 y Fv(0)167 490 y FK(of)f FH(\031)292 464 y Fv(0)336 490 y FK(has)g(premises)768 491 y FH(A)p 772 510 39 3 v -30 x Fv(0)820 513 y Fw(j)865 490 y FJ(`)928 491 y FH(B)p 931 510 43 3 v 984 461 a Fv(0)984 513 y Fw(j)1057 490 y FK(pro)n(v)n(ed)g(b)n(y)h FH(\031)1428 464 y Fv(0)1425 507 y Fw(j)1451 490 y FK(.)35 b(There)27 b(are)h(sev)n(eral)f(cases)g (to)h(consider:)251 635 y(1.)35 b FH(\031)c FK(is)c(an)h(axiom.)35 b(There)27 b(are)h(t)n(w)n(o)g(sub)r(cases:)421 773 y FJ(\017)35 b FH(\031)c FK(pro)n(v)n(es)49 b FH(C)25 b FJ(`)20 b FH(C)25 b FK(.)36 b(Then)28 b(a)h(pro)r(of)g FH($)h FK(of)48 b FH(C)q(;)1769 774 y(A)p 1773 794 39 3 v -30 x Fv(0)1842 773 y FJ(\000)15 b FH(C)25 b FJ(`)2049 774 y FH(B)p 2053 794 43 3 v 2105 744 a Fv(0)2169 773 y FK(is)j(obtained)g(from)491 858 y FH(\031)533 833 y Fv(0)577 858 y FK(b)n(y)g(means)g(of)g(structural)f(rules.)421 961 y FJ(\017)35 b FH(\031)f FK(pro)n(v)n(es)54 b FH(D)25 b FJ(`)d FH(D)i FK(.)46 b(Then)32 b(a)f(pro)r(of)i FH($)g FK(of)54 b FH(D)r(;)1832 962 y(A)p 1835 982 39 3 v -29 x Fv(0)1905 961 y FJ(\000)16 b FH(C)28 b FJ(`)22 b FH(D)r(;)2208 962 y(B)p 2212 982 43 3 v 2264 933 a Fv(0)2334 961 y FK(is)31 b(obtained)491 1046 y(from)d FH(\031)i FK(b)n(y)e(means)g(of)g (structural)f(rules.)251 1185 y(2.)35 b FH(\031)381 1159 y Fv(0)427 1185 y FK(is)28 b(an)i(axiom.)39 b(This)29 b(case)g(is)f(handled)i(as)f FG(??)q FK(;)h(but)g(notice)e(that)h(if)f FH(\031)k FK(and)e FH(\031)2535 1159 y Fv(0)2580 1185 y FK(are)339 1270 y(b)r(oth)f(axioms,)f(w)n(e)f(ha)n(v)n(e)i (arbitrarily)d(privileged)f FH(\031)s FK(.)251 1402 y(3.)35 b Fq(r)c FK(is)e(a)h(structural)f(rule.)39 b(The)30 b(induction)e(h)n (yp)r(othesis)j(for)e FH(\031)1990 1413 y FD(1)2048 1402 y FK(and)h FH(\031)2230 1377 y Fv(0)2276 1402 y FK(giv)n(es)f(a)h(pro)r (of)339 1488 y FH($)396 1499 y FD(1)455 1488 y FK(of)564 1489 y FH(A)p 567 1508 39 3 v 615 1511 a FD(1)643 1488 y FH(;)674 1489 y(A)p 678 1508 V -30 x Fv(0)747 1488 y FJ(\000)17 b FH(C)27 b FJ(`)960 1489 y FH(B)p 963 1508 43 3 v 1016 1511 a FD(1)1049 1488 y FJ(\000)16 b FH(C)q(;)1201 1489 y(B)p 1205 1508 V 1257 1459 a Fv(0)1296 1488 y FK(.)45 b(Then)31 b FH($)i FK(is)e(obtained)g(from)g FH($)2235 1499 y FD(1)2294 1488 y FK(b)n(y)g(means)h(of)339 1573 y(structural)e(rules.)42 b(Notice)29 b(that)h(in)g(the)g(case)g(where)g (the)f(last)h(rule)f(of)i FH(\031)i FK(is)c FJ(R)p Fq(C)h FK(on)339 1658 y FH(C)5 b FK(,)29 b(w)n(e)e(ha)n(v)n(e)h(more)f(o)r (ccurrences)g(of)h FH(C)33 b FK(in)27 b FH(B)1564 1669 y FD(1)1620 1658 y FK(than)i(in)e FH(B)t FK(.)251 1790 y(4.)35 b Fq(r)363 1765 y Fv(0)408 1790 y FK(is)27 b(a)h(structural)f (rule)f(\(dual)i(of)g FG(??)q FK(\).)251 1922 y(5.)35 b Fq(r)h FK(is)e(a)h(logical)e(rule,)i(other)f(than)i(a)f(righ)n(t)f (one)h(with)e(principal)g(form)n(ula)h FH(C)5 b FK(.)56 b(The)339 2008 y(induction)22 b(h)n(yp)r(othesis)i(for)e FH(\031)1128 2019 y Fw(i)1171 2008 y FK(and)h FH(\031)1346 1982 y Fv(0)1385 2008 y FK(giv)n(es)f(a)h(pro)r(of)h FH($)1847 2019 y Fw(i)1889 2008 y FK(of)1987 2009 y FH(A)p 1990 2028 39 3 v 2038 2031 a Fw(i)2058 2008 y FH(;)2089 2009 y(A)p 2093 2028 V -30 x Fv(0)2154 2008 y FJ(\000)8 b FH(C)24 b FJ(`)2353 2009 y FH(B)p 2356 2028 43 3 v 2409 2031 a Fw(i)2436 2008 y FJ(\000)8 b FH(C)q(;)2580 2009 y(B)p 2584 2028 V 2637 1979 a Fv(0)2653 2008 y FK(.)339 2093 y(The)25 b(same)g(rule)f Fq(r)j FK(is)d(applicable)g(to)i(the)f FH($)1512 2104 y Fw(i)1532 2093 y FK(,)g(and)i(since)d Fq(r)i FK(do)r(es)g(not)g(create)e(an)n(y)i(new)339 2178 y(o)r(ccurrence)19 b(of)h FH(C)25 b FK(on)20 b(the)g(righ)n(t)f(side,)i (this)e(giv)n(es)h(a)g(pro)r(of)g FH($)i FK(of)2055 2179 y FH(A)p 2059 2198 39 3 v -1 x(;)2138 2179 y(A)p 2142 2198 V -30 x Fv(0)2198 2178 y FJ(\000)t FH(C)i FJ(`)2393 2179 y FH(B)p 2396 2198 43 3 v 2441 2178 a FJ(\000)t FH(C)q(;)2581 2179 y(B)p 2584 2198 V 2637 2149 a Fv(0)2653 2178 y FK(.)251 2310 y(6.)35 b Fq(r)363 2285 y Fv(0)408 2310 y FK(is)27 b(a)h(logical)e(rule,)h(other)g(than)i(a)f(left)e(one)i (principal)e(form)n(ula)i FH(C)33 b FK(\(dual)27 b(of)i FG(??)p FK(\).)251 2442 y(7.)35 b(Both)d Fq(r)g FK(and)h Fq(r)741 2417 y Fv(0)789 2442 y FK(are)e(logical)e(rules,)j Fq(r)g FK(a)g(righ)n(t)e(one)i(and)g Fq(r)1924 2417 y Fv(0)1972 2442 y FK(a)g(left)e(one,)i(of)g(principal)339 2528 y(form)n(ula)c FH(C)5 b FK(.)36 b(This)27 b(is)g(the)g(only)h(imp) r(ortan)n(t)f(case,)h(and)h(it)d(is)h(symmetrical.)339 2666 y(First,)g(apply)h(the)g(induction)f(h)n(yp)r(othesis)h(to)421 2804 y FJ(\017)35 b FH(\031)530 2815 y Fw(i)578 2804 y FK(and)28 b FH(\031)758 2779 y Fv(0)775 2804 y FK(,)f(giving)h(a)g (pro)r(of)h FH($)1335 2815 y Fw(i)1382 2804 y FK(of)1485 2805 y FH(A)p 1488 2825 39 3 v 23 x Fw(i)1557 2804 y FH(;)1588 2805 y(A)p 1591 2825 V 1639 2776 a Fv(0)1659 2804 y FJ(\000)16 b FH(C)25 b FJ(`)1866 2805 y FH(B)p 1870 2825 43 3 v 1922 2828 a Fw(i)1946 2804 y FJ(\000)16 b FH(C)q(;)2098 2805 y(B)p 2102 2825 V 2154 2776 a Fv(0)2190 2804 y FK(;)421 2907 y FJ(\017)35 b FH(\031)30 b FK(and)f FH(\031)741 2882 y Fv(0)738 2925 y Fw(j)764 2907 y FK(,)f(giving)f(a)h (pro)r(of)h FH($)1326 2882 y Fv(0)1324 2925 y Fw(j)1377 2907 y FK(of)1480 2908 y FH(A)p 1484 2928 39 3 v -1 x(;)1563 2908 y(A)p 1566 2928 V -29 x Fv(0)1615 2931 y Fw(j)1644 2907 y FJ(\000)16 b FH(C)25 b FJ(`)1851 2908 y FH(B)p 1855 2928 43 3 v 1911 2907 a FJ(\000)16 b FH(C)q(;)2063 2908 y(B)p 2067 2928 V 2119 2879 a Fv(0)2119 2931 y Fw(j)2164 2907 y FK(.)339 3052 y(Second)33 b(apply)g Fq(r)h FK(\(and)f(some)f (structural)f(rules\))g(to)i(the)f FH($)1997 3063 y Fw(i)2049 3052 y FK(to)g(giv)n(e)g(a)h(pro)r(of)g FH(\032)f FK(of)339 3138 y FH(A)p 343 3158 39 3 v -1 x(;)422 3138 y(A)p 426 3158 V -29 x Fv(0)495 3137 y FJ(\000)17 b FH(C)29 b FJ(`)23 b FH(C)q(;)792 3138 y(B)p 796 3158 43 3 v 853 3137 a FJ(\000)17 b FH(C)q(;)1006 3138 y(B)p 1010 3158 V 1062 3109 a Fv(0)1102 3137 y FK(.)50 b(Lik)n(ewise)30 b(apply)j Fq(r)1680 3112 y Fv(0)1729 3137 y FK(\(and)h(some)e(structural)g (rules\))f(to)339 3222 y(the)d FH($)522 3197 y Fv(0)520 3240 y Fw(j)573 3222 y FK(to)g(giv)n(e)f(a)i(pro)r(of)f FH(\032)1091 3197 y Fv(0)1135 3222 y FK(of)1238 3223 y FH(A)p 1241 3243 39 3 v 1289 3222 a(;)1320 3223 y(A)p 1324 3243 V -29 x Fv(0)1392 3222 y FJ(\000)16 b FH(C)q(;)c(C)25 b FJ(`)1681 3223 y FH(B)p 1684 3243 43 3 v 1741 3222 a FJ(\000)15 b FH(C)q(;)1892 3223 y(B)p 1896 3243 V 1948 3194 a Fv(0)1984 3222 y FK(.)339 3361 y(There)34 b(is)f(one)i(o)r (ccurrence)e(of)i FH(C)40 b FK(to)r(o)34 b(man)n(y)h(on)g(the)f(righ)n (t)g(of)h(the)f(conclusion)g(to)339 3446 y FH(\032)k FK(and)g(on)h(the)e(left)f(of)i(that)g(to)g FH(\032)1332 3420 y Fv(0)1348 3446 y FK(.)66 b(Using)37 b(the)g(cut)h(rule)e(w)n(e)h (ha)n(v)n(e)i(a)f(pro)r(of)h(of)339 3532 y FH(A)p 343 3552 39 3 v -1 x(;)422 3532 y(A)p 426 3552 V -30 x Fv(0)494 3531 y FJ(\000)16 b FH(C)q(;)646 3532 y(A)p 650 3552 V -1 x(;)729 3532 y(A)p 732 3552 V 780 3502 a Fv(0)801 3531 y FJ(\000)f FH(C)25 b FJ(`)1008 3532 y FH(B)p 1011 3552 43 3 v 1068 3531 a FJ(\000)15 b FH(C)q(;)1219 3532 y(B)p 1223 3552 V 1275 3502 a Fv(0)1292 3531 y FH(;)1323 3532 y(B)p 1326 3552 V 1383 3531 a FJ(\000)g FH(C)q(;)1534 3532 y(B)p 1538 3552 V 1590 3502 a Fv(0)1607 3531 y FK(.)339 3669 y(Ho)n(w)n(ev)n(er)35 b(the)g(degree)f(of)i(this)e(cut)h(is)f FH(d)p FK(,)j(whic)n(h)d(is)g(to)r(o)i(m)n(uc)n(h.)57 b(But)35 b(w)n(e)g(observ)n(e)339 3754 y(that)27 b(this)e(is)h (precisely)e(one)i(of)h(the)f(k)n(ey)h(cases)f(presen)n(ted)g(in)f FG(??)q FK(,)i(so)f(w)n(e)g(can)g(replace)339 3840 y(this)42 b(cut)f(b)n(y)i(others)f(of)g(degree)g FH(<)29 b(d)p FK(.)78 b(Finally)40 b FH($)k FK(is)d(obtained)h(b)n(y)h(structural)339 3925 y(manipulations.)1833 b Fu(\003)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 110 113 bop 167 167 a FK(110)710 b Fz(CHAPTER)26 b(13.)64 b(CUT)27 b(ELIMINA)-6 b(TION)26 b(\(HA)n(UPTSA)-6 b(TZ\))167 404 y FE(13.3)114 b(The)28 b(Hauptsatz)167 559 y FG(Prop)r(osition)g FK(If)i FH(\031)j FK(is)c(a)i(pro)r(of)g(of)f(a)h(sequen)n(t)g(of)f (degree)g FH(d)21 b(>)g FK(0)31 b(then)f(a)g(pro)r(of)i FH($)g FK(of)e(the)167 644 y(same)d(sequen)n(t)h(can)g(b)r(e)g (constructed)g(with)e(lo)n(w)n(er)h(degree.)167 806 y FG(Pro)r(of)33 b FK(By)h(induction)f(on)h FH(h)p FK(\()p FH(\031)s FK(\).)51 b(Let)33 b Fq(r)i FK(b)r(e)e(the)g(last)g(rule)f (of)i FH(\031)i FK(and)f FH(\031)2202 817 y Fw(i)2255 806 y FK(the)e(subpro)r(ofs)167 891 y(corresp)r(onding)c(to)e(the)h (premises)e(of)i Fq(r)q FK(.)36 b(W)-6 b(e)27 b(ha)n(v)n(e)i(t)n(w)n(o) f(cases:)251 1030 y(1.)35 b Fq(r)29 b FK(is)d(not)i(a)f(cut)g(of)g (degree)g FH(d)p FK(.)35 b(The)27 b(induction)f(h)n(yp)r(othesis)i(giv) n(es)f FH($)2196 1041 y Fw(i)2243 1030 y FK(of)g(degree)g FH(<)19 b(d)p FK(,)339 1115 y(to)28 b(whic)n(h)f(w)n(e)g(apply)i Fq(r)g FK(to)f(giv)n(e)f FH($)r FK(.)251 1253 y(2.)35 b Fq(r)29 b FK(is)e(a)h(cut)g(of)g(degree)f FH(d)p FK(:)1101 1431 y FH(A)p 1104 1451 39 3 v 1172 1430 a FJ(`)20 b FH(C)q(;)1316 1431 y(B)p 1320 1451 43 3 v 82 w(A)p 1454 1451 39 3 v -30 x Fv(0)1518 1430 y FH(;)12 b(C)25 b FJ(`)1686 1431 y FH(B)p 1689 1451 43 3 v 1742 1401 a Fv(0)p 1101 1475 658 4 v 1779 1491 a Fq(Cut)1233 1553 y FH(A)p 1237 1572 39 3 v -1 x(;)1316 1553 y(A)p 1319 1572 V -30 x Fv(0)1404 1552 y FJ(`)1466 1553 y FH(B)p 1470 1572 43 3 v 1522 1552 a(;)1553 1553 y(B)p 1557 1572 V 1609 1523 a Fv(0)339 1730 y FK(The)32 b(induction)g(h)n(yp)r(othesis)g(pro)n (vides)h FH($)1493 1741 y Fw(i)1545 1730 y FK(of)f(degree)f FH(<)23 b(d)p FK(.)48 b(This)31 b(is)h(the)f(situation)339 1815 y(to)e(whic)n(h)e(the)h(principal)e(lemma)g(applies,)i(giving)g(a) g(pro)r(of)h FH($)h FK(of)2176 1816 y FH(A)p 2180 1836 39 3 v -1 x(;)2259 1816 y(A)p 2262 1836 V 2310 1787 a Fv(0)2347 1815 y FJ(`)2410 1816 y FH(B)p 2413 1836 43 3 v 2466 1815 a(;)2497 1816 y(B)p 2500 1836 V 2552 1787 a Fv(0)2617 1815 y FK(of)339 1900 y(degree)e FH(<)19 b(d)p FK(.)1930 b Fu(\003)270 2074 y FK(By)28 b(iterating)f(the)g(prop) r(osition,)h(w)n(e)f(obtain:)167 2236 y FG(Theorem)g FK(\(Gen)n(tzen,)g(1934\))j(The)d(cut)g(rule)g(is)g(redundan)n(t)i(in)e (sequen)n(t)h(calculus.)180 b Fu(\003)270 2398 y FK(One)34 b(should)i(ha)n(v)n(e)f(some)f(idea)g(of)h(ho)n(w)g(the)f(pro)r(cess)h (of)g(eliminating)d(cuts)i(explo)r(des)167 2483 y(the)c(heigh)n(t)h(of) g(pro)r(ofs.)46 b(W)-6 b(e)30 b(shall)g(just)h(giv)n(e)f(an)i(o)n(v)n (erall)e(estimate)e(whic)n(h)i(do)r(es)h(not)h(tak)n(e)167 2568 y(in)n(to)27 b(accoun)n(t)i(the)e(structural)g(rules.)270 2688 y(The)g(principal)e(lemma)f(is)i(linear:)34 b(the)26 b(elimination)e(of)j(a)g(cut)f(at)h(w)n(orst)f(m)n(ultiplies)d(the)167 2773 y(heigh)n(t)k(b)n(y)i(the)e(constan)n(t)i FH(k)22 b FK(=)d(4.)270 2894 y(The)30 b(prop)r(osition)g(is)e(exp)r(onen)n (tial:)39 b(reducing)29 b(the)g(degree)g(b)n(y)i(1)f(increases)e(the)h (heigh)n(t)167 2979 y(from)d FH(h)f FK(to)i(4)520 2953 y Fw(h)578 2979 y FK(at)f(w)n(orst,)h(since)e(in)g(using)h(the)g(lemma) e(w)n(e)i(m)n(ultiply)d(b)n(y)k(4)g(for)f(eac)n(h)g(unit)g(of)167 3064 y(heigh)n(t.)270 3184 y(Altogether,)c(the)f(Hauptsatz)g(is)g(h)n (yp)r(erexp)r(onen)n(tial:)32 b(a)22 b(pro)r(of)g(of)f(heigh)n(t)g FH(h)g FK(and)h(degree)e FH(d)167 3270 y FK(b)r(ecomes,)27 b(at)h(w)n(orst,)g(one)g(of)g(heigh)n(t)g FJ(H)q FK(\()p FH(d;)12 b(h)p FK(\),)27 b(where:)669 3431 y FJ(H)q FK(\(0)p FH(;)12 b(h)p FK(\))20 b(=)f FH(h)502 b FJ(H)q FK(\()p FH(d)15 b FK(+)h(1)p FH(;)c(h)p FK(\))19 b(=)g(4)1989 3406 y Fv(H)p FD(\()p Fw(d;h)p FD(\))270 3669 y FK(Consequen)n(tly)38 b(w)n(e)e(ha)n(v)n(e)i(the)f(all)e(to)r(o)j(common)e(situation)h(of)g (an)h(algorithm)e(whic)n(h)167 3754 y(is)41 b FM(e\013e)l(ctive)47 b FK(but)c(not)f FM(fe)l(asible)p FK(,)k(in)c(general,)j(since)c(w)n(e) h(do)h(not)f(need)g(to)h(iterate)d(the)167 3840 y(exp)r(onen)n(tial)25 b(v)n(ery)g(often)g(b)r(efore)g(w)n(e)f(exceed)h(all)e(conceiv)l(able)h (measures)h(of)h(the)e(size)g(of)h(the)167 3925 y(univ)n(erse!)p eop PStoPSsaved restore %%Page: (114,115) 58 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 111 114 bop 167 167 a Fz(13.4.)65 b(RESOLUTION)1731 b FK(111)167 404 y FE(13.4)114 b(Resolution)167 559 y FK(Gen)n(tzen's)29 b(result)f(do)r(es)i(not)g(sa)n(y)g(an)n(ything)g(ab)r(out)h(the)e (case)g(where)f(w)n(e)h(ha)n(v)n(e)h(non-trivial)167 644 y(axioms.)35 b(Nev)n(ertheless,)25 b(b)n(y)i(close)e(examination)h (of)h(the)f(pro)r(of,)i(w)n(e)e(can)g(see)g(that)h(the)f(only)167 730 y(case)37 b(in)g(whic)n(h)f(w)n(e)g(w)n(ould)i(b)r(e)f(unable)g(to) g(eliminate)d(a)k(cut)e(is)h(that)g(in)g(whic)n(h)f(one)i(of)167 815 y(the)31 b(t)n(w)n(o)h(premises)e(is)g(an)j(axiom,)f(and)h(that)e (it)g(is)g(necessary)g(to)h(extend)g(the)f(axioms)g(b)n(y)167 900 y(substitution.)270 1024 y(In)45 b(other)f(w)n(ords,)50 b(the)44 b(Hauptsatz)h(remains)e(applicable,)48 b(but)d(in)e(the)i (form)f(of)h(a)167 1109 y FM(r)l(estriction)i FK(of)41 b(the)g(cut)g(rule)f(to)h(those)h(sequen)n(ts)g(whic)n(h)e(are)h (obtained)h(from)f(prop)r(er)167 1195 y(axioms)28 b(b)n(y)g (substitution.)270 1364 y(As)23 b(a)g(consequence,)h(if)e(w)n(e)g (con\014ne)h(ourselv)n(es)f(to)h FM(atomic)k FK(sequen)n(ts)d(\(built)d (from)h(atomic)167 1449 y(form)n(ulae\))k(as)h(prop)r(er)g(axioms,)g (and)h(as)f(the)g(conclusion,)g FM(ther)l(e)f(is)h(no)g(ne)l(e)l(d)g (for)g(the)f(lo)l(gic)l(al)167 1535 y(rules)p FK(.)270 1659 y(Let)31 b(us)g(turn)g(straigh)n(t)g(to)g(the)f(case)h(of)h Fr(PROLOG)p FK(.)g(The)e(axioms)h(are)g(of)g(a)g(v)n(ery)h(sp)r(ecial) 167 1744 y(form,)37 b(namely)d(atomic)g(in)n(tuitionistic)e(sequen)n (ts)k(\(also)f(called)e FM(Horn)j(clauses)p FK(\))2428 1745 y FH(A)p 2431 1765 39 3 v 2504 1744 a FJ(`)25 b FH(B)k FK(.)167 1829 y(The)h(aim)g(is)g(to)h(pro)n(v)n(e)h FM(go)l(als)p FK(,)g FM(i.e.)f FK(atomic)f(sequen)n(ts)h(of)g(the)g (form)52 b FJ(`)22 b FH(B)k FK(.)44 b(In)31 b(doing)h(this)167 1914 y(w)n(e)27 b(ha)n(v)n(e)i(at)f(our)g(disp)r(osal)270 2069 y FJ(\017)34 b FK(instances)28 b(\(b)n(y)g(substitution\))1202 2070 y FH(A)p 1205 2090 V 1273 2069 a FJ(`)20 b FH(B)51 b FK(of)28 b(the)f(prop)r(er)h(axioms,)270 2211 y FJ(\017)34 b FK(iden)n(tit)n(y)27 b(axioms)47 b FH(A)19 b FJ(`)h FH(A)47 b FK(with)27 b FH(A)g FK(atomic,)270 2354 y FJ(\017)34 b FK(cut,)28 b(and)270 2496 y FJ(\017)34 b FK(the)28 b(structural)f(rules.)270 2651 y(But)h(the)f(con)n(traction)h(and)h(w)n (eak)n(ening)f(are)f(redundan)n(t:)167 2820 y FG(Lemma)h FK(If)i(the)h(atomic)e(sequen)n(t)1167 2821 y FH(A)p 1171 2841 V 1240 2820 a FJ(`)1305 2821 y FH(B)p 1309 2841 43 3 v 1413 2820 a FK(is)h(pro)n(v)l(able)i(using)f(these)f (rules,)h(there)e(is)h(an)167 2906 y(in)n(tuitionistic)g(sequen)n(t)866 2907 y FH(A)p 870 2926 39 3 v -30 x Fv(0)958 2906 y FJ(`)24 b FH(B)1081 2880 y Fv(0)1155 2906 y FK(pro)n(v)l(able)35 b(without)e(w)n(eak)n(ening)h(or)g(con)n(traction,)i(suc)n(h)167 2991 y(that:)270 3145 y FJ(\017)339 3146 y FH(A)p 343 3166 V -29 x Fv(0)435 3145 y FK(is)27 b(built)f(from)i(form)n(ulae)f (of)1217 3146 y FH(A)p 1221 3166 V -1 x FK(;)270 3288 y FJ(\017)34 b FH(B)395 3262 y Fv(0)439 3288 y FK(is)27 b(in)598 3289 y FH(B)p 602 3308 43 3 v 654 3288 a FK(.)167 3457 y FG(Pro)r(of)h FK(By)g(induction)f(on)h(the)f(pro)r(of)i FH(\031)h FK(of)1391 3458 y FH(A)p 1395 3478 39 3 v 1462 3457 a FJ(`)20 b FH(B)j FK(.)251 3612 y(1.)35 b(If)30 b FH(\031)h FK(is)e(an)h(axiom)f(the)g(result)f(is)h(immediate,)e(as)j (the)f(axioms,)h(prop)r(er)f(or)h(iden)n(tit)n(y)-6 b(,)339 3697 y(are)28 b(in)n(tuitionistic.)251 3840 y(2.)35 b(If)28 b FH(\031)i FK(ends)e(in)g(a)g(structural)f(rule)f(applied)h(to)1612 3841 y FH(A)p 1616 3860 V 22 x FD(1)1711 3840 y FJ(`)20 b FH(B)1826 3851 y FD(1)1874 3840 y FK(,)28 b(the)f(induction)g(h)n(yp) r(othesis)339 3925 y(giv)n(es)h(an)g(in)n(tuitionistic)d(sequen)n(t) 1296 3926 y FH(A)p 1300 3945 V -30 x Fv(0)1348 3948 y FD(1)1395 3925 y FJ(`)20 b FH(B)1514 3899 y Fv(0)1510 3942 y FD(1)1585 3925 y FK(and)29 b(w)n(e)e(put)1961 3926 y FH(A)p 1965 3945 V -30 x Fv(0)2049 3925 y FK(=)2122 3926 y FH(A)p 2126 3945 V -30 x Fv(0)2174 3948 y FD(1)2202 3925 y FK(,)h FH(B)2305 3899 y Fv(0)2340 3925 y FK(=)20 b FH(B)2470 3899 y Fv(0)2466 3942 y FD(1)2494 3925 y FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 112 115 bop 167 167 a FK(112)710 b Fz(CHAPTER)26 b(13.)64 b(CUT)27 b(ELIMINA)-6 b(TION)26 b(\(HA)n(UPTSA)-6 b(TZ\))251 404 y FK(3.)35 b(If)28 b FH(\031)i FK(ends)e(in)f(a)h(cut)1061 578 y FH(A)p 1065 597 39 3 v 22 x FD(1)1161 577 y FJ(`)19 b FH(C)q(;)1304 578 y(B)p 1308 597 43 3 v 1361 600 a FD(1)1467 578 y FH(A)p 1470 597 39 3 v 1518 600 a FD(2)1546 577 y FH(;)12 b(C)25 b FJ(`)1714 578 y FH(B)p 1717 597 43 3 v 1770 600 a FD(2)p 1061 621 737 4 v 1818 637 a Fq(Cut)1194 699 y FH(A)p 1198 719 39 3 v 23 x FD(1)1274 698 y FH(;)1305 699 y(A)p 1308 719 V 1356 722 a FD(2)1404 698 y FJ(`)1466 699 y FH(B)p 1470 719 43 3 v 1522 722 a FD(1)1550 698 y FH(;)1581 699 y(B)p 1585 719 V 1637 722 a FD(2)339 900 y FK(then)36 b(the)f(induction)g(h)n(yp)r(othesis)h (pro)n(vides)1621 901 y FH(A)p 1624 920 39 3 v 1672 871 a Fv(0)1672 923 y FD(1)1725 900 y FJ(`)25 b FH(B)1849 874 y Fv(0)1845 917 y FD(1)1934 900 y FK(and)2105 901 y FH(A)p 2109 920 V -30 x Fv(0)2157 923 y FD(2)2210 900 y FJ(`)g FH(B)2334 874 y Fv(0)2330 917 y FD(2)2418 900 y FK(and)37 b(t)n(w)n(o)339 985 y(cases)28 b(arise:)421 1146 y FJ(\017)35 b FH(B)547 1121 y Fv(0)543 1164 y FD(1)591 1146 y FJ(6)p FK(=)19 b FH(C)5 b FK(:)36 b(w)n(e)27 b(can)h(tak)n(e) 1164 1147 y FH(A)p 1168 1167 V -30 x Fv(0)1252 1146 y FK(=)1325 1147 y FH(A)p 1329 1167 V -30 x Fv(0)1377 1170 y FD(1)1432 1146 y FK(and)h FH(B)1627 1121 y Fv(0)1663 1146 y FK(=)19 b FH(B)1792 1121 y Fv(0)1788 1164 y FD(1)1816 1146 y FK(;)421 1261 y FJ(\017)35 b FH(B)547 1235 y Fv(0)543 1278 y FD(1)594 1261 y FK(=)23 b FH(C)5 b FK(,)34 b(whic)n(h)e(o)r (ccurs,)i(sa)n(y)-6 b(,)35 b FH(n)d FK(times)f(in)h FH(A)1780 1272 y FD(2)1808 1261 y FK(:)45 b(b)n(y)33 b(making)f(exc)n(hanges)i (and)491 1346 y FH(n)28 b FK(cuts)f(with)891 1347 y FH(A)p 894 1367 V -30 x Fv(0)943 1369 y FD(1)990 1346 y FJ(`)20 b FH(C)52 b FK(w)n(e)27 b(obtain)h(the)f(result)f(with)1959 1347 y FH(A)p 1963 1367 V -30 x Fv(0)2047 1346 y FK(=)2120 1347 y FH(A)p 2124 1367 V -30 x Fv(0)2172 1369 y FD(1)2200 1346 y FH(;)12 b(:)g(:)g(:)f(;)2354 1347 y(A)p 2358 1367 V -30 x Fv(0)2406 1369 y FD(1)2434 1346 y FH(;)2465 1347 y(A)p 2468 1367 V 2516 1317 a Fv(0)2516 1369 y FD(2)2548 1346 y FJ(\000)k FH(C)491 1431 y FK(and)29 b FH(B)686 1405 y Fv(0)722 1431 y FK(=)19 b FH(B)851 1405 y Fv(0)847 1448 y FD(2)875 1431 y FK(.)1723 b Fu(\003)270 1633 y FK(This)31 b(lemma)e(is)h(immediately)e(applicable)h(to)i(a)h(goal)53 b FJ(`)22 b FH(B)k FK(,)31 b(whic)n(h)g(giv)n(es)2385 1634 y FH(A)p 2389 1654 V -29 x Fv(0)2484 1633 y FK(empt)n(y)167 1719 y(and)44 b FH(B)377 1693 y Fv(0)424 1719 y FK(=)30 b FH(B)t FK(.)82 b(Notice)42 b(that)h(the)g(deduction)g(necessarily)f (lies)f(in)i(the)g(in)n(tuitionistic)167 1804 y(fragmen)n(t.)35 b(But)27 b(in)f(this)g(case,)h(it)f(is)g(p)r(ossible)g(to)h(eliminate)c (exc)n(hange)28 b(to)r(o,)f(b)n(y)h(p)r(erm)n(uting)167 1889 y(the)f(order)h(of)g(application)f(of)h(cuts.)36 b(F)-6 b(urthermore,)27 b(cut)g(with)g(an)h(iden)n(tit)n(y)f(axiom)1114 2046 y FH(A)p 1118 2066 V 1186 2045 a FJ(`)19 b FH(C)84 b(C)25 b FJ(`)20 b FH(C)p 1114 2090 458 4 v 1593 2106 a Fq(Cut)1249 2168 y FH(A)p 1253 2187 39 3 v 1320 2167 a FJ(`)g FH(C)167 2330 y FK(is)27 b(useless,)g(so)h(w)n(e)f(ha)n(v)n (e:)167 2503 y FG(Prop)r(osition)c FK(In)i(order)h(to)f(pro)n(v)n(e)h (a)g(goal,)g(w)n(e)f(only)g(need)g(to)h(use)f(cut)g(with)g(instances)g (\(b)n(y)167 2588 y(substitution\))i(of)h(prop)r(er)g(axioms.)270 2762 y(Robinson's)41 b FM(r)l(esolution)d(metho)l(d)i FK(\(1965\))h(giv)n(es)d(a)h(reasonable)h(strategy)f(for)g(\014nding) 167 2847 y(suc)n(h)25 b(pro)r(ofs.)36 b(The)24 b(idea)g(is)g(to)g(try)h (all)e(p)r(ossible)h(com)n(binations)g(of)h(cuts)f(and)i (substitutions,)167 2932 y(the)g(latter)g(b)r(eing)g(limited)e(b)n(y)j FM(uni\014c)l(ation)p FK(.)35 b(Ho)n(w)n(ev)n(er)26 b(that)i(w)n(ould)e (lead)h(us)g(to)r(o)g(far)g(a\014eld.)p eop PStoPSsaved restore %%Page: (116,117) 59 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 113 116 bop 167 880 a FF(Chapter)28 b(14)167 1179 y(Strong)g (Normalisation)e(for)i(F)167 1505 y FK(The)f(aim)g(of)h(this)f(c)n (hapter)h(is)f(to)h(pro)n(v)n(e:)167 1649 y FG(Theorem)40 b FK(All)f(terms)h(of)h FG(F)g FK(are)g(strongly)g(normalisable,)i(and) f(the)f(normal)f(form)h(is)167 1734 y(unique.)270 1943 y(The)49 b(uniqueness)g(is)f(not)i(problematic:)76 b(it)47 b(comes)h(from)h(an)g(extension)g(of)g(the)167 2028 y(Ch)n(urc)n (h-Rosser)36 b(theorem.)57 b(Existence)34 b(is)g(m)n(uc)n(h)h(more)g (delicate;)i(in)d(fact,)k(w)n(e)c(shall)h(see)167 2113 y(in)h(c)n(hapter)g FG(??)i FK(that)e(the)h(normalisation)e(theorem)h (for)h FG(F)f FK(implies)d(the)j(consistency)h(of)167 2198 y FM(se)l(c)l(ond)28 b(or)l(der)g(arithmetic)k FG(P)-23 b(A)1002 2209 y Fb(2)1033 2198 y FK(.)35 b(The)27 b(classic)f(result)h (of)h(logic,)e(if)h(an)n(ything)h(deserv)n(es)g(that)167 2283 y(name,)39 b(is)d(G\177)-34 b(odel's)36 b(second)h(incompleteness) e(theorem,)j(whic)n(h)e(sa)n(ys)h(\(assuming)g(that)g(it)167 2368 y(is)31 b(not)i(con)n(tradictory\))f(that)g(the)g(consistency)g (of)h FG(P)-23 b(A)1675 2379 y Fb(2)1738 2368 y FK(cannot)33 b(b)r(e)f(pro)n(v)n(ed)h FM(within)k FG(P)-23 b(A)2622 2379 y Fb(2)2653 2368 y FK(.)167 2454 y(Consequen)n(tly)-6 b(,)23 b(since)c(consistency)h FM(c)l(an)h FK(b)r(e)f(deduced)g(from)g (normalisation)g(within)f FG(P)-23 b(A)2506 2465 y Fb(2)2537 2454 y FK(,)20 b(the)167 2539 y(normalisation)31 b(theorem)f FM(c)l(annot)i FK(b)r(e)f(pro)n(v)n(ed)h(within)e FG(P)-23 b(A)1764 2550 y Fb(2)1796 2539 y FK(.)46 b(That)32 b(giv)n(es)f(us)h (an)g(essen)n(tial)167 2624 y(piece)24 b(of)j(information)f(for)g(the)g (pro)r(of:)36 b(w)n(e)25 b(m)n(ust)h(lo)r(ok)h(for)f(a)g(strategy)h (whic)n(h)f FM(go)l(es)g(outside)167 2709 y FG(P)-23 b(A)258 2720 y Fb(2)289 2709 y FK(.)270 2853 y(Essen)n(tially)-6 b(,)27 b FG(P)-23 b(A)726 2864 y Fb(2)785 2853 y FK(con)n(tains)28 b(the)f(Axiom)g(\(sc)n(heme\))f(of)i(comprehension)1059 3061 y FJ(9)p FH(X)r(:)12 b FJ(8)p FH(\030)s(:)g FK(\()p FH(\030)22 b FJ(2)e FH(X)h FJ(,)16 b FH(A)p FK([)p FH(\030)s FK(]\))167 3270 y(where)25 b FH(A)g FK(is)g(a)h(form)n(ula)g(in)f(whic) n(h)g(the)g(v)l(ariable)g FH(X)32 b FK(do)r(es)26 b(not)g(o)r(ccur)g (free.)33 b FH(A)26 b FK(ma)n(y)g(con)n(tain)167 3355 y(\014rst)36 b(order)h(\()p FJ(8)p FH(\030)s(:)12 b FK(,)38 b FJ(9)p FH(\030)s(:)12 b FK(\))36 b(and)i(second)f(order)f(\()p FJ(8)p FH(X)r(:)12 b FK(,)37 b FJ(9)p FH(X)r(:)12 b FK(\))36 b(quan)n(ti\014cation.)62 b(In)n(tuitiv)n(ely)-6 b(,)167 3440 y(the)32 b(\014rst)g(order)h(v)l(ariables)f(range)g(o)n(v)n(er)h (in)n(tegers)e(and)j(the)e(second)g(order)h(ones)g(o)n(v)n(er)f(sets) 167 3525 y(of)39 b(in)n(tegers.)68 b(This)38 b(system)g(su\016ces)h (for)g(ev)n(eryda)n(y)h(mathematics:)56 b(for)39 b(instance,)i(real)167 3611 y(n)n(um)n(b)r(ers)28 b(ma)n(y)g(b)r(e)f(co)r(ded)h(as)g(sets)g (of)g(in)n(tegers.)270 3754 y(So)j(w)n(e)f(seek)g(to)g(use)g(\\all)f(p) r(ossible")h(axioms)g(of)h(comprehension,)f(or)h(at)f(least)f(a)i (large)167 3840 y(class)26 b(of)g(them.)34 b(F)-6 b(or)27 b(this,)f(w)n(e)g(shall)f(lo)r(ok)h(bac)n(k)h(at)g(T)-6 b(ait's)26 b(pro)r(of)h(\(using)f(reducibilit)n(y\))d(and)167 3925 y(try)28 b(to)g(extend)f(it)g(to)h(system)f FG(F)p FK(.)1368 4101 y(113)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 114 117 bop 167 167 a FK(114)702 b Fz(CHAPTER)26 b(14.)64 b(STR)n(ONG)27 b(NORMALISA)-6 b(TION)26 b(F)n(OR)h(F)167 404 y FE(14.1)114 b(Idea)28 b(of)f(the)i(pro)s(of)167 573 y FK(W)-6 b(e)30 b(w)n(ould)g(lik)n(e)f(to)h(sa)n(y)i(that)e FH(t)g FK(of)h(t)n(yp)r(e)g(\005)p FH(X)r(:)12 b(T)39 b FK(is)30 b FM(r)l(e)l(ducible)35 b FK(i\013)29 b(for)i(all)e(t)n(yp)r (es)i FH(U)7 b FK(,)31 b FH(t)12 b(U)37 b FK(is)167 658 y(reducible)26 b(\(of)i(t)n(yp)r(e)h FH(T)10 b FK([)p FH(U)t(=X)c FK(]\).)36 b(F)-6 b(or)28 b(example,)g FH(t)g FK(of)g(t)n(yp)r(e)g(\005)p FH(X)r(:)12 b(X)34 b FK(w)n(ould)28 b(b)r(e)g(reducible)e(i\013)167 743 y FH(t)12 b(U)32 b FK(is)25 b(reducible)f(for)i(all)e FH(U)7 b FK(.)35 b(But)26 b FH(U)33 b FK(is)25 b(arbitrary)g(|)h(it)e(ma)n(y)i(b)r(e)g (\005)p FH(X)r(:)12 b(X)31 b FK(|)25 b(and)i(w)n(e)e(need)167 828 y(to)30 b(kno)n(w)h(the)e(meaning)h(of)g(reducibilit)n(y)d(of)j(t)n (yp)r(e)g FH(U)37 b FK(b)r(efore)30 b(w)n(e)f(can)h(de\014ne)g(it!)41 b(W)-6 b(e)30 b(shall)167 913 y(nev)n(er)e(get)g(an)n(ywhere)h(lik)n(e) e(this.)36 b(Moreo)n(v)n(er,)29 b(if)f(this)f(metho)r(d)i(w)n(ere)e (practicable,)g(it)g(w)n(ould)167 998 y(b)r(e)g(applicable)g(to)h(v)l (arian)n(ts)g(of)g(system)g FG(F)f FK(for)h(whic)n(h)f(normalisation)g (fails.)167 1234 y Fy(14.1.1)94 b(Reducibilit)m(y)30 b(candidates)167 1378 y FK(T)-6 b(o)34 b(solv)n(e)f(this)g(problem,)h (w)n(e)f(shall)g(in)n(tro)r(duce)g FM(r)l(e)l(ducibility)h(c)l (andidates)p FK(.)53 b(A)33 b(reducibilit)n(y)167 1463 y(candidate)26 b(of)g(t)n(yp)r(e)g FH(U)33 b FK(is)26 b(an)g FM(arbitr)l(ary)34 b FK(reducibilit)n(y)22 b(predicate)j(\(set)g (of)i(terms)e(of)h(t)n(yp)r(e)g FH(U)7 b FK(\))167 1549 y(satisfying)33 b(the)f(conditions)h(\()p FG(CR)g(1-3)p FK(\))f(of)h(c)n(hapter)g FG(??)q FK(.)51 b(Among)33 b(all)e(the)i(\\candidates",)167 1634 y(the)27 b(\\true")i(reducibilit) n(y)24 b(predicate)j(for)h FH(U)34 b FK(is)27 b(to)h(b)r(e)g(found.)270 1786 y(A)22 b(term)f(of)i(t)n(yp)r(e)f(\005)p FH(X)r(:)12 b(T)32 b FK(is)21 b(reducible)g(when,)i(for)g(ev)n(ery)f(t)n(yp)r(e)g FH(U)29 b FK(and)24 b FM(every)d(r)l(e)l(ducibility)167 1872 y(c)l(andidate)26 b FJ(R)20 b FK(of)h(t)n(yp)r(e)g FH(U)7 b FK(,)22 b(the)e(term)f FH(t)12 b(U)28 b FK(is)19 b(reducible)g(of)i(t)n(yp)r(e)g FH(T)10 b FK([)p FH(U)t(=X)c FK(],)21 b(where)f(reducibilit)n(y)167 1957 y(for)26 b(this)f(t)n(yp)r(e)h(is)f(de\014ned)h(taking)g FJ(R)g FK(as)g(the)g(de\014nition)f(of)h(reducibilit)n(y)d(for)j FH(U)7 b FK(.)34 b(Of)26 b(course,)167 2042 y(if)33 b FJ(R)h FK(is)f(the)h(\\true")g(reducibilit)n(y)d(of)k(t)n(yp)r(e)f FH(U)7 b FK(,)36 b(then)e(the)g(de\014nition)f(w)n(e)h(shall)f(b)r(e)h (using)167 2127 y(for)k FH(T)10 b FK([)p FH(U)t(=X)c FK(])37 b(will)e(also)j(b)r(e)g(the)f(\\true")h(one.)66 b(In)38 b(other)f(w)n(ords,)k(ev)n(erything)d(w)n(orks)g(as)167 2212 y(if)c(the)h(rule)e(of)j(univ)n(ersal)e(abstraction)h(\(whic)n(h)f (forms)h(functions)g(de\014ned)h(for)f(arbitrary)167 2297 y(t)n(yp)r(es\))30 b(w)n(ere)f(so)h FM(uniform)g FK(that)g(it)f(op)r(erates)h(without)f(an)n(y)i(information)f(at)f(all) g(ab)r(out)i(its)167 2382 y(argumen)n(ts.)270 2608 y(Before)g(going)i (on)f(with)e(the)i(details,)f(let)f(us)i(lo)r(ok)g(informally)e(at)h (ho)n(w)h(the)g(univ)n(ersal)167 2694 y(iden)n(tit)n(y)k(\003)p FH(X)r(:)12 b(\025x)653 2668 y Fw(X)701 2694 y FH(:)g(x)37 b FK(will)e(b)r(e)i(reducible.)63 b(It)37 b(is)f(of)i(t)n(yp)r(e)g (\005)p FH(X)r(:)12 b(X)6 b FJ(!)o FH(X)g FK(,)40 b(and)e(a)g(term)e FH(t)167 2779 y FK(of)j(this)g(t)n(yp)r(e)f(is)h(reducible)d(i\013)i (whatev)n(er)h(reducibilit)n(y)d(candidate)j FJ(R)f FK(w)n(e)h(tak)n(e) g(for)g FH(U)7 b FK(,)167 2864 y(the)29 b(term)f FH(t)12 b(U)36 b FK(is)29 b(reducible)e(of)j(t)n(yp)r(e)g FH(U)7 b FJ(!)q FH(U)g FK(,)30 b(this)e(reducibilit)n(y)f(b)r(eing)i (de\014ned)h(b)n(y)g(means)167 2949 y(of)42 b FJ(R)p FK(.)75 b(No)n(w,)44 b FH(t)12 b(U)48 b FK(is)40 b(reducible)f(of)j(t)n (yp)r(e)f FH(U)7 b FJ(!)q FH(U)48 b FK(if)40 b(for)h(all)f FH(u)h FK(reducible)e(of)j(t)n(yp)r(e)f FH(U)167 3034 y FK(\()p FM(i.e.)31 b FH(u)22 b FJ(2)g(R)p FK(\))31 b FH(t)12 b(U)7 b(u)31 b FK(is)g(reducible)e(of)i(t)n(yp)r(e)h FH(U)38 b FK(\()p FM(i.e.)31 b FH(t)12 b(U)7 b(u)22 b FJ(2)g(R)p FK(\).)46 b(W)-6 b(e)31 b(are)g(led)f(to)h(sho)n(wing)167 3119 y(that)j FH(u)24 b FJ(2)g(R)f(\))h FH(t)12 b(U)7 b(u)24 b FJ(2)g(R)p FK(;)36 b(but)e FJ(R)f FK(satis\014es)g(\()p FG(CR)h(1-3)p FK(\))f(and)h FH(t)12 b(U)7 b(u)34 b FK(is)f FM(neutr)l(al)p FK(,)h(so)h(this)167 3204 y(implication)25 b(follo)n(ws)i(from)g(manipulation)g(with)g(\()p FG(CR)h(3)p FK(\).)167 3440 y Fy(14.1.2)94 b(Remarks)167 3584 y FK(The)35 b(c)n(hoice)f(of)h(\()p FG(CR)g(1-3)p FK(\))g(is)f(crucial.)56 b(W)-6 b(e)35 b(need)g(to)g(iden)n(tify)f(some)h(useful)g(induction)167 3669 y(h)n(yp)r(otheses)40 b(on)g(a)g(set)e(of)i(terms)e(whic)n(h)g(is) h(otherwise)f(arbitrary)-6 b(,)42 b(and)e(they)f(m)n(ust)g(b)r(e)167 3754 y(preserv)n(ed)34 b(b)n(y)g(the)g(construction)g(of)g(the)g (\\true)f(reducibilit)n(y".)52 b(These)33 b(conditions)h(w)n(ere)167 3840 y(originally)27 b(found)j(b)n(y)g(trial)d(and)j(error.)38 b(In)28 b(linear)g(logic,)g(reducibilit)n(y)d(candidates)k(app)r(ear) 167 3925 y(m)n(uc)n(h)f(more)f(naturally)-6 b(,)27 b(from)h(a)g(notion) g(of)g(orthogonalit)n(y)h(on)g(terms)d([)p FG(?)q FK(].)p eop PStoPSsaved restore %%Page: (118,119) 60 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 115 118 bop 167 167 a Fz(14.1.)65 b(IDEA)26 b(OF)i(THE)f(PR)n(OOF)1442 b FK(115)270 404 y(The)30 b(case)g(of)h(the)e(univ)n(ersal)h(t)n(yp)r (e)g(\005)p FH(X)r(:)12 b(V)45 b FK(in)n(tro)r(duces)30 b(a)g(quan)n(ti\014cation)h(o)n(v)n(er)g(sets)f(of)167 490 y(terms)k(\(in)g(fact)h(o)n(v)n(er)g(all)e(reducibilit)n(y)f (candidates\).)57 b(Th)n(us)36 b(w)n(e)e(mak)n(e)h(more)f(and)i(more) 167 575 y(complex)24 b(de\014nitions)h(of)h(reducibilit)n(y)-6 b(,)23 b(and)j(there)e(is)h(no)h(second)f(order)g(form)n(ula)g Fq(RED)q FK(\()p FH(T)6 b(;)12 b(t)p FK(\))167 660 y(whic)n(h)38 b(sa)n(ys)h(\\)p FH(t)g FK(is)f(reducible)e(of)j(t)n(yp)r(e)g FH(T)10 b FK(".)68 b(This)38 b(is)f(completely)f(analogous)41 b(to)e(what)167 745 y(happ)r(ens)29 b(at)f(the)f(\014rst)h(order,)g (with)f(system)g FG(T)p FK(.)270 859 y(But)38 b(the)g(main)f(p)r(oin)n (t)h(is)g(that,)j(in)c(order)h(to)g(in)n(terpret)f(the)g(univ)n(ersal)h (application)167 944 y(sc)n(heme)33 b FH(t)12 b(U)7 b FK(,)35 b(w)n(e)e(ha)n(v)n(e)i(to)f(substitute)f(in)g(the)h (de\014nition)f(of)h(reducibilit)n(y)d(for)j FH(t)p FK(,)h(not)f(an)167 1030 y(arbitrary)f(candidate,)h(but)f(the)g(one)g(w)n(e)f(get)g(b)n(y)i (induction)e(on)h(the)g(construction)g(of)g FH(U)7 b FK(.)167 1115 y(So)26 b(w)n(e)f(m)n(ust)h(b)r(e)f(able)g(to)h(de\014ne) g(a)g(set)f(of)h(terms)f(of)h(t)n(yp)r(e)f FH(U)33 b FK(b)n(y)26 b(a)g FM(formula)p FK(,)h(and)g(this)e(uses)167 1200 y(the)i(comprehension)h(sc)n(heme)e(in)h(an)i(essen)n(tial)d(w)n (a)n(y)-6 b(.)270 1350 y(F)g(or)22 b(second)g(order)g(systems,)g(unlik) n(e)f(the)g(simpler)e(ones,)k(there)e(is)f(no)j(kno)n(wn)f(alternativ)n (e)167 1435 y(pro)r(of.)36 b(F)-6 b(or)28 b(example,)e(normalisation)g (for)i(the)e(Theory)i(of)f(Constructions)h([)p FG(?)p FK(])f(|)g(an)h(ev)n(en)167 1520 y(stronger)f(system)f(|)g(can)h(b)r(e) f(sho)n(wn)i(b)n(y)f(an)g(adaptation)h(of)f(the)f(metho)r(d)g(presen)n (ted)h(here.)167 1718 y Fy(14.1.3)94 b(De\014nitions)167 1849 y FK(A)29 b(term)g FH(t)h FK(is)f FM(neutr)l(al)36 b FK(if)29 b(it)g(do)r(es)h(not)h(start)f(with)e(an)j(abstraction)f (sym)n(b)r(ol,)h FM(i.e.)e FK(if)g(it)g(has)167 1934 y(one)f(of)g(the)g(follo)n(wing)e(forms:)735 2083 y FH(x)568 b(t)12 b(u)568 b(t)12 b(U)270 2263 y FK(A)28 b FM(r)l(e)l(ducibility)g (c)l(andidate)g FK(of)g(t)n(yp)r(e)g FH(U)35 b FK(is)27 b(a)h(set)f FJ(R)g FK(of)h(terms)f(of)h(t)n(yp)r(e)g FH(U)35 b FK(suc)n(h)28 b(that:)201 2377 y(\()p FG(CR)g(1)p FK(\))f(If)h FH(t)19 b FJ(2)h(R)p FK(,)27 b(then)h FH(t)f FK(is)g(strongly)i(normalisable.)201 2509 y(\()p FG(CR)f(2)p FK(\))f(If)h FH(t)19 b FJ(2)h(R)27 b FK(and)i FH(t)19 b Fu( )h FH(t)1036 2484 y Fv(0)1053 2509 y FK(,)27 b(then)h FH(t)1286 2484 y Fv(0)1322 2509 y FJ(2)20 b(R)p FK(.)201 2641 y(\()p FG(CR)30 b(3)p FK(\))e(If)i FH(t)f FK(is)f(neutral,)h(and)i (whenev)n(er)e(w)n(e)f(con)n(v)n(ert)i(a)f(redex)g(of)h FH(t)f FK(w)n(e)g(obtain)h(a)f(term)339 2727 y FH(t)364 2701 y Fv(0)400 2727 y FJ(2)20 b(R)p FK(,)27 b(then)h FH(t)19 b FJ(2)h(R)p FK(.)270 2841 y(F)-6 b(rom)28 b(\()p FG(CR)g(3)p FK(\))f(w)n(e)g(ha)n(v)n(e)i(in)e(particular:)201 2956 y(\()p FG(CR)h(4)p FK(\))f(If)h FH(t)f FK(is)g(neutral)g(and)i (normal,)f(then)f FH(t)20 b FJ(2)f(R)p FK(.)270 3070 y(This)28 b(sho)n(ws)g(that)h FJ(R)e FK(is)g(nev)n(er)h(empt)n(y)-6 b(,)27 b(b)r(ecause)h(it)f(alw)n(a)n(ys)h(con)n(tains)h(the)e(v)l (ariables)h(of)167 3155 y(t)n(yp)r(e)g FH(U)7 b FK(.)270 3305 y(F)-6 b(or)27 b(example,)f(the)g(set)g(of)h(strongly)g (normalisable)e(terms)h(of)h(t)n(yp)r(e)f FH(U)34 b FK(is)25 b(a)i(reducibilit)n(y)167 3390 y(candidate)h(\(see)f FG(??)q FK(\).)270 3540 y(If)i FJ(R)f FK(and)h FJ(S)k FK(are)c(reducibilit)n(y)c(candidates)k(of)g(t)n(yp)r(es)f FH(U)36 b FK(and)29 b FH(V)16 b FK(,)28 b(w)n(e)g(can)h(de\014ne)g(a)f (set)167 3625 y FJ(R)15 b(!)h(S)33 b FK(of)28 b(terms)f(of)h(t)n(yp)r (e)g FH(U)7 b FJ(!)p FH(V)43 b FK(b)n(y:)527 3775 y FH(t)20 b FJ(2)f(R)d(!)g(S)365 b FK(i\013)360 b FJ(8)p FH(u)19 b FK(\()p FH(u)h FJ(2)f(R)g(\))h FH(t)12 b(u)20 b FJ(2)f(S)5 b FK(\))167 3925 y(By)28 b FG(??)q FK(,)f(w)n(e)h(kno)n(w)g(that)g FJ(R)16 b(!)g(S)32 b FK(is)27 b(a)h(reducibilit)n(y)d(candidate)j(of)g (t)n(yp)r(e)g FH(U)7 b FJ(!)p FH(V)16 b FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 116 119 bop 167 167 a FK(116)702 b Fz(CHAPTER)26 b(14.)64 b(STR)n(ONG)27 b(NORMALISA)-6 b(TION)26 b(F)n(OR)h(F)167 404 y FE(14.2)114 b(Reducibilit)m(y)28 b(with)g(parameters)167 570 y FK(Let)38 b FH(T)10 b FK([)375 571 y FH(X)p 379 590 50 3 v 438 570 a FK(])38 b(b)r(e)g(a)h(t)n(yp)r(e,)i(where)c(w)n(e) h(understand)i(that)1741 571 y FH(X)p 1744 590 V 1842 570 a FK(con)n(tains)e(\(at)h(least\))e FM(al)t(l)44 b FK(the)167 655 y(free)37 b(v)l(ariables)h(of)h FH(T)10 b FK(.)67 b(Let)984 656 y FH(U)p 987 675 41 3 v 1076 655 a FK(b)r(e)38 b(a)h(sequence)f(of)h(t)n(yp)r(es,)i(of)e(the)f(same) g(length;)43 b(then)167 740 y(w)n(e)38 b(can)g(de\014ne)g(b)n(y)h(sim)n (ultaneous)f(substitution)f(a)i(t)n(yp)r(e)f FH(T)10 b FK([)1888 741 y FH(U)p 1892 761 V 1942 740 a(=)1976 741 y(X)p 1980 761 50 3 v 2040 740 a FK(].)66 b(No)n(w)39 b(let)2431 741 y FJ(R)p 2435 761 47 3 v 2529 740 a FK(b)r(e)f(a)167 825 y(sequence)31 b(of)h(reducibilit)n(y)c(candidates)k(of)g(corresp)r (onding)g(t)n(yp)r(es;)i(then)d(w)n(e)g(can)h(de\014ne)g(a)167 910 y(set)27 b Fq(RED)414 921 y Fw(T)453 910 y FK([)472 911 y FJ(R)p 476 931 V -1 x FH(=)566 911 y(X)p 570 931 50 3 v 629 910 a FK(])h(\(parametric)e(reducibilit)n(y\))f(of)j(terms)e (of)i(t)n(yp)r(e)g FH(T)10 b FK([)2043 911 y FH(U)p 2047 931 41 3 v 2098 910 a(=)2132 911 y(X)p 2136 931 50 3 v 2195 910 a FK(])28 b(as)g(follo)n(ws:)251 1099 y(1.)35 b(If)28 b FH(T)i FK(=)19 b FH(X)613 1110 y Fw(i)633 1099 y FK(,)28 b(then)f Fq(RED)976 1110 y Fw(T)1015 1099 y FK([)1034 1100 y FJ(R)p 1038 1119 47 3 v -1 x FH(=)1128 1100 y(X)p 1132 1119 50 3 v 1191 1099 a FK(])20 b(=)f FJ(R)1363 1110 y Fw(i)1383 1099 y FK(;)251 1259 y(2.)35 b(If)28 b FH(T)i FK(=)19 b FH(V)c FJ(!)q FH(W)10 b FK(,)27 b(then)h Fq(RED)1100 1270 y Fw(T)1139 1259 y FK([)1158 1260 y FJ(R)p 1162 1280 47 3 v -1 x FH(=)1252 1260 y(X)p 1256 1280 50 3 v 1315 1259 a FK(])20 b(=)f Fq(RED)1562 1270 y Fw(V)1605 1259 y FK([)1624 1260 y FJ(R)p 1628 1280 47 3 v -1 x FH(=)1718 1260 y(X)p 1722 1280 50 3 v 1781 1259 a FK(])d FJ(!)g Fq(RED)2037 1270 y Fw(W)2094 1259 y FK([)2113 1260 y FJ(R)p 2117 1280 47 3 v -1 x FH(=)2207 1260 y(X)p 2211 1280 50 3 v 2270 1259 a FK(];)251 1420 y(3.)35 b(If)c FH(T)h FK(=)21 b(\005)p FH(Y)t(:)12 b(W)40 b FK(then)31 b Fq(RED)1095 1431 y Fw(T)1134 1420 y FK([)1153 1421 y FJ(R)p 1157 1441 47 3 v -1 x FH(=)1247 1421 y(X)p 1251 1441 50 3 v 1310 1420 a FK(])g(is)f(the)g(set)h(of)g (terms)e FH(t)i FK(of)g(t)n(yp)r(e)g FH(T)10 b FK([)2338 1421 y FH(U)p 2342 1441 41 3 v 2392 1420 a(=)2426 1421 y(X)p 2430 1441 50 3 v 2490 1420 a FK(])31 b(suc)n(h)339 1505 y(that,)47 b(for)c(ev)n(ery)f(t)n(yp)r(e)g FH(V)58 b FK(and)43 b(reducibilit)n(y)d(candidate)i FJ(S)47 b FK(of)c(this)f(t)n(yp)r(e,)k(then)339 1590 y FH(t)12 b(V)35 b FJ(2)20 b Fq(RED)653 1601 y Fw(W)710 1590 y FK([)729 1591 y FJ(R)p 733 1611 47 3 v -1 x FH(=)823 1591 y(X)p 827 1611 50 3 v 886 1590 a(;)12 b FJ(S)5 b FH(=)t(Y)15 b FK(].)167 1834 y FG(Lemma)25 b Fq(RED)584 1845 y Fw(T)623 1834 y FK([)642 1835 y FJ(R)p 646 1854 47 3 v -1 x FH(=)736 1835 y(X)p 740 1854 50 3 v 799 1834 a FK(])j(is)f(a)h(reducibilit)n(y)c(candidate)k(of)g(t)n(yp)r(e)g FH(T)10 b FK([)1981 1835 y FH(U)p 1985 1854 41 3 v 2035 1834 a(=)2069 1835 y(X)p 2073 1854 50 3 v 2133 1834 a FK(].)167 1980 y FG(Pro)r(of)28 b FK(By)g(induction)f(on)h FH(T)10 b FK(:)35 b(the)28 b(only)g(case)f(to)h(consider)f(is)g FH(T)j FK(=)19 b(\005)p FH(Y)t(:)12 b(W)e FK(.)201 2169 y(\()p FG(CR)27 b(1)p FK(\))e(If)h FH(t)20 b FJ(2)f Fq(RED)781 2180 y Fw(T)820 2169 y FK([)839 2170 y FJ(R)p 843 2189 47 3 v -1 x FH(=)933 2170 y(X)p 937 2189 50 3 v 996 2169 a FK(],)27 b(tak)n(e)g(an)g(arbitrary)f(t)n(yp)r(e)g FH(V)42 b FK(and)27 b(an)g(arbitrary)f(candidate)339 2254 y FJ(S)46 b FK(of)41 b(t)n(yp)r(e)f FH(V)56 b FK(\(for)41 b(example,)i(the)d(strongly)h(normalisable)f(terms)f(of)i(t)n(yp)r(e)g FH(V)15 b FK(\).)339 2339 y(Then)28 b FH(t)12 b(V)35 b FJ(2)19 b Fq(RED)837 2350 y Fw(W)894 2339 y FK([)913 2340 y FJ(R)p 917 2360 47 3 v -1 x FH(=)1007 2340 y(X)p 1011 2360 50 3 v 1070 2339 a(;)12 b FJ(S)5 b FH(=)t(Y)16 b FK(],)27 b(and)i(so,)f(b)n(y)g(induction)f(h)n(yp)r(othesis)h(\()p FG(CR)g(1)p FK(\),)f(w)n(e)339 2424 y(kno)n(w)33 b(that)e FH(t)12 b(V)47 b FK(is)30 b(strongly)i(normalisable.)45 b(But)31 b FH(\027)t FK(\()p FH(t)p FK(\))22 b FJ(\024)g FH(\027)t FK(\()p FH(t)12 b(V)j FK(\),)32 b(so)g FH(t)f FK(is)f(strongly)339 2509 y(normalisable.)201 2670 y(\()p FG(CR)36 b(2)p FK(\))e(If)h FH(t)24 b FJ(2)h Fq(RED)818 2681 y Fw(T)857 2670 y FK([)876 2671 y FJ(R)p 880 2691 47 3 v -1 x FH(=)970 2671 y(X)p 974 2691 50 3 v 1033 2670 a FK(])35 b(and)h FH(t)25 b Fu( )g FH(t)1403 2644 y Fv(0)1454 2670 y FK(then)35 b(for)h(all)d(t)n(yp)r(es)j FH(V)50 b FK(and)36 b(candidate)f FJ(S)5 b FK(,)339 2755 y(w)n(e)32 b(ha)n(v)n(e)h FH(t)12 b(V)38 b FJ(2)23 b Fq(RED)938 2766 y Fw(W)995 2755 y FK([)1014 2756 y FJ(R)p 1018 2776 47 3 v -1 x FH(=)1108 2756 y(X)p 1112 2776 50 3 v 1171 2755 a(;)12 b FJ(S)5 b FH(=)t(Y)15 b FK(])33 b(and)g FH(t)12 b(V)38 b Fu( )23 b FH(t)1771 2729 y Fv(0)1799 2755 y FH(V)16 b FK(.)48 b(By)33 b(induction)e(h)n(yp)r(othesis)339 2840 y(\()p FG(CR)d(2)p FK(\))f(w)n(e)g(kno)n(w)i(that)f FH(t)1074 2815 y Fv(0)1102 2840 y FH(V)35 b FJ(2)20 b Fq(RED)1379 2851 y Fw(W)1436 2840 y FK([)1455 2841 y FJ(R)p 1459 2861 47 3 v -1 x FH(=)1549 2841 y(X)p 1553 2861 50 3 v 1612 2840 a(;)12 b FJ(S)5 b FH(=)t(Y)15 b FK(].)36 b(So)28 b FH(t)1983 2815 y Fv(0)2019 2840 y FJ(2)20 b Fq(RED)2221 2851 y Fw(T)2260 2840 y FK([)2279 2841 y FJ(R)p 2283 2861 47 3 v -1 x FH(=)2373 2841 y(X)p 2377 2861 50 3 v 2436 2840 a FK(].)201 3001 y(\()p FG(CR)i(3)p FK(\))f(Let)g FH(t)g FK(b)r(e)g(neutral)g(and)i(supp)r(ose)g(all)d(the) h FH(t)1577 2975 y Fv(0)1615 3001 y FK(one)h(step)f(from)g FH(t)g FK(are)h(in)f Fq(RED)2419 3012 y Fw(T)2458 3001 y FK([)2477 3002 y FJ(R)p 2481 3022 47 3 v -1 x FH(=)2571 3002 y(X)p 2575 3022 50 3 v 2634 3001 a FK(].)339 3086 y(T)-6 b(ak)n(e)25 b FH(V)40 b FK(and)25 b FJ(S)5 b FK(:)33 b(applying)25 b(a)f(con)n(v)n(ersion)h(inside)e FH(t)12 b(V)j FK(,)25 b(the)f(result)e(is)i(a)g FH(t)2299 3060 y Fv(0)2327 3086 y FH(V)40 b FK(since)23 b FH(t)h FK(is)339 3171 y(neutral,)h(and)g FH(t)758 3146 y Fv(0)787 3171 y FH(V)39 b FK(is)24 b(in)g Fq(RED)1154 3182 y Fw(W)1211 3171 y FK([)1230 3172 y FJ(R)p 1234 3192 47 3 v 1289 3171 a FH(=)1323 3172 y(X)p 1327 3192 50 3 v 1387 3171 a(;)12 b FJ(S)5 b FH(=)t(Y)15 b FK(])25 b(since)e FH(t)1798 3146 y Fv(0)1838 3171 y FK(is.)34 b(By)24 b(induction)g(h)n(yp)r (othesis)339 3256 y(\()p FG(CR)k(3)p FK(\))f(w)n(e)g(see)g(that)h FH(t)12 b(V)35 b FJ(2)20 b Fq(RED)1294 3267 y Fw(W)1351 3256 y FK([)1370 3257 y FJ(R)p 1374 3277 47 3 v -1 x FH(=)1464 3257 y(X)p 1468 3277 50 3 v 1527 3256 a(;)12 b FJ(S)5 b FH(=)t(Y)15 b FK(],)28 b(and)h(so)f FH(t)20 b FJ(2)f Fq(RED)2239 3267 y Fw(T)2278 3256 y FK([)2297 3257 y FJ(R)p 2301 3277 47 3 v -1 x FH(=)2391 3257 y(X)p 2395 3277 50 3 v 2454 3256 a FK(].)125 b Fu(\003)167 3485 y Fy(14.2.1)94 b(Substitution)167 3626 y FK(The)30 b(follo)n(wing)g(lemma)f(sa)n(ys)i(that)g(parametric)e(reducibilit)n(y) f(b)r(eha)n(v)n(es)j(w)n(ell)e(with)g(resp)r(ect)167 3711 y(to)f(substitution:)167 3925 y FG(Lemma)d Fq(RED)584 3936 y Fw(T)7 b FD([)p Fw(V)f(=)s(Y)k FD(])753 3925 y FK([)772 3926 y FJ(R)p 776 3945 47 3 v -1 x FH(=)866 3926 y(X)p 870 3945 50 3 v 929 3925 a FK(])20 b(=)f Fq(RED)1176 3936 y Fw(T)1215 3925 y FK([)1234 3926 y FJ(R)p 1238 3945 47 3 v -1 x FH(=)1328 3926 y(X)p 1332 3945 50 3 v 1391 3925 a(;)12 b Fq(RED)1557 3936 y Fw(V)1600 3925 y FK([)1619 3926 y FJ(R)p 1623 3945 47 3 v -1 x FH(=)1713 3926 y(X)p 1717 3945 50 3 v 1776 3925 a FK(])p FH(=)t(Y)k FK(])p eop PStoPSsaved restore %%Page: (120,121) 61 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 117 120 bop 167 167 a Fz(14.3.)65 b(REDUCIBILITY)25 b(THEOREM)1286 b FK(117)270 404 y(Here)29 b(w)n(e)g(mak)n(e)h(hidden)g(use)f(of)i(the) e(comprehension)h(sc)n(heme,)f(since,)g(in)h(order)f(to)h(b)r(e)167 490 y(able)24 b(to)h(use)g(the)g FM(pr)l(e)l(dic)l(ate)31 b Fq(RED)1070 501 y Fw(V)1113 490 y FK([)1132 491 y FJ(R)p 1136 510 47 3 v -1 x FH(=)1226 491 y(X)p 1230 510 50 3 v 1289 490 a FK(])25 b(as)g(a)g(parameter,)g(it)f(is)g(necessary)h (to)g(kno)n(w)h(that)167 575 y(it)h(is)g(a)h FM(set)p FK(.)270 740 y(This)d(lemma)f(is)h(pro)n(v)n(ed)h(b)n(y)h(a)e(straigh)n (tforw)n(ard)i(induction)e(on)h FH(T)10 b FK(.)35 b(The)25 b(only)h(di\016cult)n(y)167 825 y(w)n(as)i(to)g(form)n(ulate)f(it)g (precisely!)167 1077 y Fy(14.2.2)94 b(Univ)m(ersal)29 b(abstraction)167 1294 y FG(Lemma)c FK(If)j(for)g(ev)n(ery)f(t)n(yp)r (e)h FH(V)43 b FK(and)29 b(candidate)f FJ(S)5 b FK(,)27 b FH(w)r FK([)p FH(V)8 b(=)t(Y)16 b FK(])k FJ(2)f Fq(RED)2067 1305 y Fw(W)2123 1294 y FK([)2142 1295 y FJ(R)p 2146 1315 47 3 v -1 x FH(=)2236 1295 y(X)p 2240 1315 50 3 v 2300 1294 a(;)12 b FJ(S)5 b FH(=)t(Y)15 b FK(],)28 b(then)167 1380 y(\003)p FH(Y)t(:)12 b(w)21 b FJ(2)f Fq(RED)562 1391 y FD(\005)p Fw(Y)s(:)8 b(W)710 1380 y FK([)729 1381 y FJ(R)p 733 1400 47 3 v -1 x FH(=)823 1381 y(X)p 827 1400 50 3 v 886 1380 a FK(].)167 1631 y FG(Pro)r(of)37 b FK(W)-6 b(e)36 b(ha)n(v)n(e)h(to)g(sho)n(w)g(that)g (\(\003)p FH(Y)t(:)12 b(w)r FK(\))g FH(V)40 b FJ(2)26 b Fq(RED)1673 1642 y Fw(W)1730 1631 y FK([)1749 1632 y FJ(R)p 1753 1652 47 3 v -1 x FH(=)1843 1632 y(X)p 1847 1652 50 3 v 1906 1631 a(;)12 b FJ(S)5 b FH(=)t(Y)15 b FK(])37 b(for)g(ev)n(ery)f(t)n(yp)r(e)h FH(V)167 1717 y FK(and)29 b(candidate)g FJ(S)k FK(of)28 b(t)n(yp)r(e)h FH(V)15 b FK(.)37 b(W)-6 b(e)28 b(argue)h(b)n(y)g(induction)f(on)h FH(\027)t FK(\()p FH(w)r FK(\).)37 b(Con)n(v)n(erting)29 b(a)f(redex)167 1802 y(of)g(\(\003)p FH(Y)t(:)12 b(w)r FK(\))g FH(V)42 b FK(giv)n(es:)270 2016 y FJ(\017)34 b FK(\(\003)p FH(Y)t(:)12 b(w)540 1990 y Fv(0)557 2016 y FK(\))g FH(V)35 b FK(with)19 b FH(\027)t FK(\()p FH(w)941 1990 y Fv(0)958 2016 y FK(\))g FH(<)g(\027)t FK(\()p FH(w)r FK(\),)k(whic)n(h)c(is)g(in)h Fq(RED)1735 2027 y Fw(W)1792 2016 y FK([)1811 2017 y FJ(R)p 1815 2036 47 3 v -1 x FH(=)1905 2017 y(X)p 1909 2036 50 3 v 1968 2016 a(;)12 b FJ(S)5 b FH(=)t(Y)16 b FK(])k(b)n(y)h(the)f(induction)339 2101 y(h)n(yp)r(othesis.)270 2277 y FJ(\017)34 b FH(w)r FK([)p FH(V)8 b(=)t(Y)16 b FK(])28 b(whic)n(h)f(is)g(in)g Fq(RED)1094 2288 y Fw(W)1151 2277 y FK([)1170 2278 y FJ(R)p 1174 2298 47 3 v -1 x FH(=)1264 2278 y(X)p 1268 2298 50 3 v 1327 2277 a(;)12 b FJ(S)5 b FH(=)t(Y)16 b FK(])27 b(b)n(y)i(assumption.)270 2491 y(So)g(the)e(result)g(follo)n (ws)g(from)g(\()p FG(CR)h(3)p FK(\).)1271 b Fu(\003)167 2743 y Fy(14.2.3)94 b(Univ)m(ersal)29 b(application)167 2960 y FG(Lemma)c FK(If)i FH(t)20 b FJ(2)f Fq(RED)769 2971 y FD(\005)p Fw(Y)s(:)8 b(W)917 2960 y FK([)936 2961 y FJ(R)p 940 2981 47 3 v -1 x FH(=)1030 2961 y(X)p 1034 2981 50 3 v 1093 2960 a FK(],)28 b(then)f FH(t)12 b(V)35 b FJ(2)20 b Fq(RED)1634 2971 y Fw(W)7 b FD([)p Fw(V)f(=)s(Y)k FD(])1821 2960 y FK([)1840 2961 y FJ(R)p 1844 2981 47 3 v -1 x FH(=)1934 2961 y(X)p 1938 2981 50 3 v 1997 2960 a FK(])28 b(for)g(ev)n(ery)f(t)n(yp)r(e)h FH(V)15 b FK(.)167 3212 y FG(Pro)r(of)36 b FK(By)h(h)n(yp)r(othesis)g FH(t)12 b(V)41 b FJ(2)26 b Fq(RED)1196 3223 y Fw(W)1253 3212 y FK([)1272 3213 y FJ(R)p 1276 3233 47 3 v -1 x FH(=)1366 3213 y(X)p 1370 3233 50 3 v 1429 3212 a(;)12 b FJ(S)5 b FH(=)t(Y)15 b FK(])37 b(for)f(ev)n(ery)h(candidate)f FJ(S)5 b FK(.)62 b(W)-6 b(e)36 b(just)167 3297 y(tak)n(e)28 b FJ(S)d FK(=)19 b Fq(RED)597 3308 y Fw(V)640 3297 y FK([)659 3298 y FJ(R)p 663 3318 47 3 v -1 x FH(=)753 3298 y(X)p 757 3318 50 3 v 816 3297 a FK(])28 b(and)g(the)g(result)e (follo)n(ws)h(from)h(lemma)e FG(??)q FK(.)576 b Fu(\003)167 3580 y FE(14.3)114 b(Reducibilit)m(y)28 b(theorem)167 3754 y FK(A)j(term)g FH(t)g FK(of)h(t)n(yp)r(e)g FH(T)42 b FK(is)31 b(said)h FM(r)l(e)l(ducible)k FK(if)31 b(it)g(is)g(in)g Fq(RED)1790 3765 y Fw(T)1829 3754 y FK([)1848 3755 y FJ(S)-6 b(N)p 1852 3775 91 3 v 1952 3754 a FH(=)1986 3755 y(X)p 1990 3775 50 3 v 2049 3754 a FK(],)33 b(where)e FH(X)2385 3765 y FD(1)2413 3754 y FH(;)12 b(:)g(:)g(:)g(;)g(X)2625 3765 y Fw(m)167 3840 y FK(are)25 b(the)g(free)g(t)n(yp)r(e)g(v)l (ariables)g(of)h FH(T)10 b FK(,)25 b(and)i FJ(S)-6 b(N)1401 3851 y Fw(i)1446 3840 y FK(is)25 b(the)g(set)g(of)g(strongly)h (normalisable)e(terms)167 3925 y(of)k(t)n(yp)r(e)g FH(X)467 3936 y Fw(i)487 3925 y FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 118 121 bop 167 167 a FK(118)702 b Fz(CHAPTER)26 b(14.)64 b(STR)n(ONG)27 b(NORMALISA)-6 b(TION)26 b(F)n(OR)h(F)270 404 y FK(As)h(in)f(c)n(hapter)h FG(??)g FK(w)n(e)f(can)h(pro)n(v)n(e)h (the)167 531 y FG(Theorem)e FK(All)f(terms)g(of)i FG(F)g FK(are)f(reducible.)167 657 y(and)i(hence,)e(b)n(y)h(\()p FG(CR)g(1)p FK(\),)f(the)167 783 y FG(Corollary)e FK(All)h(terms)g(of)i FG(F)g FK(are)f(strongly)i(normalisable.)270 956 y(W)-6 b(e)29 b(need)h(a)f(more)g(general)g(result,)g(whic)n(h)f(uses)i (substitution)f FM(twic)l(e)g FK(\(once)g(for)h(t)n(yp)r(es,)167 1041 y(and)j(again)h(for)e(terms\))f(and)j(from)e(whic)n(h)f(the)h (theorem)g(follo)n(ws)f(b)n(y)i(putting)g FJ(R)2429 1052 y Fw(i)2471 1041 y FK(=)23 b FJ(S)-6 b(N)2652 1052 y Fw(i)167 1126 y FK(and)29 b FH(u)345 1137 y Fw(j)390 1126 y FK(=)20 b FH(x)503 1137 y Fw(j)529 1126 y FK(:)167 1253 y FG(Prop)r(osition)40 b FK(Let)i FH(t)g FK(b)r(e)g(a)h(term)e(of) i(t)n(yp)r(e)g FH(T)10 b FK(.)80 b(Supp)r(ose)44 b(all)d(the)h(free)f (v)l(ariables)i(of)167 1338 y FH(t)c FK(are)g(among)i FH(x)640 1349 y FD(1)668 1338 y FH(;)12 b(:)g(:)g(:)f(;)h(x)861 1349 y Fw(n)934 1338 y FK(of)40 b(t)n(yp)r(es)f FH(U)1274 1349 y FD(1)1302 1338 y FH(;)12 b(:)g(:)g(:)f(;)h(U)1503 1349 y Fw(n)1536 1338 y FK(,)43 b(and)d(all)e(the)h(free)f(t)n(yp)r(e)i (v)l(ariables)f(of)167 1423 y FH(T)6 b(;)12 b(U)291 1434 y FD(1)319 1423 y FH(;)g(:)g(:)g(:)f(;)h(U)520 1434 y Fw(n)582 1423 y FK(are)28 b(among)h FH(X)986 1434 y FD(1)1014 1423 y FH(;)12 b(:)g(:)g(:)g(;)g(X)1226 1434 y Fw(m)1273 1423 y FK(.)37 b(If)29 b FJ(R)1464 1434 y FD(1)1491 1423 y FH(;)12 b(:)g(:)g(:)g(;)g FJ(R)1706 1434 y Fw(m)1781 1423 y FK(are)28 b(reducibilit)n(y)d(candidates)k(of)167 1508 y(t)n(yp)r(es)k FH(V)399 1519 y FD(1)427 1508 y FH(;)12 b(:)g(:)g(:)f(;)h(V)621 1519 y Fw(m)700 1508 y FK(and)34 b FH(u)883 1519 y FD(1)911 1508 y FH(;)12 b(:)g(:)g(:)f(;)h(u)1104 1519 y Fw(n)1170 1508 y FK(are)32 b(terms)f(of)i(t)n(yp)r(es)f FH(U)1821 1519 y FD(1)1849 1508 y FK([)1868 1509 y FH(V)p 1872 1529 43 3 v 1924 1508 a(=)1958 1509 y(X)p 1962 1529 50 3 v 2021 1508 a FK(])p FH(;)12 b(:)g(:)g(:)g(;)g(U)2242 1519 y Fw(n)2275 1508 y FK([)2294 1509 y FH(V)p 2298 1529 43 3 v 2349 1508 a(=)2383 1509 y(X)p 2387 1529 50 3 v 2447 1508 a FK(])32 b(whic)n(h)167 1593 y(are)c(in)f Fq(RED)507 1604 y Fw(U)541 1611 y Fi(1)568 1593 y FK([)587 1594 y FJ(R)p 591 1614 47 3 v -1 x FH(=)681 1594 y(X)p 685 1614 50 3 v 744 1593 a FK(])p FH(;)12 b(:)g(:)g(:)g(;)g Fq(RED)1053 1604 y Fw(U)1087 1610 y Ff(n)1119 1593 y FK([)1138 1594 y FJ(R)p 1142 1614 47 3 v -1 x FH(=)1232 1594 y(X)p 1236 1614 50 3 v 1296 1593 a FK(])27 b(then)h FH(t)p FK([)1548 1594 y FH(V)p 1552 1614 43 3 v 1604 1593 a(=)1638 1594 y(X)p 1642 1614 50 3 v 1701 1593 a FK(][)1739 1594 y FH(u)p 1743 1614 26 3 v -1 x(=)1812 1594 y(x)p 1816 1614 V 1852 1593 a FK(])20 b FJ(2)f Fq(RED)2092 1604 y Fw(T)2131 1593 y FK([)2150 1594 y FJ(R)p 2154 1614 47 3 v -1 x FH(=)2244 1594 y(X)p 2248 1614 50 3 v 2307 1593 a FK(].)270 1766 y(The)28 b(pro)r(of)h(is)d(similar)f(to)j FG(??)q FK(.)36 b(The)27 b(new)g(cases)h(are)g(handled)g(using)g FG(??)g FK(and)h FG(??)q FK(.)p eop PStoPSsaved restore %%Page: (122,123) 62 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 119 122 bop 167 874 a FF(Chapter)28 b(15)167 1168 y(Represen)-5 b(tation)28 b(Theorem)167 1487 y FK(In)40 b(this)f(c)n(hapter)h(w)n(e)g (aim)f(to)h(study)g(the)g(\\strength")h(of)g(system)e FG(F)h FK(with)f(a)h(view)f(to)167 1573 y(iden)n(tifying)26 b(the)i(class)f(of)h(algorithms)f(whic)n(h)g(are)g(represen)n(table.)34 b(F)-6 b(or)28 b(example,)f(if)g FH(f)35 b FK(is)27 b(a)167 1658 y(closed)f(term)g(of)h(t)n(yp)r(e)g Fq(Int)p FJ(!)q Fq(Int)p FK(,)g(it)f(giv)n(es)h(rise)e(to)i(a)h(function)f(\(in)f(the)g (set-theoretic)f(sense\))167 1743 y FJ(j)p FH(f)8 b FJ(j)26 b FK(from)i(I)-12 b(N)27 b(to)h(I)-12 b(N)27 b(b)n(y)1195 1916 y FH(f)8 b FK(\()p 1264 1877 42 3 v FH(n)p FK(\))19 b Fu( )p 1441 1855 176 3 v 20 w FJ(j)p FH(f)8 b FJ(j)p FK(\()p FH(n)p FK(\))270 2089 y(The)34 b(function)g FJ(j)p FH(f)8 b FJ(j)33 b FK(is)h(recursiv)n(e,)g(indeed)g(w)n(e)f(ha)n(v)n(e) i(a)g(pro)r(cedure)f(for)g(calculating)f(it,)167 2174 y(namely:)270 2336 y FJ(\017)h FK(write)26 b(the)i(term)e FH(f)8 b FK(\()p 882 2297 42 3 v FH(n)p FK(\);)270 2479 y FJ(\017)34 b FK(normalise)44 b(it:)69 b(an)n(y)46 b(normalisation)e (strategy)i(will)c(do)k(this,)j(since)43 b(the)i(strong)339 2564 y(normalisation)d(theorem)g(sa)n(ys)h(that)g(all)e(reduction)h (paths)h(lead)f(to)h(the)f(\(same\))339 2650 y(normal)28 b(form;)270 2793 y FJ(\017)34 b FK(observ)n(e)26 b(that)g(the)f(normal) f(form)h(is)g(a)g(n)n(umeral)p 1660 2755 61 3 v 25 w FH(m)p FK(:)34 b(w)n(e)25 b(ha)n(v)n(e)h(seen)f(that)g(this)g(is)g (true)339 2879 y(for)j(system)g FG(T)p FK(,)g(and)g(this)f(is)g(also)h (v)l(alid)g(for)f(system)h FG(F)p FK(,)f(as)i(w)n(e)e(shall)g(sho)n(w)h (next;)270 3022 y FJ(\017)34 b FK(put)28 b FJ(j)p FH(f)8 b FJ(j)p FK(\()p FH(n)p FK(\))18 b(=)i FH(m)p FK(.)270 3225 y(In)41 b(the)f(\014rst)g(part,)k(w)n(e)c(shall)f(sho)n(w)j(that)e FJ(j)p FH(f)8 b FJ(j)39 b FK(is)h FM(pr)l(ovably)g(total)h FK(in)e(second)i(order)167 3310 y(P)n(eano)36 b(arithmetic,)f(b)n(y)g (close)g(examination)g(of)g(the)g(pro)r(of)h(of)g(strong)g (normalisation)f(in)167 3395 y(the)27 b(previous)h(c)n(hapter.)270 3521 y(In)i(the)e(second)i(part,)f(w)n(e)g(shall)f(use)h(Heyting's)g (ideas)g(once)g(again,)h(essen)n(tially)d(in)h(the)167 3606 y(form)h(of)h(the)f FM(r)l(e)l(alisability)36 b FK(metho)r(d)29 b(due)h(to)f(Martin-L\177)-34 b(of,)31 b(to)e(sho)n(w)h(the)f(con)n(v)n(erse)h(of)f(this,)167 3691 y(that)f(if)f(a)h(function)g(is)f(pro)n(v)l(ably)i(total)e(then)h (it)e(is)h(represen)n(table.)1368 4101 y(119)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 120 123 bop 167 167 a FK(120)837 b Fz(CHAPTER)26 b(15.)64 b(REPRESENT)-6 b(A)g(TION)26 b(THEOREM)167 404 y FE(15.1)114 b(Represen)m(table)29 b(functions)167 580 y Fy(15.1.1)94 b(Numerals)167 710 y FG(Prop)r(osition)29 b FK(An)n(y)k(closed)e (normal)g(term)g FH(t)g FK(of)i(t)n(yp)r(e)f Fq(Int)22 b FK(=)g(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FK(\()p FH(X)g FJ(!)p FH(X)g FK(\))p FJ(!)p FH(X)38 b FK(is)31 b(a)167 796 y FM(numer)l(al)p 444 757 42 3 v 35 w FH(n)d FK(for)g(some)f FH(n)20 b FJ(2)f FK(I)-12 b(N.)167 965 y FG(Pro)r(of)33 b FK(The)h(notion)f(of)h FM(he)l(ad)h(normal)e(form)39 b FK(\(section)33 b FG(??)q FK(\))g(is)f(applicable)g(to)i(system)f FG(F)p FK(,)167 1050 y(and)c(from)e(it)g(w)n(e)g(deduce)g(that)h FH(t)g FK(m)n(ust)f(b)r(e)h(of)g(the)f(form)1115 1219 y(\003)p FH(X)r(:)12 b(\025x)1332 1194 y Fw(X)1380 1219 y FH(:)g(\025y)1488 1194 y Fw(X)t Fv(!)o Fw(X)1630 1219 y FH(:)g(v)167 1388 y FK(where)31 b FH(v)j FK(is)c(of)i(t)n(yp)r(e)g FH(X)6 b FK(,)32 b(and)g(so)g(cannot)h(b)r(e)e(an)h(abstraction.)47 b(W)-6 b(e)31 b(pro)n(v)n(e)h(b)n(y)h(induction)167 1473 y(that)28 b FH(v)i FK(is)d(of)i(the)e(form)1111 1643 y FH(y)14 b FK(\()p FH(y)g FK(\()p FH(y)g(:)e(:)g(:)f FK(\()p FH(y)1111 1686 y Fo(|)p 1143 1686 114 9 v 114 w({z)p 1321 1686 V 114 w(})1109 1746 y Fx(n)27 b FB(o)r(ccurrences)1491 1643 y FH(x)p FK(\))12 b FH(:)g(:)g(:)o FK(\)\))167 1892 y(where)27 b FH(n)h FK(is)f(an)h(in)n(teger.)270 2016 y(Supp)r(ose)j(that)e FH(v)j FK(is)c FH(w)14 b(u)29 b FK(or)h FH(w)14 b(U)7 b FK(,)29 b(where)f FH(w)23 b FJ(6)p FK(=)d FH(y)s FK(.)39 b(Since)28 b FH(v)j FK(is)e(normal,)g FH(w)i FK(m)n(ust)e(b)r(e)g(of)167 2101 y(the)f(form)g FH(w)510 2076 y Fv(0)538 2101 y FH(u)577 2076 y Fv(0)622 2101 y FK(or)g FH(w)762 2076 y Fv(0)791 2101 y FH(U)845 2076 y Fv(0)861 2101 y FK(.)37 b(But)28 b(the)g(t)n(yp)r(es)g(of)h FH(x)f FK(and)h FH(y)i FK(are)d(simpler)d(than)k(that)g(of)f FH(w)2546 2076 y Fv(0)2563 2101 y FK(,)g(so)167 2186 y FH(w)218 2161 y Fv(0)261 2186 y FK(is)f(an)g(abstraction)h(and)g FH(w)h FK(is)d(a)h(redex:)35 b(con)n(tradiction.)g(So)27 b FH(v)j FK(is)c FH(x)p FK(,)h(in)g(whic)n(h)f(case)h(our)167 2272 y(result)i(holds)h(with)e FH(n)21 b FK(=)g(0,)31 b(or)f FH(v)i FK(is)d FH(y)14 b(v)1253 2246 y Fv(0)1299 2272 y FK(and)31 b(w)n(e)e(apply)h(the)f(induction)g(h)n(yp)r(othesis)i (to)f FH(v)2656 2246 y Fv(0)167 2357 y FK(of)e(t)n(yp)r(e)g FH(X)6 b FK(.)2125 b Fu(\003)167 2526 y FG(Remark)75 b FK(If)39 b(w)n(e)e(had)j(tak)n(en)f(the)f(v)l(arian)n(t)h(\005)p FH(X)r(:)12 b FK(\()p FH(X)6 b FJ(!)o FH(X)g FK(\))p FJ(!)p FK(\()p FH(X)g FJ(!)p FH(X)g FK(\))38 b(w)n(e)g(w)n(ould)g(ha)n (v)n(e)167 2611 y(obtained)28 b(almost)f(the)h(same)f(result,)g(but)h (in)f(addition)h(there)e(is)h(a)h(v)l(arian)n(t)h(for)f(1:)1194 2780 y(\003)p FH(X)r(:)12 b(\025y)1409 2755 y Fw(X)t Fv(!)o Fw(X)1550 2780 y FH(:)g(y)270 2949 y FK(This)39 b(phenomenon)h(is)f(one)g(of)h(the)e(little)e(imp)r(erfections)h(of)i (the)g(syn)n(tax.)72 b(Similar)167 3034 y(features)32 b(arise)g(with)f(inductiv)n(e)h(data)h(t)n(yp)r(es,)h FM(i.e.)e FK(the)h(closed)e(normal)h(forms)h(of)g(t)n(yp)r(e)f FH(T)167 3120 y FK(are)j(\\almost")g(the)g(terms)e(obtained)j(b)n(y)f (com)n(bining)g(the)f(functions)h FH(f)2151 3131 y Fw(i)2171 3120 y FK(,)i(but)e(in)g(general)167 3205 y(only)28 b(\\almost".)270 3329 y(Ha)n(ving)d(said)g(this,)f(the)g(recursion)g(sc)n(heme)f(for)i (inductiv)n(e)e(t)n(yp)r(es,)i(de\014ned)g(\(morally\))e(in)167 3414 y(terms)j(of)h(the)f FH(f)601 3425 y Fw(i)621 3414 y FK(,)h(sho)n(ws)h(that)f(\(in)f(a)h(sense)g(to)g(b)r(e)f(made)h (precise\))e(the)h(terms)g(constructed)167 3499 y(from)36 b(the)g FH(f)509 3510 y Fw(i)565 3499 y FK(are)g(\\dense")i(among)f (the)f(others.)62 b(T)-6 b(o)37 b(return)f(to)g(our)h(p)r(et)f(sub)t (ject,)i(the)167 3584 y(syn)n(tax)29 b(seems)e(to)g(b)r(e)h(to)r(o)g (rigid)e(and)j(m)n(uc)n(h)e(to)r(o)h(arti\014cial)e(to)i(allo)n(w)e(a)i (satisfactory)g(study)167 3669 y(of)43 b(suc)n(h)f(di\016culties.)77 b(Undoubtedly)43 b(they)f(cannot)h(b)r(e)f(resolv)n(ed)g(otherwise)f (than)i(b)n(y)167 3754 y(means)24 b(of)g(an)g(op)r(erational)g(seman)n (tics)e(whic)n(h)h(w)n(ould)h(allo)n(w)f(us)h(to)g(iden)n(tify)e(\(or)i (distinguish)167 3840 y(b)r(et)n(w)n(een\))k(algorithms)h(b)r(ey)n(ond) i(what)e(can)h(b)r(e)f(done)h(with)e(normalisation,)i(whic)n(h)e(is)h (only)167 3925 y(an)f(appro)n(ximation)h(to)f(that)g(seman)n(tics.)p eop PStoPSsaved restore %%Page: (124,125) 63 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 121 124 bop 167 167 a Fz(15.1.)65 b(REPRESENT)-6 b(ABLE)26 b(FUNCTIONS)1138 b FK(121)167 404 y Fy(15.1.2)94 b(T)-8 b(otal)28 b(recursiv)m(e)h(functions)167 535 y FK(Let)35 b(us)h(return)f(to)h(the)f(original)g(question,)j(whic)n(h)c(w)n(as)j (to)e(c)n(haracterise)g(the)g(functions)167 620 y(whic)n(h)i(are)g (represen)n(table)f(in)h FG(F)p FK(.)g(W)-6 b(e)37 b(ha)n(v)n(e)i(seen) e(that)g(suc)n(h)h(functions)g(are)f(recursiv)n(e,)167 705 y FM(i.e.)28 b FK(calculable.)167 868 y FG(Prop)r(osition)d FK(There)i(is)g(a)h(total)g(recursiv)n(e)e(function)i(whic)n(h)e(is)h (not)i(represen)n(table)d(in)h FG(F)p FK(.)167 1030 y FG(Pro)r(of)40 b FK(The)h(function)f(whic)n(h)g(w)n(e)g(shall)f(tak)n (e)i(is)f(the)g(normalisation)f(op)r(eration.)74 b(W)-6 b(e)167 1115 y(represen)n(t)33 b(terms)g(in)h(a)g(formal)g(language)h (as)g(a)f(string)g(of)h(sym)n(b)r(ols)f(from)g(a)g(\014xed)h(\014nite) 167 1200 y(alphab)r(et)26 b(and)h(hence)f(as)g(an)h(in)n(teger.)34 b(Then)26 b(this)f(function)h(tak)n(es)h(one)f(term)f(\(represen)n(ted) 167 1285 y(b)n(y)38 b(an)g(in)n(teger\))e(and)i(yields)e(another.)66 b(This)36 b(function)i(is)e(univ)n(ersal)h(\(in)f(the)h(sense)h(of)167 1370 y(T)-6 b(uring\))30 b(with)e(resp)r(ect)h(to)h(the)f(functions)h (represen)n(table)e(in)i FG(F)p FK(,)f(and)i(so)f(cannot)h(itself)c(b)r (e)167 1456 y(represen)n(ted)g(in)g FG(F)p FK(.)270 1576 y(More)h(precisely:)270 1716 y FJ(\017)34 b FH(N)7 b FK(\()p FH(n)p FK(\))20 b(=)g FH(m)28 b FK(if)e FH(n)i FK(co)r(des)g(the)f(term)g FH(t)p FK(,)g FH(m)h FK(co)r(des)g FH(u)g FK(and)h FH(u)e FK(is)g(the)h(normal)f(form)g(of)i FH(t)p FK(.)270 1855 y FJ(\017)34 b FH(N)7 b FK(\()p FH(n)p FK(\))20 b(=)g(0)28 b(if)e FH(n)i FK(do)r(es)g(not)h(co)r(de)e (an)n(y)i(term)d(of)j FG(F)p FK(.)270 1994 y(On)f(the)f(other)h(hand)h (w)n(e)e(ha)n(v)n(e)i(the)e(functions:)270 2134 y FJ(\017)34 b FH(A)p FK(\()p FH(m;)12 b(n)p FK(\))32 b(=)f FH(p)44 b FK(if)g FH(m;)12 b(n;)g(p)45 b FK(are)g(the)f(co)r(des)h(of)g FH(t;)12 b(u;)g(v)48 b FK(suc)n(h)d(that)g FH(v)35 b FK(=)c FH(t)12 b(u)p FK(,)49 b(with)339 2219 y FH(A)p FK(\()p FH(m;)12 b(n)p FK(\))20 b(=)f(0)28 b(otherwise.)270 2358 y FJ(\017)34 b FH(])p FK(\()p FH(n)p FK(\))20 b(=)f FH(m)28 b FK(if)f FH(m)g FK(co)r(des)p 988 2319 42 3 v 28 w FH(n)p FK(.)270 2496 y FJ(\017)34 b FH([)p FK(\()p FH(m)p FK(\))20 b(=)f FH(n)28 b FK(if)f FH(m)g FK(is)g(the)h(co)r(de)f (of)i(the)e(n)n(umeral)p 1636 2457 V 27 w FH(n)p FK(,)h(with)e FH([)p FK(\()p FH(m)p FK(\))20 b(=)f(0)28 b(otherwise.)270 2636 y(No)n(w)g(consider:)975 2798 y FH(D)r FK(\()p FH(n)p FK(\))19 b(=)h FH([)p FK(\()p FH(N)7 b FK(\()p FH(A)p FK(\()p FH(n;)12 b(])p FK(\()p FH(n)p FK(\)\)\)\))i(+)h(1)270 2961 y(This)44 b(is)f(certainly)f(a)i(total)f(recursiv)n(e)g(function,) 48 b(but)c(it)f(cannot)h(b)r(e)g(represen)n(ted)167 3046 y(in)39 b FG(F)p FK(.)h(Indeed,)j(supp)r(ose)e(that)f FH(t)g FK(of)g(t)n(yp)r(e)g Fq(Int)p FJ(!)p Fq(Int)g FK(represen)n(ts)f FH(D)j FK(and)f(let)d FH(n)i FK(b)r(e)f(the)167 3131 y(co)r(de)h(of)h FH(t)p FK(.)74 b(Then)40 b FH(A)p FK(\()p FH(n;)12 b(])p FK(\()p FH(n)p FK(\)\))40 b(is)f(the)h(co)r(de)h (of)g FH(t)p 1626 3092 V 12 w(n)p FK(,)i(and)f FH(N)7 b FK(\()p FH(A)p FK(\()p FH(n;)12 b(])p FK(\()p FH(n)p FK(\)\)\))39 b(that)i(of)g(its)167 3216 y(normal)28 b(form.)36 b(But)28 b(b)n(y)h(de\014nition)e(of)i FH(t)p FK(,)f FH(t)p 1348 3177 V 12 w(n)20 b Fu( )p 1499 3155 154 3 v 20 w FH(D)r FK(\()p FH(n)p FK(\),)28 b(so)h FH(N)7 b FK(\()p FH(A)p FK(\()p FH(n;)12 b(])p FK(\()p FH(n)p FK(\)\)\))19 b(=)h FH(])p FK(\()p FH(D)r FK(\()p FH(n)p FK(\)\))27 b(and)167 3301 y FH([)p FK(\()p FH(N)7 b FK(\()p FH(A)p FK(\()p FH(n;)12 b(])p FK(\()p FH(n)p FK(\)\)\)\))18 b(=)i FH(D)r FK(\()p FH(n)p FK(\))27 b(whence)g FH(D)r FK(\()p FH(n)p FK(\))20 b(=)f FH(D)r FK(\()p FH(n)p FK(\))c(+)h(1:)36 b(con)n(tradiction.)270 3422 y(F)-6 b(or)45 b(an)n(y)f(reasonable)g(co) r(ding,)k FH(A)p FK(,)g FH(])43 b FK(and)i FH([)e FK(are)g(ob)n (viously)i(represen)n(table)d(in)h FG(F)p FK(,)167 3507 y(so)28 b FH(N)35 b FK(itself)26 b(is)h FM(not)34 b FK(represen)n (table)27 b(in)g FG(F)p FK(.)1315 b Fu(\003)270 3669 y FK(This)28 b(result)f(is)g(of)i(course)f(a)h(v)l(arian)n(t)f(of)h(a)f (v)n(ery)h(famous)g(result)e(in)g(Recursion)h(Theory)167 3754 y(\(due)44 b(to)g(T)-6 b(uring\),)48 b(namely)43 b(that)h(the)g(set)f(of)h(total)g(recursiv)n(e)e(functions)i(cannot)h (b)r(e)167 3840 y(en)n(umerated)36 b(b)n(y)h(a)g(single)e(total)h (recursiv)n(e)f(function.)61 b(In)37 b(particular)e(it)g(applies)h(to)g (all)167 3925 y(sorts)28 b(of)g(calculi,)e(t)n(yp)r(ed)i(or)g(un)n(t)n (yp)r(ed,)h(whic)n(h)d(satisfy)i(the)g(normalisation)f(theorem.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 122 125 bop 167 167 a FK(122)837 b Fz(CHAPTER)26 b(15.)64 b(REPRESENT)-6 b(A)g(TION)26 b(THEOREM)167 404 y Fy(15.1.3)94 b(Pro)m(v)-5 b(ably)28 b(total)g(functions)167 536 y FK(A)k(recursiv)n(e)e(function)i FH(f)39 b FK(whic)n(h)32 b(is)f(total)g(from)h(I)-12 b(N)32 b(to)g(I)-12 b(N)31 b(is)h(called)e FM(pr)l(ovably)i(total)39 b FK(in)32 b(a)167 621 y(system)h(of)g(arithmetic)e FG(A)h FK(if)g FG(A)h FK(pro)n(v)n(es)h(the)f(form)n(ula)g(whic)n(h)f(expresses)h (\\for)h(all)e FH(n)p FK(,)i(the)167 706 y(program)d FH(e)p FK(,)g(with)f(input)g FH(n)p FK(,)i(terminates)c(and)k(returns)e (an)h(in)n(teger")f(for)h(some)f(algorithm)167 791 y FH(e)36 b FK(represen)n(ting)g FH(f)8 b FK(.)62 b(The)36 b(precise)f(form)n(ulation)h(dep)r(ends)h(on)g(ho)n(w)g(w)n(e)f(write)f (programs)167 876 y(formally)27 b(in)g FG(A)p FK(.)35 b(F)-6 b(or)28 b(example,)f(with)g(the)g(Kleene)f(notation:)971 1051 y FG(A)h FK(pro)n(v)n(es)i FJ(8)p FH(n:)12 b FJ(9)p FH(m:)g Fq(T)1565 1062 y FD(1)1592 1051 y FK(\()p FH(e;)g(n;)g(m)p FK(\))167 1227 y(where)32 b Fq(T)423 1238 y FD(1)451 1227 y FK(\()p FH(e;)12 b(n;)g(m)p FK(\))33 b(means)g(that)h(the)f (program)h FH(e)f FK(terminates)e(with)h(output)i FH(m)g FK(if)e(giv)n(en)167 1312 y(input)d FH(n)p FK(.)38 b(This)29 b(ma)n(y)g(itself)d(b)r(e)j(expressed)g(as)g FJ(9)p FH(m)1550 1286 y Fv(0)1567 1312 y FH(:)12 b(P)e FK(\()p FH(n;)i(m;)g(m)1902 1286 y Fv(0)1919 1312 y FK(\))28 b(where)g FH(P)39 b FK(is)28 b(a)h(primitiv)n(e)167 1397 y(recursiv)n(e)40 b(predicate)h(and)i FH(m)1004 1371 y Fv(0)1062 1397 y FK(is)e(the)h(\\transcript")g(of)g(the)f(computation.)78 b(The)42 b(t)n(w)n(o)167 1482 y(quan)n(ti\014ers)34 b FJ(9)p FH(m:)12 b FJ(9)p FH(m)744 1457 y Fv(0)761 1482 y FH(:)45 b FK(can)34 b(b)r(e)f(replaced)g(b)n(y)h(a)f(single)g(one)g FJ(9)p FH(p:)45 b FK(using)34 b(some)f(\(primitiv)n(e)167 1567 y(recursiv)n(e\))g(co)r(ding)h(of)h(pairs.)55 b(W)-6 b(e)34 b(prefer)f(to)i(b)r(e)f(no)h(more)f(sp)r(eci\014c)f(ab)r(out)i (this)f(precise)167 1652 y(form)n(ulation,)27 b(but)h(w)n(e)g(notice)e (that)i(termination)e(is)h(expressed)h(b)n(y)h(a)f(\005)2144 1627 y FD(0)2144 1670 y(2)2199 1652 y FK(form)n(ula)2429 1627 y FD(1)2457 1652 y FK(.)270 1828 y(In)39 b FG(??)q FK(,)i(w)n(e)d(sa)n(w)h(that)f(the)g(functions)h(represen)n(table)e(in) h FG(T)g FK(are)h(pro)n(v)l(ably)h(total)e(in)167 1913 y(P)n(eano)29 b(arithmetic)24 b FG(P)-23 b(A)p FK(,)28 b(and)g(the)g(con)n(v)n(erse)g(is)f(also)h(true.)35 b(Here)26 b(w)n(e)h(ha)n(v)n(e:)167 2088 y FG(Prop)r(osition)f FK(The)h(functions)h(represen)n(table)f(in)g FG(F)h FK(are)g(pro)n(v)l (ably)h(total)f(in)f FM(se)l(c)l(ond)h(or)l(der)167 2173 y FK(P)n(eano)h(arithmetic)24 b FG(P)-23 b(A)806 2184 y Fb(2)838 2173 y FK(.)167 2349 y FG(Pro)r(of)34 b FK(An)h(ob)t(ject)f FH(f)41 b FK(of)35 b(t)n(yp)r(e)g Fq(Int)p FJ(!)p Fq(Int)f FK(giv)n(es)h(rise)e(to)h(an)h(algorithm)f(whic)n(h,)h(giv)n(en)f(an) 167 2434 y(in)n(teger)25 b FH(n)p FK(,)i(returns)f FJ(j)p FH(f)8 b FJ(j)p FK(\()p FH(n)p FK(\);)25 b(w)n(e)h(ha)n(v)n(e)h (describ)r(ed)e(ho)n(w)i(to)g(do)f(this)g(already)-6 b(.)36 b(No)n(w)26 b(w)n(e)g(w)n(an)n(t)167 2519 y(to)k(sho)n(w)h(that) f(this)f(program)i(terminates.)40 b(W)-6 b(e)29 b(mak)n(e)h(use)g(of)g (the)g(strong)h(normalisation)167 2604 y(theorem,)26 b(and)g(b)n(y)h(examining)e(the)h(mathematical)e(principles)f(emplo)n (y)n(ed)j(in)f(the)h(pro)r(of)h(w)n(e)167 2689 y(obtain)h(the)g (result.)270 2816 y(What)39 b(matters)f(is)f(essen)n(tially)g(the)h (reducibilit)n(y)d(of)j FH(f)46 b FK(alone)38 b(\(together)g(with)g (that)167 2901 y(of)c(the)f(n)n(umerals,)h(whic)n(h)f(is)g (immediate\).)49 b(W)-6 b(e)33 b(only)h(use)f(\014nitely)f(man)n(y)i (reducibilities,)167 2987 y(whic)n(h)28 b(sa)n(v)n(es)i(us)f(from)f (the)h(fact)f(that)h(\(as)g(in)f FG(T)p FK(\))h(reducibilit)n(y)c(is)j (not)i(globally)e(de\014nable.)167 3072 y(The)i(reducibilit)n(y)d (predicates)j(are)g(de\014nable)g(b)n(y)h(second)g(order)f(quan)n (ti\014cation)h(o)n(v)n(er)g(sets)167 3157 y(of)d(\(terms)f(co)r(ded)g (as\))i(in)n(tegers.)34 b(The)28 b(mathematical)d(principles)g(w)n(e)j (ha)n(v)n(e)g(used)g(are:)270 3320 y FJ(\017)34 b FK(induction)28 b(on)g(the)f(reducibilit)n(y)e(predicates)i(for)h(the)f(t)n(yp)r(es)h (in)n(v)n(olv)n(ed)g(in)f FH(f)8 b FK(,)270 3464 y FJ(\017)34 b FK(the)e(comprehension)f(sc)n(heme)f(and)j(second)f(order)f(quan)n (ti\014cation,)i(whic)n(h)e(allo)n(w)g(us)339 3550 y(to)d(de\014ne)g(a) g(reducibilit)n(y)d(candidate)j(from)f(a)h(parametrised)f(reducibilit)n (y)-6 b(.)167 3712 y(But)28 b FG(P)-23 b(A)400 3723 y Fb(2)458 3712 y FK(is)27 b(precisely)f(the)h(system)h(of)g(arithmetic)d (with)h(induction,)i(comprehension)f(and)167 3798 y(second)h(order)g (quan)n(ti\014cation.)1606 b Fu(\003)p 167 3860 1003 3 v 246 3903 a FC(1)273 3925 y FB(See)27 b(fo)r(otnote)h(page)g Ft(??)o FB(.)p eop PStoPSsaved restore %%Page: (126,127) 64 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 123 126 bop 167 167 a Fz(15.2.)65 b(PR)n(OOFS)27 b(INTO)f(PR)n(OGRAMS) 1268 b FK(123)167 404 y FG(Remark)48 b FK(Let)25 b(us)g(p)r(oin)n(t)g (out)g(brie\015y)f(the)h(status)g(of)g(functions)g(whic)n(h)f(are)h (pro)n(v)l(ably)h(total)167 490 y(in)h(a)h(system)f(of)i(arithmetic)c (whic)n(h)h(is)h(not)i(to)r(o)f(w)n(eak:)270 694 y FJ(\017)34 b FK(If)40 b FG(A)f FK(is)g(1-consisten)n(t,)k FM(i.e.)c FK(pro)n(v)n(es)i(no)f(false)f(\006)1725 669 y FD(0)1725 712 y(1)1792 694 y FK(form)n(ula)g(\(as)h(w)n(e)f(hop)r(e)i(is)d(the) 339 779 y(case)d(for)g FG(P)-23 b(A)p FK(,)36 b FG(P)-23 b(A)851 790 y Fb(2)917 779 y FK(and)36 b(the)e(axiomatic)g(set)g (theory)h(of)g(Zermelo-F)-6 b(raenk)n(el\))33 b(then)339 864 y(a)38 b(diagonalisation)f(argumen)n(t)h(sho)n(ws)g(that)f(there)f (are)h(total)g(recursiv)n(e)f(functions)339 950 y(whic)n(h)27 b(are)h(not)g(pro)n(v)l(ably)h(total)f(in)f FG(A)p FK(.)270 1120 y FJ(\017)34 b FK(Otherwise)27 b(\(and)i(notice)e(that)i FG(A)f FK(can)h(b)r(e)f(consisten)n(t)g(without)g(b)r(eing)g (1-consisten)n(t,)339 1206 y FM(e.g.)41 b FG(A)28 b FK(=)g FG(P)-23 b(A)19 b FK(+)g FJ(:)p Fq(consis)q FK(\()p FG(P)-23 b(A)o FK(\)\))40 b FG(A)g FK(pro)n(v)n(es)i(the)e(totalit)n(y)g(of)h (recursiv)n(e)e(functions)339 1291 y(whic)n(h)e(are)f(in)h(fact)g (partial.)62 b(It)37 b(can)g(ev)n(en)g(pro)n(v)n(e)h(the)f(totalit)n(y) f(of)h FM(al)t(l)43 b FK(recursiv)n(e)339 1376 y(functions)28 b(\(but)g(for)g(wrong)h(reasons,)g(and)f(after)g(mo)r(di\014cation)f (of)h(the)f(programs\).)167 1650 y FE(15.2)114 b(Pro)s(ofs)27 b(in)m(to)h(programs)167 1821 y FK(The)f(con)n(v)n(erse)h(of)g(the)g (prop)r(osition)g(is)f(also)h(true,)f(so)h(w)n(e)g(ha)n(v)n(e:)167 2059 y FG(Theorem)g FK(The)g(functions)h(represen)n(table)f(in)g FG(F)g FK(are)g FM(exactly)34 b FK(those)29 b(whic)n(h)f(are)g(pro)n(v) l(ably)167 2144 y(total)f(in)g FG(P)-23 b(A)512 2155 y Fb(2)544 2144 y FK(.)270 2382 y(The)25 b(original)e(pro)r(of)i(in)f ([)p FG(?)q FK(])g(uses)h(an)g(argumen)n(t)g(of)g(functional)f(in)n (terpretation)f(whic)n(h)h(is)167 2468 y(tec)n(hnical)i(and)i(of)g (limited)c(in)n(terest.)34 b(W)-6 b(e)27 b(shall)g(giv)n(e)g(here)g(a)h (m)n(uc)n(h)f(simpler)e(one,)j(inspired)167 2553 y(b)n(y)g([)p FG(?)q FK(].)270 2791 y(First)j(w)n(e)f(replace)g FG(P)-23 b(A)889 2802 y Fb(2)952 2791 y FK(b)n(y)32 b(its)e(in)n(tuitionistic)e (v)n(ersion)k FG(H)-12 b(A)1926 2802 y Fb(2)1989 2791 y FK(\(Heyting)30 b(second)i(order)167 2876 y(arithmetic\),)37 b(whic)n(h)g(is)g(closer)g(to)h(system)f FG(F)p FK(.)66 b(This)37 b(is)g(p)r(ossible)g(b)r(ecause)g FG(H)-12 b(A)2452 2887 y Fb(2)2522 2876 y FM(is)38 b(as)167 2961 y(str)l(ong)28 b(as)g FG(P)-23 b(A)559 2972 y Fb(2)618 2961 y FM(in)27 b(pr)l(oving)h(totality)g(of)g(algorithms)p FK(.)270 3120 y(Indeed,)e(there)f(is)f(the)h(so)h(called)e(\\G\177)-34 b(odel)25 b(translation")h(whic)n(h)f(consists)g(of)h(putting)f FJ(::)167 3205 y FK(at)i(\\enough)h(places")e(so)h(that:)35 b(if)26 b FH(A)g FK(is)f(pro)n(v)l(able)j(in)d FG(P)-23 b(A)1710 3216 y Fb(2)1768 3205 y FK(then)26 b FH(A)1980 3179 y Fv(::)2076 3205 y FK(is)f(pro)n(v)l(able)i(in)f FG(H)-12 b(A)2621 3216 y Fb(2)2653 3205 y FK(.)270 3363 y(The)28 b FJ(::)p FK(-translation)f(of)i(a)f(\005)1085 3338 y FD(0)1085 3381 y(2)1140 3363 y FK(form)n(ula,)f(sa)n(y)i FJ(8)p FH(n:)12 b FJ(9)p FH(m:)g Fq(T)1829 3374 y FD(1)1857 3363 y FK(\()p FH(e;)g(n;)g(m)p FK(\),)27 b(is)1076 3601 y FJ(8)p FH(n:)12 b FJ(::9)p FH(m:)g Fq(T)1459 3612 y FD(1)1487 3601 y FK(\()p FH(e;)g(n;)g(m)p FK(\))167 3840 y(up)31 b(to)g(trivial)e(equiv)l(alences,)i(and)h(standard)g(pro)r (of-theoretic)e(considerations)h(sho)n(w)h(that)167 3925 y(the)27 b(second)i(one)f(is)f(pro)n(v)l(able)h(in)f FG(H)-12 b(A)1198 3936 y Fb(2)1257 3925 y FK(if)27 b(and)i(only)f(if)f (the)g(\014rst)h(is.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 124 127 bop 167 167 a FK(124)837 b Fz(CHAPTER)26 b(15.)64 b(REPRESENT)-6 b(A)g(TION)26 b(THEOREM)167 404 y Fy(15.2.1)94 b(F)-8 b(orm)m(ulation)27 b(of)g(H)-14 b(A)1273 417 y Ft(2)167 537 y FK(There)27 b(are)g(t)n(w)n(o)h(kinds)g(of)g(v)l (ariables:)270 704 y FJ(\017)34 b FH(\030)s(;)12 b(\021)s(;)g(\020)5 b(;)12 b(:)g(:)g(:)28 b FK(\(for)g(in)n(tegers\))270 851 y FJ(\017)34 b FH(X)r(;)12 b(Y)t(;)g(Z)q(;)g(:)g(:)g(:)28 b FK(\(for)g(sets)f(of)h(in)n(tegers\))167 1017 y(W)-6 b(e)30 b(could)f(ha)n(v)n(e)i FH(n)p FK(-ary)g(predicate)d(v)l (ariables)i(for)g(arbitrary)g FH(n)p FK(,)g(but)g(w)n(e)g(assume)g (them)f(to)167 1103 y(b)r(e)23 b(unary)i(for)f(the)f(sak)n(e)i(of)f (exp)r(osition.)33 b(W)-6 b(e)24 b(quite)f(delib)r(erately)d(use)k FH(X)29 b FK(as)24 b(a)g(second-order)167 1188 y(v)l(ariable)j(b)r(oth) i(for)f FG(H)-12 b(A)818 1199 y Fb(2)877 1188 y FK(and)29 b(for)f FG(F)p FK(.)270 1318 y(W)-6 b(e)32 b(shall)g(also)g(ha)n(v)n(e) i(basic)e(function)g(sym)n(b)r(ols,)i(namely)d Fq(O)h FK(\(0-ary\))h(and)h Fq(S)e FK(\(unary\).)167 1403 y(The)27 b(form)n(ulae)h(will)c(b)r(e)k(built)e(from)i(atoms)270 1570 y FJ(\017)34 b FH(a)20 b FJ(2)g FH(X)6 b FK(,)27 b(where)g FH(a)h FK(is)f(a)h(term)e(\()p FM(i.e.)i FK(a)g Fq(S)1394 1544 y Fw(n)1427 1570 y Fq(O)g FK(or)g(a)g Fq(S)1695 1544 y Fw(n)1728 1570 y FH(\030)s FK(\))g(and)h FH(X)k FK(a)28 b(set)g(v)l(ariable,)270 1717 y FJ(\017)34 b FH(a)20 b FK(=)f FH(b)p FK(,)28 b(where)f FH(a)h FK(and)h FH(b)f FK(are)f(terms,)167 1883 y(b)n(y)33 b(means)g(of)g FJ(\))p FK(,)h FJ(8)p FH(\030)s(:)12 b FK(,)34 b FJ(9)p FH(\030)s(:)45 b FK(and)33 b FJ(8)p FH(X)r(:)44 b FK(It)32 b(is)g(p)r(ossible)f(to)i(de\014ne)g(the)f(other)h(connectors)167 1968 y FJ(^)p FK(,)f FJ(_)p FK(,)g FJ(?)e FK(and)i FJ(9)p FH(X)r(:)43 b FK(in)31 b(the)f(same)h(w)n(a)n(y)h(as)g(in)f FG(??)p FK(,)h(and)h FJ(:)p FH(A)d FK(as)i FH(A)22 b FJ(\))g(?)p FK(.)45 b(In)31 b(fact)g FJ(9)p FH(\030)s(:)44 b FK(is)167 2054 y(de\014nable)28 b(to)r(o,)g(but)g(it)f(is)g(more)g (con)n(v)n(enien)n(t)g(to)h(ha)n(v)n(e)h(it)d(as)j(a)f(primitiv)n(e)c (connector.)270 2184 y(There)j(are)h(ob)n(vious)h(\(quan)n(ti\014er)f (free\))e(axioms)i(for)g(equalit)n(y)-6 b(,)27 b(and)i(for)f Fq(S)g FK(w)n(e)f(ha)n(v)n(e:)716 2365 y FJ(:)20 b Fq(S)12 b FH(\030)23 b FK(=)c Fq(O)550 b(S)12 b FH(\030)23 b FK(=)c Fq(S)12 b FH(\021)22 b FJ(\))e FH(\030)j FK(=)d FH(\021)270 2589 y FK(The)37 b(connectors)h FJ(\))p FK(,)i FJ(8)p FH(\030)s(:)49 b FK(and)38 b FJ(9)p FH(\030)s(:)50 b FK(are)37 b(handled)g(b)n(y)h(the)f(usual)h(rules)e(of)i(natural)167 2675 y(deduction)28 b(\(c)n(hapters)f FG(??)i FK(and)g FG(??)p FK(\))f(and)g FJ(8)p FH(X)r(:)39 b FK(b)n(y:)800 2844 y FJ(\001)800 2882 y(\001)800 2920 y(\001)784 2977 y FH(A)p 720 3022 181 4 v 921 3038 a FJ(8)961 3012 y FD(2)988 3038 y FJ(I)720 3098 y(8)p FH(X)r(:)12 b(A)1763 2835 y FJ(\001)1763 2873 y(\001)1763 2911 y(\001)1682 2969 y(8)p FH(X)r(:)g(A)p 1584 3014 377 4 v 1981 3029 a FJ(8)2021 3004 y FD(2)2048 3029 y FJ(E)1584 3090 y FH(A)p FK([)p FJ(f)p FH(\030)s(:)g(C)5 b FJ(g)q FH(=X)h FK(])270 3262 y(In)32 b(the)f(last)g(rule,)g FH(A)p FK([)p FJ(f)p FH(\030)s(:)12 b(C)5 b FJ(g)r FH(=X)h FK(])31 b(means)h(that)g(w)n(e)e(replace)h(all)f(the)h(atoms)h FH(a)22 b FJ(2)g FH(X)37 b FK(b)n(y)167 3347 y FH(C)5 b FK([)p FH(a=\030)s FK(])30 b(\(so)e FJ(f)p FH(\030)s(:)12 b(C)5 b FJ(g)28 b FK(is)f(not)i(part)f(of)g(the)f(syn)n(tax\).)270 3478 y(T)-6 b(o)26 b(illustrate)c(the)i(strength)h(of)h(this)e (formalism)f(\(second)i(order)g FM(\022)-35 b(a)25 b(la)f FK(T)-6 b(ak)n(euti\))25 b(observ)n(e)167 3563 y(that)j FJ(8)361 3537 y FD(2)388 3563 y FJ(E)34 b FK(is)27 b(nothing)i(but)f (the)f(principle)1072 3744 y FJ(8)p FH(X)r(:)12 b(A)19 b FJ(\))h FH(A)p FK([)p FJ(f)p FH(\030)s(:)12 b(C)5 b FJ(g)q FH(=X)h FK(])167 3925 y(and)29 b(in)e(particular,)g(with)f FH(A)i FK(the)f(pro)n(v)l(able)h(form)n(ula)p eop PStoPSsaved restore %%Page: (128,129) 65 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 125 128 bop 167 167 a Fz(15.2.)65 b(PR)n(OOFS)27 b(INTO)f(PR)n(OGRAMS) 1268 b FK(125)1041 404 y FJ(9)p FH(Y)t(:)12 b FJ(8)p FH(\030)s(:)g FK(\()p FH(\030)22 b FJ(2)e FH(X)h FJ(,)16 b FH(\030)23 b FJ(2)d FH(Y)15 b FK(\))167 581 y(w)n(e)51 b(get)h FJ(9)p FH(Y)t(:)12 b FJ(8)p FH(\030)s(:)g FK(\()p FH(C)27 b FJ(,)c FH(\030)41 b FJ(2)36 b FH(Y)16 b FK(\).)108 b(Therefore)51 b FJ(8)1600 556 y FD(2)1627 581 y FJ(E)58 b FK(app)r(ears)53 b(as)g(a)f(v)l(arian)n(t)h(of)f(the)167 666 y FM(Compr)l(ehension)29 b(Scheme)p FK(.)270 843 y(Notice)e(that)h(there)e(is)h(no)i(induction)e(sc)n(heme.)34 b(Ho)n(w)n(ev)n(er)28 b(if)e(w)n(e)i(de\014ne)518 1020 y Fq(Nat)p FK(\()p FH(\030)s FK(\))731 981 y FD(def)738 1020 y FK(=)f FJ(8)p FH(X)r(:)12 b FK(\()p Fq(O)18 b FJ(2)i FH(X)25 b FJ(\))20 b(8)p FH(\021)s(:)12 b FK(\()p FH(\021)21 b FJ(2)e FH(X)26 b FJ(\))20 b Fq(S)12 b FH(\021)22 b FJ(2)d FH(X)6 b FK(\))20 b FJ(\))g FH(\030)j FJ(2)c FH(X)6 b FK(\))167 1197 y(then)28 b(it)e(is)h(easy)i(to)e(pro)n(v)n(e)i (that)232 1374 y FH(A)p FK([)p Fq(O)p FH(=\030)s FK(])85 b FJ(^)g(8)p FH(\021)s(:)12 b FK(\()p Fq(Nat)n FK(\()p FH(\021)s FK(\))19 b FJ(\))h FH(A)p FK([)p FH(\021)s(=\030)s FK(])g FJ(\))g FH(A)p FK([)p Fq(S)12 b FH(\021)s(=\030)s FK(]\))89 b FJ(\))g(8)p FH(\021)s(:)12 b FK(\()p Fq(Nat)o FK(\()p FH(\021)s FK(\))19 b FJ(\))h FH(A)p FK([)p FH(\021)s(=\030)s FK(]\))167 1551 y(In)27 b(other)g(w)n(ords,)h(the)f(induction)g(sc)n (heme)f(holds)i(pro)n(vided)f(all)f(\014rst)h(order)h(quan)n(ti\014ers) f(are)167 1636 y(relativised)e(to)j Fq(Nat)q FK(.)167 1842 y Fy(15.2.2)94 b(T)-8 b(ranslation)28 b(of)f(H)-14 b(A)1239 1855 y Ft(2)1303 1842 y Fy(in)m(to)28 b(F)167 1974 y FK(T)-6 b(o)28 b(eac)n(h)g(form)n(ula)f FH(A)h FK(of)g FG(H)-12 b(A)963 1985 y Fb(2)1022 1974 y FK(w)n(e)27 b(asso)r(ciate)h(a)g(t)n(yp)r(e)g([)-12 b([)12 b FH(A)g FK(])-12 b(])28 b(of)g FG(F)f FK(as)i(follo)n(ws:)251 2138 y(1.)35 b([)-12 b([)12 b FH(a)22 b FK(=)f FH(b)12 b FK(])-12 b(])21 b(=)g FH(S)34 b FK(where)29 b FH(S)35 b FK(is)29 b(an)n(y)i(\014xed)f(t)n(yp)r(e)g(of)g FG(F)g FK(with)f(at)h(least)f(one)h(closed)f(term,)339 2223 y FM(e.g.)39 b FH(S)33 b FK(=)27 b(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)g FK(.)70 b(This)38 b(simply)g(sa)n(ys)j(that)e (equalit)n(y)g(has)h(no)g FM(algorithmic)339 2308 y(c)l(ontent)p FK(.)251 2453 y(2.)35 b([)-12 b([)12 b FH(a)21 b FJ(2)e FH(X)f FK(])-12 b(])20 b(=)f FH(X)33 b FK(\(considered)27 b(as)i(a)f(t)n(yp)r(e)f(v)l(ariable)h(of)g FG(F)p FK(\))251 2598 y(3.)35 b([)-12 b([)12 b FH(A)20 b FJ(\))g FH(B)c FK(])-12 b(])20 b(=)f([)-12 b([)12 b FH(A)g FK(])-12 b(])p FJ(!)q FK([)g([)12 b FH(B)k FK(])-12 b(])251 2744 y(4.)35 b([)-12 b([)12 b FJ(8)p FH(\030)s(:)g(A)g FK(])-12 b(])20 b(=)f([)-12 b([)12 b FJ(9)p FH(\030)s(:)g(A)g FK(])-12 b(])21 b(=)e([)-12 b([)12 b FH(A)g FK(])-12 b(])251 2889 y(5.)35 b([)-12 b([)12 b FJ(8)p FH(X)r(:)g(A)g FK(])-12 b(])19 b(=)h(\005)p FH(X)r(:)12 b FK([)-12 b([)12 b FH(A)g FK(])-12 b(])167 3053 y(As)27 b(w)n(e)h(ha)n(v)n(e)g(said,)g (w)n(e)f(can)h FM(de\014ne)f FK(the)g(other)h(connectiv)n(es,)f(so)h (for)g(example)837 3230 y([)-12 b([)12 b FH(A)k FJ(^)f FH(B)h FK(])-12 b(])20 b(=)f(\005)p FH(X)r(:)12 b FK(\([)-12 b([)12 b FH(A)g FK(])-12 b(])p FJ(!)q FK([)g([)12 b FH(B)k FK(])-12 b(])p FJ(!)q FH(X)6 b FK(\))p FJ(!)p FH(A)167 3407 y FK(where)27 b FH(X)33 b FK(is)27 b(not)h(free)f(in)g FH(A)g FK(or)h FH(B)t FK(.)270 3535 y(Notice)39 b(that)h(the)f(\014rst) h(order)g(v)l(ariables)f FH(\030)s FK(,)44 b FH(\021)s FK(,)e(...)72 b(completely)38 b(disapp)r(ear)i(in)f(the)167 3620 y(translation,)28 b(and)h(so)f(w)n(e)f(ha)n(v)n(e)i([)-12 b([)12 b FH(A)p FK([)p FH(a=\030)s FK(])g(])-12 b(])21 b(=)e([)-12 b([)12 b FH(A)g FK(])-12 b(].)270 3748 y(The)28 b(reader)f(is)g(in)n(vited)g(to)g(v)n(erify)h(that:)810 3925 y([)-12 b([)12 b Fq(Nat)p FK(\()p FH(\030)s FK(\))g(])-12 b(])20 b(=)f(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FK(\()p FH(X)g FJ(!)p FH(X)g FK(\))p FJ(!)p FH(X)26 b FK(=)19 b Fq(Int)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 126 129 bop 167 167 a FK(126)837 b Fz(CHAPTER)26 b(15.)64 b(REPRESENT)-6 b(A)g(TION)26 b(THEOREM)270 404 y FK(Next)21 b(w)n(e)g(ha)n(v)n(e)h(to)f(giv)n(e)g(a)h(similar)c(translation)j(of)h (the)f(deduction)g FH(\016)i FK(of)f(an)f FG(H)-12 b(A)2387 415 y Fb(2)2419 404 y FK(-form)n(ula)167 490 y FH(A)36 b FK(from)g(\(parcels)f(of)5 b(\))37 b(h)n(yp)r(otheses)g FH(A)1241 501 y Fw(i)1297 490 y FK(in)n(to)f(a)h(term)e([)-12 b([)12 b FH(\016)i FK(])-12 b(])37 b(of)g FG(F)p FK(-t)n(yp)r(e)f([)-12 b([)12 b FH(A)g FK(])-12 b(],)39 b(dep)r(ending)167 575 y(on)34 b(free)e(\014rst-order)h FG(F)p FK(-v)l(ariables)g FH(x)1155 586 y Fw(i)1208 575 y FK(of)h(t)n(yp)r(es)f([)-12 b([)12 b FH(A)1579 586 y Fw(i)1611 575 y FK(])-12 b(].)52 b(Moreo)n(v)n(er)34 b(this)e(translation)h(m)n(ust)167 660 y(resp)r(ect)27 b(the)g(con)n(v)n(ersion)h(rules.)251 781 y(1.)35 b(If)28 b FH(\016)i FK(is)d(just)h(the)f(h)n(yp)r(othesis)i FH(A)1209 792 y Fw(i)1256 781 y FK(then)e([)-12 b([)12 b FH(\016)j FK(])-12 b(])20 b(=)f FH(x)1659 792 y Fw(i)1679 781 y FK(.)251 915 y(2.)35 b(The)28 b(axioms)g(are)f(translated)h(in)n (to)f(dumm)n(y)h(terms.)251 1049 y(3.)35 b(The)27 b(rules)f(for)h FJ(!)g FK(are)g(translated)g(in)n(to)g(abstraction)g(and)h(application) e(in)h FG(F)p FK(.)35 b(If)26 b(the)339 1134 y(v)l(ariable)33 b FH(y)i FK(is)d(c)n(hosen)i(to)f(corresp)r(ond)h(to)g(the)e(parcel)g (of)i(h)n(yp)r(otheses)g FH(C)39 b FK(and)34 b FH(\016)h FK(is)339 1219 y(a)c(deduction)g(of)f FH(B)35 b FK(from)30 b(\()p FH(A)1151 1230 y Fw(i)1201 1219 y FK(and\))h FH(C)5 b FK(,)31 b(then)g(when)f(w)n(e)g(add)i FJ(\)I)k FK(the)30 b(translation)339 1304 y(b)r(ecomes)j FH(\025y)s(:)12 b FK([)-12 b([)12 b FH(\016)h FK(])-12 b(].)53 b(Con)n(v)n(ersely)-6 b(,)35 b FM(mo)l(dus)g(p)l(onens)e FK(\()p FJ(\))q(E)6 b FK(\))33 b(applied)g(to)g FH(\016)i FK(pro)n(ving)g FH(C)339 1389 y FK(and)26 b FH(")e FK(pro)n(ving)h FH(C)16 b FJ(!)11 b FH(B)28 b FK(giv)n(es)d([)-12 b([)12 b FH(")g FK(])-12 b(][)g([)12 b FH(\016)j FK(])-12 b(].)35 b(Clearly)-6 b(,)23 b(the)h(con)n(v)n(ersion)h(rule)e(is)h(resp)r(ected.)251 1523 y(4.)35 b FJ(8I)5 b FK(,)23 b FJ(8E)k FK(and)22 b FJ(9I)27 b FK(are)21 b(translated)g(in)n(to)g(nothing,)j(b)r(ecause)d ([)-12 b([)12 b FH(A)p FK([)p FH(a=\030)s FK(])g(])-12 b(])22 b(=)d([)-12 b([)12 b FH(A)g FK(])-12 b(].)34 b(F)-6 b(or)21 b FJ(9E)6 b FK(,)339 1608 y(if)32 b FH(\016)j FK(pro)n(v)n(es)e FJ(9)p FH(\030)s(:)12 b(C)39 b FK(and)33 b FH(")g FK(pro)n(v)n(es)g FH(D)i FK(from)d FH(C)38 b FK(then)33 b(the)f(full)f(pro)r(of)i(translates)g(to)339 1693 y([)-12 b([)12 b FH(")g FK(])-12 b(][[)g([)12 b FH(\016)k FK(])-12 b(])p FH(=y)s FK(],)38 b(where)d FH(y)j FK(corresp)r(onds)f(to)f(the)g(parcel)f FH(C)41 b FK(and)c(again)f(con) n(v)n(ersion)h(is)339 1779 y(resp)r(ected.)251 1912 y(5.)e(Finally)-6 b(,)27 b(for)h FJ(8)742 1887 y FD(2)797 1912 y FK(w)n(e)f(note)h (\014rst)f(that)1022 2090 y([)-12 b([)12 b FH(A)p FK([)p FJ(f)p FH(\030)s(:)g(C)5 b FJ(g)q FH(=X)h FK(])12 b(])-12 b(])20 b(=)f([)-12 b([)12 b FH(A)g FK(])-12 b(][[)g([)12 b FH(C)18 b FK(])-12 b(])q FH(=X)6 b FK(])339 2268 y(and)27 b(so)g(w)n(e)f(ma)n(y)g(translate)g FJ(8)1152 2242 y FD(2)1179 2268 y FJ(I)31 b FK(in)n(to)26 b(\003)p FH(X)r(:)12 b FK([)-12 b([)12 b FH(\016)i FK(])-12 b(])27 b(and)g FJ(8)1842 2242 y FD(2)1869 2268 y FJ(E)32 b FK(in)n(to)26 b([)-12 b([)12 b FH(\016)i FK(])-12 b(][)g([)12 b FH(C)18 b FK(])-12 b(],)27 b(resp)r(ecting)339 2353 y(con)n(v)n(ersion.)167 2552 y Fy(15.2.3)94 b(Represen)m(tation)28 b(of)f(pro)m(v)-5 b(ably)28 b(total)g(functions)167 2682 y FK(In)g FG(H)-12 b(A)368 2693 y Fb(2)400 2682 y FK(,)27 b(the)h(form)n(ula)f Fq(Nat)p FK(\()p Fq(S)998 2657 y Fw(n)1032 2682 y Fq(O)p FK(\))g(admits)g(a)h(\(normal\))f(deduction)k(\025)-37 b FH(n)p FK(,)28 b(namely)786 2827 y([)p Fq(O)20 b FJ(2)f FH(X)6 b FK(])896 2885 y FJ(\001)896 2923 y(\001)896 2961 y(\001)738 3030 y Fq(S)776 3000 y Fw(n)p Fv(\000)p FD(1)873 3030 y Fq(O)20 b FJ(2)f FH(X)1220 2908 y FK([)p FJ(8)p FH(\021)s(:)12 b FK(\()p FH(\021)21 b FJ(2)e FH(X)26 b FJ(\))20 b Fq(S)12 b FH(\021)22 b FJ(2)d FH(X)6 b FK(\)])p 1220 2953 729 4 v 1970 2969 a FJ(8E)1227 3030 y Fq(S)1265 3000 y Fw(n)p Fv(\000)p FD(1)1362 3030 y Fq(O)19 b FJ(2)h FH(X)25 b FJ(\))20 b Fq(S)1709 3000 y Fw(n)1743 3030 y Fq(O)f FJ(2)h FH(X)p 738 3074 1205 4 v 1963 3090 a FJ(\))q(E)1205 3151 y Fq(S)1243 3122 y Fw(n)1276 3151 y Fq(O)f FJ(2)h FH(X)p 804 3196 1072 4 v 1897 3211 a FJ(\)I)804 3272 y(8)p FH(\021)s(:)12 b FK(\()p FH(\021)21 b FJ(2)e FH(X)26 b FJ(\))20 b Fq(S)12 b FH(\021)22 b FJ(2)d FH(X)6 b FK(\))20 b FJ(\))g Fq(S)1643 3243 y Fw(n)1676 3272 y Fq(O)g FJ(2)f FH(X)p 650 3317 1381 4 v 2051 3333 a FJ(\))q(I)650 3393 y Fq(O)g FJ(2)h FH(X)25 b FJ(\))20 b(8)p FH(\021)s(:)12 b FK(\()p FH(\021)21 b FJ(2)e FH(X)25 b FJ(\))20 b Fq(S)12 b FH(\021)23 b FJ(2)c FH(X)6 b FK(\))19 b FJ(\))h Fq(S)1797 3364 y Fw(n)1831 3393 y Fq(O)f FJ(2)h FH(X)p 558 3438 1564 4 v 2143 3454 a FJ(8)2183 3429 y FD(2)2210 3454 y FJ(I)558 3515 y(8)p FH(X)r(:)12 b FK(\()p Fq(O)19 b FJ(2)g FH(X)26 b FJ(\))20 b(8)p FH(\021)s(:)12 b FK(\()p FH(\021)20 b FJ(2)g FH(X)25 b FJ(\))20 b Fq(S)12 b FH(\021)22 b FJ(2)e FH(X)6 b FK(\))19 b FJ(\))h Fq(S)1862 3486 y Fw(n)1895 3515 y Fq(O)g FJ(2)f FH(X)6 b FK(\))167 3655 y(whose)28 b(translation)g(in)n(to)f(system)g FG(F)h FK(is)p 1258 3616 42 3 v 27 w FH(n)p FK(.)270 3808 y(The)g(reader)f(is) g(in)n(vited)g(to)g(pro)n(v)n(e)i(the)e(follo)n(wing:)167 3925 y FG(Lemma)h FK(\025)-37 b FH(n)28 b FK(is)f(the)g(only)h(normal)f (deduction)h(of)g Fq(Nat)p FK(\()p Fq(S)1686 3899 y Fw(n)1720 3925 y Fq(O)p FK(\).)800 b Fu(\003)p eop PStoPSsaved restore %%Page: (130,131) 66 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 127 130 bop 167 167 a Fz(15.2.)65 b(PR)n(OOFS)27 b(INTO)f(PR)n(OGRAMS) 1268 b FK(127)270 404 y(This)40 b(fact)g(is)f(similar)e(to)j FG(??)q FK(,)j(but)e(the)e(pro)r(of)i(is)f(more)f(delicate,)i(b)r (ecause)f(of)g(the)167 490 y(axioms)33 b(\(esp)r(ecially)d(the)i (negativ)n(e)h(one)g FJ(:)23 b Fq(S)12 b FH(\030)26 b FK(=)d Fq(O)p FK(\))32 b(whic)n(h,)h FM(a)g(priori)p FK(,)i(could)d(app)r(ear)i(in)167 575 y(the)29 b(deduction.)42 b(The)30 b(fact)f(that)i Fq(S)12 b FH(a)21 b FK(=)g Fq(O)29 b FK(is)g(not)i(pro)n(v)l(able)f(\()p FM(c)l(onsistency)g FK(of)g FG(H)-12 b(A)2436 586 y Fb(2)2468 575 y FK(\))29 b(m)n(ust)167 660 y(b)r(e)e(exploited.)270 863 y(No)n(w)32 b(let)e FH(A)p FK([)p FH(n;)12 b(m)p FK(])32 b(b)r(e)f(a)h(form)n(ula)f (expressing)g(the)h(fact)f(that)h(an)g(algorithm,)f(if)g(giv)n(en)167 948 y(input)d FH(n)p FK(,)f(terminates)f(with)h(output)i FH(m)20 b FK(=)f FH(f)8 b FK(\()p FH(n)p FK(\).)35 b(Supp)r(ose)29 b(w)n(e)e(ha)n(v)n(e)h(can)g(pro)n(v)n(e)1023 1152 y FJ(8)p FH(n)19 b FJ(2)g FK(I)-12 b(N)p FH(:)12 b FJ(9)p FH(m)20 b FJ(2)g FK(I)-12 b(N)o FH(:)12 b(A)p FK([)p FH(n;)g(m)p FK(])167 1355 y(b)n(y)28 b(means)g(of)g(a)g(deduction)g FH(\016)i FK(in)d FG(H)-12 b(A)1207 1366 y Fb(2)1266 1355 y FK(of)863 1558 y FJ(8)p FH(\030)s(:)12 b FK(\()p Fq(Nat)o FK(\()p FH(\030)s FK(\))20 b FJ(\))g(9)p FH(\021)s(:)12 b FK(\()p Fq(Nat)p FK(\()p FH(\021)s FK(\))j FJ(^)g FH(A)p FK([)p FH(\030)s(;)d(\021)s FK(]\)\))167 1762 y(Then)28 b(w)n(e)f(get)g(a)h(term)f([)-12 b([)12 b FH(\016)i FK(])-12 b(])28 b(of)g(t)n(yp)r(e)545 1965 y([)-12 b([)12 b FJ(8)p FH(\030)s(:)g FK(\()p Fq(Nat)p FK(\()p FH(\030)s FK(\))20 b FJ(\))g(9)p FH(\021)s(:)12 b FK(\()p Fq(Nat)p FK(\()p FH(\021)s FK(\))j FJ(^)g FH(A)p FK([)p FH(\030)s(;)d(\021)s FK(]\)\))g(])-12 b(])20 b(=)f Fq(Int)p FJ(!)p FK(\()p Fq(Int)p FJ(\002)p FK([)-12 b([)12 b FH(A)g FK(])-12 b(]\))167 2168 y(and)35 b(the)f(term)e FH(t)24 b FK(=)g FH(\025x:)12 b(\031)896 2143 y FD(1)924 2168 y FK(\([)-12 b([)12 b FH(\016)i FK(])-12 b(])12 b FH(x)p FK(\))34 b(of)g(t)n(yp)r(e)g Fq(Int)p FJ(!)q Fq(Int)g FK(yields)f(an)h(ob)t (ject)g(that)g(k)n(eeps)g(the)167 2253 y FM(algorithmic)28 b(c)l(ontent)f FK(of)h(the)f(theorem:)1023 2457 y FJ(8)p FH(n)19 b FJ(2)g FK(I)-12 b(N)p FH(:)12 b FJ(9)p FH(m)20 b FJ(2)g FK(I)-12 b(N)o FH(:)12 b(A)p FK([)p FH(n;)g(m)p FK(])167 2660 y(Indeed,)28 b(for)g(an)n(y)h FH(n)19 b FJ(2)h FK(I)-12 b(N,)28 b(the)f(normal)g(form)h(of)g(the)f(deduction) 694 2968 y(\025)-37 b FH(n)702 3009 y FJ(\001)702 3047 y(\001)702 3085 y(\001)570 3147 y Fq(Nat)q FK(\()p Fq(S)742 3118 y Fw(n)775 3147 y Fq(O)p FK(\))1537 2847 y FH(\016)1543 2888 y FJ(\001)1543 2926 y(\001)1543 2964 y(\001)1010 3025 y(8)p FH(\030)s(:)12 b FK(\()p Fq(Nat)p FK(\()p FH(\030)s FK(\))20 b FJ(\))g(9)p FH(\021)s(:)12 b FK(\()p Fq(Nat)o FK(\()p FH(\021)s FK(\))j FJ(^)h FH(A)p FK([)p FH(\030)s(;)c(\021)s FK(]\)\))p 1000 3070 1107 4 v 2127 3086 a FJ(8E)1000 3147 y Fq(Nat)p FK(\()p Fq(S)1171 3118 y Fw(n)1205 3147 y Fq(O)p FK(\))19 b FJ(\))h(9)p FH(\021)s(:)12 b FK(\()p Fq(Nat)o FK(\()p FH(\021)s FK(\))j FJ(^)h FH(A)p FK([)p Fq(S)1909 3118 y Fw(n)1942 3147 y Fq(O)p FH(;)c(\021)s FK(]\))p 570 3192 1537 4 v 2127 3207 a FJ(\))q(E)981 3268 y(9)p FH(\021)s(:)g FK(\()p Fq(Nat)p FK(\()p FH(\021)s FK(\))j FJ(^)g FH(A)p FK([)p Fq(S)1498 3239 y Fw(n)1532 3268 y Fq(O)p FH(;)d(\021)s FK(]\))167 3459 y(m)n(ust)27 b(end)h(with)f(an)h(in)n(tro)r(duction:)1322 3632 y FH(\016)1353 3643 y Fw(n)1344 3683 y FJ(\001)1344 3721 y(\001)1344 3759 y(\001)977 3821 y Fq(Nat)p FK(\()p Fq(S)1148 3792 y Fw(m)1196 3821 y Fq(O)p FK(\))15 b FJ(^)h FH(A)p FK([)p Fq(S)1461 3792 y Fw(n)1494 3821 y Fq(O)p FH(;)c Fq(S)1614 3792 y Fw(m)1661 3821 y Fq(O)p FK(])p 977 3866 754 4 v 1752 3882 a FJ(9I)997 3942 y(9)p FH(\021)s(:)g FK(\()p Fq(Nat)o FK(\()p FH(\021)s FK(\))j FJ(^)h FH(A)p FK([)p Fq(S)1514 3913 y Fw(n)1547 3942 y Fq(O)p FH(;)c(\021)s FK(]\))p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 128 131 bop 167 167 a FK(128)837 b Fz(CHAPTER)26 b(15.)64 b(REPRESENT)-6 b(A)g(TION)26 b(THEOREM)167 404 y FK(No)n(w,)33 b(applying)g FJ(^)p FK(1)p FJ(E)39 b FK(to)33 b FH(\016)926 415 y Fw(n)958 404 y FK(,)h(w)n(e)d(get)h(a)h(deduction)f(of)h Fq(Nat)p FK(\()p Fq(S)1898 379 y Fw(m)1945 404 y Fq(O)p FK(\))f(whose)h(translation)f(is)167 490 y(\(equiv)l(alen)n(t)i(to\))h FH(t)p 693 451 42 3 v 12 w(n)p FK(.)56 b(By)35 b(the)g(lemma,)g(this)f (deduction)h(normalises)e(to)48 b(\025)-47 b FH(m)q FK(,)36 b(and)g(so)f FH(t)p 2631 451 V 12 w(n)167 575 y FK(normalises)21 b(to)p 587 536 61 3 v 22 w FH(m)q FK(.)33 b(But)22 b FH(A)p FK([)p Fq(S)945 549 y Fw(n)979 575 y Fq(O)p FH(;)12 b Fq(S)1099 549 y Fw(m)1146 575 y Fq(O)p FK(])22 b(is)f(pro)n(v)l(able) i(in)f FG(H)-12 b(A)1771 586 y Fb(2)1803 575 y FK(,)23 b(so)g(it)e(is)g(true)h(in)g(the)f(standard)167 660 y(mo)r(del,)26 b(whic)n(h)f(means)h(that)h FH(m)20 b FK(=)f FH(f)8 b FK(\()p FH(n)p FK(\).)34 b(So)27 b(w)n(e)f(ha)n(v)n(e)h(pro)n(v)n(ed)h (that)e FH(f)34 b FK(is)26 b(represen)n(table)f(in)167 745 y(system)i FG(F)p FK(.)270 946 y(Unfortunately)52 b(our)g(pro)r(of)g(is)f(erroneous:)83 b(it)50 b(is)h(imp)r(ossible)e (to)j(in)n(terpret)d(the)167 1031 y(axiom)i FJ(:)36 b Fq(S)12 b FH(\030)40 b FK(=)35 b Fq(O)51 b FK(in)f FG(??)q FK(,)57 b(simply)50 b(b)r(ecause)h(there)f(is)g(no)i(closed)e(term)g (of)h(t)n(yp)r(e)167 1116 y([)-12 b([)12 b FJ(:)20 b Fq(S)12 b FH(\030)23 b FK(=)c Fq(O)12 b FK(])-12 b(])20 b(=)f FH(S)t FJ(!)q Fq(Emp)p FK(.)270 1256 y(Ev)n(erything)39 b(w)n(orks)h(p)r(erfectly)d(if)g(w)n(e)i(add)g(to)g(system)f FG(F)h FK(a)g(junk)g(term)f(\012)g(of)h(t)n(yp)r(e)167 1342 y Fq(Emp)34 b FK(=)f(\005)p FH(X)r(:)12 b(X)6 b FK(,)52 b(in)n(terpreting)47 b(the)g(problematic)f(axiom)i(b)n(y)g FH(\025x)2074 1316 y Fw(S)2111 1342 y FH(:)12 b FK(\012)47 b(\(the)g(seman)n(tic)167 1427 y(analogue)29 b(of)g(\012)e(is)h Fn(?)p FK(\).)36 b(This)27 b(junk)i(term)e(disapp)r(ears)h(in)g(the)f (normalisation)h(of)g FH(t)p 2438 1388 42 3 v 12 w(n)p FK(,)g(since)167 1512 y(w)n(e)c(pro)n(v)n(ed)h(that)f(the)g(result)f (is)g(an)p 1125 1473 61 3 v 25 w FH(m)p FK(,)i(but)g(this)e(is)h(not)g (v)n(ery)h(b)r(eautiful:)32 b(it)23 b(w)n(ould)i(b)r(e)f(nicer)167 1597 y(to)30 b(remain)f(in)g(pure)h(system)g FG(F)p FK(.)42 b(W)-6 b(e)30 b(shall)f(see)g(that)h(it)f(is)h(indeed)f(p)r(ossible)g (to)h(eliminate)167 1682 y(junk)f(from)e FH(t)p FK(.)167 1903 y Fy(15.2.4)94 b(Pro)s(of)26 b(without)h(unde\014ned)g(ob)5 b(jects)167 2041 y FK(Instead)34 b(of)f(adding)h(this)e(junk)i(term,)f (w)n(e)g(can)g(in)n(terpret)f(it)f(in)n(to)i(pure)g(system)g FG(F)p FK(,)h(b)n(y)g(a)167 2126 y FM(c)l(o)l(ding)26 b FK(whic)n(h)f(maps)h(ev)n(ery)f(t)n(yp)r(e)g(to)h(an)g(inhabited)f (one)h(while)d(preserving)j(normalisation.)167 2327 y FG(Prop)r(osition)34 b FK(F)-6 b(or)38 b(an)n(y)g(\(closed\))e(term)f FH(t)i FK(of)g(t)n(yp)r(e)g Fq(Int)p FJ(!)q Fq(Int)g FK(in)f(system)g FG(F)h FK(with)f(junk,)167 2412 y(there)24 b(is)g(a)h(\(closed\))f(term)g FH(t)926 2386 y Fv(0)967 2412 y FK(of)h(pure)g(system)g FG(F)f FK(suc)n(h)i(that,)g(if)e FH(t)p 1942 2373 42 3 v 12 w(n)g FK(normalises)g(to)p 2433 2373 61 3 v 25 w FH(m)q FK(,)h(then)167 2497 y FH(t)192 2471 y Fv(0)p 220 2458 42 3 v 220 2497 a FH(n)j FK(normalises)e(to)p 720 2458 61 3 v 28 w FH(m)q FK(.)270 2637 y(In)33 b(particular,)g(if)f FH(t)g FK(represen)n(ts)g(a)h(function)g FH(f)8 b FK(,)33 b(so)g(do)r(es)g FH(t)1903 2612 y Fv(0)1920 2637 y FK(,)h(and)f(the)g (represen)n(tation)167 2722 y(theorem)27 b(is)g(\(correctly\))e(pro)n (v)n(ed.)167 2923 y FG(Pro)r(of)j FK(By)g(induction,)f(w)n(e)g (de\014ne:)270 3104 y FJ(\017)34 b(h)-12 b(h)p FH(X)6 b FJ(i)-12 b(i)22 b FK(=)d FH(X)270 3259 y FJ(\017)34 b(h)-12 b(h)p FH(U)7 b FJ(!)r FH(V)16 b FJ(i)-12 b(i)20 b FK(=)f FJ(h)-12 b(h)p FH(U)7 b FJ(i)-12 b(i!)s(h)g(h)p FH(V)17 b FJ(i)-12 b(i)270 3415 y(\017)34 b(h)-12 b(h)p FK(\005)p FH(X)r(:)12 b(V)17 b FJ(i)-12 b(i)20 b FK(=)f(\005)p FH(X)r(:)12 b(X)6 b FJ(!h)-12 b(h)p FH(V)17 b FJ(i)-12 b(i)167 3595 y FK(so)28 b(that:)992 3796 y FJ(h)-12 b(h)p FH(T)10 b FK([)p FH(U)t(=X)c FK(])p FJ(i)-12 b(i)22 b FK(=)d FJ(h)-12 b(h)p FH(T)10 b FJ(i)-12 b(i)p FK([)p FJ(h)g(h)p FH(U)7 b FJ(i)-12 b(i)5 b FH(=X)h FK(])p eop PStoPSsaved restore %%Page: (132,133) 67 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 129 132 bop 167 167 a Fz(15.2.)65 b(PR)n(OOFS)27 b(INTO)f(PR)n(OGRAMS) 1268 b FK(129)270 404 y(If)32 b FH(T)41 b FK(is)30 b(a)i(t)n(yp)r(e)f (with)f(free)h(v)l(ariables)g FH(X)1392 415 y FD(1)1420 404 y FH(;)12 b(:)g(:)g(:)f(;)h(X)1631 415 y Fw(p)1691 404 y FK(w)n(e)30 b(de\014ne)i(inductiv)n(ely)d(a)j(term)e FH(\023)2633 415 y Fw(T)167 490 y FK(of)e(t)n(yp)r(e)g FJ(h)-12 b(h)p FH(T)10 b FJ(i)-12 b(i)30 b FK(with)c(free)h(\014rst)h (order)g(v)l(ariables)f FH(x)1533 501 y FD(1)1561 490 y FH(;)12 b(:)g(:)g(:)g(;)g(x)1755 501 y Fw(p)1810 490 y FK(of)28 b(t)n(yp)r(es)g FH(X)2137 501 y FD(1)2166 490 y FH(;)12 b(:)g(:)g(:)f(;)h(X)2377 501 y Fw(p)2405 490 y FK(:)270 658 y FJ(\017)34 b FH(\023)363 669 y Fw(X)431 658 y FK(=)19 b FH(x)543 633 y Fw(X)270 807 y FJ(\017)34 b FH(\023)363 818 y Fw(U)5 b Fv(!)p Fw(V)515 807 y FK(=)19 b FH(\025y)665 781 y Fv(h)-8 b(h)p Fw(U)5 b Fv(i)-8 b(i)767 807 y FH(:)12 b(\023)822 818 y Fw(V)893 807 y FK(\(note)28 b(that)g FH(y)i FK(do)r(es)e(not)g(o)r(ccur)g(in)f FH(\023)1883 818 y Fw(V)1926 807 y FK(\))270 955 y FJ(\017)34 b FH(\023)363 966 y FD(\005)p Fw(X)q(:)9 b(V)528 955 y FK(=)19 b(\003)p FH(X)r(:)12 b(\025x)818 930 y Fw(X)866 955 y FH(:)g(\023)921 966 y Fw(V)992 955 y FK(\(where)26 b FH(x)i FM(may)35 b FK(o)r(ccur)27 b(in)h FH(\023)1748 966 y Fw(V)1791 955 y FK(\))167 1124 y(In)g(particular,)f(if)f FH(T)38 b FK(is)27 b(closed,)g FJ(h)-12 b(h)p FH(T)10 b FJ(i)-12 b(i)30 b FK(is)d(inhabited)g(b)n(y)h(the)g(closed)f(term)f FH(\023)2220 1135 y Fw(T)2259 1124 y FK(,)i(for)g(instance)611 1308 y FJ(h)-12 b(h)p FK(\005)p FH(X)r(:)12 b(X)6 b FJ(i)-12 b(i)21 b FK(=)e(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)84 b FK(and)79 b FH(\023)1623 1319 y FD(\005)p Fw(X)q(:)9 b(X)1792 1308 y FK(=)20 b(\003)p FH(X)r(:)12 b(\025x)2083 1282 y Fw(X)2130 1308 y FH(:)g(x)270 1589 y FK(If)30 b FH(t)g FK(is)f(term)f(of)i(t)n(yp)r(e)g FH(T)40 b FK(with)29 b(free)g(t)n(yp)r(e)g(v)l(ariables)h FH(X)1789 1600 y FD(1)1817 1589 y FH(;)12 b(:)g(:)g(:)g(;)g(X)2029 1600 y Fw(p)2087 1589 y FK(and)30 b(free)f(\014rst)h(order)167 1674 y(v)l(ariables)e FH(y)492 1685 y FD(1)520 1674 y FH(;)12 b(:)g(:)g(:)f(;)h(y)708 1685 y Fw(q)763 1674 y FK(of)30 b(t)n(yp)r(es)e FH(U)1082 1685 y FD(1)1110 1674 y FH(;)12 b(:)g(:)g(:)g(;)g(U)1312 1685 y Fw(q)1367 1674 y FK(w)n(e)28 b(de\014ne)h(inductiv)n(ely)e(a)i(term)e FJ(h)-12 b(h)p FH(t)p FJ(i)g(i)31 b FK(\(without)167 1760 y(junk\))24 b(of)f(t)n(yp)r(e)g FJ(h)-12 b(h)p FH(T)10 b FJ(i)-12 b(i)25 b FK(with)d(free)g(t)n(yp)r(e)i(v)l(ariables)e FH(X)1530 1771 y FD(1)1558 1760 y FH(;)12 b(:)g(:)g(:)g(;)g(X)1770 1771 y Fw(p)1821 1760 y FK(and)24 b(free)e(\014rst)h(order)g(v)l (ariables)167 1845 y FH(x)206 1856 y FD(1)234 1845 y FH(;)12 b(:)g(:)g(:)g(;)g(x)428 1856 y Fw(p)456 1845 y FH(;)g(y)521 1856 y FD(1)548 1845 y FH(;)g(:)g(:)g(:)g(;)g(y)737 1856 y Fw(q)791 1845 y FK(of)28 b(t)n(yp)r(es)g FH(X)1118 1856 y FD(1)1146 1845 y FH(;)12 b(:)g(:)g(:)g(;)g(X)1358 1856 y Fw(p)1386 1845 y FH(;)g FJ(h)-12 b(h)p FH(U)1506 1856 y FD(1)1534 1845 y FJ(i)g(i)p FH(;)12 b(:)g(:)g(:)h(;)f FJ(h)-12 b(h)p FH(U)1821 1856 y Fw(q)1849 1845 y FJ(i)g(i)p FK(:)270 2013 y FJ(\017)34 b(h)-12 b(h)p FH(y)418 1988 y Fw(T)458 2013 y FJ(i)g(i)20 b FK(=)f FH(y)630 1988 y Fv(h)-8 b(h)p Fw(T)7 b Fv(i)-8 b(i)270 2162 y FJ(\017)34 b(h)-12 b(h)p FH(\025y)458 2136 y Fw(U)501 2162 y FH(:)12 b(v)s FJ(i)-12 b(i)20 b FK(=)f FH(\025y)780 2136 y Fv(h)-8 b(h)p Fw(U)5 b Fv(i)-8 b(i)882 2162 y FH(:)12 b FJ(h)-12 b(h)p FH(v)s FJ(i)g(i)270 2310 y(\017)34 b(h)-12 b(h)p FH(t)12 b(u)p FJ(i)-12 b(i)22 b FK(=)d FJ(h)-12 b(h)p FH(t)p FJ(i)g(i)12 b(h)-12 b(h)p FH(u)p FJ(i)g(i)270 2459 y(\017)34 b(h)-12 b(h)p FK(\003)p FH(X)r(:)12 b(v)s FJ(i)-12 b(i)22 b FK(=)d(\003)p FH(X)r(:)12 b(\025x)909 2433 y Fw(X)957 2459 y FH(:)g FJ(h)-12 b(h)p FH(v)s FJ(i)g(i)29 b FK(\(note)f(that)g FH(x)g FK(ma)n(y)g(o)r(ccur)f(in)g FJ(h)-12 b(h)p FH(v)s FJ(i)g(i)p FK(\))270 2607 y FJ(\017)34 b(h)-12 b(h)p FH(t)12 b(U)7 b FJ(i)-12 b(i)22 b FK(=)d FJ(h)-12 b(h)p FH(t)p FJ(i)g(i)12 b(h)-12 b(h)p FH(U)7 b FJ(i)-12 b(i)12 b FH(\023)904 2618 y Fw(U)270 2755 y FJ(\017)34 b(h)-12 b(h)p FK(\012)p FJ(i)g(i)22 b FK(=)d FH(\023)592 2766 y Fp(Emp)710 2755 y FK(=)g(\003)p FH(X)r(:)12 b(\025x)1000 2730 y Fw(X)1048 2755 y FH(:)g(x)167 2924 y FK(Again)28 b(the)f(reader)g(can)h(c)n(hec)n(k)g(the)f(follo)n(wing)g (prop)r(erties)836 3104 y FJ(h)-12 b(h)p FH(t)p FK([)p FH(u=y)1032 3078 y Fw(U)1075 3104 y FK(])p FJ(i)g(i)60 b FK(=)e FJ(h)-12 b(h)p FH(t)p FJ(i)g(i)p FK([)p FJ(h)g(h)p FH(u)p FJ(i)g(i)t FH(=y)1634 3078 y Fv(h)k(h)p Fw(U)5 b Fv(i)-8 b(i)1737 3104 y FK(])940 3275 y FH(\023)964 3286 y Fw(T)7 b FD([)p Fw(U)r(=X)t FD(])1196 3275 y FK(=)58 b FH(\023)1332 3286 y Fw(T)1371 3275 y FK([)p FJ(h)-12 b(h)p FH(U)7 b FJ(i)-12 b(i)s FH(=X)6 b FK(][)p FH(\023)1690 3286 y Fw(U)1732 3275 y FH(=x)1805 3249 y Fv(h)-8 b(h)p Fw(U)5 b Fv(i)-8 b(i)1909 3275 y FK(])840 3446 y FJ(h)c(h)p FH(t)p FK([)p FH(U)t(=X)6 b FK(])p FJ(i)-12 b(i)61 b FK(=)d FJ(h)-12 b(h)p FH(t)p FJ(i)g(i)p FK([)p FJ(h)g(h)p FH(U)7 b FJ(i)-12 b(i)t FH(=X)6 b FK(][)p FH(\023)1737 3457 y Fw(U)1780 3446 y FH(=x)1853 3421 y Fv(h)-8 b(h)p Fw(U)5 b Fv(i)-8 b(i)1956 3446 y FK(])167 3626 y(whic)n(h)27 b(are)g(needed)h(for)g(the)f(preserv)l(ation)h(of)g(con)n(v)n(ersions:) 1017 3810 y(if)f FH(t)20 b Fu( )g FH(u)28 b FK(then)f FJ(h)-12 b(h)p FH(t)p FJ(i)g(i)22 b Fu( )e FJ(h)-12 b(h)p FH(u)p FJ(i)g(i)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 130 133 bop 167 167 a FK(130)837 b Fz(CHAPTER)26 b(15.)64 b(REPRESENT)-6 b(A)g(TION)26 b(THEOREM)270 404 y FK(No)n(w)i(w)n(e)f (see)g(that)830 558 y FJ(h)-12 b(h)p Fq(Int)q FJ(i)g(i)60 b FK(=)e(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)g FJ(!)p FK(\()p FH(X)g FJ(!)p FH(X)g FK(\))p FJ(!)p FH(X)868 728 y FJ(h)-12 b(h)p 910 689 42 3 v FH(n)q FJ(i)g(i)60 b FK(=)e(\003)p FH(X)r(:)12 b(\025x)1383 703 y Fw(X)1431 728 y FH(:)g(\025y)1539 703 y Fw(X)1586 728 y FH(:)g(\025z)1692 703 y Fw(X)t Fv(!)p Fw(X)1834 728 y FH(:)g(z)1900 703 y Fw(n)1945 728 y FH(y)503 988 y Fq(w)n(eak)n(en)p 721 950 V 12 w FH(n)20 b Fu( )g FJ(h)-12 b(h)p 914 950 V FH(n)q FJ(i)g(i)337 b FK(and)g Fq(contract)12 b FJ(h)-12 b(h)p 2073 950 V FH(n)q FJ(i)g(i)21 b Fu( )p 2268 950 V 20 w FH(n)167 1162 y FK(Finally)-6 b(,)27 b(a)h(term)e FH(t)i FK(of)g(t)n(yp)r(e)g Fq(Int)p FJ(!)p Fq(Int)g FK(with)e(junk)j(can)f(b)r(e)g(replaced)e(b)n(y)901 1335 y FH(t)926 1309 y Fv(0)962 1335 y FK(=)19 b FH(\025z)1110 1309 y Fp(Int)1171 1335 y FH(:)12 b Fq(contract)p FK(\()p FJ(h)-12 b(h)p FH(t)p FJ(i)g(i)p FK(\()p Fq(w)n(eak)n(en)14 b FH(z)s FK(\)\))167 1508 y(without)27 b(junk.)2037 b Fu(\003)p eop PStoPSsaved restore %%Page: (134,135) 68 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 131 134 bop 167 875 a FF(App)5 b(endix)28 b(A)167 1169 y(Seman)-5 b(tics)28 b(of)g(System)f(F)167 1377 y FI(b)m(y)h(P)m(aul)f (T)-10 b(a)m(ylor)167 1698 y FK(In)35 b(this)f(app)r(endix)h(w)n(e)f (shall)g(giv)n(e)g(a)h(seman)n(tics)f(for)h(system)f FG(F)g FK(in)g(terms)g(of)h(coherence)167 1783 y(spaces.)g(In)23 b(particular)g(w)n(e)g(shall)f(in)n(terpret)g(univ)n(ersal)h (abstraction)h(b)n(y)g(means)g(of)g(a)g(kind)g(of)167 1868 y(\\trace",)f(sho)n(wing)e(that)g(the)g(primary)f(and)i(secondary) g(equations)f(hold.)34 b(W)-6 b(e)20 b(shall)g(examine)167 1954 y(the)26 b(w)n(a)n(y)h(in)f(whic)n(h)f(its)h(terms)f(are)h (\\uniform")h(o)n(v)n(er)g(all)e(t)n(yp)r(es.)35 b(Finally)25 b(w)n(e)h(shall)g(attempt)167 2039 y(to)42 b(calculate)f(some)h(univ)n (ersal)g(t)n(yp)r(es)g(suc)n(h)h(as)g Fq(Emp)30 b FK(=)f(\005)p FH(X)r(:)12 b(X)6 b FK(,)45 b Fq(Sgl)30 b FK(=)g(\005)p FH(X)r(:)12 b(X)25 b FJ(!)20 b FH(X)6 b FK(,)167 2124 y Fq(Bo)r(ol)19 b FK(=)h(\005)p FH(X)r(:)12 b(X)21 b FJ(!)16 b FH(X)21 b FJ(!)16 b FH(X)34 b FK(and)28 b Fq(Int)20 b FK(=)f(\005)p FH(X)r(:)12 b(X)21 b FJ(!)16 b FK(\()p FH(X)21 b FJ(!)c FH(X)6 b FK(\))15 b FJ(!)h FH(X)6 b FK(.)167 2363 y FE(A.1)114 b(T)-10 b(erms)27 b(of)h(univ)m(ersal)g(t)m (yp)s(e)167 2539 y Fy(A.1.1)95 b(Finite)28 b(appro)m(ximation)167 2671 y FK(W)-6 b(e)34 b(ha)n(v)n(e)i(already)e(said)h(in)f(section)f FG(??)i FK(that)g(a)g(term)e(\003)p FH(X)r(:)12 b(t)34 b FK(of)h(univ)n(ersal)f(t)n(yp)r(e)h(\005)p FH(X)r(:)12 b(T)167 2757 y FK(is)29 b(in)n(tended)g(to)h(b)r(e)g(a)g(function)g (whic)n(h)f(assigns)h(to)g(an)n(y)h(t)n(yp)r(e)f FH(U)37 b FK(a)30 b(term)e FH(t)p FK([)p FH(U)t(=X)6 b FK(])30 b(of)g(t)n(yp)r(e)167 2842 y FH(T)10 b FK([)p FH(U)t(=X)c FK(].)35 b(In)26 b(particular,)g(the)g(in)n(terpretation)f(of)h(\003)p FH(X)r(:)12 b(\025x:)g(x)27 b FK(is)e(to)i(b)r(e)f(the)g(function)g (whic)n(h)167 2927 y(assigns)j(to)f(an)n(y)g(coherence)f(space)h FJ(A)g FK(\(the)f(trace)g(of)5 b(\))28 b(the)f(iden)n(tit)n(y)g (function,)h FM(i.e.)995 3106 y FJ(I)-7 b FH(d)1062 3080 y Fv(A)1125 3106 y FK(=)20 b FJ(f)p FK(\()p FJ(f)p FH(\013)p FJ(g)p FH(;)12 b(\013)p FK(\))20 b(:)39 b FH(\013)20 b FJ(2)g(jAjg)167 3285 y FK(But)34 b(w)n(e)g(ha)n(v)n(e)h(a)f(problem)g (of)g FM(size)p FK(:)49 b(there)33 b(is)g(a)i(prop)r(er)f(class)g(of)h (coherence)e(spaces,)j(so)167 3370 y(ho)n(w)28 b(can)g(this)f(b)r(e)h (a)g(legitimate)c(function?)270 3499 y(W)-6 b(e)42 b(can)h(solv)n(e)f (this)g(problem)g(in)f(the)h(same)g(w)n(a)n(y)i(as)e(w)n(e)g(did)g(for) h(functions,)j(b)n(y)167 3584 y(requiring)30 b(that)i(ev)n(ery)f (domain)h(b)r(e)f(expressible)f(as)i(a)g(\\limit")d(of)j(\014nite)e (domains.)47 b(Then)167 3669 y(b)n(y)29 b(con)n(tin)n(uit)n(y)e(w)n(e)h (can)g(deriv)n(e)f(the)g(v)l(alue)h(of)h(a)f(univ)n(ersal)g(term)e(at)i (an)h(arbitrary)f(domain)167 3754 y(from)38 b(its)f(v)l(alues)h(at)g (\014nite)f(domains.)67 b(Since)37 b(there)g(are)h(only)g(coun)n(tably) h(man)n(y)g(\014nite)167 3840 y(domains)c(up)h(to)f(isomorphism,)i(the) d(function)i(is)e(de\014ned)i(b)n(y)f(a)h FM(set)f FK(|)g(so)g(long)h (as)g(w)n(e)167 3925 y(ensure)28 b(that)g(its)e(v)l(alues)i(at)g (isomorphic)f(domains)h(are)f(equal)h(\(along)g(the)g(isomorphisms\).) 1368 4101 y(131)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 132 135 bop 167 167 a FK(132)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)167 404 y Fy(A.1.2)95 b(Saturated)28 b(domains)167 545 y FK(There)22 b(is)g(a)i(common)e(but) i(misleading)d(alternativ)n(e)h(solution.)33 b(W)-6 b(e)23 b(c)n(ho)r(ose)h(a)f(\\big")h(domain)167 630 y(\012)29 b(whic)n(h)g(is)g(saturated)h(under)g(all)e(the)h(relev)l(an)n(t)g(op)r (erations)h(on)g(t)n(yp)r(es,)h(and)f(restrict)e(our)167 715 y(notion)37 b(of)h(domain)f FJ(A)g FK(to)g(\\sub)r(domains")j(of)d (\012.)63 b(Th)n(us)38 b(for)f(instance)g(if)f FJ(A)h FK(is)f(suc)n(h)i(a)167 801 y(sub)r(domain)d(then)f(w)n(e)f(require)f FJ(A)18 b(!)g(A)34 b FK(to)g(b)r(e)f(one)i(also;)i(in)c(particular)g (\012)17 b FJ(!)h FK(\012)33 b(is)h(one.)167 886 y(Then)26 b(the)g(iden)n(tit)n(y)-6 b(,)25 b(b)r(eing)h(an)g(elemen)n(t)e(of)i (\012)13 b FJ(!)h FK(\012,)26 b(whic)n(h)f(is)g(iden)n(ti\014ed)g(with) g(a)h(subspace)167 971 y(of)32 b(\012,)h(is)e(an)i(elemen)n(t)c(of)k (\012.)47 b(Scott's)33 b FJ(P)-6 b FH(!)34 b FK(mo)r(del)d([)p FG(?)p FK(])h(is)f(a)h(w)n(ell-kno)n(wn)f(example)g(of)i(this)167 1056 y(approac)n(h,)38 b(and)d([)p FG(?)q FK(])f(examined)g(this)g(in)f (detail)g(as)i(a)f(notion)h(of)g(mo)r(del)e(of)i(the)f(un)n(t)n(yp)r (ed)167 1141 y(lam)n(b)r(da)28 b(calculus)656 1115 y FD(1)683 1141 y FK(.)270 1287 y(Ho)n(w)n(ev)n(er,)h(b)r(esides)g(the)f (fact)h(that)g(not)h(all)d(domains)j(are)e(represen)n(ted,)h(this)f (approac)n(h)167 1373 y(has)h(sev)n(eral)e(pitfalls.)270 1537 y FJ(\017)34 b FK(Whereas)f(in)g(set)f(theory)i(the)e(notions)i (of)g(elemen)n(t)c(and)k(t)n(yp)r(e)f(are)g(confused,)j(here)339 1622 y(w)n(e)c(ha)n(v)n(e)i(to)f(distinguish)f(b)r(et)n(w)n(een)f(\012) i(as)g(the)f(\\univ)n(erse)h(of)g(elemen)n(ts")e(and)i(some)339 1707 y(domain)i FJ(V)40 b FK(whose)34 b(elemen)n(ts)e(ma)n(y)i(serv)n (e)g(as)h(names)f(of)h(t)n(yp)r(es)f(|)g(a)g(\\univ)n(erse)h(of)339 1792 y(t)n(yp)r(es".)270 1952 y FJ(\017)f FK(It)e(is)f(not)h(go)r(o)r (d)h(enough)h(to)e(construct)f(suc)n(h)i(a)f FJ(V)37 b FK(with)31 b(the)h(prop)r(ert)n(y)g(that)g(ev)n(ery)339 2038 y(domain)25 b(b)r(e)g(named)g(b)n(y)h(a)f(p)r(oin)n(t)g(of)g FJ(V)6 b FK(:)34 b(this)24 b(is)g(lik)n(e)f(the)i(\\b)n(y)h(v)l(alues") f(in)n(terpretation)339 2123 y(of)31 b(recursiv)n(e)d(functions.)42 b(W)-6 b(e)29 b(need)h(that)g(ev)n(ery)f FM(variable)g FK(domain)h(b)r(e)f(named)h(b)n(y)h(a)339 2208 y(term)i(\(with)g(the)g (same)h(free)f(v)l(ariables\))h(of)g(t)n(yp)r(e)g FJ(V)6 b FK(.)54 b(The)34 b(ob)n(vious)h(c)n(hoice)e(is)g(the)339 2293 y FM(c)l(ate)l(gory)28 b FK(of)g(domains)g(and)g(em)n(b)r (eddings,)f(but)h(this)e(is)h(not)h(one)f(of)h(our)g(domains.)35 b(It)339 2378 y(is,)e(ho)n(w)n(ev)n(er,)g(p)r(ossible)f(to)g(\\co)n(v)n (er")h(it)e(with)g(a)h(domain,)i(although)f(the)f(tec)n(hniques)339 2463 y(required)25 b(for)h(this,)g(whic)n(h)f(are)h(set)f(out)h(in)g([) p FG(?)p FK(],)h FJ(x)p FK(5.6,)g(are)f(m)n(uc)n(h)f(more)h(di\016cult) e(than)339 2548 y(the)k(construction)f(of)i(\012.)270 2709 y FJ(\017)34 b FK(Isomorphic)24 b(t)n(yp)r(es)g(ma)n(y)g(b)r(e)g (represen)n(ted)f(b)n(y)h(di\013eren)n(t)f(elemen)n(ts)f(of)i FJ(V)6 b FK(,)25 b(and)g(there)e(is)339 2794 y(nothing)29 b(to)g(force)e(the)h(v)l(alues)g(of)h(univ)n(ersal)e(terms)g(at)h(suc)n (h)h(elemen)n(ts)d(to)i(b)r(e)g(equal.)339 2879 y(This)i(means)h(that)g (the)f(condition)g(at)g(the)h(end)f(of)h FG(??)g FK(for)g(\014nite)f (appro)n(ximation)h(is)339 2964 y(violated,)39 b(there)d(are)h(far)h (more)e(p)r(oin)n(ts)h(of)h(univ)n(ersal)e(t)n(yp)r(es)h(than)h (corresp)r(onding)339 3049 y(terms)22 b(in)g(the)h(syn)n(tax,)i(and)f (the)e(in)n(terpretation)g(of)h(simple)e(terms)g(suc)n(h)j(as)f(\003)p FH(X)r(:)12 b(\025x:)g(x)339 3134 y FK(is)27 b(v)n(ery)h(uneconomical.) 270 3295 y FJ(\017)34 b FK(It)49 b(is)e(p)r(ossible)h(to)h(mo)r(del)f (system)g FG(F)p FK(,)g(and)i(more)e(generally)f(the)i(Theory)g(of)339 3380 y(Constructions,)28 b(using)g(the)f(category)h(of)g(em)n(b)r (eddings)f(for)h FJ(V)6 b FK(,)27 b(as)h(has)g(b)r(een)g(done)g(in)339 3465 y([)p FG(?)q FK(])e(and)h([)p FG(?)q FK(],)f(but)g(Jung)i(has)f (sho)n(wn)g(that)f(this)f(is)h(not)g(p)r(ossible)f(for)i(all)d (categories)i(of)339 3550 y(domains)i(in)g(curren)n(t)f(use.)167 3714 y(What)h(really)e(fails)h(in)g(the)g(third)g(remark)h(is)f(the)g (\\uniformit)n(y")h(of)g(terms)e(o)n(v)n(er)i(all)f(t)n(yp)r(es.)p 167 3790 1003 3 v 246 3833 a FC(1)273 3854 y FB(As)h(an)h(exercise,)g (the)f(reader)g(is)g(in)n(vited)f(to)i(construct)f(a)h(coun)n(table)e (coherence)i(space)g(in)n(to)f(whic)n(h)167 3925 y(an)n(y)g(other)f (can)h(b)r(e)f(rigidly)e(em)n(b)r(edded)i(\()p Ft(??)o FB(\).)p eop PStoPSsaved restore %%Page: (136,137) 69 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 133 136 bop 167 167 a Fz(A.1.)63 b(TERMS)28 b(OF)f(UNIVERSAL)g(TYPE) 1177 b FK(133)167 404 y Fy(A.1.3)95 b(Uniformit)m(y)167 582 y FK(It)35 b(is)f(as)i(a)g(result)e(of)h(\\uniformit)n(y")g(that)h (the)f(mo)r(del)f(w)n(e)h(presen)n(t)g(has)h(its)e(remark)l(ably)167 667 y(economical)23 b(form.)35 b(W)-6 b(e)25 b(shall)f(ha)n(v)n(e)i(to) f(treat)g(this)f(in)h(detail)e(relativ)n(e)g(to)j(\\subspaces",)i(but) 167 752 y(\014rst)c(consider)g(the)f(consequences)i(of)f(requiring)g(a) g(construction)g(on)h(a)f(t)n(yp)r(e)g(to)h(b)r(e)e(uniform)167 837 y(with)j(resp)r(ect)h(to)g(all)f(isomorphisms)h(of)h(the)f(t)n(yp)r (e)g FM(with)g(itself)p FK(,)h FM(i.e.)f(p)l(ermutations)p FK(.)36 b(T)-6 b(aking)167 922 y(common)25 b(geometrical)f(notions,)j (the)e(construction)h(m)n(ust)f(b)r(e)h(the)f(cen)n(tre)g(of)h(a)g (sphere,)g(the)167 1007 y(axis)35 b(of)g(a)g(cone,)h(and)f(so)h(on.)56 b(A)34 b(subgroup)j(of)e(a)g(group)h(whic)n(h)d(is)h(\(set)n(wise\))f (in)n(v)l(arian)n(t)167 1092 y(under)40 b(automorphisms)g(is)f(called)f FM(char)l(acteristic)p FK(.)72 b(The)40 b(more)f(automorphisms)h(there) 167 1178 y(are,)32 b(the)e(more)g(highly)h(constrained)g(a)g (\\uniform")g(construction)g(has)g(to)g(b)r(e.)45 b(Generally)-6 b(,)167 1263 y(something)32 b(is)g(uniform)g(if)g(it)g(is)g(\\p)r (eculiar")g(|)g(describ)r(ed)g(b)n(y)h(some)f(prop)r(ert)n(y)h(whic)n (h)f(it)167 1348 y(alone)26 b(satis\014es.)35 b(In)26 b(our)h(case)f(w)n(e)f(w)n(an)n(t)i(it)e(to)h(b)r(e)g FM(de\014nable)e FK(b)n(y)j(a)g(term)d(of)j(the)f(syn)n(tax)h(\()p FM(cf.)167 1433 y FK(section)33 b FG(??)q FK(\),)j(and)f(in)f(the)g (last)g(section)f(of)i(this)f(app)r(endix)h(w)n(e)e(shall)h(examine)f (to)i(what)167 1518 y(exten)n(t)27 b(this)g(is)g(true.)270 1737 y(W)-6 b(e)42 b(obtain)g(p)r(o)n(w)n(er)g(from)f(this)g(condition) g(b)n(y)h(man)n(ufacturing)h(automorphisms)f(to)167 1822 y(order.)48 b(One)31 b(v)n(ery)h(crude)g(construction)g(su\016ces:)44 b(w)n(e)31 b(tak)n(e)h(the)g(sum)g(of)g(a)g(domain)g(with)167 1907 y(itself)e(\(either)h(lifted)f(or)j(amalgamated)f(on)h(some)f(sub) r(domain\),)j(whic)n(h)c(ob)n(viously)i(has)h(a)167 1992 y(\\left-righ)n(t")28 b(symmetry.)39 b(\(W)-6 b(e)29 b(shall)f(sa)n(y)i(what)f(w)n(e)g(mean)g(b)n(y)g(a)h(sub)r(domain)g(in) e(the)h(next)167 2077 y(section.\))68 b(Giv)n(en)38 b(a)i(subspace)f (inclusion)f FJ(A)28 b(\032)f(B)r FK(,)42 b(a)d(\\uniform")g(elemen)n (t)e(of)i FJ(B)21 b FK(+)2562 2088 y Fv(A)2624 2077 y FJ(B)167 2162 y FK(cannot)32 b(b)r(e)e(in)g(either)f(the)h(left)f(or)i (the)f(righ)n(t)g(parts)h(of)g(the)g(sum)f(|)g(it)g(has)h(to)g(b)r(e)f (in)g(the)167 2247 y(common)24 b(subspace)h FJ(A)p FK(.)34 b(This)23 b(is)h(the)f(con)n(undrum)i(of)g(the)e(donk)n(ey)j(whic)n(h)d (starv)n(es)h(to)h(death)167 2332 y(b)r(ecause)i(it)g(cannot)h(c)n(ho)r (ose)g(b)r(et)n(w)n(een)f(t)n(w)n(o)g(equally)g(in)n(viting)f(piles)g (of)i(ha)n(y)-6 b(,)29 b(equidistan)n(t)e(to)167 2418 y(its)g(left)f(and)j(righ)n(t.)270 2636 y(There)42 b(is)f(a)h(similar)e (prop)r(ert)n(y)i(\()p FM(sep)l(ar)l(ability)6 b FK(\))44 b(for)e(\014elds)g(whic)n(h)f(underlies)g(Galois)167 2721 y(Theory:)35 b(giv)n(en)25 b(a)h(sub\014eld)g(inclusion)f FH(K)f FJ(\032)19 b FH(L)p FK(,)26 b(there)f(is)g(a)h(bigger)f(\014eld) g FH(L)20 b FJ(\032)f FH(M)33 b FK(suc)n(h)26 b(that)167 2806 y(the)33 b(automorphisms)g(of)h FH(M)40 b FK(\014xing)33 b FH(K)38 b FK(\(p)r(oin)n(t)n(wise\))32 b(\014x)h FM(only)g FH(K)5 b FK(.)51 b(F)-6 b(or)34 b(\014elds,)g FH(M)40 b FK(is)32 b(the)167 2892 y FM(normal)c(closur)l(e)f FK(|)h(a)g(more)f(complex)g(construction)g(than)i(our)f FJ(B)18 b FK(+)2062 2903 y Fv(A)2120 2892 y FJ(B)r FK(.)270 3110 y(Uniformit)n(y)k(with)g(resp)r(ect)g(to)i(automorphisms)g(is)e(a) i(feature)f(of)g(an)n(y)i(functorial)d(theory)-6 b(,)167 3195 y(including)31 b(Scott's.)51 b(Ho)n(w)n(ev)n(er)32 b(for)h(suc)n(h)g(theories)e(w)n(e)h(only)h(ha)n(v)n(e)g(a)g FM(sub)t FK(uniformit)n(y)f(with)167 3280 y(resp)r(ect)37 b(to)h(sub)r(domains:)56 b(the)38 b(v)l(alue)g(of)g(a)g(univ)n(ersal)f (term)g(at)g FJ(A)h FK(need)g(only)g(b)r(e)f FM(less)167 3366 y FK(than)29 b(that)g(at)f FJ(B)i FK(\(where)e FJ(A)20 b(\032)f(B)r FK(\).)38 b(It)27 b(is)h(the)g FM(stability)g FK(condition)g(whic)n(h)f(puts)i(the)f(ab)r(o)n(v)n(e)167 3451 y(separabilit)n(y)39 b(prop)r(ert)n(y)h(to)g(use:)60 b FJ(A)40 b FK(is)f(the)g(in)n(tersection)f(of)i(the)f(t)n(w)n(o)h (copies)f(of)i FJ(B)h FK(in)167 3536 y FJ(B)16 b FK(+)283 3547 y Fv(A)338 3536 y FJ(B)r FK(,)27 b(and)g(so)g(b)n(y)g(stabilit)n (y)d(the)i(v)l(alue)g(of)h(the)f(univ)n(ersal)f(term)g(at)h(it)f(m)n (ust)h(b)r(e)g(equal)g(to)167 3621 y(\(the)32 b(in)n(tersection)e(of)5 b(\))33 b(the)f(pro)t(jection\(s\))g(of)g(its)g(v)l(alue\(s\))g(at)h FJ(B)r FK(.)50 b(Hence)31 b(the)h(coherence)167 3706 y(space)c(mo)r(del)e(is)h FM(uniform)p FK(.)270 3925 y(W)-6 b(e)28 b(mak)n(e)f(this)h(v)l(ague)h(argumen)n(t)f(precise)e(in) h(A.4.1.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 134 137 bop 167 167 a FK(134)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)167 404 y FE(A.2)114 b(Rigid)28 b(Em)m(b)s(eddings)167 565 y FK(In)f(order)g(to)g(mak)n(e)h (sense)f(of)g(the)g(idea)f(of)i(\\\014nite)f(appro)n(ximation")h(w)n(e) e(ha)n(v)n(e)i(to)g(formalise)167 650 y(the)f(notion)i(of)f(sub)r (domain)g(or)g(appro)n(ximation)h(of)f(domains.)270 787 y(The)c(idea)f(used)i(in)e(Scott's)h(domain)g(theory)h(is)e(that)h(of)g (an)h FM(emb)l(e)l(dding-pr)l(oje)l(ction)g(p)l(air)p FK(,)167 872 y FH(e)20 b FK(:)f FJ(A)h Fu(\032)g FJ(B)30 b FK(and)f FH(p)19 b FK(:)h FJ(B)i(\000)-15 b FH(.)19 b FJ(A)p FK(,)28 b(satisfying)1287 847 y FD(2)1343 872 y FK(1)1377 883 y Fv(A)1440 872 y FK(=)19 b FH(pe)27 b FK(and)i FH(ep)19 b FJ(\024)g FK(1)1940 883 y Fv(B)1978 872 y FK(.)35 b(The)28 b(latter)e(comp)r(osite)167 957 y(is)h(idemp)r(oten)n(t)g(and)h(is)f(called)f(a)i FM(c)l(o)l(closur)l (e)h FK(on)f FJ(B)r FK(.)270 1095 y(W)-6 b(e)30 b(ma)n(y)h(use)f(these) g(functions)g(to)g(de\014ne)h(when)f(an)h(elemen)n(t)c FH(a)k FK(of)f FJ(A)h FK(is)e(\\less)h(than")167 1180 y(an)35 b(elemen)n(t)c FH(b)j FK(of)g FJ(B)j FK(\(but)d(not)g FM(vic)l(e)f(versa)p FK(\),)i(namely)f(if)f FH(a)24 b FJ(\024)f FH(pb)34 b FK(in)f FJ(A)p FK(,)j(or)e(equiv)l(alen)n(tly)167 1265 y FH(ea)20 b FJ(\024)f FH(b)28 b FK(in)f FJ(B)519 1239 y FD(3)547 1265 y FK(.)270 1402 y(F)-6 b(or)29 b(coherence)e (spaces)h(w)n(e)f(shall)g(use)h(the)g(same)f(idea,)h(except)f(that)h FH(e)g FK(no)n(w)g(has)h(to)f(b)r(e)167 1487 y(stable)k(\()p FH(p)f FK(is)g(already\))i(and)g(the)f(inequalit)n(y)f FH(ep)22 b FJ(\024)1571 1498 y FD(B)1632 1487 y FK(1)1666 1498 y Fv(B)1735 1487 y FK(m)n(ust)32 b(hold)g(in)g(the)f(Berry)h (order.)167 1572 y(No)n(w)c FH(e)g FK(is)f(linear)g(and)i(iden)n (ti\014es)e FJ(A)h FK(with)f(a)i FM(down-close)l(d)e FK(subset)i(of)f FJ(B)r FK(;)h(it)e(also)h(preserv)n(es)167 1657 y(and)i(re\015ects)e(atoms)h(and)h(the)e(coherence)g(relation.)37 b(Consequen)n(tly)30 b(w)n(e)e(ma)n(y)h(represen)n(t)f(it)167 1743 y(b)n(y)g(its)e(restriction)f(to)j(the)e(w)n(eb,)i(whic)n(h)e(is)h (a)g FM(gr)l(aph)h(emb)l(e)l(dding)p FK(.)36 b(This)26 b(justi\014es)h(the)g(abuse)167 1828 y(of)32 b(notation)g FH(e\013)g FK(for)g(the)f(unique)g(tok)n(en)h FH(\014)k FK(suc)n(h)c(that)f FH(e)p FJ(f)p FH(\013)p FJ(g)23 b FK(=)f FJ(f)p FH(\014)t FJ(g)p FK(,)33 b(and)f(so)g(enables)g(us)167 1913 y(to)c(regard)g FH(e)g FK(as)g(a)g(function)g(b)r(et)n(w)n(een)f (w)n(ebs.)270 2050 y(The)h(traces)f(of)h FH(e)g FK(and)g FH(p)g FK(are)940 2239 y FJ(T)-6 b FH(r)r FK(\()p FH(e)p FK(\))20 b(=)58 b FJ(fhf)p FH(\013)p FJ(g)p FH(;)12 b(e\013)p FJ(i)22 b FK(:)39 b FH(\013)20 b FJ(2)g(jAjg)937 2324 y(T)-6 b FH(r)r FK(\()p FH(p)p FK(\))20 b(=)58 b FJ(fhf)p FH(e\013)q FJ(g)p FH(;)12 b(\013)p FJ(i)21 b FK(:)39 b FH(\013)20 b FJ(2)g(jAjg)167 2520 y FK(W)-6 b(e)25 b(shall)g(often)h(write)e FH(e)c FK(:)f FJ(A)h(!)g(B)28 b FK(as)e FH(e)1257 2494 y FD(+)1325 2520 y FK(and)g FH(p)19 b FK(:)h FJ(B)i(!)e(A)26 b FK(as)g FH(e)1913 2494 y Fv(\000)1980 2520 y FK(for)g(a)g(graph)h(em)n(b)r(edding)167 2605 y FH(e)20 b FK(:)f FJ(jAj)g Fu(\032)h FJ(jB)r(j)p FK(.)270 2742 y(F)-6 b(or)36 b(p)r(edagogical)f(purp)r(oses)h(it)d(is)h (often)h(easier)f(to)g(see)h(a)g(1{1)h(function)e(\(suc)n(h)h(as)h(a) 167 2827 y(rigid)d(em)n(b)r(edding\))g(as)h(an)h(isomorphism)e(follo)n (w)n(ed)g(b)n(y)h(an)h(inclusion:)46 b(the)34 b(isomorphism)167 2912 y(c)n(hanges)26 b(the)f(name)g(of)h(the)f(datum)g(to)h(its)e(v)l (alue)h(in)g(the)g(target)g(and)h(the)f(inclusion)f(is)h(that)167 2998 y(of)33 b(the)f(set)g(of)h(represen)n(ted)f(v)l(alues.)50 b(In)32 b(our)h(case)g(w)n(e)f(ma)n(y)h(do)g(this)f(with)f(either)g(p)r (oin)n(ts)167 3083 y FH(a)20 b FJ(2)f(A)28 b FK(or)g(tok)n(ens)h FH(\013)19 b FJ(2)h(jAj)p FK(.)p 167 3156 1003 3 v 246 3199 a FC(2)273 3220 y FB(There)35 b(are)g(reasons)h(for)f(w)n(eak)n (ening)g(this)f(to)h(1)1441 3229 y Fk(A)1503 3220 y Fl(\024)20 b Fx(pe)p FB(.)57 b(W)-5 b(e)35 b(ma)n(y)h(consider)e(that)g(a)i (domain)e(is)167 3291 y(a)e(b)r(etter)g(appro)n(ximation)f(than)g (another)h(if)f(it)h(can)g(express)g(more)g(data,)i(and)e(this)f(giv)n (es)h(rise)g(to)g(an)167 3361 y(em)n(b)r(edding.)f(Ho)n(w)n(ev)n(er)26 b(w)n(e)f(ma)n(y)g(also)f(consider)f(that)h(a)g(domain)f(is)h(inferior) e(if)i(its)f(represen)n(tation)g(mak)n(es)167 3432 y(\\)p FA(a)29 b(priori)p FB(")f(distinctions)d(b)r(et)n(w)n(een)j(things)f (whic)n(h)h(subsequen)n(tly)e(turn)i(out)g(to)g(b)r(e)g(the)f(same,)j (and)d(suc)n(h)167 3502 y(a)k(comparison)g(is)g(of)g(this)f(more)i (general)f(form.)45 b(On)30 b(the)h(other)g(hand)f(the)g(limit-colimit) d(coincidence)167 3573 y(and)32 b(other)h(imp)r(ortan)n(t)f (constructions)g(suc)n(h)g(as)i(\005)f(and)f(\006)h(t)n(yp)r(es)g (remain)f(v)m(alid.)48 b(Ho)n(w)n(ev)n(er)35 b(for)e FA(rigid)167 3643 y FB(adjunctions)26 b(1)519 3652 y Fk(A)576 3643 y FB(=)16 b Fx(pe)28 b FB(is)f FA(for)m(c)m(e)m(d)g FB(b)r(ecause)g(the)g(iden)n(tit)n(y)f(is)h(maximal)g(in)g(the)g(Berry) g(order.)246 3692 y FC(3)273 3713 y FB(In)e(fact)h Fl(\024)f FB(is)g(not)h(a)g(partial)e(order)h(but)g(a)h(category)-5 b(,)27 b(b)r(ecause)f(it)e(dep)r(ends)g(on)i Fx(e)p FB(.)34 b(Applying)23 b(this)i(to)167 3784 y(a)k(functor)f Fl(T)14 b FB(,)29 b(w)n(e)h(obtain)d(a)i(category)g(with)f(ob)s(jects)h(the)f (pairs)f(\()p Fl(A)p Fx(;)10 b(b)p FB(\))29 b(for)f Fx(b)17 b Fl(2)g(T)e FB(\()p Fl(A)p FB(\))28 b(and)g(morphisms)167 3854 y(giv)n(en)g(in)f(this)g(w)n(a)n(y)i(b)n(y)f(em)n(b)r(eddings;)f (this)g(is)g(called)g(the)h FA(total)h(c)m(ate)m(gory)g FB(or)f FA(Gr)m(othendie)m(ck)h(\014br)m(ation)f FB(of)167 3925 y Fl(T)42 b FB(and)28 b(is)f(written)f(\006)647 3920 y Fl(\016)689 3925 y Fx(X)q(:)10 b Fl(T)16 b FB(.)p eop PStoPSsaved restore %%Page: (138,139) 70 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 135 138 bop 167 167 a Fz(A.2.)63 b(RIGID)27 b(EMBEDDINGS)1499 b FK(135)270 404 y(Observ)n(e)34 b(then)h(that)f(for)h(inclusions)e (the)h(em)n(b)r(edding)f(is)h(just)g(the)g(iden)n(tit)n(y)f(and)i(the) 167 490 y(pro)t(jection)27 b(is)g(the)h(restriction:)995 735 y FH(e)p FK(\()p FH(a)p FK(\))20 b(=)f FH(a)157 b(p)p FK(\()p FH(b)p FK(\))19 b(=)g FH(b)d FJ(\\)g(jAj)167 1131 y Fy(A.2.1)95 b(F)-8 b(unctorialit)m(y)29 b(of)e(arro)m(w)167 1280 y FK(The)k(reason)i(for)f(using)g(pairs)f(of)h(maps)g(for)g(appro) n(ximations)h(is)e(that)h(w)n(e)f(need)g(to)h(mak)n(e)167 1365 y(the)g(function-space)g(functorial)g(\(p)r(ositiv)n(e\))f(in)g (its)g(\014rst)i(argumen)n(t:)44 b(if)32 b FJ(A)2221 1340 y Fv(0)2269 1365 y FK(appro)n(ximates)167 1450 y FJ(A)c FK(then)g(w)n(e)f(need)g FJ(A)740 1425 y Fv(0)773 1450 y FJ(!)16 b(B)30 b FK(to)e(appro)n(ximate)g FJ(A)15 b(!)i(B)30 b FK(and)e(not)g FM(vic)l(e)g(versa)p FK(.)270 1613 y(Indeed)23 b(if)e FH(e)f FK(:)g FJ(A)703 1587 y Fv(0)739 1613 y Fu(\032)g FJ(A)i FK(and)i FH(f)j FK(:)19 b FJ(B)1196 1587 y Fv(0)1233 1613 y Fu(\032)h FJ(B)k FK(then)f(w)n(e)e(ha)n(v)n(e)j FH(e)8 b FJ(!)f FH(f)27 b FK(:)20 b(\()p FJ(A)2117 1587 y Fv(0)2141 1613 y FJ(!)8 b(B)2267 1587 y Fv(0)2284 1613 y FK(\))19 b Fu(\032)h FK(\()p FJ(A)8 b(!)g(B)r FK(\))167 1698 y(b)n(y)927 1937 y(\()p FH(e)16 b FJ(!)g FH(f)8 b FK(\))1157 1912 y FD(+)1198 1937 y FK(\()p FH(t)1250 1912 y Fv(0)1266 1937 y FK(\)\()p FH(a)p FK(\))59 b(=)46 b FH(f)1584 1912 y FD(+)1626 1937 y FK(\()p FH(t)1678 1912 y Fv(0)1694 1937 y FK(\()p FH(e)1753 1912 y Fv(\000)1794 1937 y FH(a)p FK(\)\))927 2023 y(\()p FH(e)16 b FJ(!)g FH(f)8 b FK(\))1157 1997 y Fv(\000)1198 2023 y FK(\()p FH(t)p FK(\)\()p FH(a)1340 1997 y Fv(0)1356 2023 y FK(\))59 b(=)46 b FH(f)1584 1997 y Fv(\000)1626 2023 y FK(\()p FH(t)p FK(\()p FH(e)1737 1997 y FD(+)1778 2023 y FH(a)1814 1997 y Fv(0)1831 2023 y FK(\)\))167 2267 y(for)29 b FH(a)21 b FJ(2)f(A)p FK(,)29 b FH(a)542 2242 y Fv(0)579 2267 y FJ(2)21 b(A)703 2242 y Fv(0)719 2267 y FK(,)29 b FH(t)21 b FK(:)f FJ(A)c(!)h(B)31 b FK(and)f FH(t)1253 2242 y Fv(0)1289 2267 y FK(:)21 b FJ(A)1385 2242 y Fv(0)1418 2267 y FJ(!)16 b(B)1552 2242 y Fv(0)1569 2267 y FK(.)38 b(\(W)-6 b(e)29 b(lea)n(v)n(e)f(the)g(reader)h(to)g(c)n (hec)n(k)f(the)167 2352 y(inequalities.\))270 2515 y(Recall)33 b(that)i(the)g(tok)n(ens)h(of)f FJ(A)18 b(!)g(B)37 b FK(are)e(of)h(the)e(form)h(\()p FH(a;)12 b(\014)t FK(\))34 b(where)g FH(a)h FK(is)f(a)i(clique)167 2600 y(\(\014nite)g(coheren)n (t)h(subset\))g(of)h FJ(jAj)e FK(and)i FH(\014)j FK(is)36 b(a)h(tok)n(en)h(of)g FJ(jB)r(j)p FK(.)63 b(If)37 b FH(e)26 b FK(:)g FJ(jA)2262 2574 y Fv(0)2278 2600 y FJ(j)g Fu(\032)h FJ(jAj)36 b FK(and)167 2685 y FH(f)27 b FK(:)20 b FJ(jB)335 2659 y Fv(0)351 2685 y FJ(j)f Fu(\032)h FJ(jB)r(j)25 b FK(are)h(rigid)e(em)n(b)r(eddings)i(then)f(the)h(e\013ect)e(on)i(the) g(tok)n(en)g(\()p FH(a)2199 2659 y Fv(0)2215 2685 y FH(;)12 b(\014)2289 2659 y Fv(0)2306 2685 y FK(\))25 b(of)h FJ(A)2495 2659 y Fv(0)2524 2685 y FJ(!)13 b(B)2655 2659 y Fv(0)167 2770 y FK(is)27 b(simply)f(the)i(corresp)r(onding)g(renaming)f (throughout,)j FM(i.e.)e FK(\()p FH(e)1910 2745 y FD(+)1952 2770 y FH(a)1988 2745 y Fv(0)2004 2770 y FH(;)12 b(f)c(\014)2120 2745 y Fv(0)2136 2770 y FK(\).)270 2933 y(In)39 b(particular)e(the)h (tok)n(en)h(\()p FJ(f)p FH(\013)1148 2907 y Fv(0)1165 2933 y FJ(g)p FH(;)12 b(\013)1275 2907 y Fv(0)1291 2933 y FK(\))38 b(of)h FJ(I)-7 b FH(d)1517 2907 y Fv(A)1557 2890 y Fa(0)1615 2933 y FK(is)37 b(mapp)r(ed)i(to)f(\()p FJ(f)p FH(e\013)2214 2907 y Fv(0)2231 2933 y FJ(g)p FH(;)12 b(e\013)2373 2907 y Fv(0)2390 2933 y FK(\),)41 b(so)d(the)167 3018 y(iden)n(tit)n(y)26 b(is)h(uniform)h(in)f(the)g(sense)h(that)1059 3263 y FJ(I)-7 b FH(d)1126 3238 y Fv(A)1166 3221 y Fa(0)1205 3263 y FK(=)19 b FJ(I)-7 b FH(d)1345 3238 y Fv(A)1404 3263 y FJ(\\)16 b(jA)1543 3238 y Fv(0)1574 3263 y FJ(!)h(A)1717 3238 y Fv(0)1733 3263 y FJ(j)167 3509 y FK(where)27 b FJ(A)427 3483 y Fv(0)463 3509 y Fu(\032)20 b FJ(A)28 b FK(is)f(a)h(subspace.)270 3754 y(Coherence)53 b(spaces)g(and)h(rigid) d(em)n(b)r(eddings)i(|)g(or)g(equiv)l(alen)n(tly)f FM(G)6 b FK(raphs)54 b(and)167 3840 y FM(em)5 b FK(b)r(eddings)29 b(|)g(form)f(a)h(category)g FG(Gem)o FK(,)g(and)g(w)n(e)f(ha)n(v)n(e)h (sho)n(wn)h(that)f FJ(!)f FK(is)g(a)h FM(c)l(ovariant)167 3925 y FK(functor)f(of)g(t)n(w)n(o)g(argumen)n(ts)g(from)g FG(Gem)o FH(;)12 b FG(Gem)27 b FK(to)h FG(Gem)p FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 136 139 bop 167 167 a FK(136)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)167 404 y FE(A.3)114 b(In)m(terpretation)29 b(of)e(T)m(yp)s(es)167 582 y FK(W)-6 b(e)28 b(can)h(use)f(this)g(to)g(express)g(an)n(y)i(t)n(yp)r(e)e FH(T)38 b FK(of)29 b FG(F)f FK(with)f FH(n)i FK(free)e(t)n(yp)r(e)h(v)l (ariables)g FH(X)2434 593 y FD(1)2462 582 y FH(;)12 b(:::;)g(X)2638 593 y Fw(n)167 667 y FK(as)28 b(a)g(functor)g([)-12 b([)q FH(T)10 b FK(])-12 b(])20 b(:)g FG(Gem)888 637 y Fw(n)941 667 y FJ(!)g FG(Gem)27 b FK(as)h(follo)n(ws:)251 887 y(1.)35 b(If)28 b FH(T)38 b FK(is)27 b(a)h(constan)n(t)g(t)n(yp)r(e)g (then)g(w)n(e)f(assign)h(to)g(it)f(a)h(coherence)f(space)h FJ(T)45 b FK(and)1193 1182 y([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)1379 1193 y FD(1)1407 1182 y FH(;)12 b(:::;)g FJ(A)1582 1193 y Fw(n)1615 1182 y FK(\))20 b(=)f FJ(T)339 1477 y FK(An)n(y)29 b(morphism)d(is)h(mapp)r(ed)h(to)g(the)g (iden)n(tit)n(y)e(on)i FJ(T)19 b FK(.)251 1657 y(2.)35 b(If)28 b FH(T)38 b FK(is)27 b(the)g(v)l(ariable)g FH(X)1008 1668 y Fw(i)1056 1657 y FK(then)h(the)f(functor)h(is)f(the)g FH(i)p FK(th)h(pro)t(jection)1169 1952 y([)-12 b([)q FH(X)1253 1963 y Fw(i)1273 1952 y FK(])g(]\()p FJ(A)1382 1963 y FD(1)1410 1952 y FH(;)12 b(:::;)g FJ(A)1585 1963 y Fw(n)1619 1952 y FK(\))19 b(=)h FJ(A)1795 1963 y Fw(i)339 2247 y FK(and)29 b(similarly)c(on)j(morphisms.)251 2428 y(3.)35 b(If)27 b FH(T)36 b FK(is)25 b FH(U)c FJ(!)14 b FH(V)i FK(,)27 b(and)g FH(U)33 b FK(and)28 b FH(V)41 b FK(ha)n(v)n(e)28 b(b)r(een)e(in)n(terpreted)e(b)n(y)j(the)f(functors) h([)-12 b([)q FH(U)7 b FK(])-12 b(])27 b(and)339 2513 y([)-12 b([)q FH(V)16 b FK(])-12 b(])28 b(then)635 2807 y([)-12 b([)p FH(U)23 b FJ(!)16 b FH(V)g FK(])-12 b(]\()p FJ(A)982 2818 y FD(1)1010 2807 y FH(;)12 b(:::;)g FJ(A)1185 2818 y Fw(n)1219 2807 y FK(\))19 b(=)h([)-12 b([)p FH(U)7 b FK(])-12 b(])q(\()p FJ(A)1529 2818 y FD(1)1557 2807 y FH(;)12 b(:::;)g FJ(A)1732 2818 y Fw(n)1766 2807 y FK(\))j FJ(!)h FK([)-12 b([)q FH(V)15 b FK(])-12 b(])q(\()p FJ(A)2086 2818 y FD(1)2114 2807 y FH(;)12 b(:::;)g FJ(A)2289 2818 y Fw(n)2322 2807 y FK(\))339 3102 y(Its)28 b(v)l(alue)g(on)g (morphisms)f(is)g(as)h(giv)n(en)g(at)g(the)f(end)h(of)g(the)g(previous) g(section.)167 3323 y(This)c(de\014nition)f(resp)r(ects)h(substitution) g(of)h(t)n(yp)r(es)f FH(U)1593 3334 y FD(1)1621 3323 y FH(;)12 b(:::;)g(U)1787 3334 y Fw(n)1845 3323 y FK(for)24 b(the)g(v)l(ariables)g FH(X)2415 3334 y FD(1)2443 3323 y FH(;)12 b(:::;)g(X)2619 3334 y Fw(n)2653 3323 y FK(:)167 3408 y([)-12 b([)q FH(T)10 b FK([)p FH(U)310 3419 y Fw(i)330 3408 y FH(=X)421 3419 y Fw(i)441 3408 y FK(]])-12 b(])20 b(=)g([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\([)g([)p FH(U)783 3419 y FD(1)811 3408 y FK(])g(])q FH(;)12 b(:::;)g FK([)-12 b([)p FH(U)1030 3419 y Fw(n)1063 3408 y FK(])g(])q(\).)270 3669 y(Because)60 b(of)h(functorialit)n(y)-6 b(,)67 b(w)n(e)59 b(immediately)e(kno)n(w)k(that)f(if)f FJ(A)2265 3644 y Fv(0)2325 3669 y FJ(')42 b(A)60 b FK(then)167 3754 y([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FJ(A)353 3729 y Fv(0)370 3754 y FK(\))32 b FJ(')g FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)p FK(\).)89 b(It)45 b(is)g(con)n(v)n(enien)n (t)g(to)h(assume)g(for)g(p)r(edagogical)g(reasons)h(that)167 3840 y(if)29 b FJ(A)293 3814 y Fv(0)331 3840 y FJ(\032)21 b(A)30 b FK(is)f(a)h FM(subsp)l(ac)l(e)h FK(then)f(the)f(induced)h(em)n (b)r(edding)f([)-12 b([)q FH(T)10 b FK(])-12 b(])q(\()p FJ(A)2010 3814 y Fv(0)2026 3840 y FK(\))21 b Fu(\032)g FK([)-12 b([)q FH(T)10 b FK(])-12 b(])q(\()p FJ(A)p FK(\))29 b(is)h(also)g(a)167 3925 y FM(subsp)l(ac)l(e)e FK(inclusion.)p eop PStoPSsaved restore %%Page: (140,141) 71 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 137 140 bop 167 167 a Fz(A.3.)63 b(INTERPRET)-6 b(A)g(TION)26 b(OF)h(TYPES)1188 b FK(137)167 404 y Fy(A.3.1)95 b(T)-8 b(ok)m(ens)27 b(for)g(univ)m(ersal)i(t)m(yp)s(es)167 535 y FK(The)j(in)n(terpretation)f(is)h FM(c)l(ontinuous)p FK(:)45 b(if)32 b FH(\014)26 b FJ(2)d(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)p FK(\))p FJ(j)32 b FK(then)g(there)g(is)g(a)g(\014nite)g(subspace)167 620 y FJ(A)223 595 y Fv(0)263 620 y Fu(\032)23 b FJ(A)32 b FK(suc)n(h)h(that)g FH(\014)27 b FJ(2)c(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(]\()p FJ(A)1117 595 y Fv(0)1134 620 y FK(\))p FJ(j)p FK(.)49 b(\(Categorically)-6 b(,)32 b(w)n(e)g(w)n(ould)g(sa)n(y)i(that)f(the)f(functor)167 706 y(preserv)n(es)j FM(\014lter)l(e)l(d)g(c)l(olimits)p FK(.\))58 b(This)35 b(means)g(that,)i(as)f(in)f(section)f FG(??)q FK(,)j(w)n(e)e(ma)n(y)g(restrict)167 791 y(atten)n(tion)28 b(to)f(\014nite)g(coherence)g(spaces.)36 b(F)-6 b(or)28 b(an)h(arbitrary)e(coherence)g(space)h FJ(A)p FK(,)768 965 y FJ(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)p FK(\))p FJ(j)19 b FK(=)1113 912 y Fo(S)1172 931 y Fv(")1199 965 y FJ(fj)p FK([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FJ(A)1440 939 y Fv(0)1457 965 y FK(\))p FJ(j)19 b FK(:)39 b FJ(A)1637 939 y Fv(0)1673 965 y Fu(\032)20 b FJ(A)28 b FK(\014nite)o FJ(g)270 1181 y FK(But)g(more)f(than)i(this,) e(it)f(is)h FM(stable)p FK(:)388 1355 y(if)g FJ(A)512 1330 y Fv(0)528 1355 y FH(;)12 b FJ(A)615 1330 y Fv(00)665 1355 y FJ(\032)19 b(A)28 b FK(and)h FH(\014)23 b FJ(2)d(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(]\()p FJ(A)1296 1330 y Fv(0)1313 1355 y FK(\))p FJ(j)p FH(;)12 b FJ(j)p FK([)-12 b([)o FH(T)10 b FK(])-12 b(])q(\()p FJ(A)1596 1330 y Fv(00)1626 1355 y FK(\))p FJ(j)27 b FK(then)h FH(\014)23 b FJ(2)d(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(]\()p FJ(A)2196 1330 y Fv(0)2229 1355 y FJ(\\)15 b(A)2347 1330 y Fv(00)2377 1355 y FK(\))p FJ(j)167 1529 y FM(i.e.)30 b FK(the)g(functor)h(preserv)n(es)f FM(pul)t(lb)l(acks)1235 1504 y FD(4)1262 1529 y FK(.)43 b(F)-6 b(or)30 b(a)h(stable)f (function,)h(if)e(w)n(e)h(kno)n(w)h FH(\014)25 b FJ(2)d FH(f)8 b FK(\()p FH(a)p FK(\),)167 1615 y(then)25 b(there)f(is)h(a)g (least)f FH(a)834 1589 y Fv(0)871 1615 y FJ(\032)19 b FH(a)25 b FK(suc)n(h)h(that)f FH(\014)f FJ(2)19 b FH(f)8 b FK(\()p FH(a)1549 1589 y Fv(0)1565 1615 y FK(\).)34 b(W)-6 b(e)25 b(ha)n(v)n(e)h(a)g(similar)2193 1589 y FD(5)2243 1615 y FK(prop)r(ert)n(y)g(here:)167 1700 y(if)h FH(\014)c FJ(2)d(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(]\()p FJ(A)p FK(\))p FJ(j)28 b FK(then)f(there)g(is)g(a)h(least)f (subspace)i FJ(A)1637 1674 y Fv(0)1673 1700 y Fu(\032)20 b FJ(A)28 b FK(with)e FH(\014)e FJ(2)19 b(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)2351 1674 y Fv(0)2367 1700 y FK(\))p FJ(j)p FK(.)270 1826 y(The)28 b(tok)n(en)g FH(\014)j FK(of)d([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FJ(A)p FK(\))27 b(therefore)g(in)n(trinsically)d (carries)j(with)f(it)h(a)g(particular)g(\014nite)167 1912 y(subspace)36 b FJ(A)523 1886 y Fv(0)564 1912 y FJ(\032)24 b(A)p FK(,)37 b(namely)d(the)g(least)g(subspace)i(on)f(whic) n(h)f(it)g(can)h(b)r(e)f(de\014ned.)57 b(It)35 b(is)167 1997 y(not)d(di\016cult)f(to)h(see)f(that,)i(in)e(terms)f(of)i(the)g(w) n(eb,)g(this)f(is)g(simply)g(the)g(set)g(of)h(tok)n(ens)h FH(\013)167 2082 y FK(whic)n(h)d(o)r(ccur)g(in)g(the)h(expression)f (for)h FH(\014)t FK(.)45 b(Th)n(us)31 b(for)g(instance)f(the)g(only)h (tok)n(en)h(o)r(ccurring)167 2167 y(in)h FH(\014)28 b FK(=)23 b(\()p FJ(f)p FH(\013)p FJ(g)p FH(;)12 b(\013)p FK(\))34 b(is)f FH(\013)p FK(,)j(and)e(the)f(corresp)r(onding)i (\014nite)e(space)h(is)e FJ(S)-6 b FM(gl)6 b FK(,)35 b(whose)f(w)n(eb)g(is)f(a)167 2252 y(singleton,)27 b FJ(f\017)q(g)p FK(.)270 2379 y(W)-6 b(e)35 b(shall)f(see)h(later)e (that)j(the)e(pairs)h FJ(hA)p FH(;)12 b(\014)t FJ(i)p FK(,)38 b(where)c FH(\014)28 b FJ(2)d(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)p FK(\))p FJ(j)34 b FK(and)i(no)g(prop)r(er)167 2464 y FJ(A)223 2438 y Fv(0)259 2464 y Fu(\032)20 b FJ(A)36 b FK(has)g FH(\014)29 b FJ(2)c(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)930 2438 y Fv(0)946 2464 y FK(\))p FJ(j)p FK(,)37 b(serv)n(e)f(as)g(\(p)r(oten)n(tial\))e(tok)n(ens)i(for)g([)-12 b([)q(\005)p FH(X)r(:)12 b(T)e FK(])-12 b(].)59 b(If)35 b FJ(A)26 b(')e(A)2655 2438 y Fv(0)167 2549 y FK(then)g(the)g(tok)n(en) h FJ(hA)717 2523 y Fv(0)734 2549 y FH(;)12 b(\014)808 2523 y Fv(0)825 2549 y FJ(i)p FK(,)25 b(where)e FH(\014)1139 2523 y Fv(0)1180 2549 y FK(is)g(the)h(image)g(of)h FH(\014)j FK(under)c(the)g(induced)g(isomorphism)167 2634 y([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FJ(A)p FK(\))30 b FJ(')f FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)680 2609 y Fv(0)697 2634 y FK(\),)45 b(is)c(equiv)l(alen)n(t)g(to)h FJ(hA)p FH(;)12 b(\014)t FJ(i)p FK(.)78 b(These)42 b(tok)n(ens)g(in)n (v)n(olv)n(e)g(pairs,)j(\014nite)167 2719 y(\(en)n(umerated\))27 b(sets)h(and)h(\014nite)f(graphs,)i(and)f(so)g(there)e(are)h(at)h(most) f(coun)n(tably)h(man)n(y)g(of)167 2804 y(them)k(altogether;)j (consequen)n(tly)e(it)e(will)f(b)r(e)i(p)r(ossible)g(to)h(denote)g(an)n (y)g(t)n(yp)r(e)g(of)g FG(F)f FK(b)n(y)i(a)167 2889 y(coun)n(table)28 b(coherence)f(space.)270 3016 y(W)-6 b(e)27 b(ma)n(y)h(calculate)e FJ(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)p FK(\))o FJ(j)27 b FK(from)g(these)g(tok)n(ens)i(as)f(follo)n(ws.)34 b(F)-6 b(or)28 b(ev)n(ery)f(em)n(b)r(edding)167 3101 y FH(e)20 b FK(:)g FJ(A)314 3076 y Fv(0)351 3101 y Fu(\032)h FJ(A)28 b FK(and)i(ev)n(ery)e(tok)n(en)h FH(\014)24 b FJ(2)c(j)p FK([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FJ(A)1390 3076 y Fv(0)1407 3101 y FK(\))p FJ(j)p FK(,)28 b(w)n(e)g(ha)n(v)n(e)h(a)g(tok)n(en)g([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FH(e)p FK(\)\()p FH(\014)t FK(\))20 b FJ(2)g(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)p FK(\))o FJ(j)p FK(.)167 3186 y(Ho)n(w)n(ev)n(er)30 b(the)h(fact)f(that)h(there)f(ma)n(y)h(b)r(e)f(sev)n(eral)g(suc)n(h)h (em)n(b)r(eddings)f(\(and)i(hence)e(sev)n(eral)167 3272 y(copies)d(of)h(the)g(tok)n(en,)g(whic)n(h)f(m)n(ust)h(b)r(e)f(coheren) n(t\))g(giv)n(es)h(rise)e(to)i(additional)f(\(uniformit)n(y\))167 3357 y(conditions)32 b(on)i(the)e(tok)n(ens)i(of)f FJ(j)p FK([)-12 b([\005)p FH(X)r(:)12 b(T)e FK(])-12 b(])p FJ(j)p FK(.)50 b(F)-6 b(or)33 b(instance)f(w)n(e)h(shall)e(see)h(that)h FJ(hS)-6 b FM(gl)7 b FH(;)12 b FJ(\017i)33 b FK(is)167 3442 y(not)28 b(a)g(tok)n(en)h(for)f([)-12 b([\005)p FH(X)r(:)12 b(X)6 b FK(])-12 b(].)p 167 3508 1003 3 v 246 3551 a FC(4)273 3573 y FB(As)31 b(with)f FA(c)m(ontinuity)j FB(of)e Fl(!)o FB(,)h(this)e(follo)n(ws)h(from)g(a)h FA(limit-c)m(olimit)f(c)m(oincidenc)m(e)p FB(:)41 b(for)32 b(a)f(pullbac)n(k)e(of)167 3643 y(rigid)c(em)n(b)r(eddings,)g(the)g (corresp)r(onding)g(pro)s(jections)h(form)g(a)h(pushout,)e(and)h(if)f (this)g(o)r(ccurs)h(on)g(the)g(left)167 3713 y(of)31 b(an)f Fl(!)g FB(it)g(is)g(turned)f(bac)n(k)i(in)n(to)f(a)h(pullbac)n (k)e(of)h(em)n(b)r(eddings.)42 b(This)30 b(do)r(es)g(not,)h(ho)n(w)n (ev)n(er,)i(hold)d(for)167 3784 y(equalisers.)246 3833 y FC(5)273 3854 y FB(The)37 b(argumen)n(t)g(b)n(y)g(analogy)g(is)g(in)f (some)i(w)n(a)n(ys)g(misleading,)g(b)r(ecause)f(ev)n(en)g(for)g(a)h (con)n(tin)n(uous)167 3925 y(functor)27 b Fl(T)42 b FB(the)28 b(\014bration)e(\006)812 3920 y Fl(\016)854 3925 y Fx(X)q(:)10 b Fl(T)32 b(!)16 b Ft(Gem)28 b FB(is)f(stable.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 138 141 bop 167 167 a FK(138)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)167 404 y Fy(A.3.2)95 b(Linear)28 b(notation)f(for)g(tok)m(ens)167 535 y FK(W)-6 b(e)31 b(can)h(use)f(the)h(linear)e(logic)g(in)n(tro)r(duced)h(in)g(c)n (hapter)g FG(??)i FK(to)e(c)n(ho)r(ose)h(a)g(go)r(o)r(d)h(notation)167 620 y(for)28 b(the)f(tok)n(ens)i FH(\014)i FK(and)e(express)f(the)f (conditions)h(on)g(them.)35 b(Recall)25 b(that)918 791 y FJ(A)16 b(!)g(B)22 b(')e FK(!)p FJ(A)c Fu(\()g FJ(B)22 b(')d FK(\(!)p FJ(A)d(\012)f(B)1782 765 y Fv(?)1825 791 y FK(\))1851 751 y Fv(?)167 919 y FK(where)270 1062 y FJ(\017)34 b FK(The)26 b(tok)n(ens)h(of)f(!)p FJ(A)g FK(are)g(the)f(cliques)f(\(\014nite)h(complete)f(subgraphs\))k(of)e FJ(jAj)p FK(,)g(and)h(t)n(w)n(o)339 1147 y(cliques)22 b(are)g(coheren)n(t)g(i\013)g(their)g(union)h(is)f(a)h(clique;)f(w)n(e) g(write)f(cliques)g(as)j(en)n(umerated)339 1232 y(sets.)270 1371 y FJ(\017)34 b(B)387 1346 y Fv(?)462 1371 y FK(is)d(the)h(linear)f (negation)i(of)f FJ(B)r FK(,)i(whose)f(w)n(eb)f(is)f(the)h(complemen)n (tary)f(graph)j(to)339 1457 y(that)28 b(of)f FJ(B)r FK(;)h(it)e(is)h (con)n(v)n(enien)n(t)g(to)g(write)e(its)h(tok)n(ens)i(as)p 1838 1399 43 3 v 28 w FH(\014)t FK(.)35 b(Then)p 2119 1399 V 27 w FH(\014)2181 1434 y(_)2181 1477 y(^)p 2270 1399 60 3 v 2270 1457 a(\014)2313 1436 y Fv(0)2356 1457 y FK(i\013)27 b FH(\014)2505 1434 y(^)2505 1477 y(_)2594 1457 y(\014)2637 1431 y Fv(0)2653 1457 y FK(;)339 1542 y(this)h(a)n(v)n(oids)g(sa)n(ying)h(\\mo)r(d)f FJ(B)r FK(")h(or)f(\\mo)r(d)g FJ(B)1544 1516 y Fv(?)1586 1542 y FK(".)270 1681 y FJ(\017)34 b(jC)20 b(\012)15 b(D)s(j)29 b FK(is)h(the)g(graph)i(pro)r(duct)f(of)g FJ(jC)t(j)e FK(and)j FJ(jD)r(j)p FK(;)f(its)e(tok)n(ens)j(are)e(pairs)g FJ(h)p FH(\015)t(;)12 b(\016)s FJ(i)30 b FK(and)339 1766 y(this)e(is)e(coheren)n(t)i(with)f FJ(h)p FH(\015)1064 1740 y Fv(0)1080 1766 y FH(;)12 b(\016)1145 1740 y Fv(0)1161 1766 y FJ(i)28 b FK(i\013)f FH(\015)1362 1744 y(_)1362 1787 y(^)1450 1766 y(\015)1490 1740 y Fv(0)1534 1766 y FK(and)i FH(\016)1725 1744 y(_)1725 1787 y(^)1814 1766 y(\016)1848 1740 y Fv(0)1864 1766 y FK(.)167 1909 y(The)e(tok)n(en)i (of)f(the)f(iden)n(tit)n(y)-6 b(,)27 b(\003)p FH(X)r(:)12 b(\025x)1202 1883 y Fw(X)1250 1909 y FH(:)g(x)p FK(,)28 b(is)f(therefore)f(written)1203 2073 y FJ(hS)-6 b FM(gl)6 b FH(;)p 1354 2011 227 3 v 12 w FJ(hf\017)q(g)p FH(;)p 1518 2033 36 3 v 12 w FJ(\017)q(ii)270 2315 y FK(In)29 b(this)f(notation)h(it)e(is)g(easy)i(to)g(see)e(ho)n(w)i(w)n(e)f(can)h (ascrib)r(e)e(a)i(meaning)f(to)g(the)g(phrase)167 2400 y(\\)p FH(\013)k FK(o)r(ccurs)e(p)r(ositiv)n(ely)g(\(or)h(negativ)n (ely\))f(in)g FH(\014)t FK(".)46 b(Informally)-6 b(,)31 b(a)g(particular)f(o)r(ccurrence)g(is)167 2485 y(p)r(ositiv)n(e)d(or)h (negativ)n(e)f(according)h(as)h(it)d(is)h(o)n(v)n(er-lined)g(ev)n(enly) g(or)h(o)r(ddly)-6 b(.)270 2607 y(W)g(e)22 b(can)h(obtain)f(a)h(v)n (ery)f(useful)g(criterion)e(for)i(whether)g(a)g(p)r(oten)n(tial)f(tok)n (en)i(can)g(actually)167 2692 y(o)r(ccur.)167 2814 y FG(Lemma)g FK(Let)h FH(\013)c FJ(2)g(jAj)k FK(and)j FH(\014)c FJ(2)d(j)p FK([)-12 b([)p FH(T)10 b FK(])-12 b(]\()p FJ(A)p FK(\))p FJ(j)p FK(.)35 b(De\014ne)24 b(a)i(coherence)f(space)g FJ(A)2229 2788 y FD(+)2296 2814 y FK(b)n(y)h(adjoining)167 2899 y(an)38 b(additional)g(tok)n(en)g FH(\013)864 2873 y Fv(0)919 2899 y FK(to)g FJ(jAj)f FK(whic)n(h)g(b)r(ears)h(the)f(same) h(coherence)f(relation)f(to)i(the)167 2984 y(other)30 b(tok)n(ens)h(\(b)r(esides)e FH(\013)p FK(\))i(as)f(do)r(es)h FH(\013)p FK(,)g(and)g(is)f(coheren)n(t)f(with)h FH(\013)p FK(.)43 b(There)29 b(are)h(t)n(w)n(o)g(rigid)167 3069 y(em)n(b)r(eddings)35 b FJ(A)26 b Fu(\032)f FJ(A)796 3043 y FD(+)874 3069 y FK(\(in)35 b(whic)n(h)g FH(\013)g FK(is)g(tak)n(en)i(to)e(resp)r(ectiv)n(ely)f FH(\013)i FK(and)g FH(\013)2321 3043 y Fv(0)2338 3069 y FK(\),)i(so)e(write)167 3154 y FH(\014)t(;)12 b(\014)284 3129 y Fv(0)328 3154 y FJ(2)28 b(jAj)499 3129 y FD(+)580 3154 y FK(for)40 b(the)g(images)f(of)h FH(\014)k FK(under)c(these)f(em)n(b)r(eddings.)72 b(Similarly)37 b(w)n(e)i(ha)n(v)n(e)167 3239 y FJ(A)20 b Fu(\032)g FJ(A)397 3214 y Fv(\000)439 3239 y FK(,)27 b(in)g(whic)n(h)g FH(\013)816 3214 y Fv(0)853 3217 y FH(^)853 3260 y(_)941 3239 y(\013)p FK(.)36 b(Then)270 3382 y FJ(\017)e FK(if)27 b FH(\013)h FK(do)r(es)g(not)h(o)r(ccur)e(in) g FH(\014)k FK(then)d FH(\014)c FK(=)19 b FH(\014)1453 3356 y Fv(0)1497 3382 y FK(in)27 b(b)r(oth)h([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FJ(A)1935 3356 y FD(+)1977 3382 y FK(\))27 b(and)i([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FJ(A)2356 3356 y Fv(\000)2398 3382 y FK(\).)270 3521 y FJ(\017)34 b FK(if)23 b FH(\013)h FK(o)r(ccurs)g(p)r(ositiv)n (ely)f(but)h(not)g(negativ)n(ely)g(then)f FH(\014)1796 3499 y(_)1796 3542 y(^)1884 3521 y(\014)1927 3496 y Fv(0)1967 3521 y FK(in)h([)-12 b([)p FH(T)10 b FK(])-12 b(])q(\()p FJ(A)2235 3496 y FD(+)2276 3521 y FK(\))24 b(and)h FH(\014)2524 3499 y(^)2524 3542 y(_)2613 3521 y(\014)2656 3496 y Fv(0)339 3606 y FK(in)i([)-12 b([)q FH(T)10 b FK(])-12 b(])q(\()p FJ(A)611 3581 y Fv(\000)652 3606 y FK(\).)270 3745 y FJ(\017)34 b FK(if)27 b(it)g(o)r(ccurs)g(negativ)n(ely)h(but)g(not)g(p) r(ositiv)n(ely)e(then)i(the)f(rev)n(erse)g(holds.)167 3925 y FG(Pro)r(of)h FK(Induction)g(on)g(the)f(t)n(yp)r(e)h FH(T)10 b FK(.)1461 b Fu(\003)p eop PStoPSsaved restore %%Page: (142,143) 72 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 139 142 bop 167 167 a Fz(A.3.)63 b(INTERPRET)-6 b(A)g(TION)26 b(OF)h(TYPES)1188 b FK(139)270 404 y(W)-6 b(e)33 b(shall)f(see)g(that)h (uniformit)n(y)f(of)h(the)g(univ)n(ersal)f(term)f(\003)p FH(X)r(:)12 b(t)33 b FK(forces)f FH(e)2322 415 y FD(1)2350 404 y FH(\014)37 b FK(and)c FH(e)2601 415 y FD(2)2629 404 y FH(\014)167 490 y FK(to)f(b)r(e)g(b)r(oth)g(presen)n(t)g(in)f (\(and)i(hence)e(coheren)n(t\))g(or)h(b)r(oth)h(absen)n(t)f(from)g FJ(j)p FK([)-12 b([)p FH(t)p FK(])g(])q(\()p FJ(A)p FK(\))o FJ(j)p FK(,)33 b(where)167 575 y FJ(hA)250 549 y Fv(0)267 575 y FH(;)12 b(\014)t FJ(i)31 b FK(is)e(a)i(tok)n(en)g(for)g FH(T)40 b FK(and)32 b FH(e)1102 586 y FD(1)1130 575 y FH(;)12 b(e)1193 586 y FD(2)1242 575 y FK(:)21 b FH(A)1334 549 y Fv(0)1372 575 y Fu(\032)h FJ(A)31 b FK(are)f(t)n(w)n(o)g(em)n(b)r (eddings.)44 b(In)31 b(fact)f FJ(hA)2554 549 y Fv(0)2571 575 y FH(;)12 b(\014)t FJ(i)167 660 y FK(is)27 b(a)h(tok)n(en)g(i\013)f (this)g(holds.)36 b(F)-6 b(rom)28 b(this)f(w)n(e)g(ha)n(v)n(e)i(the)e (simple)167 777 y FG(Corollary)40 b FK(If)j FJ(hA)p FH(;)12 b(\014)t FJ(i)43 b FK(is)f(a)h(tok)n(en)h(of)f([)-12 b([)q(\005)p FH(X)r(:)12 b(T)e FK(])-12 b(])43 b(and)g FH(\013)31 b FJ(2)f(jAj)42 b FK(then)h FH(\013)g FK(o)r(ccurs)g FM(b)l(oth)167 862 y FK(p)r(ositiv)n(ely)26 b(and)j(negativ)n(ely)e(in) g FH(\014)t FK(.)1517 b Fu(\003)270 980 y FK(The)35 b(corollary)f(is)g (not)i(a)f(su\016cien)n(t)f(condition)h(on)g FJ(hA)p FH(;)12 b(\014)t FJ(i)36 b FK(for)f(it)e(to)i(b)r(e)g(a)g(tok)n(en)h (of)167 1065 y([)-12 b([)q(\005)p FH(X)r(:)12 b(T)e FK(])-12 b(],)24 b(but)g(it)f(is)f(v)n(ery)i(a)g(useful)f(criterion)f(to)h (determine)f(some)h(simple)f(univ)n(ersal)h(t)n(yp)r(es.)167 1264 y Fy(A.3.3)95 b(The)28 b(three)g(simplest)f(t)m(yp)s(es)167 1395 y FK(An)n(y)d(tok)n(en)h(for)f FH(X)15 b FJ(!)10 b FH(X)30 b FK(is)23 b(of)h(the)g(form)f FJ(hA)p FH(;)p 1395 1334 167 3 v 12 w FJ(h)p FH(a;)p 1489 1356 45 3 v 12 w(\013)q FJ(i)q(i)p FK(,)i(in)e(whic)n(h)g(only)h(the)g(tok)n(en)g FH(\013)g FK(app)r(ears)167 1480 y(p)r(ositiv)n(ely)-6 b(,)31 b(so)g FH(a)22 b FK(=)f FJ(f)p FH(\013)p FJ(g)p FK(.)46 b(Hence)30 b(the)g(only)h(tok)n(en)g(for)h(this)e(t)n(yp)r(e)h (is)f(the)g(one)h(giv)n(en,)h(and)167 1565 y([)-12 b([)q(\005)p FH(X)r(:)12 b(X)20 b FJ(!)c FH(X)6 b FK(])-12 b(])20 b FJ(')f(S)-6 b FM(gl)6 b FK(.)35 b(This)27 b(means)g(that)h(the)f (only)h(uniform)f(functions)g(of)h(t)n(yp)r(e)g FH(X)21 b FJ(!)15 b FH(X)167 1650 y FK(are)28 b(the)f(iden)n(tit)n(y)f(and)j (the)e(unde\014ned)i(function.)270 1768 y(The)35 b(case)h(of)f FH(T)g FK(=)25 b FH(X)41 b FK(is)34 b(ev)n(en)i(simpler.)56 b(No)35 b(tok)n(en)h(of)g FJ(A)f FK(can)h(app)r(ear)g(negativ)n(ely)-6 b(,)167 1853 y(and)37 b(so)g(there)f(is)f(no)i(tok)n(en)g(at)f(all:)52 b([)-12 b([\005)p FH(X)r(:)12 b(X)6 b FK(])-12 b(])26 b FJ(')f(E)-17 b FM(mp)41 b FK(has)d(the)e(empt)n(y)f(w)n(eb)h(and)i (only)167 1938 y(the)c(totally)f(unde\014ned)i(term,)g Fn(?)p FK(.)54 b(The)34 b(reason)g(for)h(this)e(is)h(that)g(if)f(a)i (term)d(is)i(de\014ned)167 2023 y(uniformly)d(for)i(all)e(t)n(yp)r(es)h (then)h(it)e(m)n(ust)h(b)r(e)g(coheren)n(t)g(with)f(an)n(y)i(term;)h (since)d(there)g(are)167 2108 y(incoheren)n(t)c(terms)f(this)i(m)n(ust) f(b)r(e)g(trivial.)270 2226 y(It)33 b(is)f(clear)f(that)i(no)h(mo)r (del)d(of)i FG(F)g FK(of)g(a)g(domain-theoretic)e(nature)i(can)h (exclude)d(the)167 2311 y(unde\014ned)g(function,)f(simply)f(b)r (ecause)h Fn(?)f FK(is)g(seman)n(tically)f(de\014nable.)42 b(F)-6 b(or)30 b(higher)g(t)n(yp)r(es)167 2396 y(this)d(leads)g(to)h (the)g(same)f(logical)f(complexities)f(as)j(in)f(section)g FG(??)q FK(.)270 2551 y(Unfortunately)-6 b(,)27 b(ev)n(en)f(accepting)f (partialit)n(y)-6 b(,)24 b(coherence)h(spaces)h(do)g(not)g(b)r(eha)n(v) n(e)g(as)h(w)n(e)167 2636 y(migh)n(t)g(wish.)35 b(The)27 b(tok)n(ens)i(for)f(the)f(in)n(terpretation)f(of)1026 2792 y Fq(Bo)r(ol)20 b FK(=)f(\005)p FH(X)r(:)12 b(X)21 b FJ(!)16 b FH(X)21 b FJ(!)16 b FH(X)167 2947 y FK(are)32 b(of)g(the)f(form)h FJ(hS)-6 b FM(gl)6 b FH(;)p 828 2886 273 3 v 12 w FJ(h)p FH(a;)12 b FJ(h)p FH(b;)p 1009 2908 36 3 v 12 w FJ(\017)q(ii)q(i)32 b FK(suc)n(h)g(that)g FH(a)17 b FJ([)g FH(b)22 b FK(=)g FJ(f\017)q(g)p FK(.)47 b(This)32 b(admits)f(not)h(t)n(w)n(o)g(but)167 3033 y FM(thr)l(e)l(e)c FK(\(incoheren)n(t\))f(solutions:)484 3188 y FJ(hS)-6 b FM(gl)6 b FH(;)p 635 3127 368 3 v 12 w FJ(hf\017)q(g)p FH(;)12 b FJ(h)p Fn(?)p FH(;)p 912 3148 36 3 v 12 w FJ(\017ii)q(i)79 b(hS)-6 b FM(gl)6 b FH(;)p 1259 3127 418 3 v 12 w FJ(hf\017)q(g)p FH(;)12 b FJ(hf\017g)p FH(;)p 1586 3148 36 3 v 12 w FJ(\017)q(ii)q(i)78 b(hS)-6 b FM(gl)6 b FH(;)p 1933 3127 368 3 v 12 w FJ(h)p Fn(?)p FH(;)12 b FJ(hf\017)q(g)p FH(;)p 2210 3148 36 3 v 12 w FJ(\017)q(iii)167 3344 y FK(of)28 b(whic)n(h)f(the)g(\014rst)h (and)h(last)e(represen)n(t)g FG(t)g FK(and)i FG(f)7 b FK(.)270 3499 y(The)32 b(middle)e(one)i(is)g FM(interse)l(ction)p FK(.)47 b(Although)33 b(it)e(is)g(not)h(de\014nable)g(in)g(System)f FG(F)p FK(,)h(it)167 3584 y(ma)n(y)25 b(b)r(e)g(though)n(t)h(of)g(as)f (the)g(program)h(whic)n(h)e(reads)h(t)n(w)n(o)g(streams)g(of)g(tok)n (ens)h(and)g(outputs)167 3669 y(those)37 b(common)f(to)g(b)r(oth)h(of)g (them.)61 b(It)36 b(is)f(a)i(uniform)f FM(line)l(ar)44 b FK(function)36 b FH(X)24 b FJ(\012)18 b FH(X)24 b Fu(\()18 b FH(X)6 b FK(,)167 3754 y(whereas)42 b FG(t)g FK(and)h FG(f)49 b FK(are)42 b(linear)e FH(X)26 b FK(&)19 b FH(X)25 b Fu(\()20 b FH(X)48 b FK(b)r(ecause)42 b(they)g(only)h(use)f(one)g(of) g(their)167 3840 y(argumen)n(ts.)35 b(Consequen)n(tly)25 b(w)n(e)g(ma)n(y)g(eliminate)c(in)n(tersection)i(b)n(y)i(considering)g (the)f(\\linear)167 3925 y(b)r(o)r(oleans")p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 140 143 bop 167 167 a FK(140)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)1144 404 y FK(\005)p FH(X)r(:)12 b(X)21 b FK(&)15 b FH(X)21 b Fu(\()16 b FH(X)270 576 y FK(Seman)n(tically)-6 b(,)57 b(this)51 b FM(bi)7 b FK(linear)50 b(function)i(is)f(just)h(binary)h(in)n(tersection,)j (whic)n(h)51 b(is)167 661 y(uniformly)33 b(de\014nable)h(in)f(our)i (domains)f(b)r(ecause)g(they)g(are)f(b)r(oundedly)i(complete)d(\(ha)n (v)n(e)167 746 y(joins)f(of)g(sets)f(of)h(p)r(oin)n(ts)g(whic)n(h)e (are)i(b)r(ounded)h(ab)r(o)n(v)n(e\).)45 b(One)30 b(migh)n(t)g (imagine,)g(therefore,)167 831 y(that)d(it)e(w)n(ould)h(cease)g(to)g(b) r(e)g(de\014nable)h(if)e(w)n(e)h(extended)g(our)h(class)f(of)h(domains) f(to)h(include)167 916 y(Jung's)34 b(\\L-domains",)g(in)d(whic)n(h)g (for)h(ev)n(ery)g(p)r(oin)n(t)g FH(a)23 b FJ(2)f(A)32 b FK(the)f(set)h FJ(#)12 b FH(a)2182 876 y FD(def)2190 916 y FK(=)30 b FJ(f)p FH(a)2345 890 y Fv(0)2384 916 y FK(:)45 b FH(a)2484 890 y Fv(0)2523 916 y FJ(\024)23 b FH(a)p FJ(g)167 1001 y FK(is)34 b(a)h(complete)d(lattice.)54 b(Unfortunately)-6 b(,)36 b(lik)n(e)d(the)h(Hydra)h(the)g(\\in)n (tersection")e(function)167 1086 y(just)i(b)r(ecomes)e(more)h (complicated:)47 b(w)n(e)33 b(can)i(de\014ne)g FH(m)p FK(\()p FH(a;)12 b(b)p FK(\))34 b(to)h(b)r(e)f(the)g(join)g(in)g FJ(#)24 b FH(a)35 b FK(of)167 1171 y(the)30 b(set)f FJ(f)p FH(c)21 b FK(:)43 b FH(c)20 b FJ(\024)h FH(a;)12 b(c)21 b FJ(\024)g FH(b)p FJ(g)p FK(.)43 b(So)31 b(long)f(as)g(w)n(e)g(only)g (consider)f(domains)i(for)f(whic)n(h)f(in)g(the)167 1256 y(lattices)23 b FJ(#)12 b FH(a)26 b FK(binary)g(meet)d(distributes)i(o) n(v)n(er)g(arbitrary)h(joins,)g FH(m)20 b FK(:)g FJ(A)12 b(\012)g(A)g Fu(\()h FJ(A)25 b FK(is)g(bilinear)167 1341 y(and)41 b(uniform)e(in)g(the)g(sense)g(w)n(e)g(ha)n(v)n(e)i (de\014ned.)71 b(By)40 b(iterating)e(it,)k(w)n(e)d(w)n(ould)h(obtain) 167 1427 y(in\014nitely)23 b(man)n(y)j(additional)f(p)r(oin)n(ts)g(of)g (\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)g FJ(!)p FH(X)31 b FK(|)25 b(except)f(that)i(it's)e(w)n(orse)h(than)167 1512 y(this,)37 b(b)r(ecause)f(the)f(original)g(size)f(problems)h (recur)f(and)j(w)n(e)e(can)h(no)g(longer)g(ev)n(en)f(form)167 1597 y(p)r(olymorphic)27 b(t)n(yp)r(es)h(in)f(the)g(seman)n(tics!)1275 1571 y FD(6)167 1832 y FE(A.4)114 b(In)m(terpretation)29 b(of)e(terms)167 1986 y FK(Ha)n(ving)34 b(sk)n(etc)n(hed)g(the)f (notation)h(w)n(e)f(shall)g(no)n(w)h(in)n(terpret)d(terms)i(and)h(giv)n (e)f(the)h(formal)167 2072 y(seman)n(tics)27 b(of)h FG(F)f FK(using)h(coherence)f(spaces.)270 2197 y(Recall)h(that)i(a)g(t)n(yp)r (e)g FH(T)39 b FK(with)29 b FH(n)h FK(free)f(t)n(yp)r(e)g(v)l(ariables) h FH(X)1831 2208 y FD(1)1859 2197 y FH(;)12 b(:::;)g(X)2035 2208 y Fw(n)2098 2197 y FK(is)29 b(in)n(terpreted)f(b)n(y)j(a)167 2282 y(stable)25 b(functor)i([)-12 b([)p FH(T)10 b FK(])-12 b(])20 b(:)g FG(Gem)937 2252 y Fw(n)990 2282 y FJ(!)g FG(Gem)p FK(.)34 b(Let)26 b FH(t)f FK(b)r(e)h(a)g(term)f(of)h(t)n(yp)r (e)g FH(T)36 b FK(with)24 b(free)h(v)l(ariables)167 2367 y FH(x)206 2378 y FD(1)234 2367 y FH(;)12 b(:::;)g(x)392 2378 y Fw(m)464 2367 y FK(of)25 b(t)n(yp)r(es)g FH(U)775 2378 y FD(1)802 2367 y FH(;)12 b(:::;)g(U)968 2378 y Fw(m)1015 2367 y FK(,)26 b(where)d(the)h(free)g(v)l(ariables)g(of)h (the)2001 2368 y FH(U)p 2004 2388 41 3 v 2079 2367 a FK(are)g(included)e(among)167 2452 y(the)294 2453 y FH(X)p 297 2473 50 3 v 357 2452 a FK(.)46 b(Then)31 b FH(t)g FK(lik)n(ewise)e(assigns)j(to)f(ev)n(ery)h FH(n)p FK(-tuple)1698 2453 y FJ(A)p 1702 2473 43 3 v 1786 2452 a FK(in)e FG(Gem)2039 2422 y Fw(n)2103 2452 y FK(and)i(ev)n(ery)g FH(m)p FK(-tuple)167 2537 y FH(b)196 2548 y Fw(j)245 2537 y FJ(2)24 b FK([)-12 b([)p FH(U)389 2548 y Fw(j)415 2537 y FK(])g(]\()468 2538 y FJ(A)p 472 2558 V -1 x FK(\))33 b(a)g(p)r(oin)n(t)g FH(c)23 b FJ(2)g FK([)-12 b([)q FH(T)10 b FK(])-12 b(]\()1094 2538 y FJ(A)p 1098 2558 V -1 x FK(\).)51 b(Of)32 b(course)h(the)g (function)1984 2538 y FH(b)p 1987 2558 16 3 v 2036 2537 a FJ(7!)24 b FH(c)32 b FK(m)n(ust)h(b)r(e)f(stable,)167 2622 y(and)27 b(w)n(e)f(ma)n(y)h(simplify)d(matters)h(b)n(y)i (replacing)e FH(t)i FK(b)n(y)g FH(\025)1670 2623 y(x)p 1674 2643 26 3 v -1 x(:)12 b(t)26 b FK(and)h FH(T)36 b FK(b)n(y)27 b FH(U)2150 2633 y FD(1)2192 2622 y FJ(!)14 b FH(:::)g FJ(!)g FH(U)2478 2633 y Fw(m)2538 2622 y FJ(!)g FH(T)167 2707 y FK(to)28 b(mak)n(e)g FH(m)19 b FK(=)h(0.)36 b(W)-6 b(e)27 b(m)n(ust)g(consider)h(what)g(happ)r(ens)h(when)e(w)n(e)h (v)l(ary)g(the)g FJ(A)2335 2718 y Fw(i)2355 2707 y FK(.)167 2911 y Fy(A.4.1)95 b(V)-8 b(ariable)29 b(coherence)f(spaces)167 3042 y FK(Let)e FJ(T)38 b FK(:)20 b FG(Gem)f FJ(!)h FG(Gem)26 b FK(b)r(e)h(an)n(y)h(stable)e(functor)h(and)h FH(\034)8 b FK(\()p FJ(A)p FK(\))19 b FJ(2)h(T)e FK(\()p FJ(A)p FK(\))27 b(a)g(c)n(hoice)e(of)j(p)r(oin)n(ts.)167 3127 y(Let)38 b FH(e)28 b FK(:)f FJ(A)468 3101 y Fv(0)512 3127 y Fu(\032)h FJ(A)39 b FK(b)r(e)g(a)g(rigid)e(em)n(b)r(edding;)45 b(w)n(e)38 b(w)n(an)n(t)h(to)g(mak)n(e)g FH(\034)46 b FK(\\monotone")41 b(with)167 3212 y(resp)r(ect)27 b(to)h(it.)34 b(W)-6 b(e)27 b(can)h(use)g(the)f(idea)h(from)f(section)g FG(??)h FK(to)g(do)h(this:)35 b(w)n(e)27 b(w)n(an)n(t)1084 3383 y FH(\034)8 b FK(\()p FJ(A)1205 3357 y Fv(0)1222 3383 y FK(\))19 b FJ(\024)g(T)g FK(\()p FH(e)p FK(\))1485 3357 y Fv(\000)1526 3383 y FK(\()p FH(\034)8 b FK(\()p FJ(A)p FK(\)\))167 3554 y(whic)n(h)27 b(b)r(ecomes,)g(when)h(the)f(em)n (b)r(eddings)h(are)f(subspace)i(inclusions,)1053 3725 y FH(\034)8 b FK(\()p FJ(A)1174 3699 y Fv(0)1190 3725 y FK(\))20 b FJ(\032)f FH(\034)8 b FK(\()p FJ(A)p FK(\))15 b FJ(\\)h(jT)i FK(\()p FJ(A)1696 3699 y Fv(0)1712 3725 y FK(\))p FJ(j)p 167 3790 1003 3 v 246 3833 a FC(6)273 3854 y FB(These)42 b(t)n(w)n(o)h(hitherto)d(unpublished)e(observ)m (ations)j(ha)n(v)n(e)h(b)r(een)f(made)g(b)n(y)h(the)f(author)g(of)h (this)167 3925 y(app)r(endix)25 b(since)i(the)g(original)f(edition)g (of)i(this)e(b)r(o)r(ok.)p eop PStoPSsaved restore %%Page: (144,145) 73 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 141 144 bop 167 167 a Fz(A.4.)63 b(INTERPRET)-6 b(A)g(TION)26 b(OF)h(TERMS)1173 b FK(141)167 404 y(W)-6 b(e)28 b(shall)f(use)h(the)f (separabilit)n(y)g(prop)r(ert)n(y)i(to)f(sho)n(w)h(that)f(stabilit)n(y) e(forces)i(equalit)n(y)g(here.)167 490 y(The)f(follo)n(wing)g(is)g(due) h(to)g(Eugenio)g(Moggi.)167 624 y FG(Lemma)j FK(Let)i FH(e)24 b FK(:)g FJ(A)744 599 y Fv(0)785 624 y Fu(\032)g FJ(A)34 b FK(b)r(e)f(a)i(rigid)d(em)n(b)r(edding.)53 b(Let)34 b FJ(A)17 b FK(+)1981 635 y Fv(A)2021 622 y Fa(0)2057 624 y FJ(A)34 b FK(b)r(e)f(the)h(coherence)167 709 y(space)28 b(whose)h(w)n(eb)f(consists)g(of)g(t)n(w)n(o)g (incoheren)n(t)g(copies)f(of)i FJ(jAj)e FK(with)g(the)h(subgraphs)i FJ(jA)2636 684 y Fv(0)2653 709 y FJ(j)167 794 y FK(iden)n(ti\014ed.)53 b(Then)34 b FJ(A)g FK(has)h(t)n(w)n(o)f(canonical)f(rigid)g(em)n(b)r (eddings)h(in)n(to)g FH(A)17 b FK(+)2220 805 y Fv(A)2260 792 y Fa(0)2295 794 y FJ(A)34 b FK(and)h(their)167 879 y(in)n(tersection)26 b(is)h FJ(A)672 854 y Fv(0)688 879 y FK(.)1910 b Fu(\003)270 1014 y FK(What)34 b(do)r(es)f(it)f(mean)h (for)h FH(\034)40 b FK(to)34 b(b)r(e)e(a)i(stable)e(function)i(from)e FG(Gem)p FK(?)51 b(W)-6 b(e)33 b(ha)n(v)n(e)h(not)167 1099 y(giv)n(en)c(the)g(co)r(domain)769 1074 y FD(7)797 1099 y FK(,)h(but)g(w)n(e)f(can)g(still)e(w)n(ork)j(out)f(in)n (tersections)f(using)i(the)f(de\014nition)167 1184 y(of)k FH(a)24 b FJ(\024)g FH(b)33 b FK(as)i FH(a)24 b FJ(\024)f FH(e)723 1159 y Fv(\000)765 1184 y FH(b)34 b FK(for)g FH(e)23 b FK(:)h FJ(A)g Fu(\032)g FJ(B)r FK(.)54 b(W)-6 b(rite)32 b FJ(A)1603 1195 y FD(1)1665 1184 y FK(and)i FJ(A)1865 1195 y FD(2)1927 1184 y FK(for)g(the)f(t)n(w)n(o)h(copies)f (of)h FJ(A)167 1269 y FK(inside)26 b FJ(A)16 b FK(+)493 1280 y Fv(A)533 1267 y Fa(0)567 1269 y FJ(A)p FK(,)28 b(whose)g(in)n(tersection)e(is)h FJ(A)1383 1244 y Fv(0)1400 1269 y FK(.)270 1404 y(Using)h(the)f(\\pro)t(jection")h(form)g(of)g (the)f(inequalit)n(y)-6 b(,)27 b FJ(hA)1788 1378 y Fv(00)1819 1404 y FH(;)12 b(\014)t FJ(i)28 b FK(is)f(in)g(the)g(in)n(tersection)f (i\013)1192 1592 y FJ(A)1248 1566 y Fv(00)1298 1592 y FJ(\032)20 b(A)1429 1603 y FD(1)1472 1592 y FJ(\\)c(A)1591 1603 y FD(2)820 1677 y FH(\014)23 b FJ(2)d FH(\034)8 b FK(\()p FJ(A)1070 1688 y FD(1)1097 1677 y FK(\))16 b FJ(\\)g(jT)h FK(\()p FJ(A)1361 1651 y Fv(00)1391 1677 y FK(\))p FJ(j)i FK(=)h FH(\034)8 b FK(\()p FJ(A)p FK(\))15 b FJ(\\)h(jT)h FK(\()p FJ(A)1915 1651 y Fv(00)1945 1677 y FK(\))p FJ(j)824 1762 y FH(\014)24 b FJ(2)19 b FH(\034)8 b FK(\()p FH(A)1070 1773 y FD(2)1097 1762 y FK(\))16 b FJ(\\)g(jT)h FK(\()p FJ(A)1361 1736 y Fv(00)1391 1762 y FK(\))p FJ(j)i FK(=)h FH(\034)8 b FK(\()p FJ(A)p FK(\))15 b FJ(\\)h(jT)h FK(\()p FJ(A)1915 1736 y Fv(00)1945 1762 y FK(\))p FJ(j)167 1947 y FK(The)27 b(in)n(tersection)f(of)i(the)g(v)l (alues)g(at)f FJ(A)1249 1958 y FD(1)1305 1947 y FK(and)i FJ(A)1500 1958 y FD(2)1556 1947 y FK(is)e(therefore)f(just)1182 2137 y FH(\034)8 b FK(\()p FJ(A)p FK(\))15 b FJ(\\)h(jT)i FK(\()p FJ(A)1567 2112 y Fv(0)1583 2137 y FK(\))p FJ(j)167 2327 y FK(By)28 b(stabilit)n(y)e(this)h(m)n(ust)h(b)r(e)f(the)g(v)l (alue)h(at)g FJ(A)1417 2301 y Fv(0)1434 2327 y FK(.)35 b(This)27 b(pro)n(v)n(es)i(the)167 2462 y FG(Prop)r(osition)j FK(Let)h FH(\034)42 b FK(b)r(e)33 b(an)i(ob)t(ject)f(of)g(the)g(v)l (ariable)f(coherence)g(space)h FJ(T)18 b FK(\()p FH(X)2388 2473 y FD(1)2416 2462 y FH(;)12 b(:::;)g(X)2592 2473 y Fw(n)2626 2462 y FK(\),)167 2547 y(and)29 b FH(e)338 2558 y Fw(i)377 2547 y FK(:)20 b FJ(A)472 2521 y Fv(0)472 2564 y Fw(i)512 2547 y Fu(\032)f FJ(A)665 2558 y Fw(i)713 2547 y FK(b)r(e)28 b(rigid)e(em)n(b)r(eddings.)35 b(Then)1541 2521 y FD(8)1053 2737 y FH(\034)8 b FK(\()1118 2738 y FJ(A)1174 2712 y Fv(0)p 1122 2757 60 3 v 1191 2737 a FK(\))19 b(=)g FH(\034)8 b FK(\()1375 2738 y FJ(A)p 1379 2757 43 3 v -1 x FK(\))16 b FJ(\\)f(jT)j FK(\()1639 2738 y FJ(A)1695 2712 y Fv(0)p 1643 2757 60 3 v 1712 2737 a FK(\))p FJ(j)167 2927 y FK(and)29 b(indeed)e(if)g FH(\034)35 b FK(satis\014es)28 b(this)f(condition)g(then)h(it)e(is)h(stable.)745 b Fu(\003)167 3141 y Fy(A.4.2)95 b(Coherence)28 b(of)f(tok)m(ens)167 3276 y FK(In)33 b(fact)g(the)g(lemma)e(tells)f(us)k(sligh)n(tly)d (more.)51 b FJ(B)26 b FK(=)d FJ(A)17 b FK(+)1771 3287 y Fv(A)1811 3274 y Fa(0)1846 3276 y FJ(A)34 b FK(has)f(an)h (automorphism)f FH(e)167 3361 y FK(exc)n(hanging)c(the)f(t)n(w)n(o)g (copies)g(of)h FJ(A)p FK(.)37 b(This)27 b(m)n(ust)h(\014x)h FH(\034)8 b FK(\()p FJ(B)r FK(\),)28 b(so)h(if)e FH(\014)d FJ(2)19 b(T)-6 b FH(r)r FK(\()p FH(\034)8 b FK(\()p FJ(B)r FK(\)\))29 b(then)f(also)167 3446 y FH(e\014)j FK(is)c(in)g(this)g (trace)h FM(and)f(c)l(onse)l(quently)g(must)h(b)l(e)g(c)l(oher)l(ent)g (with)f FH(\014)t FK(.)35 b(So,)167 3580 y FG(Lemma)25 b FK(Let)h FH(\014)e FJ(2)19 b(jT)f FK(\()p FJ(A)p FK(\))p FJ(j)27 b FK(and)h FH(e)1108 3591 y FD(1)1136 3580 y FH(;)12 b(e)1199 3591 y FD(2)1246 3580 y FK(:)20 b FJ(A)g Fu(\032)g FJ(B)29 b FK(b)r(e)f(t)n(w)n(o)f(em)n(b)r(eddings.)35 b(Then)28 b FH(e)2391 3591 y FD(1)2419 3580 y FH(\014)2481 3558 y(_)2481 3601 y(^)2569 3580 y(e)2601 3591 y FD(2)2629 3580 y FH(\014)167 3666 y FK(in)f FJ(B)r FK(.)2298 b Fu(\003)p 167 3719 1003 3 v 246 3763 a FC(7)273 3784 y FB(It)27 b(is)g(the)g(total)h(category)g(\006)916 3779 y Fl(\016)958 3784 y Fx(X)q(:)10 b Fl(T)16 b FB(\()p Fx(X)5 b FB(\))26 b(whic)n(h)h(w)n(e)i(met)e(in)g(section)g Ft(??)o FB(.)246 3833 y FC(8)273 3854 y FB(Note)f(that)f(this)f (equalit)n(y)h(only)g(holds)f(for)i FA(typ)m(e)h FB(v)m(ariables)d(and) h(not)h(for)g(dep)r(endency)d(o)n(v)n(er)k(ordinary)167 3925 y(domains.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 142 145 bop 167 167 a FK(142)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)270 404 y FK(The)g(con)n(v)n(erse)g (holds:)167 538 y FG(Lemma)36 b FK(Let)i FH(\014)31 b FJ(2)d(jT)17 b FK(\()p FJ(A)p FK(\))p FJ(j)38 b FK(b)r(e)h(suc)n(h)g (that)g(\(i\))f FJ(A)g FK(is)g(minimal)e(for)j FH(\014)j FK(and)e(\(ii\))d FH(\014)42 b FK(has)167 623 y(coheren)n(t)31 b(images)f(under)h(an)n(y)h(pair)e(of)i(em)n(b)r(eddings)e(of)i FJ(A)f FK(in)n(to)f(another)i(domain.)45 b(Then)167 708 y(there)27 b(is)g(an)h(ob)t(ject)g FH(\034)766 719 y Fv(hA)p Fw(;\014)r Fv(i)919 708 y FK(of)g(t)n(yp)r(e)g FJ(T)46 b FK(whose)28 b(v)l(alue)g(at)g FJ(T)18 b FK(\()p FJ(B)r FK(\))27 b(is)1056 895 y FJ(fT)19 b FK(\()p FH(e)p FK(\)\()p FH(\014)t FK(\))f(:)40 b FH(e)19 b FK(:)h FJ(A)g Fu(\032)g FJ(B)r(g)167 1082 y FK(and)29 b(moreo)n(v)n(er)e(this)g(is)g FM(atomic)p FK(,)i FM(i.e.)e FK(has)i(no)f(non)n(trivial)f(sub)r(ob)t (ject.)568 b Fu(\003)270 1215 y FK(T)-6 b(o)29 b(test)e(this)g (condition)h(w)n(e)f(only)h(need)g(to)g(consider)g(graphs)h(up)f(to)h (t)n(wice)d(the)h(size)g(of)167 1300 y FJ(jAj)p FK(,)h(and)h(so)g(it)e (is)g(a)h(\014nite)903 1274 y FD(9)959 1300 y FK(calculation)e(to)j (determine)d(whether)h FJ(hA)p FH(;)12 b(\014)t FJ(i)29 b FK(satis\014es)f(it.)36 b(F)-6 b(or)167 1385 y(an)n(y)30 b(giv)n(en)e(t)n(yp)r(e)h(these)f(tok)n(ens)i(are)e(recursiv)n(ely)f (en)n(umerable.)37 b(Because)29 b FH(\034)2221 1396 y Fv(hA)p Fw(;\014)r Fv(i)2375 1385 y FK(is)f(atomic,)167 1470 y(w)n(e)i(m)n(ust)h(ha)n(v)n(e)g(just)g FM(one)f FK(tok)n(en)i(for)f(\005)p FH(X)r(:)12 b FJ(T)17 b FK(\()p FH(X)6 b FK(\),)31 b(so)h FJ(hA)p FH(;)12 b(\014)t FJ(i)31 b FK(and)h FJ(hA)2107 1444 y Fv(0)2124 1470 y FH(;)12 b(\014)2198 1444 y Fv(0)2214 1470 y FJ(i)31 b FK(are)f(iden)n(ti\014ed) 167 1555 y(for)e(an)n(y)h FH(e)19 b FK(:)h FJ(A)g(')f(A)708 1530 y Fv(0)753 1555 y FK(with)26 b FH(e\014)e FK(=)19 b FH(\014)1125 1530 y Fv(0)1141 1555 y FK(.)270 1742 y(W)-6 b(e)28 b(still)d(ha)n(v)n(e)k(to)e(sa)n(y)i(when)f(these)f(tok)n (ens)i(are)e(coheren)n(t.)167 1875 y FG(Lemma)i FK(Let)h FH(\014)623 1886 y FD(1)673 1875 y FJ(2)22 b(jT)c FK(\()p FJ(A)901 1886 y FD(1)929 1875 y FK(\))p FJ(j)31 b FK(and)h FH(\014)1188 1886 y FD(2)1238 1875 y FJ(2)22 b(jT)c FK(\()p FJ(A)1466 1886 y FD(2)1494 1875 y FK(\))o FJ(j)31 b FK(eac)n(h)h (satisfy)f(these)g(conditions.)46 b(Then)167 1960 y FH(\034)197 1971 y Fv(hA)256 1978 y Fi(1)281 1971 y Fw(;\014)323 1978 y Fi(1)347 1971 y Fv(i)369 1960 y FK(\()p FJ(B)r FK(\))491 1938 y FH(_)491 1981 y(^)579 1960 y(\034)609 1971 y Fv(hA)668 1978 y Fi(2)693 1971 y Fw(;\014)735 1978 y Fi(2)760 1971 y Fv(i)782 1960 y FK(\()p FJ(B)r FK(\))22 b(at)g(ev)n(ery)f(coherence)g(space)h FJ(B)i FK(i\013)e(for)g(ev)n(ery)f(pair)h(of)g(em)n(b)r(eddings)167 2045 y FH(e)199 2056 y FD(1)246 2045 y FK(:)e FJ(A)341 2056 y FD(1)389 2045 y Fu(\032)g FJ(C)t FK(,)28 b FH(e)607 2056 y FD(2)654 2045 y FK(:)20 b FJ(A)749 2056 y FD(2)796 2045 y Fu(\032)g FJ(C)t FK(,)28 b(w)n(e)f(ha)n(v)n(e)i FJ(T)18 b FK(\()p FH(e)1367 2056 y FD(1)1395 2045 y FK(\)\()p FH(\014)t FK(\))1538 2023 y FH(_)1538 2066 y(^)1626 2045 y FJ(T)h FK(\()p FH(e)1742 2056 y FD(2)1769 2045 y FK(\)\()p FH(\014)t FK(\).)705 b Fu(\003)270 2178 y FK(Finally)33 b(this)g(enables)g(us)h(to)g(calculate)d(the)j(univ)n(ersal)f (abstraction)h(of)g(an)n(y)g(v)l(ariable)167 2263 y(coherence)27 b(space.)167 2397 y FG(Prop)r(osition)38 b FK(Let)i FJ(T)47 b FK(:)29 b FG(Gem)f FJ(!)h FG(Gem)40 b FK(b)r(e)g(a)h(stable)f (functor.)74 b(Then)41 b(its)f(univ)n(ersal)167 2482 y(abstraction,)24 b(\005)p FH(X)r(:)12 b FJ(T)17 b FK(\()p FH(X)6 b FK(\),)23 b(is)e(the)g(coherence)g(space)h(whose)g(tok)n(ens)g (are)g(equiv)l(alence)f(classes)167 2567 y(of)28 b(pairs)g FJ(hA)p FH(;)12 b(\014)t FJ(i)28 b FK(suc)n(h)g(that)270 2737 y FJ(\017)34 b FH(\014)24 b FJ(2)19 b(jT)f FK(\()p FJ(A)p FK(\))p FJ(j)270 2887 y(\017)34 b(A)29 b FK(is)f(minimal)e(for)j (this,)g FM(i.e.)f FK(if)g FJ(A)1292 2861 y Fv(0)1329 2887 y FJ(\032)20 b(A)29 b FK(and)h FH(\014)24 b FJ(2)c(jT)e FK(\()p FJ(A)1918 2861 y Fv(0)1934 2887 y FK(\))p FJ(j)28 b FK(then)h FJ(A)2228 2861 y Fv(0)2265 2887 y FK(=)20 b FJ(A)29 b FK(\(so)g FJ(A)g FK(is)339 2972 y(\014nite\).)270 3121 y FJ(\017)34 b FK(for)28 b(an)n(y)h(t)n(w)n(o)f(rigid)f(em)n(b)r (eddings)g FH(e)1297 3132 y FD(1)1325 3121 y FH(;)12 b(e)1388 3132 y FD(2)1435 3121 y FK(:)20 b FJ(A)g Fu(\032)g FJ(B)r FK(,)28 b(w)n(e)f(ha)n(v)n(e)1172 3338 y FJ(T)18 b FK(\()p FH(e)1287 3349 y FD(1)1315 3338 y FK(\)\()p FH(\014)t FK(\))1457 3316 y FH(_)1457 3359 y(^)1546 3338 y FJ(T)g FK(\()p FH(e)1661 3349 y FD(2)1689 3338 y FK(\)\()p FH(\014)t FK(\))339 3555 y(in)27 b FJ(T)19 b FK(\()p FJ(B)r FK(\).)270 3705 y FJ(\017)34 b(hA)p FH(;)12 b(\014)t FJ(i)27 b FK(is)f(iden)n(ti\014ed)f(with)g FJ(hA)1170 3679 y Fv(0)1187 3705 y FH(;)12 b(\014)1261 3679 y Fv(0)1277 3705 y FJ(i)27 b FK(i\013)e FH(e)20 b FK(:)g FJ(A)f(')h(A)1713 3679 y Fv(0)1756 3705 y FK(and)27 b FJ(T)18 b FK(\()p FH(e)p FK(\)\()p FH(\014)t FK(\))h(=)g FH(\014)2267 3679 y Fv(0)2310 3705 y FK(\(so)26 b FJ(jAj)g FK(ma)n(y)339 3790 y(b)r(e)i(tak)n(en)g(to)g(b)r(e)g(a)g(subset)g(of)g(I)-12 b(N\).)p 167 3860 1003 3 v 246 3903 a FC(9)273 3925 y FB(Though)27 b(it)g(w)n(ould)g(app)r(ear)g(to)h(b)r(e)f(exp)r(onen)n (tial)f(in)g Fl(jAj)1593 3903 y FC(2)1620 3925 y FB(.)p eop PStoPSsaved restore %%Page: (146,147) 74 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 143 146 bop 167 167 a Fz(A.4.)63 b(INTERPRET)-6 b(A)g(TION)26 b(OF)h(TERMS)1173 b FK(143)270 404 y FJ(\017)34 b(hA)p FH(;)12 b(\014)t FJ(i)32 b FK(is)f(coheren)n(t)g(with)g FJ(hA)1168 379 y Fv(0)1185 404 y FH(;)12 b(\014)1259 379 y Fv(0)1275 404 y FJ(i)32 b FK(i\013)e(for)i(ev)n(ery)f(pair)g(of)h (em)n(b)r(eddings)f FH(e)22 b FK(:)h FJ(A)f Fu(\032)h FJ(B)339 490 y FK(and)29 b FH(e)510 464 y Fv(0)546 490 y FK(:)20 b FJ(A)641 464 y Fv(0)677 490 y Fu(\032)g FJ(B)30 b FK(w)n(e)d(ha)n(v)n(e)i FJ(T)18 b FK(\()p FH(e)p FK(\)\()p FH(\014)t FK(\))1379 467 y FH(_)1379 510 y(^)1467 490 y FJ(T)g FK(\()p FH(e)1582 464 y Fv(0)1599 490 y FK(\)\()p FH(\014)1696 464 y Fv(0)1712 490 y FK(\).)167 669 y FG(Pro)r(of)36 b FK(\005)p FH(X)r(:)12 b FJ(T)17 b FK(\()p FH(X)6 b FK(\))35 b(is)g(a)h(coherence)f(space)h(b)r(ecause)g(if)e(an)n(y)j FJ(hA)p FH(;)12 b(\014)t FJ(i)36 b FK(o)r(ccurs)g(in)f(a)h(p)r(oin)n(t) 167 754 y(then)30 b(so)h(do)r(es)g(the)e(whole)h(of)g FH(\034)1029 765 y Fv(hA)p Fw(;\014)r Fv(i)1155 754 y FK(,)h(and)g(an)n(y)h(coheren)n(t)d(union)i(of)g(these)e(giv)n(es)h (rise)f(to)i(a)167 840 y(uniform)c(elemen)n(t.)1934 b Fu(\003)270 961 y FK(One)39 b(ough)n(t)h(to)e(pro)n(v)n(e)i(that)f(if)e FJ(T)d FK(:)28 b FG(Gem)18 b FJ(\002)g FG(Gem)27 b FJ(!)h FG(Gem)38 b FK(is)g(stable)g(then)h(so)g(is)167 1046 y(\005)p FH(X)r(:)12 b FJ(T)42 b FK(:)25 b FG(Gem)f FJ(!)h FG(Gem)p FK(,)37 b(and)e(also)g(c)n(hec)n(k)g(that)g(the)g(p)r(ositiv)n (e)f(and)h(negativ)n(e)g(criterion)167 1131 y(remains)27 b(v)l(alid.)167 1333 y Fy(A.4.3)95 b(In)m(terpretation)28 b(of)f(F)167 1464 y FK(Let)e(us)h(sum)f(up)h(b)n(y)h(setting)e(out)h (in)f(full)f(the)h(coherence)g(space)g(seman)n(tics)g(of)h FG(F)p FK(.)f(The)g FM(typ)l(e)167 1549 y FH(U)34 b FK(in)27 b FH(n)g FK(free)f(v)l(ariables)827 1550 y FH(X)p 831 1570 50 3 v 917 1549 a FK(is)g(in)n(terpreted)g(as)h(a)h(stable)f (functor)g([)-12 b([)q FH(U)7 b FK(])-12 b(])20 b(:)g FG(Gem)2276 1519 y Fw(n)2329 1549 y FJ(!)g FG(Gem)26 b FK(as)167 1634 y(in)h FJ(x)p FK(A.3,)h(with)f(the)h(additional)f (clause)251 1777 y(4.)35 b(If)21 b FH(U)26 b FK(=)20 b(\005)p FH(X)r(:)12 b(T)30 b FK(then)20 b(the)g(w)n(eb)g(of)h([)-12 b([)q FH(U)7 b FK(])-12 b(])q(\()1383 1778 y FJ(A)p 1387 1798 43 3 v -1 x FK(\))20 b(is)f(giv)n(en)i(as)g(in)f(the)g(preceding)f (prop)r(osition,)339 1862 y(where)31 b FJ(T)18 b FK(\()p FH(X)6 b FK(\))21 b(=)h([)-12 b([)q FH(T)10 b FK(])-12 b(]\()947 1863 y FJ(A)p 951 1883 V -1 x FH(;)12 b(X)6 b FK(\).)46 b(The)30 b(em)n(b)r(edding)h(induced)g(b)n(y)2064 1863 y FH(e)p 2067 1883 19 3 v 2118 1862 a FK(:)2159 1863 y FJ(A)2215 1838 y Fv(0)p 2162 1883 60 3 v 2254 1862 a Fu(\032)2354 1863 y FJ(A)p 2357 1883 43 3 v 2441 1862 a FK(is)f(tak)n(es)339 1948 y(tok)n(ens)f(of)f([)-12 b([)q FH(U)7 b FK(])-12 b(]\()776 1949 y FJ(A)832 1923 y Fv(0)p 780 1968 60 3 v 849 1948 a FK(\))27 b(to)h(the)g(corresp)r (onding)g(tok)n(ens)h(with)d FH(\013)1988 1922 y Fv(0)1988 1965 y Fw(i)2036 1948 y FK(replaced)g(b)n(y)j FH(e)2445 1959 y Fw(i)2465 1948 y FH(\013)2509 1922 y Fv(0)2509 1965 y Fw(i)2529 1948 y FK(.)270 2170 y(The)40 b FM(term)g FH(t)g FK(of)h(t)n(yp)r(e)f FH(T)50 b FK(with)40 b FH(m)g FK(free)f(v)l(ariables)1759 2171 y FH(x)p 1763 2190 26 3 v 1839 2170 a FK(of)h(t)n(yp)r(es)2134 2171 y FH(U)p 2137 2190 41 3 v 2228 2170 a FK(\(the)g(free)f(t)n(yp)r(e)167 2255 y(v)l(ariables)29 b(of)h FH(T)6 b(;)621 2256 y(U)p 625 2276 V 705 2255 a FK(b)r(eing)897 2256 y FH(X)p 901 2276 50 3 v 960 2255 a FK(\))29 b(is)g(in)n(terpreted)f(as)i(an)h (assignmen)n(t)e(to)h(eac)n(h)2261 2256 y FJ(A)p 2264 2276 43 3 v 2346 2255 a FK(of)h(a)e(stable)167 2340 y(function)764 2504 y([)-12 b([)q FH(t)p FK(])g(]\()869 2505 y FJ(A)p 873 2525 V -1 x FK(\))20 b(:)f([)-12 b([)q FH(U)1084 2515 y FD(1)1112 2504 y FK(])g(]\()1165 2505 y FJ(A)p 1169 2525 V -1 x FK(\))16 b(&)f FH(:::)h FK(&)g([)-12 b([)p FH(U)1549 2515 y Fw(m)1596 2504 y FK(])g(])q(\()1650 2505 y FJ(A)p 1654 2525 V -1 x FK(\))15 b FJ(!)h FK([)-12 b([)q FH(T)10 b FK(])-12 b(]\()1964 2505 y FJ(A)p 1968 2525 V -1 x FK(\))167 2668 y(suc)n(h)28 b(that)g(for)591 2669 y FH(e)p 595 2689 19 3 v 643 2668 a FK(:)681 2669 y FJ(A)737 2643 y Fv(0)p 685 2689 60 3 v 774 2668 a Fu(\032)872 2669 y FJ(A)p 875 2689 43 3 v 955 2668 a FK(and)h FH(b)1123 2679 y Fw(j)1169 2668 y FJ(2)19 b FK([)-12 b([)q FH(U)1309 2679 y Fw(j)1335 2668 y FK(])g(]\()1388 2669 y FJ(A)p 1392 2689 V -1 x FK(\))28 b(the)f FM(uniformity)i(e)l(quation)e FK(holds:)794 2832 y([)-12 b([)q FH(T)10 b FK(])-12 b(]\()924 2833 y FH(e)p 928 2853 19 3 v -1 x FK(\))983 2807 y Fv(\000)1025 2832 y FK(\([)g([)p FH(t)p FK(])g(]\()1156 2833 y FJ(A)p 1160 2853 43 3 v -1 x FK(\)\()1266 2833 y FH(b)p 1270 2853 16 3 v -1 x FK(\)\))20 b(=)f([)-12 b([)p FH(t)p FK(])g(])q(\()1547 2833 y FJ(A)1603 2807 y Fv(0)p 1551 2853 60 3 v 1619 2832 a FK(\)\([)g([)1700 2833 y FH(U)p 1703 2853 41 3 v 1754 2832 a FK(])g(]\()1807 2833 y FH(e)p 1811 2853 19 3 v -1 x FK(\))1866 2807 y Fv(\000)1908 2832 y FK(\()1935 2833 y FH(b)p 1939 2853 16 3 v -1 x FK(\)\))167 2996 y(In)28 b(detail,)251 3139 y(1.)35 b(The)28 b FM(variable)f FH(x)786 3150 y Fw(j)839 3139 y FK(is)g(in)n(terpreted) f(b)n(y)j(the)e FH(j)t FK(th)g(pro)r(duct)h(pro)t(jection.)1263 3331 y([)-12 b([)p FH(x)1328 3342 y Fw(j)1354 3331 y FK(])g(])q(\()1408 3332 y FJ(A)p 1412 3351 43 3 v -1 x FK(\)\()1518 3332 y FH(b)p 1522 3351 16 3 v -1 x FK(\))19 b(=)g FH(b)1695 3342 y Fw(j)251 3549 y FK(2.)35 b(The)e(in)n (terpretation)e(of)h FH(\025)p FM(-abstr)l(action)h FH(\025x:)12 b(u)33 b FK(is)f(giv)n(en)g(in)g(terms)f(of)i(that)g(of)g FH(u)f FK(b)n(y)339 3634 y(the)c(trace)606 3825 y([)-12 b([)p FH(\025x:)12 b(u)p FK(])-12 b(])q(\()835 3826 y FJ(A)p 839 3846 43 3 v -1 x FK(\)\()945 3826 y FH(b)p 949 3846 16 3 v -1 x FK(\))20 b(=)f FJ(f)p 1129 3754 149 3 v(h)p FH(c;)p 1217 3768 34 3 v 12 w(\016)r FJ(i)h FK(:)39 b FH(\016)22 b FJ(2)e FK([)-12 b([)p FH(u)p FK(])g(])q(\()1594 3826 y FJ(A)p 1598 3846 43 3 v -1 x FK(\)\()1704 3826 y FH(b)p 1708 3846 16 3 v -1 x(;)12 b(c)p FK(\))p FH(;)39 b FK(with)27 b FH(c)g FK(minimal)m FJ(g)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 144 147 bop 167 167 a FK(144)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)251 404 y FK(3.)35 b(The)28 b FM(applic)l(ation)g FH(uv)j FK(is)c(in)n(terpreted)f(using)i(the)f (form)n(ula)h(\()p FG(App)p FK(\))f(of)h(section)f FG(??)q FK(:)697 640 y([)-12 b([)p FH(uv)s FK(])g(])q(\()852 641 y FJ(A)p 856 661 43 3 v -1 x FK(\)\()962 641 y FH(b)p 966 661 16 3 v -1 x FK(\))19 b(=)g FJ(f)p FH(\016)j FK(:)40 b FJ(9)p FH(c)19 b FJ(\032)g FK([)-12 b([)q FH(v)s FK(])g(])q(\()1536 641 y FJ(A)p 1540 661 43 3 v -1 x FK(\)\()1646 641 y FH(b)p 1650 661 16 3 v -1 x FK(\))p FH(:)p 1733 569 149 3 v 12 w FJ(h)p FH(c;)p 1821 583 34 3 v 12 w(\016)q FJ(i)20 b(2)g FK([)-12 b([)p FH(u)p FK(])g(])q(\()2086 641 y FJ(A)p 2090 661 43 3 v -1 x FK(\)\()2196 641 y FH(b)p 2200 661 16 3 v -1 x FK(\))p FJ(g)251 893 y FK(4.)35 b(The)28 b FM(universal)f(abstr)l(action)p FK(,)h(\003)p FH(X)r(:)12 b(v)s FK(,)27 b(is)g(also)h(giv)n(en)g(b)n(y)g(a)g (\\trace":)559 1113 y([)-12 b([\003)p FH(X)r(:)12 b(v)s FK(])-12 b(])q(\()813 1114 y FJ(A)p 817 1134 43 3 v -1 x FK(\)\()923 1114 y FH(b)p 927 1134 16 3 v -1 x FK(\))19 b(=)g FJ(f)p FK([)p FJ(hC)t FH(;)12 b(\016)s FJ(i)p FK(])20 b(:)40 b FH(\016)21 b FJ(2)f FK([)-12 b([)p FH(v)s FK(])g(])q(\()1618 1114 y FJ(A)p 1622 1134 43 3 v -1 x FH(;)12 b FJ(C)t FK(\)\()1800 1114 y FH(b)p 1804 1134 16 3 v -1 x FK(\))p FH(;)39 b FK(with)27 b FJ(C)32 b FK(minimal)m FJ(g)339 1333 y FK(where)f([)p FJ(hC)t FH(;)12 b(\016)s FJ(i)p FK(])32 b(denotes)g(the)f(equiv)l(alence)f(class:)43 b FJ(hC)t FH(;)12 b(\016)s FJ(i)32 b FK(is)e(iden)n(ti\014ed)h(with)f FJ(hC)2547 1308 y Fv(0)2564 1333 y FH(;)12 b(\016)2629 1308 y Fv(0)2645 1333 y FJ(i)339 1419 y FK(whenev)n(er)28 b FH(e)19 b FK(:)h FJ(C)k(')19 b(C)913 1393 y Fv(0)957 1419 y FK(and)29 b([)-12 b([)q FH(v)s FK(])g(]\()1212 1420 y FJ(A)p 1216 1439 43 3 v -1 x FH(;)12 b(e)p FK(\)\()1385 1420 y FH(b)p 1389 1439 16 3 v -1 x FK(\)\()p FH(\016)s FK(\))18 b(=)h FH(\016)1654 1393 y Fv(0)1670 1419 y FK(.)251 1569 y(5.)35 b(The)28 b FM(universal)f(applic)l(ation)p FK(,)h FH(tU)7 b FK(,)28 b(is)f(giv)n(en)h(b)n(y)g(an)g(application)f (form)n(ula)647 1790 y([)-12 b([)p FH(tU)7 b FK(])-12 b(])q(\()806 1791 y FJ(A)p 810 1810 43 3 v -1 x FK(\)\()916 1791 y FH(b)p 920 1810 16 3 v -1 x FK(\))19 b(=)g FJ(f)p FH(\016)j FK(:)40 b FJ(9)p FH(e)19 b FK(:)h FJ(C)k Fu(\032)c FK([)-12 b([)p FH(U)7 b FK(])-12 b(])q(\()1633 1791 y FJ(A)p 1637 1810 43 3 v -1 x FK(\))p FH(:)12 b FK([)p FJ(hC)t FH(;)g(\016)s FJ(i)p FK(])20 b FJ(2)f FK([)-12 b([)q FH(t)p FK(])g(]\()2136 1791 y FJ(A)p 2140 1810 V -1 x FK(\)\()2246 1791 y FH(b)p 2250 1810 16 3 v -1 x FK(\))p FJ(g)270 2167 y FK(The)22 b(con)n(v)n(ersion)h(rules)e(are)h (satis\014ed)g(b)r(ecause)h(they)f(amoun)n(t)h(to)f(the)g(bijection)f (b)r(et)n(w)n(een)167 2252 y(ob)t(jects)30 b(of)g(\005)p FH(X)r(:)12 b FJ(T)18 b FK(\()p FH(X)6 b FK(\))29 b(and)i(v)l(ariable)f (ob)t(jects)g(of)g FJ(T)48 b FK(\(w)n(e)29 b(need)h(to)g(pro)n(v)n(e)h (a)f(substitution)167 2337 y(lemma)c(similar)f(to)j(that)g(in)f (section)g FG(??)q FK(\).)167 2582 y FE(A.5)114 b(Examples)167 2762 y Fy(A.5.1)95 b(Of)28 b(course)167 2897 y FK(W)-6 b(e)41 b(aim)f(to)i(calculate)d(the)i(coherence)g(space)g(denotations)h (of)g(the)f(simple)e(t)n(yp)r(es)j(w)n(e)167 2982 y(in)n(terpreted)25 b(using)i(system)f FG(F)g FK(in)g(section)g FG(??)q FK(,)g(whic)n(h)g (w)n(ere)g FM(pr)l(o)l(duct)p FK(,)i FM(sum)f FK(and)g FM(existential)167 3067 y FK(t)n(yp)r(es.)61 b(These)35 b(are)h(all)e(essen)n(tially)h(deriv)n(ed)1417 3041 y FD(10)1505 3067 y FK(from)g(\005)p FH(X)r(:)12 b FK(\()p FJ(U)25 b(!)18 b FH(X)6 b FK(\))18 b FJ(!)g FH(X)6 b FK(,)38 b(so)e(w)n(e)g(shall)167 3152 y(consider)27 b(this)g(in)g (detail)g(and)h(simply)f(state)g(the)g(other)h(results)f(afterw)n (ards.)270 3287 y(The)k(p)r(ositiv)n(e)e(and)j(negativ)n(e)f(criterion) d(remains)i(v)l(alid)g(ev)n(en)g(with)g(constan)n(ts)i(lik)n(e)d FJ(U)7 b FK(,)167 3372 y(and)29 b(so)f(a)g(tok)n(en)g(for)g(this)f(t)n (yp)r(e)h(is)f(of)h(the)g(form)938 3577 y FJ(hS)-6 b FM(gl)6 b FH(;)p 1089 3502 758 3 v 12 w FJ(hf)p 1151 3516 181 3 v(h)p FH(u)1217 3588 y Fw(i)1238 3577 y FH(;)p 1269 3538 36 3 v 12 w FJ(\017i)20 b FK(:)39 b FH(i)19 b FK(=)h(1)p FH(;)12 b(:::;)g(k)r FJ(g)p FH(;)p 1783 3538 V 12 w FJ(\017)q(ii)p 167 3649 1003 3 v 223 3692 a FC(10)273 3713 y FB([)-10 b([)p Fd(Bo)r(ol)q FB(])g(])30 b(is)f(also)g(a)h(sp)r(ecial)e(case)i(if)e(w)n(e)j(admit)d(the)h(t)n(w) n(o-elemen)n(t)g(discrete)g(p)r(oset)g(\(not)f(a)i(coherence)167 3784 y(space\))k(for)g(the)f(domain)g Fl(U)6 b FB(,)35 b(in)e(a)h(category)h(with)e(copro)r(ducts.)52 b(The)34 b(other)f(three)h(examples)f(whic)n(h)167 3854 y(w)n(e)f(are)g(ab)r (out)f(to)h(consider)e(are)i(deriv)n(ed)f(b)n(y)g(means)h(of)g(the)f (iden)n(tities)e Fl(U)19 b(!)14 b(V)19 b(!)13 b Fx(X)23 b Fl(')18 b FB(\()p Fl(U)6 b(\002)o(V)f FB(\))14 b Fl(!)g Fx(X)5 b FB(,)167 3925 y(\()p Fl(A)13 b(!)f Fx(X)5 b FB(\))p Fl(\002)o FB(\()p Fl(B)14 b(!)f Fx(X)5 b FB(\))16 b Fl(')f FB(\()p Fl(A)e FB(+)g Fl(B)r FB(\))f Fl(!)h Fx(X)32 b FB(and)27 b(\005)p Fx(X)q(:)10 b FB(\()p Fl(V)5 b FB(\()p Fx(X)g FB(\))11 b Fl(!)i Fx(Y)g FB(\))j Fl(')g FB(\(\006)1779 3920 y Fl(\016)1821 3925 y Fx(X)q(:)10 b Fl(V)5 b FB(\()p Fx(X)g FB(\)\))13 b Fl(!)f Fx(Y)h FB(.)p eop PStoPSsaved restore %%Page: (148,149) 75 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 145 148 bop 167 167 a Fz(A.5.)63 b(EXAMPLES)1826 b FK(145)167 404 y(where)27 b FH(u)410 415 y Fw(i)458 404 y FK(range)h(o)n(v)n(er)g (\014nite)f(cliques)g(of)h FJ(U)7 b FK(,)28 b FM(i.e.)g FK(tok)n(ens)g(of)g(!)q FJ(U)7 b FK(.)35 b(Ho)n(w)n(ev)n(er)28 b(although)h(there)167 490 y(is)c(only)h(one)h(tok)n(en,)g(namely)p 975 450 36 3 v 25 w FJ(\017)p FK(,)g(a)n(v)l(ailable)e(to)h(tag)h(the)e FH(u)1711 501 y Fw(i)1731 490 y FK(s,)i(it)e(ma)n(y)h(o)r(ccur)g(rep)r (eatedly;)f(the)167 575 y(tok)n(en)j(is)f(therefore)g(giv)n(en)h(b)n(y) g(a)g(\014nite)f(\(pairwise)f(incoheren)n(t\))h(set)g(of)h(tok)n(ens)h (of)f(!)p FJ(U)7 b FK(.)270 702 y(In)28 b(other)g(w)n(ords,)g (denotationally)-6 b(,)806 891 y(\005)p FH(X)r(:)12 b FK(\()p FJ(U)23 b(!)16 b FH(X)6 b FK(\))15 b FJ(!)h FH(X)25 b FJ(')20 b FK(\(!\(\(!)o FJ(U)7 b FK(\))1672 857 y Fv(?)1714 891 y FK(\)\))1768 843 y Fv(?)1829 891 y FK(=)19 b(?!)p FJ(U)167 1066 y FK(whic)n(h)27 b(\(b)n(y)h(a)g(sligh)n(t)f(abuse\))h(w) n(e)g(shall)e(call)g FJ(:)-12 b(:U)7 b FK(.)270 1193 y(The)28 b(e\013ect)e(of)j(the)e(program)1017 1383 y FJ(hS)-6 b FM(gl)7 b FH(;)p 1169 1307 599 3 v 12 w FJ(hf)p 1231 1321 189 3 v(h)p FH(u)1297 1394 y FD(1)1326 1383 y FH(;)p 1357 1343 36 3 v 12 w FJ(\017i)p FH(;)p 1450 1321 189 3 v 12 w FJ(h)p FH(u)1516 1394 y FD(2)1545 1383 y FH(;)p 1576 1343 36 3 v 12 w FJ(\017ig)p FH(;)p 1704 1343 V 12 w FJ(\017i)q(i)167 1557 y FK(at)32 b(the)f(t)n(yp)r(e)h FJ(A)g FK(and)h(giv)n(en)f(the)f(stable)h(function)f FH(f)f FK(:)23 b FJ(U)30 b(!)22 b(A)32 b FK(is)f(to)h(examine)f(the)h (trace)167 1642 y FJ(T)-6 b FH(r)r FK(\()p FH(f)8 b FK(\))28 b(and)h(output)g(those)g(tok)n(ens)g FH(\013)f FK(for)g(whic)n(h)g FM(b)l(oth)g FJ(h)p FH(u)1732 1653 y FD(1)1761 1642 y FH(;)p 1792 1603 45 3 v 12 w(\013)p FJ(i)g FM(and)g FJ(h)p FH(u)2094 1653 y FD(2)2123 1642 y FH(;)p 2154 1603 V 12 w(\013)p FJ(i)h FK(lie)d(in)h(it.)36 b(This)167 1727 y(generalises)26 b(the)i(in)n(tersection)d(w)n(e)j(found)h(in)e([)-12 b([)p Fq(Bo)r(ol)p FK(])g(])q(.)270 1896 y(It)35 b(is)e(clearly)g(an)i (inevitable)e(feature)h(of)h(domain)f(mo)r(dels)g(of)h(system)f FG(F)g FK(that)h Fn(?)f FK(b)r(e)167 1981 y(added)29 b(to)f FJ(U)7 b FK(,)27 b(since)g(a)h(program)g(of)h(t)n(yp)r(e)e FJ(:)-12 b(:U)35 b FK(is)27 b(under)h(no)h(obligation)e(to)h (terminate.)270 2108 y(What)c(seems)f(sligh)n(tly)f(p)r(eculiar)g(is)h (that)h(w)n(e)f(ma)n(y)h(ha)n(v)n(e)g FH(u)1836 2119 y FD(1)1884 2108 y FJ(\024)19 b FH(u)1997 2119 y FD(2)2025 2108 y FK(,)25 b(t)n(w)n(o)f(\014nite)e(p)r(oin)n(ts)i(\(or)167 2193 y(cliques\))e(of)h FJ(U)7 b FK(,)25 b(whic)n(h)d(giv)n(e)i(rise)e (to)h FM(atomic)h FK(tok)n(ens)g(of)g(t)n(yp)r(e)g FJ(:)-12 b(:U)30 b FK(\(on)24 b(some)f(functions)h(one)167 2278 y(will)d(output)k FH(\013)f FK(and)h(the)f(other)g(not,)h(and)g(on)g (others)f(the)g(rev)n(erse\).)33 b(This)23 b(is)g(a)i(consequence)167 2363 y(of)31 b(the)f FM(stable)g FK(in)n(terpretation)f(and)i(the)f FM(Berry)i FK(order,)f(whic)n(h)f(is)f(m)n(uc)n(h)i(w)n(eak)n(er)f (than)h(the)167 2448 y(p)r(oin)n(t)n(wise)g(order,)i(since)e(the)g (test)h(on)g(the)g(function)g(is)f(not)i(just)f(whether)f(the)h(datum)g FH(u)167 2533 y FK(is)g FM(su\016cient)f FK(for)i(output)h FH(\013)e FK(\(as)h(it)f(w)n(ould)g(b)r(e)h(with)e(Scott's)i(domain)g (theory\),)h(but)f(also)167 2618 y(whether)27 b(it)g(is)f FM(ne)l(c)l(essary)35 b FK(w)n(e)27 b(ha)n(v)n(e)i(already)f(remark)n (ed)f(on)h(this)g(in)f(section)f FG(??)q FK(.)270 2793 y(W)-6 b(e)28 b(can)g(no)n(w)g(easily)f(calculate)f(the)h(pro)r(duct,)h (sum)g(and)h(existen)n(tial)c(t)n(yp)r(es.)633 2967 y(\005)p FH(X)r(:)12 b FK(\()p FJ(U)22 b(!)16 b(V)22 b(!)16 b FH(X)6 b FK(\))15 b FJ(!)h FH(X)26 b FJ(')19 b(:)-12 b(:)p FK(\()p FJ(U)23 b FK(&)15 b FJ(V)6 b FK(\))19 b FJ(')h FK(?)o(\(!)p FJ(U)j(\012)15 b FK(!)q FJ(V)6 b FK(\))167 3142 y(where)27 b(w)n(e)g(see)g FJ(\012)g FK(as)i(\\linear)d (conjunction".)524 3316 y(\005)p FH(X)r(:)12 b FK(\()p FJ(U)22 b(!)16 b FH(X)6 b FK(\))15 b FJ(!)i FK(\()p FJ(V)k(!)16 b FH(X)6 b FK(\))15 b FJ(!)h FH(X)26 b FJ(')19 b(:)-12 b(:)p FK(\()p FJ(U)23 b FK(+)15 b FJ(V)6 b FK(\))19 b FJ(')h FK(?)o(\(!)p FJ(U)j(\010)16 b FK(!)p FJ(V)6 b FK(\))167 3491 y(Note)23 b(that)g(\(apart)h(from)f(the)g(\\?"\))g(this) g(is)f(the)h(kind)g(of)h(sum)f(w)n(e)g(settled)e(on)j(in)f(c)n(hapter)g FG(??)q FK(.)825 3665 y(\005)p FH(Y)t(:)12 b FK(\(\005)p FH(X)r(:)g FK(\()p FJ(V)21 b(!)16 b FH(Y)f FK(\)\))g FJ(!)i FH(Y)34 b FJ(')20 b(:)-12 b(:)p FK(\(\006)1770 3659 y FJ(\016)1821 3665 y FH(X)r(:)12 b FJ(V)6 b FK(\))167 3840 y(where)39 b(for)g(a)h(v)l(ariable)f(t)n(yp)r(e)g FJ(T)c FK(:)28 b FG(Gem)f FJ(!)h FG(Gem)p FK(,)42 b(\006)1663 3834 y FJ(\016)1714 3840 y FH(X)r(:)12 b FJ(T)18 b FK(\()p FH(X)6 b FK(\))39 b(is)f(the)h(total)g(category)167 3925 y(whic)n(h)27 b(w)n(e)g(met)g(in)g(section)g FG(??)p FK(.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 146 149 bop 167 167 a FK(146)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)167 404 y Fy(A.5.2)95 b(Natural)28 b(Num)m(b)s(ers)167 539 y FK(Finally)e(let)g(us)j(apply)f (our)g(tec)n(hniques)f(to)h(calculating)e(the)i(denotation)g(of)944 726 y Fq(Int)20 b FK(=)f(\005)p FH(X)r(:)12 b(X)21 b FJ(!)16 b FK(\()p FH(X)21 b FJ(!)16 b FH(X)6 b FK(\))16 b FJ(!)g FH(X)167 914 y FK(Recall)32 b(that)i(b)r(esides)g(the)g(terms) f(of)h FG(F)g FK(w)n(e)g(ha)n(v)n(e)h(already)f(met)f(the)h (unde\014ned)i(term)c FJ(?)167 999 y FK(and)27 b(the)f(binary)h(in)n (tersection)d FJ(^)p FK(.)35 b(W)-6 b(e)26 b(shall)f(see)h(that)g (linear)f(logic)g(arises)g(again)i(when)g(w)n(e)167 1084 y(try)h(to)g(classify)e(the)i(tok)n(ens)g(for)g(this)f(t)n(yp)r(e.)270 1218 y(In)h(terms)f(of)h(the)f(\\linear")g(t)n(yp)r(e)h(constructors,)h (w)n(e)e(m)n(ust)g(consider)971 1426 y(\(!)p FJ(A)16 b(\012)g FK(!\(\(!)p FJ(A)g(\012)f(A)1450 1400 y Fv(?)1492 1426 y FK(\))1519 1386 y Fv(?)1561 1426 y FK(\))g FJ(\012)h(A)1730 1400 y Fv(?)1772 1426 y FK(\))1798 1372 y Fv(?)167 1614 y FK(whose)28 b(tok)n(ens)h(are)e(of)h(the)g(form)p 962 1726 888 3 v 962 1801 a FJ(h)p FH(a;)12 b FJ(hf)p 1118 1740 191 3 v(h)p FH(b)1174 1812 y Fw(i)1196 1801 y FH(;)p 1227 1762 56 3 v 12 w(\015)1263 1812 y Fw(i)1282 1801 y FJ(i)20 b FK(:)39 b FH(i)19 b FK(=)h(1)p FH(;)12 b(:::;)g(k)r FJ(g)p FH(;)p 1761 1744 34 3 v 12 w(\016)s FJ(ii)167 1989 y FK(Using)27 b(the)h(\\p)r(ositiv)n(e)f(and)i(negativ)n(e")f (criterion)d(w)n(e)j(m)n(ust)f(ha)n(v)n(e)887 2217 y FJ(jAj)19 b FK(=)g FJ(f)p FH(\016)s FJ(g)c([)1283 2150 y Fw(k)1268 2165 y Fo(S)1257 2278 y Fw(i)p FD(=1)1349 2217 y FH(b)1378 2228 y Fw(i)1418 2217 y FK(=)k FH(a)d FJ([)g(f)p FH(\015)1677 2228 y FD(1)1704 2217 y FH(;)c(:::;)g(\015)1859 2228 y Fw(k)1890 2217 y FJ(g)270 2499 y FK(The)23 b(simplest)d(case)i (is)g FH(k)g FK(=)d(0,)24 b(so)f FH(a)d FK(=)f FJ(f)p FH(\016)s FJ(g)p FK(.)33 b(This)22 b(giv)n(es)g(the)g(n)n(umeral)p 2180 2445 35 3 v 22 w(0,)i(in)n(terpreted)c(as)167 2584 y(the)25 b(program)h(whic)n(h)f(copies)g(the)g(starting)g(v)l(alue)h (to)g(the)f(output,)i(ignoring)e(the)h(transition)167 2669 y(function.)36 b(The)27 b(corresp)r(onding)h(tok)n(en)h(for)f Fq(Int)f FK(is)g(just)1133 2856 y FJ(hS)-6 b FM(gl)6 b FH(;)p 1284 2795 368 3 v 12 w FJ(hf\017)q(g)p FH(;)12 b FJ(h)p Fn(?)p FH(;)p 1561 2817 36 3 v 12 w FJ(\017ii)q(i)167 3044 y FK(The)27 b(in)n(tersection)f(phenomenon)j(manifests)e(itself)f (\(in)h(the)g(simplest)e(case\))j(as)g(the)g(tok)n(en)994 3251 y FJ(hS)-6 b FM(gl)6 b FH(;)p 1145 3176 646 3 v 12 w FJ(hf)p FH(\013)p FJ(g)p FH(;)12 b FJ(hf)p 1379 3190 245 3 v(hf)p FH(\013)p FJ(g)p FH(;)p 1551 3212 45 3 v 12 w(\013)s FJ(ig)p FH(;)p 1691 3212 V 12 w(\013)q FJ(iii)167 3439 y FK(but)28 b(the)f(similar)e(p)r(oten)n(tial)i(tok)n (en)944 3652 y FJ(h)p FH(\013)1035 3630 y(_)1035 3673 y(^)1124 3652 y(\014)t(;)p 1198 3566 643 3 v 12 w FJ(hf)p FH(\013)p FJ(g)p FH(;)12 b FJ(hf)p 1432 3580 242 3 v(hf)p FH(\014)t FJ(g)p FH(;)p 1603 3595 43 3 v 12 w(\014)6 b FJ(ig)p FH(;)p 1741 3613 45 3 v 12 w(\013)p FJ(ii)q(i)167 3840 y FK(\(although)39 b(it)d(passes)j(the)f(p)r(ositiv)n(e)e(and)j (negativ)n(e)f(criterion\))d(is)i(not)h(actually)f(a)h(v)l(alid)167 3925 y(tok)n(en)28 b(of)g(this)g(t)n(yp)r(e.)p eop PStoPSsaved restore %%Page: (150,151) 76 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 147 150 bop 167 167 a Fz(A.5.)63 b(EXAMPLES)1826 b FK(147)270 404 y(It)41 b(is)g(more)g(enligh)n(tening)f(to)h(turn)h(to)f(the)g(syn) n(tax)i(and)f(\014nd)g(the)f(tok)n(ens)i(of)e(the)167 490 y(n)n(umeral)p 445 436 35 3 v 34 w(1)q(.)57 b(Calculating)33 b([)-12 b([)q(\003)p FH(X)r(:)12 b(\025x:)g(\025y)s(:)g(y)s(x)p FK(])-12 b(])34 b(using)h(section)f FG(??)q FK(,)j(w)n(e)d(get)h(tok)n (ens)h(of)f(the)167 575 y(form)1095 742 y FJ(hA)p FH(;)p 1209 667 480 3 v 12 w FJ(h)p FH(a;)12 b FJ(hf)p 1365 681 162 3 v(h)p FH(a;)p 1459 703 40 3 v 12 w(\015)6 b FJ(ig)p FH(;)p 1594 703 V 12 w(\015)t FJ(ii)q(i)167 910 y FK(where)27 b FJ(jAj)g FK(consists)g(of)i(the)e(clique)f FH(a)i FK(and)g(the)g(tok)n(en)g FH(\015)t FK(.)270 1060 y FJ(\017)34 b FK(If)c FH(a)21 b FK(=)f Fn(?)29 b FK(w)n(e)g(ha)n(v)n (e)i(the)e(program)h(whic)n(h)f(ignores)g(the)g(starting)h(v)l(alue)f (stream)g(and)339 1145 y(ev)n(erything)d(on)h(the)f(transition)f (function)h(stream)f(apart)i(from)f(the)g(\\constan)n(t")i(part)339 1230 y(of)h(its)d(v)l(alue,)i(whic)n(h)f(is)g(copied)g(to)h(the)g (output.)270 1371 y FJ(\017)34 b FK(If)28 b FH(a)g FK(has)h FH(m)g FK(elemen)n(ts,)d(the)h(program)i(reads)g(that)f(part)g(of)h (the)e(transition)h(function)339 1456 y(whic)n(h)e(reads)g(its)f(input) g(exactly)h FH(m)g FK(times,)e(and)j(applies)e(this)g(to)i(the)e (starting)h(v)l(alue)339 1541 y(\(whic)n(h)h(it)g(reads)h FH(m)g FK(times\).)33 b FM(But,)270 1682 y FJ(\017)h FK(If)42 b FH(\015)33 b FJ(2)c FH(a)42 b FK(then)g(the)f(program)h (outputs)h(only)f(that)g(part)g(of)g(the)f(result)f(of)i(the)339 1767 y(transition)28 b(function)f(whic)n(h)g(is)g(con)n(tained)h(in)f (the)g(input.)270 1908 y FJ(\017)34 b FK(If)28 b FH(\015)c FJ(62)c FH(a)28 b FK(then)g(it)f(only)i(outputs)g(that)f(part)h(whic)n (h)e(is)h FM(not)f FK(con)n(tained)i(in)e(the)h(input.)339 1993 y FM(But,)270 2134 y FJ(\017)34 b FK(If)c FH(\015)475 2112 y(_)475 2155 y(^)565 2134 y(\013)p FK(,)g(where)e FH(\013)i FK(ranges)g(o)n(v)n(er)g FH(r)h FK(of)f(the)f FH(m)h FK(tok)n(ens)g(of)g(the)f(clique)e FH(a)p FK(,)k(then)e FH(\015)k FK(is)339 2220 y(only)c(output)h(in)e(those)i(cases)f(where)f (the)g(input)h(and)g(output)h(are)f(coheren)n(t)f(in)h(this)339 2305 y(w)n(a)n(y)-6 b(.)270 2493 y(So)36 b(ev)n(en)e(the)g(n)n(umeral)p 953 2439 35 3 v 33 w(1)h(is)f(a)h(v)n(ery)f(complex)g(b)r(east:)49 b(it)33 b(amoun)n(ts)i(to)g(a)g(resolution)167 2578 y(of)e(the)f (transition)f(function)i(in)n(to)f(a)g(\\p)r(olynomial",)i(the)e FH(m)p FK(th)g(term)f(of)i(whic)n(h)e(reads)i(its)167 2663 y(input)27 b(exactly)g FH(m)h FK(times.)33 b(It)27 b(further)h(resolv)n(es)e(the)i(terms)e(according)i(to)f(the)g (relationship)167 2748 y(b)r(et)n(w)n(een)g(the)g(input)h(and)g (output.)270 2916 y(Clearly)34 b(these)h(complications)f(m)n(ultiply)g (as)i(w)n(e)f(consider)g(larger)g(n)n(umerals.)58 b(Along)167 3001 y(with)31 b Fn(?)h FK(and)h(in)n(tersection,)f(do)g(they)h(pro)n (vide)f(a)g(complete)f(classi\014cation)g(of)h(the)g(tok)n(ens)167 3086 y(of)c Fq(Int)p FK(?)35 b(What)28 b(do)r(es)g Fq(Int)16 b FJ(!)g Fq(Int)28 b FK(lo)r(ok)g(lik)n(e?)167 3289 y Fy(A.5.3)95 b(Linear)28 b(n)m(umerals)167 3419 y FK(W)-6 b(e)31 b(can)h(try)g(to)g(bring)g(some)f(order)h(to)g(this)f(c)n(haos)i (b)n(y)f(considering)f(a)i(linear)d(v)n(ersion)i(of)167 3505 y(the)27 b(natural)h(n)n(um)n(b)r(ers)g(analogous)i(to)e(the)f (linear)g(b)r(o)r(oleans.)891 3672 y Fq(LInt)20 b FK(=)f(\005)p FH(X)r(:)12 b(X)21 b Fu(\()16 b FK(\(\()p FH(X)21 b Fu(\()16 b FH(X)6 b FK(\))15 b FJ(!)h FH(X)6 b FK(\))167 3840 y(\(w)n(e)30 b(lea)n(v)n(e)h(one)g(classical)e(implication)f(b)r (ehind!\))45 b(The)31 b(e\013ect)f(of)h(this)f(is)h(to)g(replace)e FH(a)i FK(b)n(y)167 3925 y FJ(f)p FH(\013)p FJ(g)d FK(and)h FH(b)477 3936 y Fw(i)525 3925 y FK(b)n(y)f FJ(f)p FH(\014)699 3936 y Fw(i)719 3925 y FJ(g)p FK(,)g(and)h(then)f(the)f(p)r(ositiv)n(e) g(and)i(negativ)n(e)e(criterion)f(giv)n(es)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 148 151 bop 167 167 a FK(148)947 b Fz(APPENDIX)26 b(A.)55 b(SEMANTICS)27 b(OF)g(SYSTEM)h(F)873 404 y FJ(jAj)19 b FK(=)g FJ(f)p FH(\013;)12 b(\015)1207 415 y FD(1)1235 404 y FH(;)g(:::;)g(\015)1390 415 y Fw(k)1421 404 y FJ(g)19 b FK(=)h FJ(f)p FH(\014)1623 415 y FD(1)1651 404 y FH(;)12 b(:::;)g(\014)1809 415 y Fw(k)1839 404 y FH(;)g(\016)r FJ(g)167 578 y FK(whic)n(h)31 b(are)h(not)h(necessarily)d(distinct.)47 b(Besides)31 b(the)h(undirected)e(graph)k(structure)d(giv)n(en)167 663 y(b)n(y)d(coherence,)f(the)h(pairing)p 967 601 201 3 v 27 w FJ(h)p FH(\014)1033 674 y Fw(i)1053 663 y FH(;)p 1084 624 56 3 v 12 w(\015)1120 674 y Fw(i)1140 663 y FJ(i)g FK(induces)f(a)h(\\transition)g(relation")f(on)h FJ(A)p FK(.)270 789 y(The)g FM(line)l(ar)f(numer)l(al)p 891 732 39 3 v 35 w FH(k)j FK(consists)e(of)g(the)f(tok)n(ens)i(of)f (the)f(form)805 962 y FH(\013)20 b FK(=)f FH(\015)978 973 y FD(1)1006 962 y FH(;)39 b(\014)1103 973 y FD(1)1150 962 y FK(=)20 b FH(\015)1260 973 y FD(2)1287 962 y FH(;)40 b(:::;)g(\014)1501 973 y Fw(k)q Fv(\000)p FD(1)1614 962 y FK(=)19 b FH(\015)1723 973 y Fw(k)1753 962 y FH(;)40 b(\014)1851 973 y Fw(k)1900 962 y FK(=)20 b FH(\016)167 1135 y FK(sub)t(ject)j(only)g(to)h FH(\013)687 1146 y Fw(i)726 1113 y FH(_)726 1156 y(^)814 1135 y(\013)858 1146 y Fw(j)923 1135 y FJ(\()-12 b(\))40 b FH(\013)1135 1146 y Fw(i)p FD(+1)1239 1113 y FH(_)1239 1156 y(^)1327 1135 y(\013)1371 1146 y Fw(j)s FD(+1)1484 1135 y FK(|)23 b(so)g(there)f(are)h(still)e(quite)h(a)i(lot)e(of)i(them!)167 1220 y(More)36 b(generally)-6 b(,)36 b(the)g(transition)f(relation)f (preserv)n(es)h(coherence,)i(re\015ects)d(incoherence,)167 1305 y(and)g(con)n(tains)f(a)g(path)g(from)g FH(\013)f FK(to)h FH(\016)i FM(via)e FK(an)n(y)g(giv)n(en)g(tok)n(en.)51 b(The)32 b(reader)h(is)e(in)n(vited)h(to)167 1391 y(v)n(erify)24 b(this)g(c)n(haracterisation)f(and)j(also)f(determine)d(when)i(t)n(w)n (o)h(suc)n(h)g(tok)n(ens)g(are)f(coheren)n(t.)167 1626 y FE(A.6)114 b(T)-10 b(otal)29 b(domains)167 1781 y FK (Domain-theoretic)35 b(in)n(terpretations,)j(as)g(w)n(e)f(ha)n(v)n(e)h (said,)i(necessarily)35 b(in)n(tro)r(duce)i(partial)167 1866 y(elemen)n(ts)31 b(suc)n(h)i(as)h Fn(?)p FK(,)g(and)g(in)e(the)h (case)g(of)g(coherence)f(spaces)h(also)g(the)g(\\in)n(tersection")167 1951 y(op)r(eration.)87 b(Ho)n(w)n(ev)n(er)45 b(w)n(e)f(ma)n(y)h(use)g (a)g(metho)r(d)g(similar)d(to)j(the)f(one)h(w)n(e)g(used)g(for)167 2036 y(reducibilit)n(y)25 b(and)j(realisabilit)n(y)d(to)j(attempt)f(to) h(get)f(rid)g(of)h(these.)270 2162 y(As)j(with)g(the)g(t)n(w)n(o)g (previous)g(cases,)i(w)n(e)d(allo)n(w)h FM(any)37 b FK(subset)32 b FJ(R)22 b(\032)g(A)31 b FK(to)g(b)r(e)g(a)h FM(totality)167 2247 y(c)l(andidate)h FK(for)28 b(the)g(coherence)e(space)i FJ(A)p FK(.)36 b(Then)251 2409 y(1.)f(If)29 b FJ(R)f FK(is)g(a)g(totalit)n(y)g(candidate)h(for)f FJ(A)h FK(and)g FJ(S)34 b FK(for)28 b FJ(B)j FK(then)e(w)n(e)f(write)e FJ(R!S)34 b FK(for)28 b(the)339 2494 y(set)g(of)g(ob)t(jects)f FH(f)36 b FK(of)28 b(t)n(yp)r(e)f FJ(A!)q(B)j FK(suc)n(h)e(that)g FH(a)20 b FJ(2)g(R)f(\))h FH(f)8 b(a)19 b FJ(2)h(S)251 2638 y FK(2.)35 b(If)21 b FH(T)10 b FK([)p FH(X)r(;)565 2639 y(Y)p 569 2658 42 3 v 621 2638 a FK(])21 b(is)f(a)h(t)n(yp)r(e)g (with)f(free)g(v)l(ariables)h FH(X)27 b FK(and)1721 2639 y FH(Y)p 1724 2658 V 1797 2638 a FK(and)1929 2639 y FJ(S)p 1932 2658 35 3 v 1998 2638 a FK(are)21 b(totalit)n(y)f(candidates)339 2723 y(for)31 b(coherence)f(spaces)993 2724 y FJ(B)p 996 2743 V 1072 2723 a FK(then)g FH(f)f FJ(2)22 b FK(\005)p FH(X)r(:)12 b(T)e FK([)1579 2724 y FJ(S)p 1583 2743 V 1626 2723 a FK(],)32 b FM(i.e.)e FH(f)38 b FK(is)30 b(total)g(for)h (the)f(coherence)339 2808 y(space)35 b([)-12 b([\005)p FH(X)r(:)12 b(T)e FK(])-12 b(])q(\()807 2809 y FJ(B)p 811 2829 V 855 2808 a FK(\))34 b(if)f(for)i(ev)n(ery)f(space)h FJ(A)f FK(and)h(candidate)g FJ(R)e FK(for)i([)-12 b([)q FH(T)10 b FK(])-12 b(]\()p FJ(A)p FH(;)2484 2809 y FJ(B)p 2488 2829 V 2533 2808 a FK(\))34 b(w)n(e)339 2893 y(ha)n(v)n(e)29 b FH(f)8 b FK(\()p FJ(A)p FK(\))19 b FJ(2)h FH(T)10 b FK([)p FJ(R)p FH(;)901 2894 y FJ(S)p 904 2914 V 948 2893 a FK(].)167 3054 y(As)27 b(with)g(reducibilit)n(y)e(and)j(realisabilit) n(y)-6 b(,)26 b(no)i(parametricit)n(y)e(remains)g(for)i(closed)f(t)n (yp)r(es.)270 3181 y(This)33 b(topic)g(is)g(discussed)g(more)g (extensiv)n(ely)f(in)h([)p FG(?)q FK(],)i(from)e(whic)n(h)g(w)n(e)g (merely)e(quote)167 3266 y(the)c(follo)n(wing)g(results:)167 3439 y FG(Prop)r(osition)e FK(If)j FH(t)f FK(is)g(a)h(closed)f(term)g (of)h(closed)f(t)n(yp)r(e)h FH(T)10 b FK(,)27 b(then)h([)-12 b([)q FH(t)p FK(])g(])28 b(is)f(total.)331 b Fu(\003)167 3612 y FG(Prop)r(osition)26 b FK(The)j(total)g(ob)t(jects)f(in)h(the)f (denotation)i(of)f Fq(Bo)r(ol)g FK(and)h Fq(Int)e FK(are)h(exactly)f (the)167 3697 y(truth)g(v)l(alues)g(and)g(the)g(n)n(umerals.)1503 b Fu(\003)p eop PStoPSsaved restore %%Page: (152,153) 77 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 149 152 bop 167 874 a FF(App)5 b(endix)28 b(B)167 1168 y(What)f(is)g(Linear)g(Logic?)167 1375 y FI(b)m(y)h(Yv)m(es)g(Lafon)m (t)167 1695 y FK(Linear)g(logic)g(w)n(as)h(originally)e(disco)n(v)n (ered)h(in)g(coherence)g(seman)n(tics)g(\(see)g(c)n(hapter)g FG(??)q FK(\).)38 b(It)167 1780 y(app)r(ears)c(no)n(w)f(as)g(a)g (promising)f(approac)n(h)i(to)f(fundamen)n(tal)g(questions)g(arising)f (in)g(pro)r(of)167 1866 y(theory)c(and)h(in)e(computer)g(science.)270 1993 y(In)39 b(ordinary)h(\(classical)d(or)i(in)n(tuitionistic\))c (logic,)41 b(y)n(ou)f(can)f(use)g(an)h(h)n(yp)r(othesis)f(as)167 2078 y(man)n(y)30 b(times)d(as)i(y)n(ou)h(w)n(an)n(t:)39 b(this)28 b(feature)h(is)f(expressed)h(b)n(y)g(the)g(rules)f(of)h FM(we)l(akening)f FK(and)167 2163 y FM(c)l(ontr)l(action)33 b FK(of)g(Sequen)n(t)g(Calculus.)49 b(There)32 b(are)h(go)r(o)r(d)h (reasons)f(for)g(considering)f(a)h(logic)167 2248 y(without)27 b(those)h(rules:)270 2410 y FJ(\017)34 b FK(F)-6 b(rom)29 b(the)f(viewp)r(oin)n(t)g(of)h(pro)r(of)g(theory)-6 b(,)30 b(it)d(remo)n(v)n(es)h(pathological)h(situations)f(from)339 2496 y(classical)39 b(logic)g(\(see)g(next)i(section\))e(and)i(in)n (tro)r(duces)f(a)h(new)f(kind)g(of)h(in)n(v)l(arian)n(t)339 2581 y(\(pro)r(of)29 b(nets\).)270 2725 y FJ(\017)34 b FK(F)-6 b(rom)49 b(the)f(viewp)r(oin)n(t)g(of)h(computer)f(science,) 53 b(it)47 b(giv)n(es)i(a)g(new)f(approac)n(h)j(to)339 2810 y(questions)44 b(of)g(laziness,)i(side)d(e\013ects)g(and)h(memory) f(allo)r(cation)f([)p FG(?)q FK(,)h FG(?)q FK(,)g FG(?)q FK(])g(with)339 2895 y(promising)27 b(applications)h(to)f(parallelism.) 167 3132 y FE(B.1)114 b(Classical)28 b(logic)f(is)g(not)h(constructiv)m (e)167 3287 y FK(In)n(tuitionistic)33 b(logic)h(is)h(called)e FM(c)l(onstructive)i FK(b)r(ecause)g(of)h(the)f(corresp)r(ondence)h(b)r (et)n(w)n(een)167 3372 y(pro)r(ofs)43 b(and)g(algorithms)e(\(the)g (Curry-Ho)n(w)n(ard)h(isomorphism,)j(c)n(hapter)d FG(??)p FK(\).)78 b(So,)46 b(for)167 3457 y(example,)29 b(if)f(w)n(e)g(pro)n(v) n(e)i(a)f(form)n(ula)g FJ(9)p FH(n)21 b FJ(2)f FK(I)-12 b(N)p FH(:)12 b(P)e FK(\()p FH(n)p FK(\),)29 b(w)n(e)g(can)g(exhibit)f (an)i(in)n(teger)e FH(n)h FK(whic)n(h)167 3542 y(satis\014es)f(the)f (prop)r(ert)n(y)h FH(P)10 b FK(.)270 3669 y(Suc)n(h)30 b(an)f(in)n(terpretation)e(is)h(not)h(p)r(ossible)f(with)g(classical)e (logic:)37 b(there)27 b(is)h(no)h(sensible)167 3754 y(w)n(a)n(y)24 b(of)g(considering)f(pro)r(ofs)i(as)f(algorithms.)34 b(In)23 b(fact,)i(classical)c(logic)i(has)h FM(no)f(denotational)167 3840 y(semantics)p FK(,)29 b(except)f(the)g(trivial)f(one)i(whic)n(h)f (iden)n(ti\014es)f(all)g(the)h(pro)r(ofs)i(of)f(the)f(same)h(t)n(yp)r (e.)167 3925 y(This)e(is)f(related)g(to)i(the)f FM(nondeterministic)f FK(b)r(eha)n(viour)i(of)g(cut)f(elimination)d(\(c)n(hapter)j FG(??)q FK(\).)1368 4101 y(149)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 150 153 bop 167 167 a FK(150)987 b Fz(APPENDIX)27 b(B.)55 b(WHA)-6 b(T)27 b(IS)g(LINEAR)g(LOGIC?)270 404 y FK(Indeed,)h(w)n(e)f (ha)n(v)n(e)i(t)n(w)n(o)f(di\013eren)n(t)f(w)n(a)n(ys)h(of)g(reducing)g (a)g(cut)1028 555 y FH(A)p 1031 575 39 3 v 1099 554 a FJ(`)19 b FH(C)q(;)1242 555 y(B)p 1246 575 43 3 v 83 w(D)p 1381 575 46 3 v 1436 554 a(;)12 b(C)25 b FJ(`)1604 555 y FH(E)p 1607 575 42 3 v 1028 599 632 4 v 1680 615 a Fq(Cut)1160 677 y FH(A)p 1164 696 39 3 v -1 x(;)1243 677 y(D)p 1246 696 46 3 v 1322 676 a FJ(`)1384 677 y FH(B)p 1388 696 43 3 v 1440 676 a(;)1471 677 y(E)p 1475 696 42 3 v 167 837 a FK(when)j(the)g(form)n(ula)g FH(C)33 b FK(is)27 b(in)n(tro)r(duced)h(b)n(y)h(w)n(eak)n(enings)g(\(or)f(con)n (tractions\))g(on)h(b)r(oth)f(sides.)167 922 y(F)-6 b(or)28 b(example,)f(a)h(pro)r(of)1041 1064 y FJ(\001)1041 1102 y(\001)1041 1140 y(\001)956 1199 y FH(A)p 959 1218 39 3 v 1027 1198 a FJ(`)1090 1199 y FH(B)p 1093 1218 43 3 v 915 1243 272 4 v 1207 1258 a FJ(R)p Fq(W)915 1320 y FH(A)p 919 1340 39 3 v 986 1319 a FJ(`)20 b FH(C)q(;)1130 1320 y(B)p 1134 1340 43 3 v 1611 1064 a FJ(\001)1611 1102 y(\001)1611 1140 y(\001)1522 1199 y FH(D)p 1526 1218 46 3 v 1601 1198 a FJ(`)1664 1199 y FH(E)p 1667 1218 42 3 v 1480 1243 282 4 v 1782 1258 a FJ(L)p Fq(W)1480 1320 y FH(D)p 1483 1340 46 3 v 1539 1319 a(;)12 b(C)25 b FJ(`)1706 1320 y FH(E)p 1710 1340 42 3 v 915 1364 847 4 v 1782 1380 a Fq(Cut)1155 1441 y FH(A)p 1159 1461 39 3 v -1 x(;)1238 1441 y(D)p 1241 1461 46 3 v 1317 1440 a FJ(`)1379 1441 y FH(B)p 1383 1461 43 3 v 1435 1440 a(;)1466 1441 y(E)p 1470 1461 42 3 v 167 1597 a FK(reduces)i(to)739 1726 y FJ(\001)739 1764 y(\001)739 1802 y(\001)654 1861 y FH(A)p 657 1880 39 3 v 725 1860 a FJ(`)788 1861 y FH(B)p 791 1880 43 3 v 566 1920 a FK(=)-31 b(=)-16 b(=)g(=)g(=)g(=)g(=)g(=)g (=)-31 b(=)566 1982 y FH(A)p 569 2002 39 3 v -1 x(;)649 1982 y(D)p 652 2002 46 3 v 727 1981 a FJ(`)790 1982 y FH(B)p 793 2002 43 3 v 846 1981 a(;)877 1982 y(E)p 880 2002 42 3 v 1331 1792 a FK(or)28 b(to)2053 1726 y FJ(\001)2053 1764 y(\001)2053 1802 y(\001)1964 1861 y FH(D)p 1968 1880 46 3 v 2043 1860 a FJ(`)2106 1861 y FH(E)p 2109 1880 42 3 v 1880 1920 a FK(=)-31 b(=)-16 b(=)g(=)g(=)g(=)g(=)g(=)g(=) -31 b(=)1880 1982 y FH(A)p 1883 2002 39 3 v 1931 1981 a(;)1962 1982 y(D)p 1966 2002 46 3 v 2041 1981 a FJ(`)2104 1982 y FH(B)p 2107 2002 43 3 v 2160 1981 a(;)2191 1982 y(E)p 2194 2002 42 3 v 167 2142 a FK(\(where)25 b(the)h(double)g(bar)h (is)f(a)g(succession)g(of)h(w)n(eak)n(enings)f(and)i(exc)n(hanges\))f (dep)r(ending)f(on)167 2227 y(whether)h(w)n(e)g(lo)r(ok)h(at)g(the)f (left)g(or)h(at)f(the)h(righ)n(t)f(side)g(\014rst.)270 2350 y(In)g(particular,)f(if)f(w)n(e)h(ha)n(v)n(e)i(t)n(w)n(o)e(pro)r (ofs)i FH(\031)h FK(and)f FH(\031)1627 2324 y Fv(0)1669 2350 y FK(of)f(the)f(same)g(form)n(ula)h FH(B)t FK(,)f(and)i FH(C)k FK(is)167 2435 y(an)n(y)d(form)n(ula,)f(the)f(pro)r(of)1075 2591 y FH(\031)1086 2632 y FJ(\001)1086 2670 y(\001)1086 2708 y(\001)1036 2766 y(`)20 b FH(B)p 995 2811 201 4 v 1216 2827 a FJ(R)p Fq(W)995 2887 y FJ(`)g FH(C)q(;)12 b(B)1556 2591 y(\031)1598 2562 y Fv(0)1575 2632 y FJ(\001)1575 2670 y(\001)1575 2708 y(\001)1526 2766 y(`)19 b FH(B)p 1489 2811 193 4 v 1702 2827 a FJ(L)p Fq(W)1489 2887 y FH(C)25 b FJ(`)19 b FH(B)p 995 2932 653 4 v 1669 2948 a Fq(Cut)1157 3003 y FJ(`)h FH(B)t(;)12 b(B)p 1157 3048 206 4 v 1383 3064 a FJ(R)p Fq(C)1200 3124 y FJ(`)20 b FH(B)167 3261 y FK(reduces)27 b(to)728 3391 y FH(\031)739 3432 y FJ(\001)739 3470 y(\001)739 3508 y(\001)690 3566 y(`)19 b FH(B)690 3626 y FK(=)-21 b(=)e(=)690 3687 y FJ(`)19 b FH(B)1331 3472 y FK(or)28 b(to)2034 3403 y FH(\031)2076 3374 y Fv(0)2053 3444 y FJ(\001)2053 3482 y(\001)2053 3520 y(\001)2003 3578 y(`)20 b FH(B)2003 3639 y FK(=)-21 b(=)f(=)2003 3699 y FJ(`)20 b FH(B)167 3840 y FK(where)26 b(the)g(double)h(bar)h(is)e(a)h(w)n(eak)n(ening)g (\(with)f(an)h(exc)n(hange)h(in)e(the)g(\014rst)h(case\))g(follo)n(w)n (ed)167 3925 y(b)n(y)h(a)g(con)n(traction.)p eop PStoPSsaved restore %%Page: (154,155) 78 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 151 154 bop 167 167 a Fz(B.2.)63 b(LINEAR)27 b(SEQUENT)g(CALCULUS)1174 b FK(151)270 404 y(But)28 b(y)n(ou)h(will)c(certainly)h(admit)h(that)h (in)f(b)r(oth)h(cases,)1346 565 y FJ(`)20 b FH(B)1346 626 y FK(=)-21 b(=)f(=)1346 687 y FJ(`)20 b FH(B)167 837 y FK(is)28 b(essen)n(tially)e(nothing.)38 b(So)29 b FH(\031)i FK(and)e FH(\031)1215 811 y Fv(0)1260 837 y FK(are)f(obtained)h(b)n(y)g(reducing)e(the)h(same)g(pro)r(of,)i(and) 167 922 y(they)e(m)n(ust)f(b)r(e)h(denotationally)f(equal.)270 1099 y(More)38 b(generally)-6 b(,)38 b(all)e(the)h(pro)r(ofs)h(of)f(a)h (giv)n(en)f(sequen)n(t)1870 1100 y FH(A)p 1874 1120 39 3 v 1948 1099 a FJ(`)2017 1100 y FH(B)p 2021 1120 43 3 v 2110 1099 a FK(are)g(iden)n(ti\014ed.)62 b(So)167 1185 y(classical)23 b(logic)h(is)g FM(inc)l(onsistent)p FK(,)h(not)h(from)e(a)i FM(lo)l(gic)l(al)e FK(viewp)r(oin)n(t)g(\()p FJ(?)g FK(is)g(not)h(pro)n(v)l(able\),)i(but)167 1270 y(from)34 b(an)h FM(algorithmic)g FK(one.)56 b(This)34 b(is)g(also)g(expressed)h(b)n(y)g(the)f(fact)g(\(noticed)g(b)n(y)h(Jo)n (y)n(al\))167 1355 y(that)29 b FM(any)g(Cartesian)g(close)l(d)g(c)l (ate)l(gory)g(with)g(an)f(initial)h(obje)l(ct)f FK(0)h FM(such)g(that)g FK(0)2320 1329 y FD(0)2345 1313 y Ff(A)2404 1355 y FJ(')20 b FH(A)28 b FM(is)h(a)167 1440 y(p)l(oset)f FK(\(see)f([)p FG(?)q FK(])h(page)g(67\).)270 1617 y(Of)35 b(course,)i(our)e(example)f(sho)n(ws)i(that)f(cut)g(elimination)c(in)k (sequen)n(t)g(calculus)f(do)r(es)167 1703 y(not)28 b(satisfy)h(the)e (Ch)n(urc)n(h-Rosser)i(prop)r(ert)n(y:)36 b(it)27 b(ev)n(en)h(div)n (erges)g(in)f(the)h(w)n(orst)g(w)n(a)n(y!)37 b(There)167 1788 y(are)28 b(t)n(w)n(o)f(options)i(to)f(eliminate)c(this)j (pathology:)270 1952 y FJ(\017)34 b FK(making)28 b(the)g(calculus)e (asymmetric:)34 b(this)27 b(leads)g(to)h FM(intuitionistic)g(lo)l(gic)p FK(;)270 2098 y FJ(\017)34 b FK(forbidding)25 b(structural)e(rules,)h (except)f(the)h FM(exchange)e FK(whic)n(h)h(is)g(harmless:)33 b(this)23 b(leads)339 2183 y(to)28 b FM(line)l(ar)g(lo)l(gic)p FK(.)167 2421 y FE(B.2)114 b(Linear)27 b(Sequen)m(t)j(Calculus)167 2577 y FK(W)-6 b(e)27 b(simply)f(discard)h FM(we)l(akening)f FK(and)i FM(c)l(ontr)l(action)p FK(.)36 b FM(Exchange)p FK(,)26 b FM(identity)h FK(and)i FM(cut)d FK(are)h(left)167 2662 y(unc)n(hanged,)j(but)e(logical)e(rules)h(need)h(some)g(adjustmen) n(ts:)36 b(for)28 b(example,)g(the)f(rules)g(for)h FJ(^)167 2747 y FK(are)f(no)n(w)h(inadequate)g(\(since)e(cut)h(elimination)e(in) h FG(??)j FK(requires)d(w)n(eak)n(enings\).)36 b(In)27 b(fact,)h(w)n(e)167 2832 y(need)g FM(two)f FK(conjunctions:)36 b(a)28 b FM(tensor)g(pr)l(o)l(duct)g FK(\(or)g FM(cumulative)f(c)l (onjunction)p FK(\))575 3001 y FH(A)p 579 3021 39 3 v -1 x(;)12 b(C)q(;)g(D)22 b FJ(`)880 3001 y FH(B)p 884 3021 43 3 v 546 3045 421 4 v 987 3061 a FJ(L\012)546 3122 y FH(A)p 549 3142 39 3 v 597 3121 a(;)12 b(C)21 b FJ(\012)16 b FH(D)21 b FJ(`)910 3122 y FH(B)p 913 3142 43 3 v 1468 3004 a(A)p 1472 3024 39 3 v 1540 3003 a FJ(`)e FH(C)q(;)1683 3004 y(B)p 1687 3024 43 3 v 83 w(A)p 1822 3024 39 3 v -30 x Fv(0)1906 3003 y FJ(`)g FH(D)r(;)2058 3004 y(B)p 2062 3024 43 3 v 2114 2974 a Fv(0)p 1468 3048 663 4 v 2152 3064 a FJ(R\012)1488 3126 y FH(A)p 1492 3145 39 3 v -1 x(;)1571 3126 y(A)p 1574 3145 V -31 x Fv(0)1659 3125 y FJ(`)g FH(C)i FJ(\012)16 b FH(D)r(;)1952 3126 y(B)p 1955 3145 43 3 v 2008 3125 a(;)2039 3126 y(B)p 2042 3145 V 2095 3095 a Fv(0)167 3296 y FK(and)29 b(a)f FM(dir)l(e)l(ct)g(pr)l(o)l(duct)h FK(\(or)f FM(alternative)e(c)l (onjunction)p FK(\):)378 3462 y FH(A)p 382 3482 39 3 v -1 x(;)12 b(C)25 b FJ(`)598 3462 y FH(B)p 601 3482 43 3 v 306 3506 421 4 v 747 3522 a FJ(L)p FK(1)p Fc(N)306 3584 y FH(A)p 309 3603 39 3 v 357 3583 a(;)12 b(C)21 b Fc(N)16 b FH(D)22 b FJ(`)670 3584 y FH(B)p 674 3603 43 3 v 1094 3462 a(A)p 1097 3482 39 3 v 1145 3461 a(;)12 b(D)22 b FJ(`)1318 3462 y FH(B)p 1321 3482 43 3 v 1023 3506 421 4 v 1465 3522 a FJ(L)p FK(2)p Fc(N)1023 3584 y FH(A)p 1027 3603 39 3 v -1 x(;)12 b(C)21 b Fc(N)16 b FH(D)21 b FJ(`)1388 3584 y FH(B)p 1391 3603 43 3 v 1741 3462 a(A)p 1745 3482 39 3 v 1812 3461 a FJ(`)f FH(C)q(;)1956 3462 y(B)p 1960 3482 43 3 v 83 w(A)p 2094 3482 39 3 v 2162 3461 a FJ(`)g FH(D)r(;)2315 3462 y(B)p 2318 3482 43 3 v 1741 3506 630 4 v 2391 3522 a FJ(R)p Fc(N)1846 3584 y FH(A)p 1849 3603 39 3 v 1917 3583 a FJ(`)g FH(C)h Fc(N)15 b FH(D)r(;)2210 3584 y(B)p 2214 3603 43 3 v 270 3754 a FK(Dually)-6 b(,)32 b(w)n(e)f(shall)g(ha)n(v)n(e)h(a)g FM(tensor)f(sum)g Fc(O)g FK(\(dual)h(of)f FJ(\012)p FK(\))g(and)i(a)e FM(dir)l(e)l(ct)h(sum)g FJ(\010)f FK(\(dual)167 3840 y(of)j Fc(N)p FK(\),)g(with)f(symmetrical)d(rules:)46 b(left)32 b(b)r(ecoming)h(righ)n(t)g(and)h FM(vic)l(e)f(versa)p FK(.)52 b(There)33 b(is)f(an)167 3925 y(easy)c(w)n(a)n(y)h(to)f(a)n(v)n (oid)g(this)f(b)r(oring)h(rep)r(etition,)e(b)n(y)j(using)f (asymmetrical)d(sequen)n(ts.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 152 155 bop 167 167 a FK(152)987 b Fz(APPENDIX)27 b(B.)55 b(WHA)-6 b(T)27 b(IS)g(LINEAR)g(LOGIC?)270 404 y FK(F)-6 b(or)29 b(this,)e(w)n(e)g(in)n(tro)r(duce)g(the)g FM(line)l(ar)h(ne)l (gation)p FK(:)270 556 y FJ(\017)34 b FK(Eac)n(h)28 b(atomic)e(form)n (ula)h(is)g(giv)n(en)g(in)f(t)n(w)n(o)i(forms:)35 b(p)r(ositiv)n(e)26 b(\()p FH(A)p FK(\))h(and)h(negativ)n(e)f(\()p FH(A)2585 530 y Fv(?)2626 556 y FK(\).)339 641 y(By)h(de\014nition,)g(the)f (linear)f(negation)i(of)h FH(A)e FK(is)g FH(A)1675 615 y Fv(?)1716 641 y FK(,)h(and)h FM(vic)l(e)e(versa)p FK(.)270 782 y FJ(\017)34 b FK(Linear)28 b(negation)g(is)f(extended)g(to)h(comp) r(osed)g(form)n(ulae)g(b)n(y)g FM(de)f(Mor)l(gan)h FK(la)n(ws:)601 950 y(\()p FH(A)16 b FJ(\012)f FH(B)t FK(\))849 925 y Fv(?)949 950 y FK(=)59 b FH(A)1114 925 y Fv(?)1171 950 y Fc(O)15 b FH(B)1297 925 y Fv(?)1673 950 y FK(\()p FH(A)g Fc(N)g FH(B)t FK(\))1920 925 y Fv(?)2021 950 y FK(=)58 b FH(A)2185 925 y Fv(?)2242 950 y FJ(\010)15 b FH(B)2368 925 y Fv(?)601 1036 y FK(\()p FH(A)h Fc(O)f FH(B)t FK(\))849 1010 y Fv(?)949 1036 y FK(=)59 b FH(A)1114 1010 y Fv(?)1171 1036 y FJ(\012)15 b FH(B)1297 1010 y Fv(?)1673 1036 y FK(\()p FH(A)g FJ(\010)g FH(B)t FK(\))1920 1010 y Fv(?)2021 1036 y FK(=)58 b FH(A)2185 1010 y Fv(?)2242 1036 y Fc(N)15 b FH(B)2368 1010 y Fv(?)270 1205 y FK(Linear)45 b(negation)h(is)f(not)h (itself)d(a)j(connector:)71 b(for)45 b(example,)k(if)c FH(A)g FK(and)h FH(B)j FK(are)167 1290 y(atomic)34 b(form)n(ulae,)j(\() p FH(A)17 b FJ(\012)h FH(B)947 1265 y Fv(?)989 1290 y FK(\))1016 1265 y Fv(?)1092 1290 y FK(is)35 b(just)g(a)h(meta-notation) f(for)h FH(A)2022 1265 y Fv(?)2081 1290 y Fc(O)18 b FH(B)t FK(,)37 b(whic)n(h)d(is)h(also)167 1376 y(con)n(v)n(en)n(tionally)e (written)f(as)i FH(A)17 b Fu(\()g FH(B)38 b FK(\()p FM(line)l(ar)33 b(implic)l(ation)p FK(\).)53 b(Note)33 b(that)g FH(A)2281 1350 y Fv(??)2395 1376 y FK(is)f(alw)n(a)n(ys)167 1461 y FM(e)l(qual)27 b FK(to)h FH(A)p FK(.)270 1584 y(A)g(t)n(w)n(o-sided)f (sequen)n(t)1038 1752 y FH(A)1090 1763 y FD(1)1118 1752 y FH(;)12 b(:)g(:)g(:)f(;)h(A)1324 1763 y Fw(n)1377 1752 y FJ(`)19 b FH(B)1491 1763 y FD(1)1520 1752 y FH(;)12 b(:)g(:)g(:)f(;)h(B)1726 1763 y Fw(m)167 1920 y FK(is)27 b(replaced)g(b)n(y:)1021 2088 y FJ(`)20 b FH(A)1136 2063 y Fv(?)1136 2106 y FD(1)1177 2088 y FH(;)12 b(:)g(:)g(:)g(;)g(A)1384 2063 y Fv(?)1384 2106 y Fw(n)1425 2088 y FH(;)g(B)1508 2099 y FD(1)1536 2088 y FH(;)g(:)g(:)g(:)g(;)g(B)1743 2099 y Fw(m)167 2256 y FK(In)28 b(particular,)f(the)g(iden)n(tit)n(y)f (axiom)i(b)r(ecomes)46 b FJ(`)20 b FH(A)1605 2231 y Fv(?)1646 2256 y FH(;)12 b(A)47 b FK(and)29 b(the)e(cut:)1074 2420 y FJ(`)19 b FH(C)q(;)1217 2421 y(A)p 1221 2441 39 3 v 1367 2420 a FJ(`)h FH(C)1484 2391 y Fv(?)1526 2420 y FH(;)1557 2421 y(B)p 1560 2441 43 3 v 1074 2465 540 4 v 1634 2481 a Fq(Cut)1243 2542 y FJ(`)1305 2543 y FH(A)p 1309 2562 39 3 v -1 x(;)1388 2543 y(B)p 1391 2562 43 3 v 167 2700 a FK(Of)27 b(course,)h(the)g(only)g(structural)e(rule)h (is)1186 2851 y FJ(`)1249 2852 y FH(A)p 1252 2872 39 3 v -1 x(;)12 b(C)q(;)g(D)r(;)1503 2852 y(B)p 1507 2872 43 3 v 1186 2896 373 4 v 1580 2912 a Fq(X)1186 2973 y FJ(`)1249 2974 y FH(A)p 1252 2993 39 3 v -1 x(;)g(D)r(;)g(C)q(;)1503 2974 y(B)p 1507 2993 43 3 v 167 3131 a FK(and)29 b(the)e(logical)f (rules)h(are)h(no)n(w)g(expressed)g(b)n(y:)660 3282 y FJ(`)20 b FH(C)q(;)804 3283 y(A)p 808 3303 39 3 v 954 3282 a FJ(`)f FH(D)r(;)1106 3283 y(B)p 1110 3303 43 3 v 660 3327 503 4 v 1183 3343 a FJ(\012)695 3404 y(`)h FH(C)h FJ(\012)16 b FH(D)r(;)989 3405 y(A)p 992 3424 39 3 v 1040 3404 a(;)1071 3405 y(B)p 1075 3424 43 3 v 1761 3282 a FJ(`)j FH(C)q(;)12 b(D)r(;)1994 3283 y(A)p 1998 3303 39 3 v 1731 3327 345 4 v 2097 3343 a Fc(O)1731 3404 y FJ(`)20 b FH(C)h Fc(O)15 b FH(D)r(;)2024 3405 y(A)p 2028 3424 39 3 v 416 3645 a FJ(`)k FH(C)q(;)559 3646 y(A)p 563 3666 V 709 3645 a FJ(`)h FH(D)r(;)862 3646 y(A)p 865 3666 V 416 3690 498 4 v 934 3706 a Fc(N)492 3766 y FJ(`)g FH(C)h Fc(N)15 b FH(D)r(;)785 3767 y(A)p 789 3787 39 3 v 1312 3645 a FJ(`)20 b FH(C)q(;)1456 3646 y(A)p 1460 3666 V 1238 3690 345 4 v 1603 3706 a FK(1)p FJ(\010)1238 3766 y(`)f FH(C)i FJ(\010)16 b FH(D)r(;)1531 3767 y(A)p 1534 3787 39 3 v 2011 3645 a FJ(`)k FH(D)r(;)2164 3646 y(A)p 2168 3666 V 1941 3690 345 4 v 2307 3706 a FK(2)p FJ(\010)1941 3766 y(`)g FH(C)h FJ(\010)15 b FH(D)r(;)2234 3767 y(A)p 2238 3787 39 3 v 167 3925 a FK(There)27 b(is)g(nothing)h (deep)g(in)f(this)g(con)n(v)n(en)n(tion:)36 b(it)27 b(is)g(just)h(a)g (matter)e(of)j(econom)n(y!)p eop PStoPSsaved restore %%Page: (156,157) 79 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 153 156 bop 167 167 a Fz(B.2.)63 b(LINEAR)27 b(SEQUENT)g(CALCULUS)1174 b FK(153)270 404 y(Units)27 b(\()p FG(1)g FK(for)h FJ(\012)p FK(,)g FJ(?)e FK(for)i Fc(O)p FK(,)g FJ(>)e FK(for)i Fc(N)f FK(and)i FG(0)e FK(for)h FJ(\010)p FK(\))f(are)h(also)g(in)n (tro)r(duced:)479 650 y FG(1)519 625 y Fv(?)580 650 y FK(=)20 b FJ(?)311 b(?)1077 625 y Fv(?)1137 650 y FK(=)19 b FG(1)312 b FJ(>)1618 625 y Fv(?)1678 650 y FK(=)19 b FG(0)312 b(0)2143 625 y Fv(?)2204 650 y FK(=)19 b FJ(>)p 431 1053 103 4 v 554 1069 a FG(1)431 1130 y FJ(`)g FG(1)900 1023 y FJ(`)962 1024 y FH(A)p 966 1043 39 3 v 857 1067 200 4 v 1077 1083 a FJ(?)857 1144 y(`)g(?)p FH(;)1006 1145 y(A)p 1009 1165 39 3 v 1396 1043 200 4 v 1616 1059 a FJ(>)1396 1119 y(`)g(>)p FH(;)1545 1120 y(A)p 1548 1140 39 3 v 1935 1018 a FK(\(no)28 b(rule)f(for)h FG(0)p FK(\))270 1445 y(Finally)-6 b(,)38 b(the)e(lost)g(structural)f(rules)h (come)f(bac)n(k)j(with)d(a)i(logical)d(dressing,)39 b FM(via)d FK(the)167 1530 y(mo)r(dalities)h(!)12 b FH(A)27 b FK(\()p FM(of)h(c)l(ourse)g FH(A)p FK(\))f(and)41 b(?)12 b FH(A)26 b FK(\()p FM(why)i(not)f FH(A)p FK(\):)718 1776 y(\()12 b(!)g FH(A)p FK(\))867 1750 y Fv(?)927 1776 y FK(=)g(?)g FH(A)1090 1750 y Fv(?)1681 1776 y FK(\()g(?)g FH(A)p FK(\))1844 1750 y Fv(?)1904 1776 y FK(=)g(!)g FH(A)2053 1750 y Fv(?)375 2157 y FJ(`)20 b FH(B)t(;)j FK(?)581 2158 y FH(A)p 584 2178 V 364 2202 281 4 v 664 2218 a FK(!)364 2279 y FJ(`)12 b FK(!)g FH(B)t(;)23 b FK(?)593 2280 y FH(A)p 596 2299 39 3 v 942 2157 a FJ(`)1004 2158 y FH(A)p 1008 2178 V 880 2202 238 4 v 1138 2218 a Fq(W)q FK(?)880 2279 y FJ(`)12 b FK(?)g FH(B)t(;)1067 2280 y(A)p 1070 2299 39 3 v 1433 2157 a FJ(`)g FK(?)g FH(B)t(;)23 b FK(?)12 b FH(B)t(;)1763 2158 y(A)p 1766 2178 V 1433 2202 381 4 v 1834 2218 a Fq(C)p FK(?)1505 2279 y FJ(`)g FK(?)g FH(B)t(;)1692 2280 y(A)p 1694 2299 39 3 v 2126 2157 a FJ(`)19 b FH(B)t(;)2275 2158 y(A)p 2279 2178 V 2108 2202 238 4 v 2366 2218 a Fq(D)p FK(?)2108 2279 y FJ(`)12 b FK(?)g FH(B)t(;)2295 2280 y(A)p 2297 2299 39 3 v 167 2515 a FK(The)35 b(last)g(is)f(called)g FM(der)l(eliction)5 b FK(:)50 b(it)34 b(is)h(equiv)l(alen)n(t)g(to)g (the)g(axiom)g FH(B)t Fu(\()12 b FK(?)g FH(B)t FK(,)37 b(or)e(dually)167 2600 y(!)12 b FH(B)20 b Fu(\()15 b FH(B)t FK(.)270 2762 y(This)42 b(allo)n(ws)g(us)h(to)f(represen)n(t)g (in)n(tuitionistic)d(form)n(ulae)j(in)g(linear)f(logic,)k FM(via)i FK(the)167 2847 y(follo)n(wing)27 b(de\014nitions)274 3093 y FH(A)15 b FJ(^)g FH(B)24 b FK(=)19 b FH(A)d Fc(N)f FH(B)110 b(A)16 b FJ(_)f FH(B)24 b FK(=)12 b(!)g FH(A)p FJ(\010)g FK(!)g FH(B)109 b(A)19 b FJ(\))h FH(B)k FK(=)12 b(!)g FH(A)i Fu(\()i FH(B)111 b FJ(:)p FH(A)19 b FK(=)12 b(!)g FH(A)i Fu(\()i FG(0)167 3339 y FK(in)28 b(suc)n(h)i(a)f(w)n(a)n (y)h(that)f(an)h(in)n(tuitionistic)c(form)n(ula)j(is)f(v)l(alid)h (i\013)f(its)g(translation)h(is)f(pro)n(v)l(able)167 3424 y(in)j(Linear)g(Sequen)n(t)h(Calculus)e(\(so,)j(for)f(example,)f (dereliction)e(expresses)j(that)f FH(B)c FJ(\))22 b FH(B)t FK(\).)167 3509 y(This)40 b(translation)g(is)g(in)g(fact)h(used)g(for)g (the)f(coherence)f(seman)n(tics)h(of)h(t)n(yp)r(ed)g(lam)n(b)r(da)167 3594 y(calculus)27 b(\(c)n(hapters)g FG(??)q FK(,)h FG(??)q FK(,)f FG(??)i FK(and)g(app)r(endix)f FG(??)q FK(\).)270 3840 y(It)35 b(is)f(also)i(p)r(ossible)e(to)h(add)h(\(\014rst)f(and)i (second)e(order\))g(quan)n(ti\014ers,)j(but)d(the)g(main)167 3925 y(features)28 b(of)g(linear)e(logic)g(are)i(already)g(con)n (tained)g(in)f(the)g(prop)r(ositional)h(fragmen)n(t.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 154 157 bop 167 167 a FK(154)987 b Fz(APPENDIX)27 b(B.)55 b(WHA)-6 b(T)27 b(IS)g(LINEAR)g(LOGIC?)167 404 y FE(B.3)114 b(Pro)s(of)27 b(nets)167 560 y FK(Here,)g(w)n(e)g(shall)f(concen)n (trate)i(on)g(the)f(so-called)g FM(multiplic)l(ative)32 b FK(fragmen)n(t)c(of)g(linear)e(logic,)167 645 y FM(i.e.)40 b FK(the)g(connectors)g FJ(\012)p FK(,)j FG(1)p FK(,)g Fc(O)d FK(and)h FJ(?)p FK(.)71 b(In)41 b(this)e(fragmen)n(t,)44 b(rules)39 b(are)h FM(c)l(onservative)167 730 y FK(o)n(v)n(er)31 b(con)n(texts:)41 b(the)30 b(con)n(text)g(in)g(the)f(conclusion)h(is)g (the)g(disjoin)n(t)g(union)g(of)h(those)g(of)f(the)167 815 y(premises.)47 b(The)32 b(rules)f(for)h Fc(N)g FK(and)h FJ(>)d FK(are)i(not,)i(and)f(if)e(w)n(e)h(renounce)g(these)g (connectors,)167 900 y(w)n(e)27 b(m)n(ust)h(renounce)f(their)g(duals)h FJ(\010)f FK(and)i FG(0)p FK(.)270 1027 y(F)-6 b(rom)36 b(an)g(algorithmic)d(viewp)r(oin)n(t,)k(this)d(fragmen)n(t)i(is)e(v)n (ery)i FM(unexpr)l(essive)p FK(,)h(but)f(this)167 1112 y(restriction)27 b(is)h(necessary)i(if)e(w)n(e)g(w)n(an)n(t)i(to)f(tac) n(kle)f(problems)h(progressiv)n(ely)-6 b(.)40 b(F)-6 b(urthermore,)167 1197 y(m)n(ultiplicativ)n(e)50 b(connectors)k(and)g (rules)f(can)h(b)r(e)g(generalised)e(to)i(mak)n(e)g(a)g(gen)n(uine)167 1282 y(programming)28 b(language)860 1256 y FD(1)889 1282 y FK(.)270 1409 y(Sequen)n(t)h(pro)r(ofs)f(con)n(tain)g(a)g(lot)g (of)g(redundancy:)37 b(in)27 b(a)h(rule)e(suc)n(h)i(as)1225 1566 y FJ(`)20 b FH(C)q(;)12 b(D)r(;)1459 1567 y(A)p 1463 1587 39 3 v 1196 1611 345 4 v 1561 1627 a Fc(O)1196 1688 y FJ(`)19 b FH(C)i Fc(O)16 b FH(D)r(;)1489 1689 y(A)p 1492 1708 39 3 v 167 1852 a FK(the)32 b(con)n(text)550 1853 y FH(A)p 553 1873 V 601 1852 a FK(,)i(whic)n(h)e(pla)n(ys)h(a)f (passiv)n(e)h(r^)-34 b(ole,)33 b(is)f(rewritten)e(without)i(an)n(y)h(c) n(hange.)51 b(By)167 1937 y(exp)r(elling)37 b(all)h(those)i(b)r(oring)f (con)n(texts,)k(w)n(e)38 b(obtain)i(the)f FM(substanti\014que)f(mo)l (el)t(le)g FK(of)h(the)167 2022 y(pro)r(of,)29 b(called)d(the)h FM(pr)l(o)l(of)j(net)p FK(.)270 2149 y(F)-6 b(or)29 b(example,)d(the)i (pro)r(of)852 2319 y FJ(`)20 b FH(A;)12 b(A)1050 2290 y Fv(?)1189 2319 y FJ(`)19 b FH(B)t(;)12 b(B)1394 2290 y Fv(?)p 852 2364 584 4 v 1457 2380 a FJ(\012)889 2441 y(`)20 b FH(A)15 b FJ(\012)h FH(B)t(;)c(A)1229 2412 y Fv(?)1270 2441 y FH(;)g(B)1357 2412 y Fv(?)1644 2441 y FJ(`)19 b FH(C)q(;)12 b(C)1841 2412 y Fv(?)p 889 2486 995 4 v 1905 2501 a FJ(\012)973 2562 y(`)20 b FK(\()p FH(A)15 b FJ(\012)h FH(B)t FK(\))f FJ(\012)g FH(C)q(;)d(A)1502 2533 y Fv(?)1544 2562 y FH(;)g(B)1631 2533 y Fv(?)1673 2562 y FH(;)g(C)1758 2533 y Fv(?)973 2623 y FK(=)-28 b(=)-16 b(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g (=)g(=)g(=)g(=)-29 b(=)973 2683 y FJ(`)20 b FH(A)1088 2654 y Fv(?)1129 2683 y FH(;)12 b(B)1216 2654 y Fv(?)1258 2683 y FH(;)g FK(\()p FH(A)j FJ(\012)g FH(B)t FK(\))h FJ(\012)f FH(C)q(;)d(C)1757 2654 y Fv(?)p 946 2728 882 4 v 1848 2744 a Fc(O)946 2805 y FJ(`)19 b FH(A)1060 2776 y Fv(?)1117 2805 y Fc(O)d FH(B)1244 2776 y Fv(?)1286 2805 y FH(;)c FK(\()p FH(A)j FJ(\012)g FH(B)t FK(\))g FJ(\012)h FH(C)q(;)c(C)1785 2776 y Fv(?)167 2966 y FK(b)r(ecomes)575 3290 y FH(A)78 b(B)p 571 3335 194 4 v 571 3411 a(A)15 b FJ(\012)h FH(B)878 3412 y(C)p 558 3456 388 4 v 558 3533 a FK(\()p FH(A)f FJ(\012)g FH(B)t FK(\))h FJ(\012)f FH(C)1371 3550 y(C)1425 3525 y Fv(?)1953 3423 y FH(A)2005 3394 y Fv(?)2125 3423 y FH(B)2181 3394 y Fv(?)p 1949 3468 278 4 v 1949 3544 a FH(A)2001 3515 y Fv(?)2058 3544 y Fc(O)h FH(B)2185 3515 y Fv(?)p 618 3134 1370 3 v 617 3216 3 84 v 1986 3350 3 218 v 735 3050 1420 3 v 734 3216 3 168 v 2153 3350 3 301 v 902 3267 502 3 v 901 3333 3 67 v 1402 3483 3 218 v 167 3649 1003 3 v 246 3692 a FC(1)273 3713 y FB(The)25 b(idea)g(is)g(to)h(use,)g(not)f(a)h(\014xed)f(logic,)g (but)g(an)g(extensible)f(one.)34 b(The)25 b(program)h(declares)g(its)e (o)n(wn)167 3784 y(connectors)h(\()p FA(i.e.)g FB(p)r(olymorphic)d(t)n (yp)r(es\))j(and)f(rules)g(\()p FA(i.e.)h FB(constructors)g(and)g (destructors\),)g(and)f(describ)r(es)167 3854 y(the)29 b(con)n(v)n(ersions)g(\()p FA(i.e.)g FB(the)g(program\).)40 b(Cut)29 b(elimination)d(is)j(in)f(fact)h FA(p)m(ar)m(al)s(lel)g(c)m (ommunic)m(ation)i(b)m(etwe)m(en)167 3925 y(pr)m(o)m(c)m(esses)p FB(.)j(In)28 b(this)e(language,)i(logic)f(do)r(es)g(not)h(ensure)f FA(termination)p FB(,)h(but)f FA(absenc)m(e)h(of)f(de)m(ad)s(lo)m(ck)p FB(.)p eop PStoPSsaved restore %%Page: (158,159) 80 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 155 158 bop 167 167 a Fz(B.3.)63 b(PR)n(OOF)27 b(NETS)1755 b FK(155)167 404 y(whic)n(h)27 b(could)g(also)h(come)f(from:)852 610 y FJ(`)20 b FH(A;)12 b(A)1050 581 y Fv(?)1189 610 y FJ(`)19 b FH(B)t(;)12 b(B)1394 581 y Fv(?)p 852 655 584 4 v 1457 671 a FJ(\012)889 731 y(`)20 b FH(A)15 b FJ(\012)h FH(B)t(;)c(A)1229 702 y Fv(?)1270 731 y FH(;)g(B)1357 702 y Fv(?)889 792 y FK(=)-16 b(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g (=)g(=)889 853 y FJ(`)20 b FH(A)1004 824 y Fv(?)1045 853 y FH(;)12 b(B)1132 824 y Fv(?)1174 853 y FH(;)g(A)j FJ(\012)h FH(B)p 862 897 565 4 v 1447 913 a Fc(O)862 974 y FJ(`)j FH(A)976 945 y Fv(?)1034 974 y Fc(O)c FH(B)1160 945 y Fv(?)1202 974 y FH(;)d(A)j FJ(\012)g FH(B)862 1035 y FK(=)-26 b(=)-17 b(=)h(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)g(=)-26 b(=)862 1095 y FJ(`)19 b FH(A)d FJ(\012)f FH(B)t(;)d(A)1201 1066 y Fv(?)1258 1095 y Fc(O)k FH(B)1385 1066 y Fv(?)1644 1095 y FJ(`)j FH(C)q(;)12 b(C)1841 1066 y Fv(?)p 862 1140 1023 4 v 1905 1156 a FJ(\012)932 1217 y(`)20 b FK(\()p FH(A)15 b FJ(\012)g FH(B)t FK(\))h FJ(\012)f FH(C)q(;)d(A)1461 1187 y Fv(?)1519 1217 y Fc(O)j FH(B)1645 1187 y Fv(?)1687 1217 y FH(;)d(C)1772 1187 y Fv(?)270 1431 y FK(Essen)n(tially)-6 b(,)27 b(w)n(e)g(lose)g(the)h(\(inessen)n(tial\))d(application)i(order) h(of)g(rules.)270 1654 y(A)n(t)g(this)f(p)r(oin)n(t,)i(precise)d (de\014nitions)i(are)g(needed.)36 b(A)28 b FM(pr)l(o)l(of)i(structur)l (e)e FK(is)f(just)h(a)h(graph)167 1739 y(built)d(from)i(the)f(follo)n (wing)g(comp)r(onen)n(ts:)270 1934 y FJ(\017)34 b FM(link)8 b FK(:)1396 2248 y FH(A)95 b(A)1595 2222 y Fv(?)p 1422 2082 168 3 v 1421 2164 3 84 v 1588 2164 V 270 2474 a FJ(\017)34 b FM(cut)7 b FK(:)1380 2711 y FH(A)78 b(A)1562 2682 y Fv(?)p 1380 2756 224 4 v 270 3096 a FJ(\017)34 b FM(lo)l(gic)l(al)28 b(rules)6 b FK(:)692 3333 y FH(A)78 b(B)p 688 3378 194 4 v 688 3455 a(A)16 b FJ(\012)f FH(B)1235 3333 y(A)78 b(B)p 1231 3378 V 1231 3455 a(A)16 b Fc(O)f FH(B)p 1774 3357 79 4 v 1793 3433 a FG(1)p 2202 3357 94 4 v 388 w FJ(?)270 3754 y FK(Eac)n(h)31 b(form)n(ula)e(m)n(ust)h(b)r (e)g(the)f(conclusion)h(of)g(exactly)f(one)i(rule)d(and)j(a)f(premise)e (of)j(at)167 3840 y(most)24 b(one)g(rule.)33 b(F)-6 b(orm)n(ulae)24 b(whic)n(h)f(are)h(not)g(premises)f(are)g(called)g FM(c)l(onclusions)g (of)i(the)e(pr)l(o)l(of)167 3925 y(structur)l(e)5 b FK(:)36 b(these)27 b(conclusions)g(are)h(not)g(ordered.)36 b(Links)27 b(and)i(cuts)f(are)f(symmetrical.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 156 159 bop 167 167 a FK(156)987 b Fz(APPENDIX)27 b(B.)55 b(WHA)-6 b(T)27 b(IS)g(LINEAR)g(LOGIC?)270 404 y FM(Pr)l(o)l(of)h(nets) e FK(are)g(pro)r(of)h(structures)f(whic)n(h)f(are)h(constructed)g (according)h(to)f(the)g(rules)g(of)167 490 y(Linear)h(Sequen)n(t)h (Calculus:)270 649 y FJ(\017)34 b FK(Links)28 b(are)g(pro)r(of)g(nets.) 270 792 y FJ(\017)34 b FK(If)24 b FH(A)f FK(is)g(a)h(conclusion)g(of)g (a)g(pro)r(of)h(net)e FH(\027)28 b FK(and)d FH(A)1633 767 y Fv(?)1698 792 y FK(is)e(a)h(conclusion)g(of)g(a)g(pro)r(of)h(net) e FH(\027)2636 767 y Fv(0)2653 792 y FK(,)1352 997 y FH(\027)1362 1038 y FJ(\001)1362 1075 y(\001)1362 1113 y(\001)1346 1171 y FH(A)1564 983 y(\027)1602 954 y Fv(0)1582 1024 y FJ(\001)1582 1062 y(\001)1582 1100 y(\001)1545 1171 y FH(A)1597 1142 y Fv(?)p 1346 1215 293 4 v 339 1463 a FK(is)k(a)h(pro)r(of)h(net.)270 1606 y FJ(\017)34 b FK(If)26 b FH(A)f FK(is)g(a)h(conclusion)g(of)g(a)g(pro)r(of)h(net)e FH(\027)30 b FK(and)d FH(B)i FK(is)c(a)h(conclusion)g(of)g(a)g(pro)r (of)h(net)e FH(\027)2636 1581 y Fv(0)2653 1606 y FK(,)1371 1797 y FH(\027)1381 1838 y FJ(\001)1381 1876 y(\001)1381 1914 y(\001)1365 1971 y FH(A)1564 1797 y(\027)1602 1768 y Fv(0)1582 1838 y FJ(\001)1582 1876 y(\001)1582 1914 y(\001)1563 1971 y FH(B)p 1365 2016 255 4 v 1395 2092 a(A)15 b FJ(\012)h FH(B)339 2269 y FK(is)27 b(a)h(pro)r(of)h(net.)270 2412 y FJ(\017)34 b FK(If)28 b FH(A)f FK(and)i FH(B)i FK(are)d(conclusions)g(of)g(the)f(same)g(pro)r(of)i(net)f FH(\027)t FK(,)1473 2578 y FH(\027)1381 2637 y FJ(\001)1381 2675 y(\001)1381 2713 y(\001)1365 2770 y FH(A)1582 2637 y FJ(\001)1582 2675 y(\001)1582 2713 y(\001)1563 2770 y FH(B)p 1330 2815 324 4 v 1395 2891 a(A)15 b Fc(O)h FH(B)339 3068 y FK(is)27 b(a)h(pro)r(of)h(net.)270 3224 y FJ(\017)p 359 3190 40 4 v 359 3267 a FG(1)446 3224 y FK(is)e(a)h(pro)r(of)g(net.)270 3380 y FJ(\017)34 b FK(If)28 b FH(\027)k FK(is)27 b(a)h(pro)r(of)h(net,)1473 3546 y FH(\027)p 1465 3677 55 4 v 1465 3754 a FJ(?)339 3925 y FK(is)e(a)h(pro)r(of)h(net.)p eop PStoPSsaved restore %%Page: (160,161) 81 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 157 160 bop 167 167 a Fz(B.4.)63 b(CUT)27 b(ELIMINA)-6 b(TION)1557 b FK(157)270 404 y(There)40 b(is)f(a)i(funn)n(y)h (correctness)d(criterion)f(\(the)i FM(long)g(trip)g FK(condition,)j (see)d([)p FG(?)q FK(]\))g(to)167 490 y(c)n(haracterise)28 b(pro)r(of)j(nets)e(among)i(pro)r(of)g(structures.)41 b(F)-6 b(or)30 b(example,)f(the)g(follo)n(wing)g(pro)r(of)167 575 y(structure)1327 916 y FH(A)78 b(B)p 1323 960 194 4 v 1323 1037 a(A)15 b Fc(O)g FH(B)1039 1026 y(A)1091 1000 y Fv(?)1705 1026 y FH(B)1761 1000 y Fv(?)p 1086 777 268 3 v 1084 943 3 168 v 1352 842 3 67 v 1486 777 268 3 v 1752 943 3 168 v 1485 842 3 67 v 167 1216 a FK(is)50 b(not)h(a)g(pro)r(of)h(net,)57 b(and)51 b(indeed,)56 b(do)r(es)c(not)f(satisfy)g(the)f(long)h(trip)f(condition.)167 1301 y(Unfortunately)-6 b(,)39 b(this)d(criterion)f(w)n(orks)i(only)f (for)h(the)f(\()p FJ(\012)p FH(;)12 b Fc(O)p FH(;)g FG(1)p FK(\))35 b(fragmen)n(t)i(of)g(the)f(logic)167 1386 y(\(not)28 b FJ(?)p FK(\).)167 1646 y FE(B.4)114 b(Cut)29 b(elimination)167 1812 y FK(Pro)r(ofs)g(nets)e(pro)n(vide)h(a)g(v)n(ery)g(nice)e(framew)n (ork)i(for)g(describing)f(cut)g(elimination.)270 1959 y(Con)n(v)n(ersions)i(are)f(purely)f(lo)r(cal:)676 2257 y FH(A)806 2261 y(A)858 2232 y Fv(?)1029 2128 y FJ(\001)1029 2166 y(\001)1029 2204 y(\001)1012 2261 y FH(A)p 806 2306 258 4 v 690 2303 a FJ(\001)690 2341 y(\001)690 2378 y(\001)p 701 2091 134 3 v 700 2190 3 101 v 834 2190 V 1384 2257 a Fu( )1794 2124 y FJ(\001)1794 2162 y(\001)1794 2200 y(\001)1778 2257 y FH(A)1792 2303 y FJ(\001)1792 2341 y(\001)1792 2378 y(\001)360 2503 y(\001)360 2541 y(\001)360 2579 y(\001)344 2636 y FH(A)561 2503 y FJ(\001)561 2541 y(\001)561 2579 y(\001)543 2636 y FH(B)p 344 2681 255 4 v 375 2757 a(A)15 b FJ(\012)h FH(B)783 2489 y FJ(\001)783 2527 y(\001)783 2565 y(\001)746 2636 y FH(A)798 2607 y Fv(?)1026 2489 y FJ(\001)1026 2527 y(\001)1026 2565 y(\001)987 2636 y FH(B)1043 2607 y Fv(?)p 746 2681 339 4 v 777 2757 a FH(A)829 2728 y Fv(?)886 2757 y Fc(O)g FH(B)1013 2728 y Fv(?)p 375 2802 680 4 v 1419 2681 a Fu( )1839 2564 y FJ(\001)1839 2601 y(\001)1839 2639 y(\001)1823 2697 y FH(A)2059 2550 y FJ(\001)2059 2588 y(\001)2059 2626 y(\001)2022 2697 y FH(A)2074 2667 y Fv(?)p 1823 2741 293 4 v 2212 2564 a FJ(\001)2212 2601 y(\001)2212 2639 y(\001)2194 2697 y FH(B)2436 2550 y FJ(\001)2436 2588 y(\001)2436 2626 y(\001)2397 2697 y FH(B)2453 2667 y Fv(?)p 2194 2741 301 4 v 843 3008 40 4 v 843 3085 a FG(1)p 1030 3008 55 4 v 147 w FJ(?)p 843 3130 242 4 v 1419 3103 a Fu( )334 b FK(\(nothing\))167 3404 y FG(Prop)r(osition)25 b FK(The)j(con)n(v)n(ersions)g(preserv)n(e)f(the)h(prop)r(ert)n(y)g(of) g(b)r(eing)f(a)i(pro)r(of)f(net.)270 3551 y(T)-6 b(o)34 b(pro)n(v)n(e)f(this,)h(y)n(ou)g(sho)n(w)f(that)g(con)n(v)n(ersions)h (of)f(pro)r(of)h(nets)e(re\015ect)g(con)n(v)n(ersions)i(of)167 3637 y(sequen)n(t)28 b(pro)r(ofs,)h(or)f(alternativ)n(ely)-6 b(,)26 b(y)n(ou)j(mak)n(e)f(use)g(of)g(the)f(long)h(trip)f(condition.) 216 b Fu(\003)167 3852 y FG(Prop)r(osition)25 b FK(An)n(y)j(pro)r(of)h (net)e(reduces)h(to)g(a)g(\(unique\))f(cut)g(free)g(one.)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 158 161 bop 167 167 a FK(158)987 b Fz(APPENDIX)27 b(B.)55 b(WHA)-6 b(T)27 b(IS)g(LINEAR)g(LOGIC?)270 404 y FK(F)-6 b(or)29 b(example,)d(the)i(pro)r(of)h(net)333 736 y FH(A)78 b(B)p 329 781 194 4 v 329 858 a(A)15 b FJ(\012)h FH(B)116 b(C)p 315 902 388 4 v 315 979 a FK(\()p FH(A)16 b FJ(\012)f FH(B)t FK(\))g FJ(\012)h FH(C)979 997 y(C)1033 971 y Fv(?)1337 992 y FH(A)1389 963 y Fv(?)1446 992 y Fc(O)g FH(B)1573 963 y Fv(?)1693 992 y FH(A)f FJ(\012)g FH(B)p 1337 1037 550 4 v 2131 997 a(B)2187 971 y Fv(?)2467 997 y FH(A)2519 971 y Fv(?)p 359 580 1003 3 v 358 663 3 84 v 1360 930 3 351 v 493 497 1053 3 v 491 663 3 168 v 1544 930 3 435 v 660 714 351 3 v 658 779 3 67 v 1009 930 3 218 v 1729 747 769 3 v 1727 930 3 184 v 2496 930 V 1862 831 301 3 v 1861 930 3 101 v 2162 930 V 270 1153 a FK(reduces)28 b(\(in)f(three)f(steps\))i(to)575 1489 y FH(A)78 b(B)p 571 1534 194 4 v 571 1610 a(A)15 b FJ(\012)h FH(B)878 1611 y(C)p 558 1655 388 4 v 558 1732 a FK(\()p FH(A)f FJ(\012)g FH(B)t FK(\))h FJ(\012)f FH(C)1371 1749 y(C)1425 1724 y Fv(?)1872 1749 y FH(B)1928 1724 y Fv(?)2208 1749 y FH(A)2260 1724 y Fv(?)p 735 1333 1170 3 v 734 1415 3 84 v 1903 1682 3 351 v 618 1249 1621 3 v 617 1415 3 168 v 2237 1682 3 435 v 902 1466 502 3 v 901 1549 3 84 v 1402 1682 3 218 v 270 1946 a FK(T)-6 b(o)26 b(pro)n(v)n(e)g(the)f (prop)r(osition,)i(it)d(is)g(enough)j(to)f(see)f(that)g Fu( )h FK(de\014nes)g(a)f FM(terminating)g FK(and)167 2031 y FM(c)l(on\015uent)j FK(relation,)e(and)j(a)f(normal)f(form)h(is) f(necessarily)f(cut)h(free,)g(unless)h(it)e(con)n(tains)1308 2326 y FH(A)1360 2297 y Fv(?)1480 2326 y FH(A)p 1308 2371 224 4 v 1336 2165 168 3 v 1335 2264 3 101 v 1502 2264 V 167 2529 a FK(whic)n(h)j(is)f(imp)r(ossible)g(in)g(a)i(pro)r(of) h(net.)40 b FM(T)-5 b(ermination)30 b FK(is)e(ob)n(vious)j(\(the)e (size)f(decreases)h(at)167 2614 y(eac)n(h)i(step\))f(and)i FM(c)l(on\015uenc)l(e)e FK(comes)g(from)g(the)h(fact)f(that)h(con)n(v)n (ersions)g(are)g(purely)f(lo)r(cal,)167 2699 y(the)d(only)h(p)r (ossible)f(con\015icts)h(b)r(eing:)475 2957 y FH(A)640 2953 y(A)692 2924 y Fv(?)811 2953 y FH(A)p 640 2998 224 4 v 955 2957 a(A)1007 2932 y Fv(?)p 501 2791 168 3 v 500 2890 3 101 v 667 2890 V 835 2791 168 3 v 834 2890 3 101 v 1001 2890 V 1364 2957 a FK(and)1829 2806 y FJ(\001)1829 2844 y(\001)1829 2882 y(\001)1792 2953 y FH(A)1844 2924 y Fv(?)1998 2953 y FH(A)p 1792 2998 258 4 v 76 w(A)2178 2924 y Fv(?)2348 2820 y FJ(\001)2348 2858 y(\001)2348 2896 y(\001)2332 2953 y FH(A)p 2126 2998 V 2021 2791 151 3 v 2020 2890 3 101 v 2170 2890 V 167 3114 a FK(The)f(reader)h(can) g(easily)e(c)n(hec)n(k)i(the)f(con\015uence)h(in)f(b)r(oth)i(cases.)689 b Fu(\003)270 3285 y FK(It)40 b(is)g(imp)r(ortan)n(t)g(to)h(notice)e (that)i(cuts)f(are)h(eliminated)c(in)j(arbitrary)g(order:)61 b(cut)167 3370 y(elimination)25 b(is)i(a)h FM(p)l(ar)l(al)t(lel)34 b FK(pro)r(cess.)270 3540 y(A)28 b(link)1156 3762 y FH(A)15 b FJ(\012)g FH(B)103 b(A)1500 3737 y Fv(?)1557 3762 y Fc(O)16 b FH(B)1684 3737 y Fv(?)p 1253 3619 335 3 v 1251 3701 3 84 v 1585 3701 V 167 3925 a FK(can)28 b(alw)n(a)n(ys)g(b)r(e)g (replaced)e(b)n(y)p eop PStoPSsaved restore %%Page: (162,163) 82 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 159 162 bop 167 167 a Fz(B.4.)63 b(CUT)27 b(ELIMINA)-6 b(TION)1557 b FK(159)1160 566 y FH(A)78 b(B)p 1156 611 194 4 v 1156 687 a(A)15 b FJ(\012)g FH(B)1452 574 y(A)1504 545 y Fv(?)1624 574 y FH(B)1680 545 y Fv(?)p 1448 619 278 4 v 1448 696 a FH(A)1500 667 y Fv(?)1557 696 y Fc(O)h FH(B)1684 667 y Fv(?)p 1186 419 301 3 v 1185 501 3 84 v 1485 501 V 1319 335 335 3 v 1318 501 3 168 v 1652 501 V 167 818 a FK(and)29 b(similarly)24 b(for)k FG(1)f FK(and)i FJ(?)p FK(.)34 b(So)29 b(w)n(e)e(can)h(also)g(restrict)d(links)i(to)h FM(atomic)k FK(form)n(ulae.)270 978 y(Consider)23 b(no)n(w)g(a)g(cut)f (free)f(pro)r(of)j(net)e(with)g(\014xed)h(conclusions.)33 b(Since)22 b(the)g(logical)f(rules)167 1063 y(follo)n(w)35 b(faithfully)g(the)h(structure)f(of)i(these)e(conclusions,)k(our)d(pro) r(of)h(net)f(is)f(completely)167 1148 y(determined)26 b(b)n(y)i(its)f(\(atomic\))f(links.)35 b(So)28 b(our)g(\014rst)g (example)f(comes)g(to)558 1553 y(\()p FH(A)15 b FJ(\012)g FH(B)t FK(\))h FJ(\012)f FH(C)1371 1554 y(C)1425 1528 y Fv(?)1949 1548 y FH(A)2001 1522 y Fv(?)2058 1548 y Fc(O)h FH(B)2185 1522 y Fv(?)p 618 1304 1370 3 v 617 1487 3 184 v 1986 1487 V 751 1221 1403 3 v 750 1487 3 268 v 2153 1487 V 919 1388 485 3 v 917 1487 3 101 v 1402 1487 V 167 1687 a FK(whic)n(h)30 b(is)g(just)h(an)g(in)n(v)n(olutiv)n (e)f(p)r(erm)n(utation,)h(sending)g(an)g(\(o)r(ccurrence)e(of)5 b(\))31 b(atom)g(to)g(\(an)167 1773 y(o)r(ccurrence)c(of)5 b(\))27 b(its)g(negation.)270 1932 y(The)38 b(cut)g(itself)e(has)j(a)f (natural)g(in)n(terpretation)f(in)g(terms)g(of)i(those)f(p)r(erm)n (utations.)167 2017 y(Instead)28 b(of)g(eliminating)d(it)i(in)333 2326 y FH(A)78 b(B)p 329 2371 194 4 v 329 2447 a(A)15 b FJ(\012)h FH(B)116 b(C)p 315 2492 388 4 v 315 2568 a FK(\()p FH(A)16 b FJ(\012)f FH(B)t FK(\))g FJ(\012)h FH(C)979 2586 y(C)1033 2560 y Fv(?)1337 2582 y FH(A)1389 2553 y Fv(?)1446 2582 y Fc(O)g FH(B)1573 2553 y Fv(?)1693 2582 y FH(A)f FJ(\012)g FH(B)p 1337 2626 550 4 v 2131 2586 a(B)2187 2560 y Fv(?)2467 2586 y FH(A)2519 2560 y Fv(?)p 359 2170 1003 3 v 358 2252 3 84 v 1360 2519 3 351 v 493 2086 1053 3 v 491 2252 3 168 v 1544 2519 3 435 v 660 2303 351 3 v 658 2386 3 84 v 1009 2519 3 218 v 1729 2337 769 3 v 1727 2519 3 184 v 2496 2519 V 1862 2420 301 3 v 1861 2519 3 101 v 2162 2519 V 167 2720 a FK(y)n(ou)29 b(connect)e(the)h(p)r(erm)n(utations)315 3121 y(\()p FH(A)16 b FJ(\012)f FH(B)t FK(\))g FJ(\012)h FH(C)979 3122 y(C)1033 3096 y Fv(?)1323 3116 y FH(A)1375 3090 y Fv(?)1432 3116 y Fc(O)f FH(B)1558 3090 y Fv(?)1698 3116 y FH(A)h FJ(\012)f FH(B)2131 3122 y(B)2187 3096 y Fv(?)2467 3122 y FH(A)2519 3096 y Fv(?)p 376 2872 986 3 v 375 3055 3 184 v 1360 3055 V 509 2789 1036 3 v 508 3055 3 268 v 1544 3055 V 676 2956 335 3 v 675 3055 3 101 v 1009 3055 V 1729 2872 769 3 v 1727 3055 3 184 v 2496 3055 V 1862 2956 301 3 v 1861 3055 3 101 v 2162 3055 V 1361 3206 368 3 v 1360 3205 3 51 v 1727 3205 V 1545 3256 318 3 v 1544 3255 3 101 v 1861 3255 V 167 3389 a FK(to)28 b(obtain)g(the)f(normal)h(form)f(b)n(y)i(iteration:)315 3790 y(\()p FH(A)16 b FJ(\012)f FH(B)t FK(\))g FJ(\012)h FH(C)979 3791 y(C)1033 3766 y Fv(?)2131 3791 y FH(B)2187 3766 y Fv(?)2467 3791 y FH(A)2519 3766 y Fv(?)p 376 3542 986 3 v 375 3724 3 184 v 1360 3875 3 335 v 509 3458 1036 3 v 508 3724 3 268 v 1544 3925 3 468 v 676 3625 335 3 v 675 3724 3 101 v 1009 3724 V 1729 3542 769 3 v 1727 3875 3 335 v 2496 3724 3 184 v 1862 3625 301 3 v 1861 3925 3 301 v 2162 3724 3 101 v 1361 3876 368 3 v 1545 3926 318 3 v eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 160 163 bop 167 167 a FK(160)987 b Fz(APPENDIX)27 b(B.)55 b(WHA)-6 b(T)27 b(IS)g(LINEAR)g(LOGIC?)270 404 y FK(This)k FM(turb)l(o)h(cut)f(elimination)g FK(mec)n(hanism)f(is)h(the)g(basic)g (idea)g(for)h(generalising)e(pro)r(of)167 490 y(nets)e(to)f(non-m)n (ultiplicativ)n(e)e(connectiv)n(es)i(\()p FM(ge)l(ometry)h(of)g(inter)l (action)p FK(\).)167 720 y FE(B.5)114 b(Pro)s(of)27 b(nets)i(and)g (natural)g(deduction)167 875 y FK(It)24 b(is)g(fair)g(to)h(sa)n(y)h (that)f(pro)r(of)h(nets)e(are)h(the)f(natural)h(deductions)g(of)g (linear)f(logic,)g(but)h(with)167 960 y(t)n(w)n(o)j(notable)g (di\013erences:)270 1082 y FJ(\017)34 b FK(Thanks)c(to)d(linearit)n(y) -6 b(,)26 b(there)h(is)g(no)i(need)e(for)h FM(p)l(ar)l(c)l(els)h(of)f (hyp)l(otheses)p FK(.)270 1217 y FJ(\017)34 b FK(Thanks)d(to)f(linear)d (negation,)k(there)d(is)h(no)h(need)f(for)g FM(dischar)l(ge)h FK(or)g(for)f FM(elimination)339 1302 y(rules)p FK(.)270 1424 y(F)-6 b(or)47 b(example,)j(if)45 b(w)n(e)h(follo)n(w)f(the)h(ob)n (vious)h(analogy)h(b)r(et)n(w)n(een)e(the)g(in)n(tuitionistic)167 1509 y(implication)25 b FH(A)19 b FJ(\))h FH(B)32 b FK(and)c(the)g (linear)e(one)i FH(A)15 b Fu(\()h FH(B)24 b FK(=)19 b FH(A)1728 1484 y Fv(?)1785 1509 y Fc(O)c FH(B)t FK(,)28 b(the)f(in)n(tro)r(duction)1293 1651 y([)p FH(A)p FK(])1329 1709 y FJ(\001)1329 1747 y(\001)1329 1785 y(\001)1310 1842 y FH(B)p 1230 1887 218 4 v 1468 1903 a FJ(\)I)1230 1963 y FH(A)19 b FJ(\))h FH(B)167 2087 y FK(corresp)r(onds)29 b(to)1288 2468 y FH(A)1340 2439 y Fv(?)1497 2294 y FH(A)1513 2335 y FJ(\001)1513 2373 y(\001)1513 2411 y(\001)1495 2468 y FH(B)p 1288 2513 263 4 v 1302 2589 a(A)1354 2560 y Fv(?)1411 2589 y Fc(O)15 b FH(B)p 1336 2145 184 3 v 1335 2395 3 251 v 1519 2228 3 84 v 167 2718 a FK(and)29 b(the)e(elimination)e(\()p FM(mo)l(dus)k(p)l(onens)p FK(\))1229 2851 y FJ(\001)1229 2889 y(\001)1229 2927 y(\001)1130 2984 y FH(A)20 b FJ(\))g FH(B)1511 2851 y FJ(\001)1511 2889 y(\001)1511 2927 y(\001)1495 2984 y FH(A)p 1130 3029 417 4 v 1567 3044 a FJ(\))q(E)1310 3105 y FH(B)167 3223 y FK(to)1122 3449 y FJ(\001)1122 3487 y(\001)1122 3525 y(\001)1014 3596 y FH(A)1066 3567 y Fv(?)1123 3596 y Fc(O)15 b FH(B)1412 3342 y FJ(\001)1412 3380 y(\001)1412 3418 y(\001)1396 3475 y FH(A)113 b(B)1617 3446 y Fv(?)p 1396 3519 263 4 v 1410 3596 a FH(A)15 b FJ(\012)g FH(B)1603 3567 y Fv(?)p 1014 3641 632 4 v 1759 3600 a FH(B)p 1587 3268 201 3 v 1585 3400 3 134 v 1786 3534 3 268 v 167 3723 a FK(whic)n(h)27 b(sho)n(ws)i(that)f FM(mo)l(dus)h(p)l(onens)f FK(is)e(written)g(upside)i(do)n(wn!)270 3840 y(So)j(linear)c(logic)i(is)f(not)i(just)g(another)g(exotic)e (logic:)38 b(it)28 b(giv)n(es)h(new)g(insigh)n(t)g(in)n(to)g(basic)167 3925 y(notions)f(whic)n(h)f(had)i(seemed)e(to)g(b)r(e)h(\014xed)g (forev)n(er.)p eop PStoPSsaved restore %%Page: (164,165) 83 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 161 164 bop 167 877 a FF(Bibliograph)-5 b(y)167 1200 y FK([Abr87])36 b(S.)26 b(Abramsky)-6 b(,)28 b FM(Domain)f(the)l(ory)g (and)g(the)f(lo)l(gic)g(of)h(observable)e(pr)l(op)l(erties)p FK(,)j(Ph.D.)409 1285 y(thesis)f(\(Queen)g(Mary)h(College,)e(Univ)n (ersit)n(y)h(of)h(London,)i(1987\).)167 1409 y([Abr88])36 b(S.)26 b(Abramsky)-6 b(,)28 b(Domain)e(theory)h(in)f(logical)f(form,)i FM(A)n(nnals)f(of)h(Pur)l(e)f(and)g(Applie)l(d)409 1494 y(L)l(o)l(gic)32 b FG(51)27 b FK(\(1991\))i(1{77.)167 1618 y([AbrVic)n(k])34 b(S.)42 b(Abramsky)h(and)g(S.J.)g(Vic)n(k)n (ers,)h(Quan)n(tales,)i(Observ)l(ational)c(Logic)g(and)409 1703 y(Pro)r(cess)51 b(Seman)n(tics,)57 b FM(Mathematic)l(al)52 b(Structur)l(es)f(in)g(Computer)h(Scienc)l(e)p FK(,)57 b FG(3)409 1788 y FK(\(1993\))29 b(161{227.)167 1912 y([Barendregt])35 b(H.)50 b(Barendregt,)55 b FM(The)50 b(lamb)l(da-c)l(alculus:)79 b(its)50 b(syntax)g(and)g(semantics)p FK(,)409 1997 y(North-Holland)27 b(\(1980\).)167 2121 y([Barwise])34 b(J.)25 b(Barwise)f(\(ed.\),)i FM(Handb)l(o)l(ok)g(of)f (mathematic)l(al)h(lo)l(gic)p FK(,)g(North-Holland)e(\(1977\).)167 2245 y([Berry])34 b(G.)e(Berry)-6 b(,)33 b(Stable)f(Mo)r(dels)g(of)g(T) n(yp)r(ed)h(lam)n(b)r(da-calculi,)d(in:)44 b FM(Pr)l(o)l(c)l(e)l(e)l (dings)33 b(of)f(the)409 2330 y(\014fth)27 b(ICALP)h(Confer)l(enc)l(e,) g FK(Springer-V)-6 b(erlag)27 b(LNCS)g FG(62)g FK(\(Udine,)g(1978\))i (72{89.)167 2454 y([BTM])42 b(V.)k(Breazu-T)-6 b(annen)48 b(and)f(A.)g(Mey)n(er,)k(P)n(olymorphism)46 b(is)g(conserv)l(ativ)n(e)h (o)n(v)n(er)409 2539 y(simple)26 b(t)n(yp)r(es,)i(in)f(the)h(pro)r (ceedings)f(of)i(the)e(second)i(IEEE)e(symp)r(osium)h(on)g FM(L)l(o)l(gic)409 2624 y(in)f(Computer)i(Scienc)l(e)i FK(\(Cornell,)26 b(1987\).)167 2748 y([BruLon])36 b(K.)e(Bruce)f(and)j (G.)f(Longo,)j(A)c(mo)r(dest)g(mo)r(del)f(of)i(records,)h(inheritance)d (and)409 2833 y(b)r(ounded)e(quan)n(ti\014cation,)f(in)f(the)g(pro)r (ceedings)g(of)h(the)f(third)f(IEEE)h(symp)r(osium)409 2918 y(on)f FM(L)l(o)l(gic)h(in)e(Computer)i(Scienc)l(e)i FK(\(Edin)n(burgh,)e(1988\).)167 3042 y([CAML])35 b Fr(CAML)p FK(,)28 b FM(the)g(r)l(efer)l(enc)l(e)f(manual)p FK(,)h(Pro)t(jet)f(F) -6 b(ormel,)27 b(INRIA-ENS)f(\(P)n(aris,)i(1987\))167 3166 y([Co)r(quand])37 b(T.)32 b(Co)r(quand,)k FM(Une)c(th)n(\023)-33 b(eorie)33 b(des)f(c)l(onstructions)p FK(,)i(Th)n(\022)-33 b(ese)33 b(de)g(troisi)n(\022)-33 b(eme)31 b(cycle)409 3251 y(\(Univ)n(ersit)n(\023)-33 b(e)26 b(P)n(aris)i(VI)r(I,)f(1985\).) 167 3375 y([CGW86])36 b(Th.)h(Co)r(quand,)43 b(C.A.)37 b(Gun)n(ter)g(and)i(G.)f(Winsk)n(el,)h(dI-domains)f(as)g(a)g(mo)r(del) 409 3460 y(of)h(p)r(olymorphism,)i(in)c(Main,)42 b(Melton,)f(Mislo)n(v) n(e)c(and)j(Sc)n(hmidt)e(\(eds.\),)j FM(Thir)l(d)409 3545 y(Workshop)c(on)g(the)f(Mathematic)l(al)h(F)-5 b(oundations)37 b(of)f(Pr)l(o)l(gr)l(amming)j(L)l(anguag)d(e)409 3631 y(Semantics)p FK(,)22 b(Springer{V)-6 b(erlag)22 b(Lecture)e(Notes)i (in)f(Computer)g(Science)f FG(298)h FK(\(1987\))409 3716 y(344{363.)167 3840 y([CGW87])36 b(Th.)c(Co)r(quand,)k(C.A.)c(Gun)n (ter)g(and)i(G.)e(Winsk)n(el,)h(Domain-theoretic)d(mo)r(dels)409 3925 y(of)e(p)r(olymorphism,)f FM(Information)h(and)g(Computation)34 b FG(81)27 b FK(\(1989\))i(123{167.)1368 4101 y(161)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 162 165 bop 167 167 a FK(162)1852 b Fz(BIBLIOGRAPHY)167 404 y FK([CurryF)-6 b(eys])35 b(H.B.)26 b(Curry)g(and)h(R.)f(F)-6 b(eys,)27 b FM(Combinatory)g(L)l(o)l(gic)f(I)p FK(,)g(North-Holland)f (\(1958\).)167 531 y([Gallier])32 b(J.)d(Gallier,)c FM(L)l(o)l(gic)j (for)g(Computer)h(Scienc)l(e)p FK(,)d(Harp)r(er)i(and)g(Ro)n(w)g (\(1986\).)167 658 y([Gandy])36 b(R.O.)28 b(Gandy)-6 b(,)29 b FM(Pr)l(o)l(of)g(of)f(str)l(ong)g(normalisation)p FK(,)g(in)g([)p FG(?)p FK(].)167 785 y([Gir71])35 b(J.Y.)j(Girard,)h (Une)e(extension)g(de)h(l'in)n(terpr)n(\023)-33 b(etation)36 b(de)h(G\177)-34 b(odel)37 b(\022)-34 b(a)38 b(l'analyse,)i(et)409 870 y(son)35 b(application)f(\022)-34 b(a)35 b(l')n(\023)-33 b(elimination)32 b(des)i(coupures)h(dans)h(l'analyse)e(et)g(la)g(th)n (\023)-33 b(eorie)409 956 y(des)34 b(t)n(yp)r(es,)h(in:)47 b(J.E.)34 b(F)-6 b(enstad)35 b(\(ed.\),)g FM(Pr)l(o)l(c)l(e)l(e)l (dings)g(of)e(the)h(Sc)l(andinavian)f(L)l(o)l(gic)409 1041 y(Symp)l(osium)p FK(,)d(North-Holland)d(\(1971\))i(63{92.)167 1168 y([Gir72])35 b(J.Y.)29 b(Girard,)f FM(Interpr)n(\023)-33 b(etation)28 b(fonctionnel)t(le)e(et)g(\023)-33 b(elimination)28 b(des)g(c)l(oupur)l(es)i(dans)409 1253 y(l'arithm)n(\023)-33 b(etique)22 b(d'or)l(dr)l(e)i(sup)n(\023)-33 b(erieur)p FK(,)23 b(Th)n(\022)-33 b(ese)23 b(de)f(do)r(ctorat)h(d')n(\023)-33 b(etat)23 b(\(Univ)n(ersit)n(\023)-33 b(e)21 b(P)n(aris)409 1338 y(VI)r(I,)27 b(1972\).)167 1465 y([Gir85])35 b(J.Y.)d(Girard,)g (Normal)e(F)-6 b(unctors,)33 b(p)r(o)n(w)n(er)e(series)f(and)j(lam)n(b) r(da-calculus,)e FM(A)n(nnals)409 1550 y(of)d(Pur)l(e)f(and)h(Applie)l (d)g(L)l(o)l(gic)33 b FG(37)27 b FK(\(1988\))i(129{177.)167 1677 y([Gir86])35 b(J.Y.)23 b(Girard,)g(The)f(system)g FG(F)g FK(of)h(v)l(ariable)f(t)n(yp)r(es,)i(\014fteen)e(y)n(ears)h (later,)f FM(The)l(or)l(etic)l(al)409 1762 y(Computer)28 b(Scienc)l(e)k FG(45)27 b FK(\(1986\))i(159{192.)167 1889 y([Gir87])35 b(J.Y.)28 b(Girard,)f(Linear)g(logic,)g FM(The)l(or)l(etic)l(al)i(Computer)f(Scienc)l(e)k FG(50)27 b FK(\(1987\))i(1{102.)167 2016 y([Gir])103 b(J.Y.)22 b(Girard,)h FM(Pr)l(o)l(of)h(the)l(ory)f(and)f(lo)l(gic)l(al)g(c)l (omplexity)p FK(,)i(Bibliop)r(olis)19 b(\(Nap)r(oli,)j(1987\).)167 2143 y([Gir87a])35 b(J.Y.)28 b(Girard,)g FM(T)-5 b(owar)l(ds)29 b(a)e(ge)l(ometry)i(of)e(inter)l(action)p FK(,)h(in)f([)p FG(?)q FK(],)h(69{108.)167 2270 y([Gir88])35 b(J.Y.)i(Girard,)h (Geometry)d(of)i(in)n(teraction)e(I:)h(in)n(terpretation)f(of)i(System) f FG(F)p FK(,)g(in:)409 2355 y FM(Pr)l(o)l(c)l(e)l(e)l(dings)29 b(of)f(the)f(ASL)h(me)l(eting)33 b FK(\(P)n(ado)n(v)l(a,)d(1988\),)g (221{260.)167 2482 y([GirLaf)5 b(])34 b(J.Y.)47 b(Girard)f(and)h(Y.)e (Lafon)n(t,)52 b(Linear)46 b(logic)f(and)i(lazy)e(computation,)51 b(in:)409 2567 y FM(T)-5 b(APSOFT)27 b('87)p FK(,)i(v)n(ol.)e FG(2)p FK(,)h(Springer-V)-6 b(erlag)27 b(LNCS)g FG(250)g FK(\(Pisa,)g(1987\).)167 2694 y([GLR])56 b(J.-Y.)26 b(Girard,)g(Y.)f (Lafon)n(t,)i(L.)f(Regnier)f(\(eds.\),)h FM(A)l(dvanc)l(es)g(in)f(Line) l(ar)h(L)l(o)l(gic)p FK(,)h(Lon-)409 2779 y(don)h(Mathematical)e(So)r (ciet)n(y)h(Lecture)f(Note)h(Series)f(222,)j(Cam)n(bridge)d(Univ)n (ersit)n(y)409 2864 y(Press)h(\(1995\))167 2991 y([GOS])58 b(J.-Y.)37 b(Girard,)h(M.)f(Ok)l(ada,)k(A.)36 b(Scedro)n(v)h(\(eds.\),) i(Linear)d(Logic,)j(to)e(app)r(ear)h(in)409 3076 y FM(The)l(or)l(etic)l (al)29 b(Computer)f(Scienc)l(e)k FK(\(2003\).)167 3203 y([GrSc])54 b(J.W.)40 b(Gra)n(y)g(and)h(A.)e(Scedro)n(v)h(\(eds.\),)i FM(Cate)l(gories)e(in)f(c)l(omputer)h(scienc)l(e)f(and)409 3288 y(lo)l(gic)p FK(,)27 b(American)f(Mathematical)h(So)r(ciet)n(y)g (\(Boulder,)g(1987\).)167 3415 y([HinSel])33 b(J.R.)k(Hindley)f(and)i (J.P)-6 b(.)38 b(Seldin,)g FM(T)-5 b(o)37 b(H.B.)g(Curry:)54 b(Essays)38 b(on)f(c)l(ombinatory)409 3501 y(lo)l(gic,)27 b(L)l(amb)l(da)j(Calculus)d(and)h(F)-5 b(ormalism)p FK(,)28 b(Academic)e(Press)h(\(1980\).)167 3627 y([Ho)n(w)n(ard])36 b(W.A.)27 b(Ho)n(w)n(ard,)i FM(The)e(formulae-as-typ)l(es)i(notion)e (of)h(c)l(onstruction)p FK(,)g(in)f([)p FG(?)q FK(].)167 3754 y([Hyland])35 b(J.M.E.)55 b(Hyland,)60 b(The)53 b(e\013ectiv)n(e)f(top)r(os,)61 b(in)53 b FM(L.E.J.)g(Br)l(ouwer)h(c)l (entenary)409 3840 y(symp)l(osium)p FK(,)e(A.S.)46 b(T)-6 b(ro)r(elstra)44 b(and)i(D.S.)g(v)l(an)g(Dalen)f(\(eds.\),)k (North-Holland)409 3925 y(\(1982\))29 b(165{216.)p eop PStoPSsaved restore %%Page: (166,167) 84 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 163 166 bop 167 167 a Fz(BIBLIOGRAPHY)1849 b FK(163)167 404 y([HylPit])33 b(J.M.E.)f(Hyland)g(and)g(A.M.)g(Pitts,)f FM(The)g(the)l(ory)i(of)e(c)l(onstructions:)43 b(c)l(ate)l(goric)l(al) 409 490 y(semantics)28 b(and)f(top)l(os-the)l(or)l(etic)i(mo)l(dels)p FK(,)g(in)e([)p FG(?)p FK(],)h(137{199.)167 609 y([Jung])59 b(A.)24 b(Jung,)j FM(Cartesian)e(close)l(d)f(c)l(ate)l(gories)h(of)g (domains)p FK(,)h(Ph.)f(D.)f(thesis)g(\(T)-6 b(ec)n(hnisc)n(he)409 694 y(Ho)r(c)n(hsc)n(h)n(ule)27 b(Darmstadt,)h(1988\).)167 813 y([Ko)n(w)n(alski])34 b(R.)24 b(Ko)n(w)n(alski,)h FM(L)l(o)l(gic)g(for)g(pr)l(oblem)f(solving)30 b FK([)p Fr(PROLOG)p FK(],)c(North-Holland)e(\(1979\).)167 932 y([Ko)n(ymans])36 b(C.P)-6 b(.J.)33 b(Ko)n(ymans,)j FM(Mo)l(dels)d(of)g (the)f FH(\025)p FM(-c)l(alculus)p FK(,)i(Cen)n(truum)e(v)n(o)r(or)i (Wiskunde)409 1017 y(en)27 b(Informatica,)h FG(9)f FK(\(1984\).)167 1136 y([KrLev])34 b(G.)23 b(Kreisel)d(and)j(A.)f(L)n(\023)-33 b(evy)-6 b(,)26 b(Re\015ection)21 b(principles)f(and)j(their)f(use)g (for)h(establishing)409 1221 y(the)35 b(complexit)n(y)e(of)i(axiomatic) f(systems,)j FM(Z.)e(Math.)h(L)l(o)l(gik)f(Grund)t(lagen)f(Math.)409 1306 y FG(33)27 b FK(\(1968\).)167 1425 y([KriP)n(ar])34 b(J.L.)26 b(Krivine)d(and)j(M.)f(P)n(arigot,)h(Programming)f(with)f (pro)r(ofs,)j FM(Sixth)e(symp)l(osium)409 1510 y(on)i(somputation)i (the)l(ory)35 b FK(\(W)-6 b(endisc)n(h-Rietz,)25 b(1987\).)167 1629 y([Laf87])38 b(Y.)24 b(Lafon)n(t,)j FM(L)l(o)l(giques,)f(c)l(at)n (\023)-33 b(egories)25 b(et)f(machines)p FK(,)i(Th)n(\022)-33 b(ese)25 b(de)g(do)r(ctorat)g(\(Univ)n(ersit)n(\023)-33 b(e)409 1714 y(P)n(aris)27 b(VI)r(I,)g(1988\).)167 1833 y([Laf88])38 b(Y.)27 b(Lafon)n(t,)i(The)e(linear)e(abstract)j(mac)n (hine,)e FM(The)l(or)l(etic)l(al)j(Computer)f(Scienc)l(e)j FG(59)409 1918 y FK(\(1988\))e(157{180.)167 2037 y([LamSco])35 b(J.)f(Lam)n(b)r(ek)g(and)h(P)-6 b(.J.)34 b(Scott,)h FM(A)n(n)e(intr)l(o)l(duction)i(to)e(higher)g(or)l(der)i(c)l(ate)l (goric)l(al)409 2122 y(lo)l(gic)p FK(,)27 b(Cam)n(bridge)h(Univ)n (ersit)n(y)e(Press)h(\(1986\).)167 2241 y([Lei83])42 b(D.)31 b(Leiv)l(an)n(t,)h(Reasoning)g(ab)r(out)h(functional)e (programs)h(and)h(complexit)n(y)d(classes)409 2326 y(asso)r(ciated)23 b(with)e(t)n(yp)r(e)i(disciplines,)d FM(Twenty)j(fourth)f(annual)g (symp)l(osium)j(on)d(foun-)409 2411 y(dations)30 b(of)g(c)l(omputer)g (scienc)l(e,)f FK(IEEE)g(Computer)g(So)r(ciet)n(y)g(Press,)h(\(W)-6 b(ashington)409 2496 y(DC,)27 b(1983\).)167 2615 y([Lei90])42 b(D.)23 b(Leiv)l(an)n(t,)h(Con)n(tracting)f(pro)r(ofs)h(to)f(programs,) i(in:)33 b(P)n(ergiorgio)22 b(Odifreddi)f(\(ed.\),)409 2700 y FM(L)l(o)l(gic)28 b(in)g(Computer)g(Scienc)l(e)p FK(,)f(Academic)e(Press)j(\(1990\).)167 2819 y([ML70])36 b(P)-6 b(.)32 b(Martin-L\177)-34 b(of,)33 b FM(A)f(c)l(onstruction)g (of)g(the)f(pr)l(ovable)h(wel)t(l-or)l(dering)e(of)i(the)f(the)l(ory) 409 2904 y(of)d(sp)l(e)l(cies)34 b FK(\(unpublished\).)167 3023 y([ML84])i(P)-6 b(.)28 b(Martin-L\177)-34 b(of,)28 b FM(Intuitionistic)f(typ)l(e)h(the)l(ories)p FK(,)h(Bibliop)r(olis)c (\(Nap)r(oli,)h(1984\))167 3142 y([Pra)n(witz])34 b(D.)j(Pra)n(witz,)j (Ideas)e(and)h(results)e(in)h(pro)r(of-theory)-6 b(,)42 b(in:)56 b FM(Pr)l(o)l(c)l(e)l(e)l(dings)39 b(of)f(the)409 3227 y(se)l(c)l(ond)28 b(Sc)l(andinavian)g(lo)l(gic)f(symp)l(osium)36 b FK(,)27 b(North-Holland)h(\(1971\))h(237{309.)167 3346 y([Reynolds])35 b(J.C.)30 b(Reynolds,)g(T)-6 b(o)n(w)n(ards)30 b(theory)g(of)g(t)n(yp)r(e)f(structure,)g FM(Paris)h(c)l(ol)t(lo)l (quium)f(on)409 3431 y(pr)l(o)l(gr)l(amming)p FK(,)h(Springer-V)-6 b(erlag)27 b(LNCS)g FG(19)g FK(\(1974\).)167 3550 y([ReyPlo])34 b(J.C.)24 b(Reynolds)f(and)h(G.)f(Plotkin,)g FM(On)f(functors)h(expr)l (essible)f(in)h(the)f(p)l(olymorphic)409 3636 y(lamb)l(da)28 b(c)l(alculus)p FK(.)167 3754 y([ERobinson])36 b(E.)42 b(Robinson,)47 b(Logical)42 b(asp)r(ects)h(of)g(denotational)g(seman)n (tics)e(in:)64 b(D.H.)409 3840 y(Pitt,)25 b(A.)g(P)n(oign)n(\023)-33 b(e)27 b(and)f(D.E.)g(Rydeheard)g(\(eds.\),)g FM(Cate)l(gory)g(the)l (ory)h(and)f(c)l(omputer)409 3925 y(scienc)l(e)32 b FK(LNCS)c FG(283)p FK(,)e(Springer-V)-6 b(erlag)27 b(\(Edin)n(burgh,)i(1987\).)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 164 167 bop 167 167 a FK(164)1852 b Fz(BIBLIOGRAPHY)167 404 y FK([JARobinson])36 b(J.A.)g(Robinson,)k(A)35 b(mac)n(hine)g (orien)n(ted)g(logic)g(based)i(on)g(the)f(resolution)409 490 y(principle,)30 b FM(Journal)h(of)h(the)g(Asso)l(ciation)g(of)g (Computing)g(Machinery)38 b FG(12)31 b FK(\(1965\))409 575 y(23{41.)167 695 y([Scott69])36 b(D.)42 b(Scott,)47 b(Outline)41 b(of)i(a)g(mathematical)e(theory)i(of)g(computation,)k(in) 42 b FM(4th)409 780 y(A)n(nnual)52 b(Princ)l(eton)h(Confer)l(enc)l(e)g (on)f(Information)h(Scienc)l(es)f(and)h(Systems)p FK(,)409 865 y(Princeton)27 b(Univ)n(ersit)n(y)f(\(1970\))j(169{176.)167 986 y([Scott76])36 b(D.)29 b(Scott,)i(Data)f(t)n(yp)r(es)f(as)i (lattices,)d FM(SIAM)h(Journal)g(of)h(Computing)36 b FG(5)30 b FK(\(1976\))409 1071 y(522{587.)167 1191 y([Scott82])36 b(D.)f(Scott,)j(Domains)d(for)h(denotational)g(seman)n(tics,)g(in:)51 b FM(ICALP)35 b('82)p FK(,)j(LNCS)409 1276 y FG(140)p FK(,)26 b(Springer-V)-6 b(erlag)27 b(\(Aarh)n(us,)i(1982\).)167 1396 y([ScoGun])36 b(D.S.)28 b(Scott)f(and)h(C.A.)g(Gun)n(ter,)f(Seman) n(tic)f(domains,)i FM(Handb)l(o)l(ok)h(of)e(Computer)409 1482 y(Scienc)l(e)p FK(,)f(North-Holland)i(\(1988\).)167 1602 y([Seely])48 b(R.A.G.)33 b(Seely)-6 b(,)33 b(Linear)f(logic,)h (*-autonomous)j(categories)c(and)h(cofree)f(algebras,)409 1687 y(in)27 b([)p FG(?)q FK(].)167 1807 y([Sm)n(yth])35 b(M.)28 b(Sm)n(yth,)g(P)n(o)n(w)n(erdomains)f(and)h(predicate)e (transformers:)36 b(a)27 b(top)r(ological)g(view)409 1892 y(in:)34 b(J.)26 b(Diaz)e(\(ed.\),)i FM(A)n(utomata,)h(L)l (anguages)e(and)h(Pr)l(o)l(gr)l(amming)p FK(,)i(Springer-V)-6 b(erlag)409 1978 y(LNCS)27 b FG(154)g FK(\(1983\))i(662{675.)167 2098 y([T)-6 b(ait])79 b(W.W.)47 b(T)-6 b(ait,)51 b(In)n(tensional)46 b(in)n(terpretation)g(of)h(functionals)g(of)g(\014nite)f(t)n(yp)r(e)h (I,)409 2183 y FM(Journal)27 b(of)h(Symb)l(olic)g(L)l(o)l(gic)33 b FG(32)27 b FK(\(1967\))i(198{212.)167 2303 y([T)-6 b(a)n(y86])37 b(P)-6 b(.)29 b(T)-6 b(a)n(ylor,)29 b FM(R)l(e)l(cursive) g(domains,)h(indexe)l(d)e(c)l(ate)l(gory)h(the)l(ory)h(and)e(p)l (olymorphism)p FK(,)409 2388 y(Ph.D.)g(thesis)f(\(Univ)n(ersit)n(y)f (of)i(Cam)n(bridge,)f(1986\).)167 2509 y([T)-6 b(a)n(y88])37 b(P)-6 b(.)28 b(T)-6 b(a)n(ylor,)28 b(An)f(algebraic)g(approac)n(h)j (to)e(stable)f(domains,)h FM(Journal)g(of)f(Pur)l(e)h(and)409 2594 y(Applie)l(d)g(A)n(lgebr)l(a)33 b FG(64)27 b FK(\(1990\))i (171{203.)167 2714 y([T)-6 b(a)n(y89])37 b(P)-6 b(.)30 b(T)-6 b(a)n(ylor,)30 b FM(The)g(tr)l(ac)l(e)g(factorisation)g(of)g (stable)e(functors)p FK(,)i(1989,)i(a)n(v)l(ailable)d(from)409 2799 y Fr(www.di.unito.it/)p FJ(\030)p Fr(pt/stable)167 2920 y FK([T)-6 b(a)n(y89a])37 b(P)-6 b(.)49 b(T)-6 b(a)n(ylor,)55 b(Quan)n(titativ)n(e)47 b(Domains,)54 b(Group)r(oids)c(and)g(Linear)e (Logic,)53 b(in:)409 3005 y(D.)41 b(Pitt)f(\(ed.\),)45 b FM(Cate)l(gory)e(The)l(ory)f(and)g(Computer)g(Scienc)l(e)k FK(Springer-V)-6 b(erlag)409 3090 y(\(Manc)n(hester,)28 b(1989\))h(155{181.)167 3210 y([T)-6 b(a)n(y99])37 b(P)-6 b(.)36 b(T)-6 b(a)n(ylor,)38 b FM(Pr)l(actic)l(al)d(F)-5 b(oundations)36 b(of)g(Mathematics)p FK(,)h(Cam)n(bridge)e(Univ)n (ersit)n(y)409 3295 y(Press)27 b(\(1999\).)167 3416 y([v)l(anHeijeno)r (ort])35 b(J.)54 b(v)l(an)g(Heijeno)r(ort,)59 b FM(F)-5 b(r)l(om)53 b(F)-5 b(r)l(e)l(ge)53 b(to)g(G\177)-35 b(odel,)60 b(a)53 b(sour)l(c)l(e)h(b)l(o)l(ok)f(in)409 3501 y(mathematic)l(al)28 b(lo)l(gic,)g(1879{1931)p FK(,)i(Harv)l(ard)e(Univ)n(ersit)n(y)f(Press) g(\(1967\).)167 3621 y([Vic)n(k)n(ers])34 b(S.)28 b(Vic)n(k)n(ers,)e FM(T)-5 b(op)l(olo)l(gy)29 b(via)f(lo)l(gic)p FK(,)g(Cam)n(bridge)f (Univ)n(ersit)n(y)f(Press)h(\(1989\).)167 3741 y([Winsk)n(el])34 b(G.)46 b(Winsk)n(el,)51 b(Ev)n(en)n(t)46 b(structures,)51 b(in:)73 b FM(A)l(dvanc)l(e)l(d)47 b(c)l(ourse)g(on)g(Petri)e(nets)p FK(,)409 3826 y(Springer-V)-6 b(erlag)27 b(LNCS)g FG(255)g FK(\(1987\).)p eop PStoPSsaved restore %%Page: (168,169) 85 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 165 168 bop 167 729 a FF(Index)167 1034 y FG(Notation)284 1122 y FK(v)l(ariables,)23 b FH(x)p FK(,)h FH(y)s FK(,)e FH(z)343 1209 y FK(ob)t(ject)h(language,)h FH(\030)s FK(,)g FH(\021)343 1297 y FK(second)g(order,)f FH(X)6 b FK(,)23 b FH(Y)15 b FK(,)23 b FH(Z)284 1385 y FK(terms,)g FH(t)p FK(,)g FH(u)p FK(,)g FH(v)s FK(,)g FH(w)343 1472 y FK(ob)t(ject)g(language,)h FH(a)p FK(,)g FH(b)284 1560 y FK(t)n(yp)r(es,)g FH(S)t FK(,)g FH(T)10 b FK(,)23 b FH(U)7 b FK(,)23 b FH(V)16 b FK(,)23 b FH(W)284 1647 y FK(prop)r(ositions,)h FH(A)p FK(,)f FH(B)t FK(,)g FH(C)5 b FK(,)24 b FH(D)284 1735 y FK(coherence)f(spaces,)g FJ(A)p FK(,)h FJ(B)r FK(,)f FJ(C)343 1822 y FK(p)r(oin)n(ts,)h FH(a)p FK(,)f FH(b)p FK(,)g FH(c)343 1910 y FK(tok)n(ens,)h FH(\013)p FK(,)g FH(\014)t FK(,)f FH(\015)284 1998 y FK(n)n(um)n(b)r(ers,)h FH(m)p FK(,)f FH(n)p FK(,)h FH(p)p FK(,)e FH(q)167 2085 y FK(Brac)n(k)n(ets)284 2173 y(denotation,)i([)-12 b([)q FH(T)10 b FK(])-12 b(])q(,)23 b([)-12 b([)p FH(t)p FK(])g(])284 2260 y(pairing,)23 b(\()p FH(a;)12 b(b)p FK(\))23 b(and)h FJ(h)p FH(a;)12 b(b)p FJ(i)284 2348 y FK(set,)23 b FJ(f)p FH(n)d FK(:)39 b FH(P)10 b FK([)p FH(n)p FK(])p FJ(g)284 2436 y FK(substitution,)23 b FH(t)p FK([)p FH(u=x)p FK(])284 2523 y(w)n(eb,)g FJ(jAj)167 2611 y FK(Connectiv)n(es)g(on)g(t)n(yp)r(es)284 2698 y(conjunction,)h FJ(^)284 2786 y FK(direct)e(pro)r(duct,)i(&)284 2874 y(direct)e(sum,)h FJ(\010)284 2961 y FK(disjunction,)g FJ(_)284 3049 y FK(function-space,)h FJ(!)284 3136 y FK(implication,)d FJ(\))284 3224 y FK(linear)h(implication,)e Fu(\()284 3312 y FK(pro)r(duct,)k FJ(\002)284 3399 y FK(sum,)g(+,)545 3346 y Fo(`)284 3487 y FK(tensor)g(pro)r(duct,)f FJ(\012)284 3574 y FK(tensor)h(sum)f(or)g(par,)h Fc(O)167 3662 y FK(Quan)n(ti\014ers)284 3750 y(existen)n(tial,)d FJ(9)284 3837 y FK(existen)n(tial)g(t)n(yp)r(e,)j(\006,)f(\006)884 3831 y FJ(\016)935 3837 y FK(,)f FJ(r)284 3925 y FK(univ)n(ersal,)h FJ(8)1640 1034 y FK(univ)n(ersal)f(t)n(yp)r(e,)i(\005)1522 1119 y(Relations)1640 1204 y(coherence,)1993 1182 y FH(_)1993 1225 y(^)1640 1310 y FK(de\014nitional)e(equalit)n(y)-6 b(,)2276 1271 y FD(def)2283 1310 y FK(=)1640 1395 y(em)n(b)r(edding)22 b(and)i(pro)t(jection,)f Fu(\032)p FK(,)h FJ(\000)-15 b FH(.)1640 1481 y FK(if)22 b(and)i(only)f(if)g(\(i\013)5 b(\),)41 b FJ(\()-12 b(\))1640 1566 y FK(incoherence,)2050 1544 y FH(^)2050 1586 y(_)1640 1651 y FK(in)n(tercon)n(v)n(ertible)20 b(with,)i FJ(\030)1640 1736 y FK(isomorphism,)g FJ(')1640 1821 y FK(reduces)g(\(con)n(v)n(erts\))h(to,)h Fu( )1640 1906 y FK(result)e(of)h(function,)g FJ(7!)1640 1992 y FK(sequen)n(t,)g FJ(`)1522 2077 y FK(Miscellaneous)1640 2162 y(comp)r(osition,)f FJ(\016)1640 2247 y FK(directed)f(union)j(and) g(join,)2385 2194 y Fo(S)2444 2213 y Fv(")2471 2247 y FK(,)2514 2194 y Fo(W)2572 2213 y Fv(")1640 2332 y FK(negation,)g FJ(:)e FK(\(linear,)2246 2307 y Fv(?)2288 2332 y FK(\))1640 2417 y(of)h(course)g(and)h(wh)n(y)g(not,)g(!,)f(?)1640 2503 y(sequence,)1945 2504 y FH(A)p 1948 2523 39 3 v 1522 2647 a FG(A)p FK(bramsky)-6 b(,)25 b(i,)d(55)1522 2732 y(abstraction)i(\()p FH(\025)p FK(\))1640 2818 y(con)n(v)n (ersion,)f(13)1640 2903 y(in)n(tro)r(duction,)f(12,)j(20)1640 2988 y(realisabilit)n(y)-6 b(,)20 b(127)1640 3073 y(reducibilit)n(y)-6 b(,)20 b(45)1640 3158 y(seman)n(tics,)i(68,)i(144)1640 3243 y(syn)n(tax,)h(15,)f(82)1522 3329 y(absurdit)n(y)g(\()p FJ(?)p FK(\),)e(6,)h(95)1640 3414 y(comm)n(uting)f(con)n(v)n(ersion,)i (78)1640 3499 y(denotation)g(\()p FG(f)7 b FK(\),)23 b FM(se)l(e)28 b FK(b)r(o)r(oleans)c FM(and)1757 3584 y FK(unde\014ned)g(ob)t(ject)f(\()p Fn(?)p FK(\))1640 3669 y(empt)n(y)f(t)n(yp)r(e)i(\()p Fq(Emp)e FK(and)j FH(")2353 3680 y Fw(U)2394 3669 y FK(\),)e(80)1640 3754 y(linear)e(logic)h(\()p FJ(?)g FK(and)i FG(0)p FK(\),)e(154)1640 3840 y(natural)h(deduction)g(\()p FJ(?E)6 b FK(\),)22 b(73)1640 3925 y(realisabilit)n(y)-6 b(,)20 b(129)1368 4101 y(165)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 166 169 bop 167 167 a FK(166)2175 b Fz(INDEX)284 404 y FK(sequen)n(t)24 b(calculus)e(\()p Fn(?)d FJ(`)h Fn(?)p FK(\),)i(29)167 491 y(Ac)n(k)n(ermann's)h(function,)h(51)167 577 y(algebraic)e(domain,)i(56)167 663 y(aliv)n(e)e(h)n(yp)r(othesis,)i (9)167 749 y(all)e(\()p FJ(8)p FK(\),)g FM(se)l(e)28 b FK(univ)n(ersal)23 b(quan)n(ti\014er)167 835 y(alternations)g(of)g (quan)n(ti\014ers,)h(58,)g(124)167 922 y(alternativ)n(e)e(conjunction)h (\(&\),)g FM(se)l(e)402 1007 y FK(direct)e(pro)r(duct)167 1093 y(amalgamated)i(sum,)g(96,)i(134)167 1179 y(analysis)e(\(second)h (order)f(arithmetic\),)402 1264 y(114)167 1350 y(and,)h FM(se)l(e)29 b FK(conjunction)167 1437 y(application)284 1523 y(con)n(v)n(ersion,)24 b(13)284 1609 y(elimination,)d(12,)j(20)284 1695 y(realisabilit)n(y)-6 b(,)21 b(127)284 1781 y(reducibilit)n(y)-6 b(,)21 b(43)284 1868 y(seman)n(tics)h(\()p FJ(A)p FM(pp)5 b FK(\),)23 b(69)284 1954 y(stabilit)n(y=Berry)e(order,)i(65)284 2040 y(syn)n(tax,)i(15,)f(82)284 2126 y(trace)f(form)n(ula)g(\()p FG(App)p FK(\),)f(63,)i(64,)h(144)167 2212 y(appro)n(ximation)f(of)f(p) r(oin)n(ts)h(and)g(domains,)402 2297 y(57,)g(134)167 2384 y(arro)n(w)f(t)n(yp)r(e,)h FM(se)l(e)k FK(implication)20 b FM(and)402 2469 y FK(function-space)167 2555 y(asso)r(ciativit)n(y)i (of)i(sum)f(t)n(yp)r(e,)g(98)167 2641 y(asymmetrical)e(in)n (terpretation,)h(34)167 2727 y(atomic)g(form)n(ulae,)h(4,)g(5,)h(30,)g (112,)h(160)167 2814 y(atomic)d(p)r(oin)n(ts,)i FM(se)l(e)k FK(tok)n(ens)167 2900 y(atomic)22 b(sequen)n(ts,)i(112)167 2986 y(atomic)e(t)n(yp)r(es,)i(15,)g(48)167 3072 y(automated)g (deduction,)f(28,)h(34)167 3158 y(automorphisms,)g(134)167 3245 y(axiom)284 3331 y(comprehension,)f(114,)i(118,)g(123)284 3417 y(excluded)e(middle,)e(6,)j(156)284 3503 y(h)n(yp)r(othesis,)g(10) 284 3589 y(iden)n(tit)n(y)-6 b(,)23 b(30)284 3676 y(link,)g(156)284 3762 y(prop)r(er,)h(112)167 3925 y FG(B)p FK(ad)g(elimination,)c(77) 1522 404 y(Barendregt,)k(22)1522 491 y(Berry)-6 b(,)23 b(54)1522 577 y(Berry)g(order)g(\()p FJ(\024)1977 588 y FD(B)2015 577 y FK(\),)g(65,)h(66,)g(135,)h(146)1522 663 y(b)r(eta)e(\()p FH(\014)t FK(\))g(rule,)f FM(se)l(e)28 b FK(con)n(v)n(ersion)1522 749 y(binary)c(completeness,)d(56)1522 835 y(binary)j(trees)e(\()p Fq(Bintree)o FK(\),)h(93)1522 921 y(binding)g(v)l(ariables,)g(5,)h(12,)g(15,)g(83,)g(161)1522 1008 y(Bo)r(ole,)f(3)1522 1094 y(b)r(o)r(oleans,)h(4)1640 1180 y(coherence)e(space)1698 1266 y FJ(B)-10 b FM(o)l(ol)9 b FK(,)23 b(56,)h(60,)g(70)1698 1352 y([)-12 b([)q(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)g FJ(!)p FH(X)g FK(])-12 b(],)23 b(140)1640 1439 y(comm)n(uting)f(con)n(v)n(ersion,)i(86)1640 1525 y(con)n(v)n(ersion,)f(48)1640 1611 y(denotation)h(\()p FG(t)e FK(and)i FG(f)7 b FK(\),)24 b(4)1640 1697 y(in)e FG(F)h FK(\(\005)p FH(X)r(:)12 b(X)6 b FJ(!)p FH(X)g FJ(!)p FH(X)g FK(\),)22 b(84,)j(140)1640 1783 y(in)d FG(T)h FK(\()p Fq(Bo)r(ol)p FK(,)g Fq(T)p FK(,)g Fq(F)p FK(\),)g(48,)i(50,)f(70)1640 1869 y(in)e(system)h FG(F)p FK(,)g(84)1640 1956 y(totalit)n(y)-6 b(,)22 b(149)1522 2042 y(b)r(ounded)j(meet,)d FM(se)l(e)28 b FK(pullbac)n(k)1522 2128 y(b)r(oundedly)c(complete)e(domains,)h(140)1522 2214 y(Brou)n(w)n(er,)g(6)1522 2300 y(b)n(y)h(v)l(alues,)g(51,)g(70,)g (91,)g(133)1522 2463 y Fq(C)p FK(,)f Fq(C)p FK(?,)g FM(se)l(e)29 b FK(con)n(traction)1522 2549 y(camem)n(b)r(ert,)22 b(3)1522 2635 y Fr(CAML)p FK(,)i(81)1522 2721 y(candidate)1640 2808 y(reducibilit)n(y)-6 b(,)20 b(43,)k(115,)h(116)1640 2894 y(totalit)n(y)-6 b(,)22 b(58,)i(149)1522 2980 y(Can)n(tor,)g(1) 1522 3066 y(Cartesian)f(closed)f(category)-6 b(,)25 b(54,)f(62,)g(67,) 1757 3151 y(69,)g(95,)g(152)1522 3237 y(Cartesian)f(natural)g (transformation,)h FM(se)l(e)1757 3323 y FK(Berry)f(order)1522 3409 y(Cartesian)g(pro)r(duct,)h FM(se)l(e)k FK(pro)r(duct)1522 3495 y(casewise)22 b(de\014nition)h(\()p Fq(D)p FK(\),)f(48,)i(83,)g (97)1522 3581 y(category)-6 b(,)24 b(59,)h(95,)f(133,)g(135)1522 3667 y(c)n(haracteristic)d(subgroup,)k(134)1522 3753 y(Ch)n(urc)n(h-Rosser)f(prop)r(ert)n(y)-6 b(,)24 b(16,)g(22,)g(49,)1757 3839 y(74,)g(79,)g(90,)g(114,)h(152,)g(159)1522 3925 y(clique,)d(57,)i(62,)g(101,)h(138)p eop PStoPSsaved restore %%Page: (170,171) 86 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 167 170 bop 167 167 a Fz(INDEX)2173 b FK(167)167 404 y(closed)22 b(normal)h(form,)g(19,)h(52,)g(121)167 490 y(co)r(closure,)e(135)167 576 y(coherence)g(space,)i(56)284 662 y(b)r(o)r(oleans)343 748 y FJ(B)-10 b FM(o)l(ol)9 b FK(,)23 b(56,)h(60,)g(70)343 834 y([)-12 b([)q(\005)p FH(X)r(:)12 b(X)6 b FJ(!)o FH(X)g FJ(!)q FH(X)g FK(])-12 b(],)23 b(140)284 920 y(coherence)g(relation)e(\()898 898 y FH(_)898 941 y(^)986 920 y FK(\),)i(56)284 1006 y(direct)f(pro)r(duct)h(\(&\),)g(62)284 1092 y(direct)f(sum)h(\()p FJ(\010)p FK(\),)f(96,)i(103)284 1178 y(empt)n(y)f(t)n(yp)r(e)g(\()p FJ(E)-17 b FM(mp)5 b FK(\),)23 b(104,)i(139)284 1264 y(function)f(space)f(\()p FJ(!)p FK(\),)g(64,)h(102,)h(138)284 1350 y(in)n(tegers)343 1435 y(\015at)f(\()p FJ(I)-7 b FM(nt)7 b FK(\),)23 b(56,)h(60,)g(66,)g(70)343 1521 y(lazy)f(\()p FJ(I)-7 b FM(nt)614 1496 y FD(+)655 1521 y FK(\),)23 b(71,)i(98)343 1607 y([)-12 b([)q(\005)p FH(X)r(:)12 b(X)6 b FJ(!)o FK(\()p FH(X)g FJ(!)p FH(X)g FK(\))p FJ(!)p FH(X)g FK(\)])-12 b(])q(,)23 b(147)284 1693 y(linear)f(implication)e (\()p Fu(\()p FK(\),)j(100,)i(104,)402 1778 y(138)284 1864 y(linear)d(negation)i(\()p FJ(A)839 1839 y Fv(?)880 1864 y FK(\),)f(100,)i(138)284 1950 y(of)f(course)f(\(!\),)g(101,)i (138,)f(145)284 2036 y FJ(P)-18 b FM(air)9 b FK(,)23 b(\005)503 2011 y FD(1)530 2036 y FK(,)h(\005)625 2011 y FD(2)652 2036 y FK(,)f(68)284 2122 y(partial)g(functions)g(\()p FJ(P)-6 b(F)6 b FK(\),)23 b(66)284 2208 y(\005)g(t)n(yp)r(es,)h(143)284 2294 y(seman)n(tics,)f(67,)h(132)284 2380 y(singleton)f(\()p FJ(S)-6 b FM(gl)6 b FK(\),)23 b(104,)h(139)284 2466 y(tensor)g(pro)r (duct)f(\()p FJ(\012)p FK(\),)g(104,)h(138)284 2552 y(tensor)g(sum)f (or)g(par)h(\()p Fc(O)o FK(\),)f(104)284 2638 y(tok)n(ens)h(and)g(w)n (eb,)f(56)167 2723 y(coheren)n(t)g(or)g(sp)r(ectral)f(space,)i(56)167 2809 y Fq(collect)d FK(\(forming)h(trees\),)h(94)167 2895 y(comm)n(unicating)f(pro)r(cesses,)h(155)167 2981 y(comm)n(utativit)n(y)f(of)h(logic,)f(29)167 3067 y(comm)n(uting)g(con) n(v)n(ersion)i(of)f(sum,)h FM(se)l(e)402 3152 y FK(con)n(v)n(ersion)167 3238 y(compact,)f(59,)h(66)167 3324 y(compact-op)r(en)g(top)r(ology)-6 b(,)24 b(55)167 3410 y(complemen)n(tary)e(graph,)i FM(se)l(e)29 b FK(linear)402 3495 y(negation)167 3581 y(complete)21 b(subgraph,)26 b FM(se)l(e)i FK(clique)167 3667 y(complexit)n(y)284 3753 y(algorithmic,)22 b(53,)i(111,)g(143)284 3839 y(logical,)e(42,)i (58,)g(114,)h(122,)g(124,)f(140)167 3925 y(comp)r(onen)n(ts)g(\()p FH(\031)616 3899 y FD(1)666 3925 y FK(and)g FH(\031)842 3899 y FD(2)870 3925 y FK(\))1640 404 y(elimination,)c(19)1640 490 y(reducibilit)n(y)-6 b(,)20 b(43)1522 576 y(comp)r(osition)1640 662 y(stable)i(functions,)i(69)1522 748 y(comprehension)f(sc)n(heme,)f (114,)j(118,)f(123,)1757 833 y(126)1522 919 y(computational)f (signi\014cance,)g(1,)g(11,)i(17,)1757 1004 y(112,)g(120)1522 1090 y(con\015uen)n(t)f(relation,)e FM(se)l(e)29 b FK(Ch)n(urc)n (h-Rosser)1757 1175 y(prop)r(ert)n(y)1522 1261 y(conjunction,)24 b(5)1640 1347 y(and)g(pro)r(duct,)g(11,)g(15,)g(19)1640 1433 y Fq(conj)f FK(in)g Fq(Bo)r(ol)p FK(,)g(50)1640 1519 y(con)n(v)n(ersion,)g(13)1640 1605 y(cut)f(elimination,)f(105)1640 1691 y(in)h FG(F)p FK(:)35 b(\005)p FH(X)r(:)12 b FK(\()p FH(U)7 b FJ(!)p FH(V)15 b FJ(!)q FH(X)6 b FK(\))p FJ(!)p FH(X)g FK(,)23 b(84)1640 1777 y(linear)e(logic,)h(152)1640 1863 y(natural)h(deduction)1698 1949 y FJ(^I)5 b FK(,)24 b FJ(^)p FK(1)p FJ(E)30 b FK(and)24 b FJ(^)p FK(2)p FJ(E)6 b FK(,)24 b(10)1640 2034 y(realisabilit)n(y)-6 b(,)20 b(126)1640 2120 y(sequen)n(t)j(calculus)1698 2206 y FJ(L)p FK(1)p FJ(^)p FK(,)h FJ(L)p FK(2)p FJ(^)f FK(and)h FJ(R^)o FK(,)f(31)1522 2292 y Fq(cons)h FK(\(add)g(to)f(list\),)f(91)1522 2378 y(consistency)1640 2464 y(equational,)h(16,)h(23,)g(152)1640 2550 y(logical)d(\()p Fq(consis)p FK(\),)j(42,)g(114,)g(124)1522 2636 y(constan)n(ts)h(b)n(y)e(v)n(o)r(cation,)h(60,)g(66)1522 2722 y(constructors,)g FM(se)l(e)k FK(data)c(t)n(yp)r(es)g(in)e FG(F)1522 2808 y FK(con)n(tin)n(uit)n(y)-6 b(,)23 b(54,)h(59,)h(137) 1522 2894 y(con)n(traction)1640 2980 y FJ(L)p Fq(C)d FK(and)i FJ(R)p Fq(C)p FK(,)f(29)1640 3065 y(linear)e(logic)h(\()p Fq(C)p FK(?\),)h(154)1522 3151 y(con)n(tractum,)g(18,)h FM(se)l(e)29 b FK(redex)1522 3237 y(con)n(trol)23 b(features)g(of)h Fr(PROLOG)p FK(,)g(28)1522 3323 y(con)n(v)n(ersion)g(\()p Fu( )p FK(\),)f(18)1640 3409 y(b)r(ogus)h(example,)f(75)1640 3495 y(b)r(o)r(oleans)h(\()p Fq(D)p FK(\),)e(48)1640 3581 y(comm)n(uting,)g(74,)i(78,)g(85,)g(97,)h(103)1640 3667 y(conjunction)e(\()p FJ(^)p FK(\),)g(13)1640 3753 y(degree,)f(25)1640 3839 y(denotational)h(equalit)n(y)-6 b(,)23 b(69,)h(132)1640 3925 y(disjunction)e(\()p FJ(_)p FK(\),)h(75,)h(97)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 168 171 bop 167 167 a FK(168)2175 b Fz(INDEX)284 404 y FK(existen)n(tial)21 b(quan)n(ti\014er)j(\()p FJ(9)p FK(\),)f(75)167 491 y(con)n(v)n(ersion)h(\()p Fu( )p FK(\))284 577 y(implication)d(\()p FJ(\))p FK(\),)i(13)284 663 y(in)g FG(F)p FK(,)g(83,)h(94)284 749 y(in\014nit)n(y)f(\()p FJ(1)p FK(\),)g(72)284 835 y(in)n(tegers)g(\()p Fq(R)p FK(,)g Fq(It)p FK(\),)g(48,)h(51)284 921 y FH(\025)p FK(-calculus,)f(11,)h(16,)g(18,)g(69)284 1007 y(linear)e(logic)g(\(pro) r(of)i(nets\),)f(158)284 1094 y(natural)h(deduction,)f(13,)h(20)284 1180 y(reducibilit)n(y)-6 b(,)21 b(43,)j(116)284 1266 y(rewrite)d(rules,)h(14)284 1352 y(second)i(order,)f(94)167 1438 y(Co)r(quand,)i(116,)g(133)167 1524 y(correctness)d(criterion)284 1610 y(for)i(pro)r(of)g(nets,)f(158)284 1696 y(for)h(tok)n(ens)g(of)f (\005)g(t)n(yp)r(es,)g(139,)i(142)167 1783 y Fq(couple)e FK(\(forming)f(trees\),)g(93)167 1869 y(\()p FG(CR)h(1)p FJ(\000)p FG(3)o FK(\),)g FM(se)l(e)28 b FK(reducibilit)n(y)167 1955 y(cum)n(ulativ)n(e)22 b(conjunction,)h FM(se)l(e)29 b FK(tensor)402 2040 y(pro)r(duct)167 2126 y(Curry-Ho)n(w)n(ard)24 b(isomorphism,)e(5,)i(150)284 2212 y(conjunction)g(and)g(pro)r(duct,)g (14)284 2298 y(disjunction)f(and)h(sum,)f(80)284 2385 y(implication)e(and)j(functions,)f(14)284 2471 y(none)h(in)f(sequen)n (t)g(calculus,)f(28)284 2557 y(second)i(order,)f(94)167 2643 y(cut)g(rule)284 2729 y Fq(Cut)q FK(,)g(30)284 2815 y(elimination)e(of,)i(3,)h(105,)g(151,)h(158)284 2901 y(linear)d(logic,)g(153,)j(156,)f(158)284 2988 y(natural)g(deduction,)f (35,)h(40)284 3074 y(not)g(Ch)n(urc)n(h-Rosser,)g(150)284 3160 y(pro)r(ofs)h(without,)e(33,)h(159)284 3246 y(restriction)d(of,)j (112)167 3408 y Fq(D)p FK(,)f FJ(D)r FK(,)g FM(se)l(e)28 b FK(casewise)22 b(de\014nition)167 3494 y(data)i(t)n(yp)r(es)f(in)g FG(F)p FK(,)g(87,)h(89)167 3580 y(dead)g(h)n(yp)r(othesis,)g(9)167 3666 y(deadlo)r(c)n(k,)g(155)167 3752 y(deduction)f(\(natural\),)g(9) 167 3839 y(degree,)g(24,)h(109)284 3925 y FH(@)t FK(\(\),)f(of)h(form)n (ula)f(or)g(t)n(yp)r(e)1640 404 y FH(d)p FK(\(\),)f(of)i(cut)f(or)g (redex)1522 491 y FJ(D)-10 b FM(elin)5 b FK(,)23 b FM(se)l(e)29 b FK(linearisation)1522 577 y(denotation,)24 b(1)1522 663 y(denotational)g(seman)n(tics,)e(14,)i(54,)g(67,)1757 748 y(95,)g(132)1522 834 y(dereliction)c(\()p Fq(D)p FK(?\),)i(154)1522 920 y(dI-domains,)i(71,)g(98)1522 1006 y(direct)e(pro)r(duct)h(\(&\))1640 1093 y(coherence)f(space,)h (61,)h(67)1640 1179 y(linear)d(logic,)h(152)1522 1265 y(direct)g(sum)h(\()p FJ(\010)p FK(\))1640 1351 y(coherence)f(space,)h (96,)h(103,)h(146)1698 1437 y(example,)e(66)1640 1523 y(linear)e(logic,)h(152)1522 1609 y(directed)g(joins,)h(57,)h(59,)g(66) 1522 1695 y(disc)n(harge,)g(9,)f(12,)h(37,)g(73,)h(161)1522 1782 y(discrete)d(graph,)i FM(se)l(e)k FK(\015at)c(domain)1522 1868 y(disjunction,)f(5,)h(6,)f(95)1640 1954 y(and)h(sum,)f(81)1640 2040 y(comm)n(uting)f(con)n(v)n(ersion,)i(78)1640 2126 y(con)n(v)n(ersion,)f(75)1640 2212 y(cut)f(elimination,)f(106)1640 2298 y Fq(disj)i FK(in)f Fq(Bo)r(ol)p FK(,)h(50)1640 2385 y(in)n(tuitionistic)c(prop)r(ert)n(y)-6 b(,)24 b(8,)g(33)1640 2471 y(linear)d(logic)h(\()p FJ(\010)h FK(and)h Fc(O)p FK(\),)f(152)1640 2557 y(natural)g(deduction)1698 2643 y FJ(_)p FK(1)p FJ(I)5 b FK(,)25 b FJ(_)o FK(2)p FJ(I)k FK(and)c FJ(_E)6 b FK(,)23 b(73)1640 2729 y(sequen)n(t)g(calculus)1698 2815 y FJ(L_)p FK(,)g FJ(R)p FK(1)p FJ(_)g FK(and)h FJ(R)p FK(2)p FJ(_)p FK(,)g(31)1698 2901 y(in)n(tuitionistic)c FJ(L_)p FK(,)j(32)1522 2988 y(domain)h(theory)-6 b(,)23 b(56,)i(132)1640 3074 y(dI-domains,)e(71,)i(98)1640 3160 y(domain)e(equations,)h(98)1640 3246 y(Girard)e FM(versus)h FK(Scott,)g(54,)h(66,)h(98)1640 3332 y(L-domains,)e(140)1640 3418 y(lifted)e(sum,)i(96)1522 3504 y(donk)n(ey)-6 b(,)25 b(134)1522 3590 y(dynamic,)e(2,)h(14,)g(54)1522 3752 y FJ(9)p FK(,)g FM(se)l(e)k FK(existen)n(tial)21 b(quan)n(ti\014er)1522 3839 y(elimination,)g(8,)i(48)1640 3925 y FJ(^)p FK(1)p FJ(E)6 b FK(,)24 b FJ(^)p FK(2)p FJ(E)6 b FK(,)24 b FJ(\)E)30 b FK(and)24 b FJ(8E)6 b FK(,)23 b(10)p eop PStoPSsaved restore %%Page: (172,173) 87 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 169 172 bop 167 167 a Fz(INDEX)2173 b FK(169)284 404 y Fq(R)24 b FK(and)g Fq(D)e FK(in)h FG(T)p FK(,)g(48)167 493 y(elimination)284 581 y FJ(_E)6 b FK(,)24 b FJ(?E)k FK(and)c FJ(9E)6 b FK(,)24 b(73)284 669 y FJ(8)324 644 y FD(2)351 669 y FJ(E)6 b FK(,)24 b(94,)g(125)284 757 y(application)f(and)h(comp)r(onen)n(ts,)g(19)284 846 y(go)r(o)r(d)h(and)f(bad,)g(77)284 934 y(left)e(logical)g(rules,)g(37,) i(40)284 1022 y(linear)e(logic,)g(161)284 1110 y(linearit)n(y)f(of,)j (99,)g(103)167 1199 y(em)n(b)r(edding-pro)t(jection)e(pair,)h(133,)i (134)167 1287 y(empt)n(y)e(t)n(yp)r(e)284 1375 y(and)i(absurdit)n(y)-6 b(,)24 b(80)284 1463 y(coherence)f(space)g(\()p FJ(E)-17 b FM(mp)5 b FK(\),)23 b(95,)h(104,)402 1548 y(139)284 1637 y Fq(Emp)f FK(and)h FH(")604 1648 y Fw(U)646 1637 y FK(,)g(80)284 1725 y(in)f FG(F)p FK(:)34 b Fq(Emp)20 b FK(=)f(\005)p FH(X)r(:)12 b(X)6 b FK(,)23 b(85,)h(139)284 1813 y(linear)e(logic)g(\()p FJ(?)f FK(and)k FG(0)p FK(\),)d(154)284 1901 y(realisabilit)n(y)-6 b(,)21 b(129)167 1990 y(equalisers,)h(137) 167 2078 y(equations)i(b)r(et)n(w)n(een)e(terms)g(and)i(pro)r(ofs,)402 2163 y FM(se)l(e)k FK(con)n(v)n(ersion)167 2251 y(espace)23 b(coh)n(\023)-33 b(eren)n(t,)24 b(56)167 2339 y(eta)f(rule,)f FM(se)l(e)28 b FK(secondary)d(equations)167 2428 y(ev)l(aluation,)f FM(se)l(e)k FK(application)167 2516 y(ev)n(en)n(t)23 b(structures,)g(98)167 2604 y(exc)n(hange)284 2692 y FJ(L)p Fq(X)g FK(and)h FJ(R)p Fq(X)p FK(,)e(29)284 2781 y(linear)g(logic)g(\()p Fq(X)p FK(\),)g(153)167 2869 y(existen)n(tial)f(quan)n(ti\014er,)i(5,)h(6)284 2957 y(comm)n(uting)f(con)n(v)n(ersion,)g(78)284 3045 y(con)n(v)n(ersion,)h (75)284 3134 y(cut)f(elimination,)d(108)284 3222 y(in)n(tuitionistic)g (prop)r(ert)n(y)-6 b(,)24 b(8,)g(33)284 3310 y(natural)g(deduction)343 3398 y FJ(9I)29 b FK(and)24 b FJ(9E)6 b FK(,)24 b(73)284 3487 y(sequen)n(t)g(calculus)343 3575 y FJ(L9)f FK(and)h FJ(R9)p FK(,)f(32)167 3663 y(existen)n(tial)e(t)n(yp)r(e)i(in)g FG(F)f FK(\(\006,)h FJ(r)p FK(\),)g(86,)h(145)167 3751 y(exp)r(onen)n(tial)284 3840 y(ob)t(ject,)f FM(se)l(e)29 b FK(implication)20 b FM(and)402 3925 y FK(function-space)1640 404 y(pro)r(cess,)j FM(se)l(e)28 b FK(complexit)n(y)-6 b(,)1757 490 y(algorithmic)1522 576 y(expressiv)n(e)23 b(p)r(o)n(w)n(er,)g(50,)h(89,)g(155)1522 662 y(extraction,)f FM(se)l(e)28 b FK(univ)n(ersal)23 b(application)1522 824 y FG(F)g FK(\(Girard-Reynolds)g(system\))1640 910 y(represen)n(table)f(functions,)h(120)1640 996 y(seman)n(tics,)f(132) 1640 1082 y(strong)i(normalisation,)e(42,)i(114)1640 1168 y(syn)n(tax,)h(82)1522 1254 y FH(F)1567 1265 y FD(0)1618 1254 y FK(\(parallel)c(or\),)i(61,)h(70)1522 1341 y(false)1640 1427 y(denotation)g(\()p FG(f)7 b FK(,)23 b FJ(F)7 b FK(,)23 b Fq(F)p FK(\),)g FM(se)l(e)28 b FK(b)r(o)r(oleans)1640 1513 y(prop)r(osition)23 b(\()p FJ(?)p FK(\),)f FM(se)l(e)28 b FK(absurdit)n(y)1522 1599 y(feasible,)22 b FM(se)l(e)28 b FK(complexit)n(y)-6 b(,)22 b(algorithmic)1522 1685 y(\014elds)h(of)g(n)n(um)n(b)r(ers,)h(134)1522 1771 y(\014ltered)e (colimits,)e(59,)k(137)1522 1857 y(\014nite)1640 1944 y(appro)n(ximation,)g(57,)g(66,)g(132,)g(134)1640 2030 y(branc)n(hing)g(tree,)e(27)1640 2116 y(normalisation,)g(24)1640 2202 y(p)r(oin)n(ts)h(\()p FJ(A)1930 2213 y Fm(\014n)1994 2202 y FK(\),)f(57)1640 2288 y(presen)n(tabilit)n(y)-6 b(,)22 b(66)1640 2374 y(sense)h(and)h(denotation,)g(2)1640 2460 y(v)n(ery)-6 b(,)23 b(59,)i(66)1522 2547 y(\014xed)f(p)r(oin)n(t,) f(72,)h(95)1522 2633 y(\015at)g(domain,)f(57,)h(60,)g(66,)h(70,)f(140) 1522 2719 y(for)g(all)d(\()p FJ(8)p FK(\),)h FM(se)l(e)29 b FK(univ)n(ersal)22 b(quan)n(ti\014er)1522 2805 y(for)i(some)e(\()p FJ(9)p FK(\),)h FM(se)l(e)29 b FK(existen)n(tial)21 b(quan)n(ti\014er) 1522 2891 y(F)-6 b(rege,)23 b(1,)h(2)1522 2977 y(function,)g(1,)f(17) 1640 3063 y(Berry)f(order)h(\()p FJ(\024)2094 3074 y FD(B)2132 3063 y FK(\),)g(65)1640 3149 y(comp)r(osition,)f(69)1640 3236 y(con)n(tin)n(uous,)i(55,)g(58)1640 3322 y(\014xed)f(p)r(oin)n(t,) h(72)1640 3408 y(graph,)g(1,)g(66)1640 3494 y(linear,)d(99,)k(148)1640 3580 y(not)e(represen)n(table,)f(122)1640 3666 y(on)h(pro)r(ofs,)i(6,)f (11)1640 3752 y(on)f(t)n(yp)r(es,)h(83,)g(132,)h(136)1640 3839 y(partial,)d(60,)i(66)1640 3925 y(partial)e(recursiv)n(e,)g(55)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 170 173 bop 167 167 a FK(170)2175 b Fz(INDEX)167 404 y FK(function)284 492 y(p)r(oin)n(t)n(wise)22 b(order,)i(66)284 580 y(p)r(olynomial)f(resolution,)f(147)284 668 y(pro)n(v)l(ably)j (total,)e(52,)h(123)284 755 y(recursion,)f(50,)h(90,)g(120)284 843 y(represen)n(table,)e(52,)j(121)284 931 y(sequen)n(tial,)e(54)284 1018 y(stable,)g(58,)h(62,)g(68)284 1106 y(total)f(recursiv)n(e,)f(122) 284 1194 y(trace)h(\()p FJ(T)-6 b FH(r)r FK(\),)23 b(62)284 1282 y(t)n(w)n(o)h(argumen)n(ts,)f(61)167 1369 y(function-space)284 1457 y(and)i(implication,)20 b(12,)k(15,)g(20)284 1545 y(in)f FG(F)p FK(,)g(82)284 1632 y FH(\025)p FK(-calculus,)g(12,)h(15) 284 1720 y(linear)e(decomp)r(osition,)h(101)284 1808 y(seman)n(tics,)g(54,)h(62,)g(64,)g(67,)g(136)167 1896 y(functor,)g(59,)g(134,)g(136,)h(141)167 2085 y FG(G)p FK(allier,)c(28)167 2173 y(Galois)i(Theory)-6 b(,)23 b(134)167 2261 y(Gandy)-6 b(,)25 b(27)167 2348 y(garbage)g(collection,) 20 b(150)167 2436 y FG(Gem)o FK(,)k(136)167 2524 y(general)f (recursion,)f(72)167 2612 y(Gen)n(tzen,)h(3,)g(28,)i(105)167 2699 y(geometry)e(of)g(in)n(teraction,)f(4,)i(160)167 2787 y(Girard,)f(30,)h(42,)g(80,)g(82,)g(114,)h(124,)g(150)167 2875 y(goals)f(in)e Fr(PROLOG)p FK(,)j(112)167 2962 y(G\177)-34 b(odel,)23 b(1,)h(6,)f(47,)h(54)284 3050 y(incompleteness)d(theorem,)i (42,)h(114)284 3138 y(n)n(um)n(b)r(ering,)f(53)284 3226 y FJ(::)p FK(-translation,)h(124)167 3313 y(go)r(o)r(d)h(elimination,) 20 b(77)167 3401 y(graph)284 3489 y(em)n(b)r(edding,)j(133,)i(134)284 3576 y(function,)f(1,)f(66)284 3664 y(pro)r(duct,)h(104,)h(138)284 3752 y(w)n(eb,)e(56)167 3840 y(Grothendiec)n(k)g(\014bration)g(\(\006) 902 3834 y FJ(\016)953 3840 y FK(\),)g(135,)i(137,)402 3925 y(141)1522 404 y FG(H)p FK(auptsatz)f(\(cut)f(elimination\),)d(3,) k(105,)1757 490 y(151,)h(158)1522 576 y(head)f(normal)f(form,)g(19,)h (52,)g(76,)g(121)1522 662 y(heigh)n(t)f(of)h(a)f(pro)r(of)h(\()p FH(h)p FK(\),)f(109)1522 748 y(Herbrand,)h(4)1522 834 y(hereditarily)d(e\013ectiv)n(e)g(op)r(erations,)j(55)1522 920 y(Heyting,)f(5,)h(15,)g(80,)g(120)1640 1007 y(arithmetic)c(\()p FG(H)-12 b(A)2110 1018 y Fb(2)2142 1007 y FK(\),)23 b(124)1522 1093 y(Horn)h(clause,)e FM(se)l(e)29 b FK(in)n(tuitionistic)19 b(sequen)n(t)1522 1179 y(Ho)n(w)n(ard,)24 b FM(se)l(e)29 b FK(Curry-Ho)n(w)n(ard)1757 1264 y(isomorphism)1522 1350 y(Hyland,)24 b(133)1522 1436 y(h)n(yp)r(erexp)r(onen)n(tial)g (function,)f(111)1522 1523 y(h)n(yp)r(otheses,)i(9)1640 1609 y(disc)n(harge,)e(9,)h(161)1640 1695 y(parcels)e(of,)i(11,)g(36,)g (40,)g(161)1640 1781 y(subform)n(ula)f(prop)r(ert)n(y)-6 b(,)24 b(76)1640 1867 y(v)l(ariables,)f(11)1522 2030 y FJ(I)5 b FK(,)24 b FM(se)l(e)k FK(in)n(tro)r(duction)1522 2116 y(idemp)r(otence)22 b(of)h(logic,)f(29)1522 2202 y(iden)n(ti\014cation)g(of)i(terms)e(and)i(pro)r(ofs,)g FM(se)l(e)1757 2287 y FK(con)n(v)n(ersion)1522 2374 y(iden)n(tit)n(y) 1640 2460 y(axiom,)f(30,)h(112,)h(156)1640 2546 y(h)n(yp)r(othesis,)f (10)1640 2632 y(maximal)d(in)i(Berry)f(order,)i(65,)g(135)1640 2718 y(p)r(olymorphic,)e(83,)i(132,)h(136,)g(138)1640 2804 y(pro)r(of)f(of)f FH(A)d FJ(\))g FH(A)p FK(,)i(6)1522 2891 y(if,)h FM(se)l(e)28 b FK(casewise)22 b(de\014nition)1522 2977 y(implication,)f(5)1640 3063 y(and)j(function-space,)f(12,)h(15,)h (20)1640 3149 y(con)n(v)n(ersion,)e(13)1640 3235 y(cut)f(elimination,)f (107)1640 3321 y(linear)g(\()p Fu(\()p FK(\),)i(100,)i(153)1640 3408 y(natural)e(deduction)1698 3494 y FJ(\))q(I)28 b FK(and)c FJ(\))q(E)6 b FK(,)24 b(10)1640 3580 y(realisabilit)n(y)-6 b(,)20 b(127)1640 3666 y(seman)n(tics,)i(54)1640 3752 y(sequen)n(t)h(calculus)1698 3839 y FJ(L\))g FK(and)h FJ(R\))q FK(,)f(32)1522 3925 y(inclusion)f(order,)h(56)p eop PStoPSsaved restore %%Page: (174,175) 88 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 171 174 bop 167 167 a Fz(INDEX)2173 b FK(171)167 404 y(incoherence)22 b(\()585 382 y FH(^)585 425 y(_)674 404 y FK(\),)h(100)167 490 y(incompleteness)e(theorem,)h(6,)i(42,)g (114,)402 575 y(124)167 661 y(inductiv)n(e)e(data)i(t)n(yp)r(es,)f(87,) i(121)167 747 y(inductiv)n(e)d(de\014nition)g(of)i(+,)f FJ(\002)p FK(,)g FM(etc.)p FK(,)f(50)167 833 y(in\014nite)g(static)g (denotation,)i(2)167 919 y(in\014nit)n(y)f(\()p Fo(f)-70 b FJ(1)23 b FK(and)h FJ(1)p FK(\),)f(71)167 1005 y(initial)d(ob)t (ject,)j(95,)h(152)167 1091 y(input,)f(1,)h(17)167 1177 y(in)n(tegers,)e(1)284 1263 y(coherence)h(space)343 1349 y(\015at)h(\()p FJ(I)-7 b FM(nt)7 b FK(\),)23 b(56,)h(60,)g(66,)g(70) 343 1435 y(lazy)f(\()p FJ(I)-7 b FM(nt)614 1409 y FD(+)655 1435 y FK(\),)23 b(71,)i(98)343 1521 y([)-12 b([)q(\005)p FH(X)r(:)12 b(X)6 b FJ(!)o FK(\()p FH(X)g FJ(!)p FH(X)g FK(\))p FJ(!)p FH(X)g FK(\)])-12 b(])q(,)23 b(147)284 1607 y(con)n(v)n(ersion,)h(48)284 1692 y(dI-domain)g(\()p FJ(I)-7 b FM(nt)743 1667 y Fw(<)785 1692 y FK(\),)22 b(98)284 1778 y(in)h FG(F)p FK(,)g(89,)h(121,)h(147)284 1864 y(in)e FG(H)-12 b(A)475 1875 y Fb(2)507 1864 y FK(,)23 b(125)284 1950 y(in)g FG(T)g FK(\()p Fq(Int)p FK(,)g Fq(O)p FK(,)g Fq(S)p FK(,)g Fq(R)p FK(\),)h(48,)g(70)284 2036 y(iteration)e(\()p Fq(It)p FK(\),)h(51,)h(70,)g(90)284 2122 y(linear)e(t)n(yp)r(e)h(\()p Fq(LInt)p FK(\),)g(148)284 2208 y(normal)g(form,)g(52,)h(121)284 2294 y(realisabilit)n(y)c(\()p Fq(Nat)q FK(\),)i(126,)j(127)284 2380 y(recursor)e(\()p Fq(R)p FK(\),)g(48,)h(91)284 2466 y(totalit)n(y)-6 b(,)23 b(149)167 2552 y(in)n(ternalisation,)f(27)167 2638 y(in)n(tersection,)f FM(se)l(e)29 b FK(conjunction)284 2723 y(b)r(ounded)c(ab)r(o)n(v)n(e,)g FM(se)l(e)j FK(pullbac)n(k)284 2809 y(in)23 b([)-12 b([)p Fq(Bo)r(ol)p FK(])g(])q(,)23 b(140)167 2895 y(in)n(tro)r(duction,)g(8,) g(48)284 2981 y FJ(^I)5 b FK(,)24 b FJ(\)I)29 b FK(and)24 b FJ(8I)5 b FK(,)23 b(10)284 3067 y Fq(O)p FK(,)g Fq(S)p FK(,)h Fq(T)f FK(and)h Fq(F)f FK(in)g FG(T)p FK(,)g(48)284 3153 y FJ(_)p FK(1)p FJ(I)5 b FK(,)25 b FJ(_)o FK(2)p FJ(I)30 b FK(and)24 b FJ(9I)5 b FK(,)23 b(73)284 3239 y FJ(8)324 3213 y FD(2)351 3239 y FJ(I)5 b FK(,)24 b(94,)g(125)284 3325 y(linear)e(logic,)g(161)284 3411 y(pairing)h(and)h FH(\025)p FK(-abstraction,)g(11,)g(12,)402 3496 y(19)284 3582 y(righ)n(t)f(logical)f(rules,)g(37,)i(40)284 3668 y(sums,)g(81)167 3754 y(in)n(tuitionism,)d(6,)i(150)167 3840 y(in)n(tuitionistic)d(sequen)n(t,)j(8,)h(30,)g(32,)g(33,)402 3925 y(112,)g(152)1522 404 y(in)n(v)n(ersion)f(in)f(linear)g(algebra,)i (101)1522 490 y(isomorphisms,)f(132{134)1522 575 y(iteration)f(\()p Fq(It)o FK(\),)h(51,)i(70,)f(90)1522 724 y FG(J)p FK(oin,)f FM(se)l(e)29 b FK(disjunction)1640 809 y(preserv)l(ation)23 b(\(linearit)n(y\),)e(99)1522 895 y(join)n(t)i(con)n(tin)n(uit)n(y)g (and)h(stabilit)n(y)-6 b(,)22 b(61)1522 980 y(Jung,)j(133,)g(140)1522 1129 y FG(K)p FK(leene,)d(123)1522 1214 y(K\177)-34 b(onig's)24 b(lemma,)d(27)1522 1300 y(Ko)n(ymans,)j(133)1522 1385 y(Kreisel,)d(55)1522 1508 y Fv(L)1560 1534 y FK(,)i FM(se)l(e)28 b FK(asymmetrical)21 b(in)n(terpretation)1522 1619 y FJ(L)i FK(\(left)e(logical)h(rules\),)g FM(se)l(e)28 b FK(sequen)n(t)1757 1704 y(calculus)1522 1790 y FH(`)p FK(\()p FH(t)p FK(\),)23 b(length)g(of)g(normal)g(form,)g(49)1522 1875 y(Lafon)n(t,)i(150)1522 1961 y FH(\025)p FK(,)f FM(se)l(e)k FK(abstraction)1522 2046 y(\003,)23 b FM(se)l(e)29 b FK(univ)n(ersal)22 b(abstraction)1522 2131 y FH(\025)p FK(-calculus,)h(12,)h(15)1640 2217 y(Ch)n(urc)n(h-Rosser)f(prop)r(ert)n (y)-6 b(,)24 b(22)1640 2302 y(con)n(v)n(ersion,)f(18)1640 2388 y(head)g(normal)g(form,)g(19)1640 2473 y(natural)g(deduction,)g (11,)h(19)1640 2558 y(normalisation,)e(24,)i(42)1640 2644 y(second)f(order)g(p)r(olymorphic,)g(82)1640 2729 y(seman)n(tics,)f(54,)i(67)1640 2815 y(un)n(t)n(yp)r(ed,)g(19,)g(22,)g (133)1522 2900 y(last)f(rule)f(of)h(a)h(pro)r(of,)g(8,)g(33)1522 2985 y(lazy)f(ev)l(aluation,)h(150)1522 3071 y(lazy)f(natural)g(n)n(um) n(b)r(ers,)h(71,)g(98)1522 3156 y(L-domains,)g(140)1522 3242 y(least)f(appro)n(ximan)n(t,)h(59,)g(137)1522 3327 y(left)e(logical)g(rules,)g FM(se)l(e)28 b FK(sequen)n(t)c(calculus) 1522 3412 y(lifted)d(sum,)j(96)1522 3498 y(limit-colimit)17 b(coincidence,)k(137)1522 3583 y(linear)h(algebra,)h(101)1522 3669 y(linear)f(logic,)g(30,)i(35,)g(74,)g(161)1640 3754 y(Ch)n(urc)n(h-Rosser)f(prop)r(ert)n(y)-6 b(,)24 b(159)1640 3839 y(cut)e(rule,)h(153,)h(156,)h(158)1522 3925 y(linear)d(logic)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 172 175 bop 167 167 a FK(172)2175 b Fz(INDEX)284 404 y FK(direct)22 b(pro)r(duct)h(\(&\),)g(61,)h(104,)h(152)284 491 y(direct)d(sum)h(\()p FJ(\010)p FK(\),)f(96,)i(103,)h(146,)g(152) 284 577 y(implication)c(\()p Fu(\()p FK(\),)i(100,)h(104,)h(153)284 663 y(in)n(tegers)e(\()p Fq(LInt)p FK(\),)g(148)284 749 y(in)n(tuitionistic)d(logic,)i(154)284 835 y(linear)g(maps,)i(99,)g (101)284 921 y(link)e(rule,)h(156)284 1008 y(natural)h(deduction,)f (161)284 1094 y(negation)h(\()591 1068 y Fv(?)633 1094 y FK(\),)f(100,)h(138,)h(153)284 1180 y(notation)f(for)g(tok)n(ens,)g (138)284 1266 y(of)g(course)f(\(!\),)g(101,)i(145,)f(154)284 1352 y(p)r(olynomial)f(resolution,)f(147)284 1438 y(pro)r(of)i(nets,)g (155)284 1524 y(reducibilit)n(y)-6 b(,)21 b(115)284 1611 y(seman)n(tics,)i(95)284 1697 y(sequen)n(t)h(calculus,)e(152)284 1783 y(sum)h(decomp)r(osition,)g(95,)h(103,)h(146)284 1869 y(syn)n(tax,)g(150)284 1955 y(tensor)f(pro)r(duct)f(\()p FJ(\012)p FK(\),)g(104,)h(146,)h(152,)402 2040 y(156)284 2127 y(tensor)f(sum)f(or)g(par)h(\()p Fc(O)o FK(\),)f(104,)i(152,)402 2212 y(156)284 2298 y(trace)e(\()p FJ(T)-6 b FM(rlin)5 b FK(\),)23 b(100)284 2384 y(units)g(\()p FG(1)p FK(,)g FJ(?)p FK(,)f FJ(>)f FK(and)k FG(0)p FK(\),)d(104,)j(154)284 2470 y(wh)n(y)f(not)g(\(?)o(\),)f(102,)i(154)167 2556 y(link)d(axiom,)h(156)167 2642 y(lists,)f(47,)i(91)167 2729 y(lo)r(cally)d(compact)i(space,)h(55)167 2815 y(logical)e(rules,)g (31)284 2901 y(cut)h(elimination,)d(105,)25 b(112)284 2987 y(linear)d(logic,)g(153,)j(156)284 3073 y(natural)f(deduction,)f (37)167 3159 y(logical)f(view)g(of)h(top)r(ology)-6 b(,)25 b(55)167 3245 y(long)e(trip)g(condition,)f(158)167 3332 y(L\177)-34 b(ow)n(enheim,)22 b(1,)i(3)167 3494 y FG(M)p FK(artin-L\177)-34 b(of,)24 b(88)167 3580 y Fq(match)e FK(\(patterns\),)i(81)167 3666 y(maximally)d(consisten)n(t)i (extensions,)g(54)167 3752 y(meet,)f FM(se)l(e)28 b FK(conjunction)284 3839 y(b)r(ounded)d(ab)r(o)n(v)n(e,)g FM(se)l(e)j FK(pullbac)n(k)167 3925 y(memory)22 b(allo)r(cation,)h(150)1522 404 y(mo)r(d,)h(coherence) e(relation,)g(56)1522 490 y(mo)r(dalities,)f(101,)k(154)1522 576 y(mo)r(del)d(theory)-6 b(,)24 b(3)1522 662 y(mo)r(dules,)f(17,)h (47)1522 748 y(mo)r(dus)g(p)r(onens)g(\()p FJ(\)E)6 b FK(\),)24 b FM(se)l(e)k FK(elimination)1522 834 y(Moggi,)c(141)1522 992 y(I)-12 b(N)20 b(=)f FJ(f)p FK(0)p FH(;)12 b FK(1)p FH(;)g FK(2)p FH(;)g(:::)r FJ(g)p FK(,)23 b(set)g(of)g(in)n(tegers)1522 1077 y Fq(Nat)h FK(predicate)d(in)i FG(H)-12 b(A)2141 1088 y Fb(2)2173 1077 y FK(,)23 b(126)1522 1163 y(natural)h(deduction,) f(8)1640 1249 y FJ(^)p FK(,)g FJ(\))g FK(and)h FJ(8)p FK(,)f(10)1640 1335 y FJ(_)p FK(,)g FJ(?)f FK(and)i FJ(9)p FK(,)f(73)1640 1421 y(con)n(v)n(ersion,)g(13,)i(20,)f(75,)g(78)1640 1507 y FH(\025)p FK(-calculus,)e(11,)i(19)1640 1593 y(linear)d(logic,)h (161)1640 1679 y(normalisation,)g(24,)i(42)1640 1765 y(second)f(order,)h(94,)g(125)1640 1850 y(sequen)n(t)f(calculus,)f(35) 1640 1936 y(subform)n(ula)h(prop)r(ert)n(y)-6 b(,)24 b(76)1522 2022 y(natural)g(n)n(um)n(b)r(ers,)f FM(se)l(e)28 b FK(in)n(tegers)1522 2108 y(negation,)c(5)1640 2194 y FH(A)15 b FJ(_)h(:)p FH(A)p FK(,)22 b(6)1640 2294 y FJ(:)p FH(A)1758 2254 y FD(def)1766 2294 y FK(=)k FH(A)20 b FJ(\))g(?)p FK(,)i(6,)h(73)1640 2379 y(cut)f(elimination,)f(107)1640 2465 y(linear)g(\()1858 2440 y Fv(?)1900 2465 y FK(\),)i(100,)h(138,)h (153)1640 2551 y Fq(neg)e FK(in)g Fq(Bo)r(ol)p FK(,)g(50)1640 2637 y(sequen)n(t)g(calculus)f(\()p FJ(L:)p FK(,)h FJ(R:)p FK(\),)f(31)1522 2723 y(neutralit)n(y)-6 b(,)23 b(43,)h(49,)g(116)1522 2809 y Fq(nil)e FK(\(empt)n(y)h(tree)f(or)h(list\),)e(91)1522 2895 y FG(N)-12 b(J)23 b FK(\(Pra)n(witz')f(system\),)h FM(se)l(e)28 b FK(natural)1757 2980 y(deduction)1522 3066 y(No)r(etherian,)23 b(66)1522 3152 y(noncon)n(v)n(ergen)n(t)i (rewriting,)c(72)1522 3238 y(nondeterminism,)h(150)1522 3323 y(normal)h(closure)f(of)i(a)f(\014eld,)g(134)1522 3409 y(normal)g(form,)g(18,)h(76)1640 3495 y(cut-free,)e(41)1640 3581 y(existence,)f(24)1640 3667 y(head)i(normal)g(form,)g(19)1640 3753 y(in)n(tegers,)f(52,)i(121)1640 3839 y(linear)d(logic,)h(159)1522 3925 y(normal)h(form)p eop PStoPSsaved restore %%Page: (176,177) 89 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 173 176 bop 167 167 a Fz(INDEX)2173 b FK(173)284 404 y(uniqueness,)24 b(22)167 490 y(normalisation)e(theorem)284 575 y(for)i FG(F)p FK(,)f(114)284 660 y(for)h FG(T)p FK(,)f(49)284 745 y(length)g(of)h(pro)r(cess)f(\()p FH(\027)t FK(\),)g(27,)h(43,)g(49)284 830 y(linear)e(logic,)g(155)284 915 y(strong,)j(42)284 1000 y(w)n(eak,)f(22,)g(24)167 1085 y(not)g(\()p FJ(:)p FK(\),)e FM(se)l(e)29 b FK(negation)167 1228 y Fq(O)p FK(,)23 b FJ(O)i FK(\(zero\),)d FM(se)l(e)29 b FK(in)n(tegers)167 1313 y(ob)t(ject)23 b(language,)h(10)167 1399 y(Oc)n(kham's)f(razor,)h(3)167 1484 y(of)g(course)f(\(!\),)g(101,) h(138,)h(145,)f(154)167 1569 y(op)r(erational)f(seman)n(tics,)f(14,)i (121)167 1654 y(or,)f FM(se)l(e)29 b FK(disjunction)23 b FM(and)g FK(parallel)e(or)167 1739 y(orthogonal)k(\()539 1713 y Fv(?)580 1739 y FK(\),)e FM(se)l(e)29 b FK(linear)21 b(negation)167 1824 y(output,)j(17)167 1967 y FG(P)-23 b(A)o FK(,)24 b FG(P)-23 b(A)391 1978 y Fb(2)422 1967 y FK(,)23 b FM(se)l(e)28 b FK(P)n(eano)c(arithmetic)167 2052 y(pairing)284 2137 y(conjunction,)g(11)284 2222 y(in)f FG(F)p FK(,)g(84)284 2308 y(in)n(tro)r(duction,)g(19)284 2393 y(seman)n(tics)f(\()p FJ(P)-18 b FM(air)9 b FK(\),)23 b(61,)h(68)167 2478 y(par)g(\()p Fc(O)o FK(\),)f FM(se)l(e)28 b FK(tensor)c(sum)167 2563 y(parallel)d(or,)j(50,)g(60,)g(70,)g(81)167 2648 y(parallel)d(pro)r(cess,)j(150,)g(159)167 2733 y(parcels)e(of)i(h) n(yp)r(otheses,)g(11,)g(36,)h(40,)f(161)167 2818 y(partial)e(equiv)l (alence)g(relation,)g(55)167 2903 y(partial)g(function,)i(60)284 2988 y(coherence)f(space)g(\()p FJ(P)-6 b(F)6 b FK(\),)23 b(66)284 3074 y(recursiv)n(e,)f(55)167 3159 y(partial)g(ob)t(jects,)h (57)167 3244 y Fr(PASCAL)p FK(,)i(47)167 3329 y(pattern)e(matc)n(hing,) g(81)167 3414 y(P)n(eano)h(arithmetic)c(\()p FG(P)-23 b(A)p FK(\),)23 b(42,)h(53)284 3499 y(second)g(order)f(\()p FG(P)-23 b(A)805 3510 y Fb(2)836 3499 y FK(\),)23 b(114,)i(123)167 3584 y(p)r(eculiar,)d(134)167 3669 y(p)r(erm)n(utations,)h(134)167 3754 y(\005,)g FM(se)l(e)28 b FK(system)23 b FG(F)167 3840 y FH(\031)209 3814 y FD(1)237 3840 y FK(,)g FH(\031)321 3814 y FD(2)348 3840 y FK(,)g(\005)442 3814 y FD(1)470 3840 y FK(,)g(\005)564 3814 y FD(2)592 3840 y FK(,)g FM(se)l(e)28 b FK(comp)r(onen)n(ts)167 3925 y(Pitts,)22 b(133)1522 404 y(Plotkin,)h(56)1522 490 y(plugging,)h(17)1522 575 y(p)r(olynomial,)f(148)1522 660 y FJ(P)-6 b FH(!)s FK(,)23 b FM(se)l(e)28 b FK(Scott)1522 745 y(p)r(ositiv)n(e)22 b(negativ)n(e,)i(34,)g(87,)g(139,)g(142)1522 830 y(p)r(oten)n(tial)e (tok)n(ens,)j(138)1522 915 y(Pra)n(witz,)d(8,)i(80)1522 1000 y(predecessor)f(\()p Fq(p)n(red)p FK(\),)h(51,)g(72,)g(91)1522 1085 y(preserv)l(ation)g(of)f(joins)g(\(linearit)n(y\),)e(99)1522 1170 y(primary)i(equations,)h FM(se)l(e)k FK(con)n(v)n(ersion)1522 1256 y(principal)22 b(branc)n(h)i(or)f(premise,)e(75,)j(76)1522 1341 y(pro)r(duct)1640 1426 y(and)g(conjunction,)g(11,)g(15,)g(19)1640 1511 y(coherence)e(space)h(\(&\),)g(61,)h(68)1640 1596 y(in)e FG(F)p FK(,)h(84,)h(145)1640 1681 y(linear)d(logic)h(\()p FJ(\012)h FK(and)h(&\),)e(152)1640 1766 y(pro)t(jection,)g(11,)j(61,)f (68,)g(84)1522 1851 y(programs,)h(17,)f(53,)g(72,)g(84,)g(124)1522 1936 y(pro)t(jection)f(\(em)n(b)r(edding\),)f(135,)j(142)1522 2022 y Fr(PROLOG)p FK(,)g(28,)f(105,)h(112)1522 2107 y(pro)r(of,)g(5)1522 2192 y(pro)r(of)f(net,)f(155)1522 2277 y(pro)r(of)h(of)g(program,)g(53)1522 2362 y(pro)r(of)g(structure,) f(156)1522 2447 y(pro)n(v)l(ably)i(total,)e(53,)h(124)1522 2532 y(Ptolomeic)d(astronom)n(y)-6 b(,)25 b(1)1522 2617 y(pullbac)n(k,)e(54,)h(59,)h(61,)f(65,)g(137,)g(141)1522 2760 y FG(Q)p FK(uan)n(ti\014ers,)g FM(se)l(e)k FK(univ)n(ersal,)23 b(existen)n(tial)1757 2845 y FM(and)g FK(second)h(order)1522 2988 y FJ(R)f FK(\(righ)n(t)f(logical)g(rules\),)g FM(se)l(e)28 b FK(sequen)n(t)1757 3074 y(calculus)1522 3133 y Fv(R)1568 3159 y FK(,)23 b FM(se)l(e)28 b FK(asymmetrical)21 b(in)n(terpretation) 1522 3244 y(real)h(n)n(um)n(b)r(ers,)i(114)1522 3329 y(realisabilit)n(y)-6 b(,)21 b(7)1522 3414 y(recursion)1640 3499 y(and)j(iteration,)e(51,)i(70,)g(90)1640 3584 y(recurrence)d (relation,)h(50)1640 3669 y(recursor)g(\()p Fq(R)p FK(\),)i(48)1640 3754 y(seman)n(tics,)e(70)1522 3840 y(redex,)h(18,)h(24,)g(48)1522 3925 y(reducibilit)n(y)-6 b(,)21 b(27,)j(58,)g(123)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat 174 177 bop 167 167 a FK(174)2175 b Fz(INDEX)284 404 y FK(in)23 b FG(F)p FK(,)g(115)284 491 y(in)g FG(T)p FK(,)g(49)284 577 y FH(\025)p FK(-calculus,)g(42)167 663 y(reduction,)g(18)167 749 y(re\015exiv)n(e)f(symmetric)f(relation,) h(57)167 835 y(represen)n(table)g(functions,)h(52,)i(120)167 921 y(resolution)d(metho)r(d,)i(112)167 1008 y(rewrite)d(rules,)h FM(se)l(e)28 b FK(con)n(v)n(ersion)167 1094 y(Reynolds,)23 b(82)167 1180 y(righ)n(t)g(logical)e(rules,)i FM(se)l(e)28 b FK(sequen)n(t)402 1265 y(calculus)167 1351 y(rigid)22 b(em)n(b)r(eddings,)h(134)167 1437 y(ring)g(theory)-6 b(,)24 b(66)167 1523 y(Robinson,)g(112)167 1610 y(Rosser,)f FM(se)l(e)29 b FK(Ch)n(urc)n(h-Rosser)23 b(prop)r(ert)n(y)167 1772 y Fq(S)p FK(,)g FJ(S)28 b FK(\(successor\),)23 b FM(se)l(e)29 b FK(in)n(tegers)167 1858 y(saturated)24 b(domains,)f(133)167 1944 y(Scott,)g(54,)h(55,)g(64,)h(66,)f(133)167 2030 y(second)g(incompleteness)d(theorem,)h(42)167 2116 y(second)i(order)f(logic,)f(94,)i(114,)g(123)167 2203 y(secondary)g(equations,)g(16,)g(69,)h(81,)f(85,)402 2288 y(97,)g(132)167 2374 y(seman)n(tic)e(de\014nabilit)n(y)-6 b(,)22 b(140)167 2460 y(sense,)h(1)167 2546 y(separabilit)n(y)-6 b(,)22 b(134)167 2632 y(sequen)n(t)h(calculus,)g(28)284 2719 y Fq(Cut)h FK(rule,)e(30)284 2805 y(linear)g(logic,)g(150)284 2891 y(logical)g(rules,)g(31)284 2977 y(natural)i(deduction,)f(35)284 3063 y Fr(PROLOG)p FK(,)i(112)284 3149 y(structural)e(rules,)f(29)167 3235 y(sequen)n(tial)g(algorithm,)h(54)167 3322 y(side)f(e\013ects,)h (150)167 3408 y(\006)g(\(existen)n(tial)e(t)n(yp)r(e\))i(in)f FG(F)p FK(,)h(86,)h(145)167 3494 y(\006)170 3488 y FJ(\016)244 3494 y FK(\(total)e(category\),)i(135)167 3580 y(signature,)f(34,)i (87,)f(139)167 3666 y(simple)d(t)n(yp)r(es,)i(84,)i(139,)f(145)167 3752 y(singleton)f(t)n(yp)r(e)g(\()p FJ(S)-6 b FM(gl)5 b FK(\),)23 b(104,)i(139)167 3839 y(size)d(problem,)g(83,)i(112,)h(132) 167 3925 y(Sm)n(yth,)f(55)1522 404 y FJ(S)-6 b(N)33 b FK(\(strongly)23 b(normalisable)f(terms\),)1757 490 y(119)1522 576 y(sp)r(eci\014cation,)h(17)1522 662 y(sp)r(ectral)f(space,)i(56) 1522 748 y(stabilit)n(y)-6 b(,)22 b(54,)i(134,)h(137)1640 834 y(de\014nition)d(\()p FG(St)p FK(\),)h(58,)h(100)1522 920 y(static,)f(2,)g(14,)h(54)1522 1006 y(strict)e(\(preserv)n(e)g Fn(?)p FK(\),)h(97)1522 1093 y(strong)h(\014niteness,)f(59,)h(66)1522 1179 y(strong)g(normalisation,)f(26,)h(42,)g(114)1522 1265 y(structural)f(rules)1640 1351 y(cut)f(elimination,)f(106,)j(112) 1640 1437 y(linear)d(logic,)h(152,)j(153)1640 1523 y(natural)e (deduction,)g(36)1640 1610 y(sequen)n(t)g(calculus,)f(29)1522 1696 y(sub)r(domain,)i(134)1522 1782 y(subform)n(ula)g(prop)r(ert)n(y) 1640 1868 y FH(\025)p FK(-calculus,)e(19)1640 1954 y(natural)h (deduction,)g(76)1640 2040 y(sequen)n(t)g(calculus,)f(33)1522 2127 y(substan)n(ti\014que)j(mo)r(elle,)20 b(155)1522 2213 y(substitution,)j(5,)h(25,)g(69,)g(112,)h(118)1522 2299 y(subuniformit)n(y)-6 b(,)24 b(134)1522 2385 y(successor)f(\()p Fq(S)h FK(and)g FJ(S)5 b FK(\),)23 b FM(se)l(e)28 b FK(in)n(tegers)1522 2471 y(sum)23 b(t)n(yp)r(e,)h(95)1640 2557 y(+,)e FH(\023)1759 2532 y FD(1)1788 2557 y FK(,)h FH(\023)1854 2532 y FD(2)1905 2557 y FK(and)h FH(\016)s FK(,)f(81)1640 2643 y(and)h(disjunction,)f (81)1640 2730 y(coherence)f(space,)h(103,)i(146)1640 2816 y(linear)c(decomp)r(osition,)i(96,)h(103)1640 2902 y(linear)d(logic)h(\()p FJ(\010)h FK(and)h Fc(O)p FK(\),)f(152)1522 2988 y(symmetry)-6 b(,)23 b(10,)h(18,)g(28,)g(30,)g(31,)g(97,)h(105,) 1757 3073 y(134)1522 3235 y Fq(T)p FK(,)e FG(t)p FK(,)g FJ(T)c FK(,)k FM(se)l(e)28 b FK(true)1522 3322 y FG(T)23 b FK(\(G\177)-34 b(odel's)23 b(system\),)g(47,)h(67,)g(70,)g(123)1522 3408 y(tableaux,)g(28)1522 3494 y(T)-6 b(ait,)23 b(42,)h(49,)g(114)1522 3580 y(T)-6 b(ak)n(euti,)23 b(125)1522 3666 y(T)-6 b(arski,)24 b(4)1522 3752 y(tautology)1640 3839 y(linear)d(logic)h(\()p FG(1)h FK(and)h FJ(>)p FK(\),)d(154)1522 3925 y(T)-6 b(a)n(ylor,)24 b(133)p eop PStoPSsaved restore %%Page: (178,179) 90 userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 -15.874016 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip /showpage{}def/copypage{}def/erasepage{}def PStoPSxform concat 175 178 bop 167 167 a Fz(INDEX)2173 b FK(175)167 404 y(tensor)23 b(pro)r(duct)h(\()p FJ(\012)p FK(\))284 491 y(coherence)f(space,)g(104,)i(138,)f(146)284 577 y(linear)e(logic,)g (152)167 663 y(tensor)h(sum)g(or)h(par)f(\()p Fc(O)p FK(\))284 749 y(coherence)g(space,)g(104)284 835 y(linear)f(logic,)g (152)167 922 y(terminal)f(ob)t(ject,)i(104)167 1008 y(terminating)e (relation,)i FM(se)l(e)402 1093 y FK(normalisation)167 1179 y(terms)284 1265 y(in)g FG(F)p FK(,)g(82)284 1352 y(in)g FG(H)-12 b(A)475 1363 y Fb(2)507 1352 y FK(,)23 b(125)284 1438 y(in)g FG(T)p FK(,)g(68)284 1524 y FH(\025)p FK(-calculus,)g(15)284 1610 y(ob)t(ject)g(language,)i(5)167 1696 y(theory)e(of)h(constructions,)f(116,)i(133)167 1782 y(tok)n(en,)f(56,)g(64,)g(137)167 1869 y(top)r(ological)f(space,)g (55)167 1955 y(total)g(category)h(\(\006)640 1949 y FJ(\016)691 1955 y FK(\),)e(135,)j(137,)f(141,)h(146)167 2041 y(total)e(ob)t (jects,)g(57,)h(149)167 2127 y(total)f(recursiv)n(e)f(function,)h(53,)h (122)167 2213 y(trace)e(\()p FJ(T)-6 b FH(r)r FK(\),)24 b(62,)g(67,)g(144)284 2300 y(linear)e(\()p FJ(T)-6 b FM(rlin)5 b FK(\),)23 b(100)167 2386 y(transp)r(osition)g(in)g(linear)f (algebra,)h(101)167 2472 y(trees,)f(8,)i(47,)g(93)167 2558 y(true)284 2644 y(denotation)g(\()p FG(t)p FK(,)f FJ(T)18 b FK(,)23 b Fq(T)p FK(\),)g FM(se)l(e)402 2730 y FK(b)r(o)r(oleans)284 2816 y(prop)r(osition)h(\()p FJ(>)p FK(\),)d FM(se)l(e)29 b FK(tautology)167 2902 y(turb)r(o)24 b(cut)e(elimination,)f(160)167 2988 y(T)-6 b(uring,)23 b(122)167 3074 y(t)n(yp)r(e)g(v)l(ariables,)g(82)167 3161 y(t)n(yp)r(es,)h(15,)g(54,)g(67)167 3323 y FG(U)p FK(nde\014ned)g(ob)t(ject)f(\()p Fn(?)p FK(\),)f(56,)i(96,)g(129,)402 3409 y(139,)g(146,)h(149)167 3495 y(uni\014cation,)e(113)167 3581 y(uniform)g(con)n(tin)n(uit)n(y)-6 b(,)23 b(55)167 3667 y(uniformit)n(y)f(of)i(\005)e(t)n(yp)r(es,)i(83,)g(132,)h(134,)402 3752 y(143)167 3838 y(units)e(\()p FG(0)p FK(,)f FJ(>)p FK(,)g FG(1)h FK(and)h FJ(?)p FK(\),)e(104)167 3925 y(univ)n(ersal)h (algebra,)g(66)1522 404 y(univ)n(ersal)g(domain,)g(133)1522 490 y(univ)n(ersal)g(program)h(\(T)-6 b(uring\),)23 b(122)1522 575 y(univ)n(ersal)g(quan)n(ti\014er,)g(5,)h(6)1640 660 y(cut)e(elimination,)f(108)1640 745 y(natural)i(deduction)1698 830 y FJ(8I)28 b FK(and)c FJ(8E)6 b FK(,)23 b(10)1640 915 y(sequen)n(t)g(calculus)1698 1000 y FJ(L8)f FK(and)i FJ(R8)p FK(,)e(32)1522 1085 y(univ)n(ersal)h(quan)n(ti\014er)g (\(second)h(order\),)1757 1170 y(82,)g(126)1640 1256 y FJ(8)1680 1230 y FD(2)1707 1256 y FJ(I)k FK(and)c FJ(8)1947 1230 y FD(2)1974 1256 y FJ(E)6 b FK(,)24 b(94,)g(125)1640 1341 y(reducibilit)n(y)-6 b(,)20 b(118)1640 1426 y(seman)n(tics,)i (132,)i(143,)h(149)1522 1570 y FG(V)p FK(ariable)d(coherence)g(spaces,) i(141)1522 1655 y(v)l(ariables)1640 1740 y(h)n(yp)r(otheses,)g(11,)g (15,)g(19)1640 1825 y(ob)t(ject)e(language,)j(10,)f(125)1640 1910 y(t)n(yp)r(e,)f(82,)h(125)1522 1995 y(v)n(ery)g(\014nite,)e(59,)i (66)1522 2080 y(Vic)n(k)n(ers,)e(55)1522 2224 y FG(W)p FK(eak)i(normalisation,)e(24)1522 2309 y(w)n(eak)n(ening)1640 2394 y FJ(L)p Fq(W)h FK(and)h FJ(R)p Fq(W)q FK(,)f(29)1640 2479 y(linear)e(logic)h(\()p Fq(W)q FK(?\),)g(154)1522 2564 y(w)n(eb,)h(56,)h(135)1522 2650 y(wh)n(y)g(not)f(\(?\),)g(102,)h (154)1522 2735 y(Winsk)n(el,)e(98,)i(133)1522 2879 y Fq(X)p FK(,)f FJ(L)p Fq(X)p FK(,)f FJ(R)p Fq(X)h FK(\(exc)n(hange\),)g (29,)h(153)1522 3022 y Fq(Y)f FK(\(\014xed)g(p)r(oin)n(t\),)g(72)1522 3166 y FG(Z)p FK(ero)1640 3251 y FG(0)p FK(,)f(unit)h(of)h FJ(\010)p FK(,)f(154)1640 3336 y Fq(O)g FK(and)h FJ(O)r FK(,)f FM(se)l(e)28 b FK(in)n(tegers)p eop PStoPSsaved restore userdict/PStoPSsaved save put PStoPSmatrix setmatrix 819.779528 400.818898 translate 90 rotate 1.000000 dup scale userdict/PStoPSmatrix matrix currentmatrix put userdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip PStoPSxform concat showpage PStoPSsaved restore %%Trailer end userdict /end-hook known{end-hook}if %%EOF