(* Title: HOL/llist
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1993 University of Cambridge
SHOULD LListD_Fun_CONS_I, etc., be equations (for rewriting)?
*)
open LList;
(** Simplification **)
val llist_ss = univ_ss addcongs [split_weak_cong, sum_case_weak_cong]
setloop split_tac [expand_split, expand_sum_case];
(*For adding _eqI rules to a simpset; we must remove Pair_eq because
it may turn an instance of reflexivity into a conjunction!*)
fun add_eqI ss = ss addsimps [range_eqI, image_eqI]
delsimps [Pair_eq];
(*This justifies using llist in other recursive type definitions*)
goalw LList.thy llist.defs "!!A B. A<=B ==> llist(A) <= llist(B)";
by (rtac gfp_mono 1);
by (REPEAT (ares_tac basic_monos 1));
val llist_mono = result();
goal LList.thy "llist(A) = {Numb(0)} <+> (A <*> llist(A))";
let val rew = rewrite_rule [NIL_def, CONS_def] in
by (fast_tac (univ_cs addSIs (equalityI :: map rew llist.intrs)
addEs [rew llist.elim]) 1)
end;
val llist_unfold = result();
(*** Type checking by coinduction, using list_Fun
THE COINDUCTIVE DEFINITION PACKAGE COULD DO THIS!
***)
goalw LList.thy [list_Fun_def]
"!!M. [| M : X; X <= list_Fun(A, X Un llist(A)) |] ==> M : llist(A)";
be llist.coinduct 1;
be (subsetD RS CollectD) 1;
ba 1;
val llist_coinduct = result();
goalw LList.thy [list_Fun_def, NIL_def] "NIL: list_Fun(A,X)";
by (fast_tac set_cs 1);
val list_Fun_NIL_I = result();
goalw LList.thy [list_Fun_def,CONS_def]
"!!M N. [| M: A; N: X |] ==> CONS(M,N) : list_Fun(A,X)";
by (fast_tac set_cs 1);
val list_Fun_CONS_I = result();
(*Utilise the "strong" part, i.e. gfp(f)*)
goalw LList.thy (llist.defs @ [list_Fun_def])
"!!M N. M: llist(A) ==> M : list_Fun(A, X Un llist(A))";
by (etac (llist.mono RS gfp_fun_UnI2) 1);
val list_Fun_llist_I = result();
(*** LList_corec satisfies the desired recurion equation ***)
(*A continuity result?*)
goalw LList.thy [CONS_def] "CONS(M, UN x.f(x)) = (UN x. CONS(M, f(x)))";
by (simp_tac (univ_ss addsimps [In1_UN1, Scons_UN1_y]) 1);
val CONS_UN1 = result();
(*UNUSED; obsolete?
goal Prod.thy "split(p, %x y.UN z.f(x,y,z)) = (UN z. split(p, %x y.f(x,y,z)))";
by (simp_tac (prod_ss setloop (split_tac [expand_split])) 1);
val split_UN1 = result();
goal Sum.thy "sum_case(s,f,%y.UN z.g(y,z)) = (UN z.sum_case(s,f,%y. g(y,z)))";
by (simp_tac (sum_ss setloop (split_tac [expand_sum_case])) 1);
val sum_case2_UN1 = result();
*)
val prems = goalw LList.thy [CONS_def]
"[| M<=M'; N<=N' |] ==> CONS(M,N) <= CONS(M',N')";
by (REPEAT (resolve_tac ([In1_mono,Scons_mono]@prems) 1));
val CONS_mono = result();
val corec_fun_simps = [LList_corec_fun_def RS def_nat_rec_0,
LList_corec_fun_def RS def_nat_rec_Suc];
val corec_fun_ss = llist_ss addsimps corec_fun_simps;
(** The directions of the equality are proved separately **)
goalw LList.thy [LList_corec_def]
"LList_corec(a,f) <= sum_case(%u.NIL, \
\ split(%z w. CONS(z, LList_corec(w,f))), f(a))";
by (rtac UN1_least 1);
by (res_inst_tac [("n","k")] natE 1);
by (ALLGOALS (asm_simp_tac corec_fun_ss));
by (REPEAT (resolve_tac [allI, impI, subset_refl RS CONS_mono, UN1_upper] 1));
val LList_corec_subset1 = result();
goalw LList.thy [LList_corec_def]
"sum_case(%u.NIL, split(%z w. CONS(z, LList_corec(w,f))), f(a)) <= \
\ LList_corec(a,f)";
by (simp_tac (corec_fun_ss addsimps [CONS_UN1]) 1);
by (safe_tac set_cs);
by (ALLGOALS (res_inst_tac [("x","Suc(?k)")] UN1_I THEN'
asm_simp_tac corec_fun_ss));
val LList_corec_subset2 = result();
(*the recursion equation for LList_corec -- NOT SUITABLE FOR REWRITING!*)
goal LList.thy
"LList_corec(a,f) = sum_case(%u. NIL, \
\ split(%z w. CONS(z, LList_corec(w,f))), f(a))";
by (REPEAT (resolve_tac [equalityI, LList_corec_subset1,
LList_corec_subset2] 1));
val LList_corec = result();
(*definitional version of same*)
val [rew] = goal LList.thy
"[| !!x. h(x) == LList_corec(x,f) |] ==> \
\ h(a) = sum_case(%u.NIL, split(%z w. CONS(z, h(w))), f(a))";
by (rewtac rew);
by (rtac LList_corec 1);
val def_LList_corec = result();
(*A typical use of co-induction to show membership in the gfp.
Bisimulation is range(%x. LList_corec(x,f)) *)
goal LList.thy "LList_corec(a,f) : llist({u.True})";
by (res_inst_tac [("X", "range(%x.LList_corec(x,?g))")] llist_coinduct 1);
by (rtac rangeI 1);
by (safe_tac set_cs);
by (stac LList_corec 1);
by (simp_tac (llist_ss addsimps [list_Fun_NIL_I, list_Fun_CONS_I, CollectI]
|> add_eqI) 1);
val LList_corec_type = result();
(*Lemma for the proof of llist_corec*)
goal LList.thy
"LList_corec(a, %z.sum_case(Inl, split(%v w.Inr(<Leaf(v),w>)), f(z))) : \
\ llist(range(Leaf))";
by (res_inst_tac [("X", "range(%x.LList_corec(x,?g))")] llist_coinduct 1);
by (rtac rangeI 1);
by (safe_tac set_cs);
by (stac LList_corec 1);
by (asm_simp_tac (llist_ss addsimps [list_Fun_NIL_I]) 1);
by (fast_tac (set_cs addSIs [list_Fun_CONS_I]) 1);
val LList_corec_type2 = result();
(**** llist equality as a gfp; the bisimulation principle ****)
(*This theorem is actually used, unlike the many similar ones in ZF*)
goal LList.thy "LListD(r) = diag({Numb(0)}) <++> (r <**> LListD(r))";
let val rew = rewrite_rule [NIL_def, CONS_def] in
by (fast_tac (univ_cs addSIs (equalityI :: map rew LListD.intrs)
addEs [rew LListD.elim]) 1)
end;
val LListD_unfold = result();
goal LList.thy "!M N. <M,N> : LListD(diag(A)) --> ntrunc(k,M) = ntrunc(k,N)";
by (res_inst_tac [("n", "k")] less_induct 1);
by (safe_tac set_cs);
by (etac LListD.elim 1);
by (safe_tac (prod_cs addSEs [diagE]));
by (res_inst_tac [("n", "n")] natE 1);
by (asm_simp_tac (univ_ss addsimps [ntrunc_0]) 1);
by (rename_tac "n'" 1);
by (res_inst_tac [("n", "n'")] natE 1);
by (asm_simp_tac (univ_ss addsimps [CONS_def, ntrunc_one_In1]) 1);
by (asm_simp_tac (univ_ss addsimps [CONS_def, ntrunc_In1, ntrunc_Scons]) 1);
val LListD_implies_ntrunc_equality = result();
(*The domain of the LListD relation*)
goalw LList.thy (llist.defs @ [NIL_def, CONS_def])
"fst``LListD(diag(A)) <= llist(A)";
by (rtac gfp_upperbound 1);
(*avoids unfolding LListD on the rhs*)
by (res_inst_tac [("P", "%x. fst``x <= ?B")] (LListD_unfold RS ssubst) 1);
by (simp_tac fst_image_ss 1);
by (fast_tac univ_cs 1);
val fst_image_LListD = result();
(*This inclusion justifies the use of coinduction to show M=N*)
goal LList.thy "LListD(diag(A)) <= diag(llist(A))";
by (rtac subsetI 1);
by (res_inst_tac [("p","x")] PairE 1);
by (safe_tac HOL_cs);
by (rtac diag_eqI 1);
by (rtac (LListD_implies_ntrunc_equality RS spec RS spec RS mp RS
ntrunc_equality) 1);
by (assume_tac 1);
by (etac (fst_imageI RS (fst_image_LListD RS subsetD)) 1);
val LListD_subset_diag = result();
(** Coinduction, using LListD_Fun
THE COINDUCTIVE DEFINITION PACKAGE COULD DO THIS!
**)
goalw LList.thy [LListD_Fun_def]
"!!M. [| M : X; X <= LListD_Fun(r, X Un LListD(r)) |] ==> M : LListD(r)";
be LListD.coinduct 1;
be (subsetD RS CollectD) 1;
ba 1;
val LListD_coinduct = result();
goalw LList.thy [LListD_Fun_def,NIL_def] "<NIL,NIL> : LListD_Fun(r,s)";
by (fast_tac set_cs 1);
val LListD_Fun_NIL_I = result();
goalw LList.thy [LListD_Fun_def,CONS_def]
"!!x. [| x:A; <M,N>:s |] ==> <CONS(x,M), CONS(x,N)> : LListD_Fun(diag(A),s)";
by (fast_tac univ_cs 1);
val LListD_Fun_CONS_I = result();
(*Utilise the "strong" part, i.e. gfp(f)*)
goalw LList.thy (LListD.defs @ [LListD_Fun_def])
"!!M N. M: LListD(r) ==> M : LListD_Fun(r, X Un LListD(r))";
by (etac (LListD.mono RS gfp_fun_UnI2) 1);
val LListD_Fun_LListD_I = result();
(*This converse inclusion helps to strengthen llist_equalityI*)
goal LList.thy "diag(llist(A)) <= LListD(diag(A))";
by (rtac subsetI 1);
by (etac LListD_coinduct 1);
by (rtac subsetI 1);
by (eresolve_tac [diagE] 1);
by (eresolve_tac [ssubst] 1);
by (eresolve_tac [llist.elim] 1);
by (ALLGOALS
(asm_simp_tac (llist_ss addsimps [diagI, LListD_Fun_NIL_I,
LListD_Fun_CONS_I])));
val diag_subset_LListD = result();
goal LList.thy "LListD(diag(A)) = diag(llist(A))";
by (REPEAT (resolve_tac [equalityI, LListD_subset_diag,
diag_subset_LListD] 1));
val LListD_eq_diag = result();
goal LList.thy
"!!M N. M: llist(A) ==> <M,M> : LListD_Fun(diag(A), X Un diag(llist(A)))";
by (rtac (LListD_eq_diag RS subst) 1);
br LListD_Fun_LListD_I 1;
by (asm_simp_tac (HOL_ss addsimps [LListD_eq_diag, diagI]) 1);
val LListD_Fun_diag_I = result();
(** To show two LLists are equal, exhibit a bisimulation!
[also admits true equality]
Replace "A" by some particular set, like {x.True}??? *)
goal LList.thy
"!!r. [| <M,N> : r; r <= LListD_Fun(diag(A), r Un diag(llist(A))) \
\ |] ==> M=N";
by (rtac (LListD_subset_diag RS subsetD RS diagE) 1);
by (etac LListD_coinduct 1);
by (asm_simp_tac (HOL_ss addsimps [LListD_eq_diag]) 1);
by (safe_tac prod_cs);
val llist_equalityI = result();
(*** Finality of llist(A): Uniqueness of functions defined by corecursion ***)
(*abstract proof using a bisimulation*)
val [prem1,prem2] = goal LList.thy
"[| !!x. h1(x) = sum_case(%u.NIL, split(%z w. CONS(z,h1(w))), f(x)); \
\ !!x. h2(x) = sum_case(%u.NIL, split(%z w. CONS(z,h2(w))), f(x)) |]\
\ ==> h1=h2";
by (rtac ext 1);
(*next step avoids an unknown (and flexflex pair) in simplification*)
by (res_inst_tac [("A", "{u.True}"),
("r", "range(%u. <h1(u),h2(u)>)")] llist_equalityI 1);
by (rtac rangeI 1);
by (safe_tac set_cs);
by (stac prem1 1);
by (stac prem2 1);
by (simp_tac (llist_ss addsimps [LListD_Fun_NIL_I,
CollectI RS LListD_Fun_CONS_I]
|> add_eqI) 1);
val LList_corec_unique = result();
val [prem] = goal LList.thy
"[| !!x. h(x) = sum_case(%u.NIL, split(%z w. CONS(z,h(w))), f(x)) |] \
\ ==> h = (%x.LList_corec(x,f))";
by (rtac (LList_corec RS (prem RS LList_corec_unique)) 1);
val equals_LList_corec = result();
(** Obsolete LList_corec_unique proof: complete induction, not coinduction **)
goalw LList.thy [CONS_def] "ntrunc(Suc(0), CONS(M,N)) = {}";
by (rtac ntrunc_one_In1 1);
val ntrunc_one_CONS = result();
goalw LList.thy [CONS_def]
"ntrunc(Suc(Suc(k)), CONS(M,N)) = CONS (ntrunc(k,M), ntrunc(k,N))";
by (simp_tac (HOL_ss addsimps [ntrunc_Scons,ntrunc_In1]) 1);
val ntrunc_CONS = result();
val [prem1,prem2] = goal LList.thy
"[| !!x. h1(x) = sum_case(%u.NIL, split(%z w. CONS(z,h1(w))), f(x)); \
\ !!x. h2(x) = sum_case(%u.NIL, split(%z w. CONS(z,h2(w))), f(x)) |]\
\ ==> h1=h2";
by (rtac (ntrunc_equality RS ext) 1);
by (res_inst_tac [("x", "x")] spec 1);
by (res_inst_tac [("n", "k")] less_induct 1);
by (rtac allI 1);
by (stac prem1 1);
by (stac prem2 1);
by (simp_tac (sum_ss setloop (split_tac [expand_split,expand_sum_case])) 1);
by (strip_tac 1);
by (res_inst_tac [("n", "n")] natE 1);
by (res_inst_tac [("n", "xc")] natE 2);
by (ALLGOALS(asm_simp_tac(nat_ss addsimps
[ntrunc_0,ntrunc_one_CONS,ntrunc_CONS])));
val LList_corec_unique = result();
(*** Lconst -- defined directly using lfp, but equivalent to a LList_corec ***)
goal LList.thy "mono(CONS(M))";
by (REPEAT (ares_tac [monoI, subset_refl, CONS_mono] 1));
val Lconst_fun_mono = result();
(* Lconst(M) = CONS(M,Lconst(M)) *)
val Lconst = standard (Lconst_fun_mono RS (Lconst_def RS def_lfp_Tarski));
(*A typical use of co-induction to show membership in the gfp.
The containing set is simply the singleton {Lconst(M)}. *)
goal LList.thy "!!M A. M:A ==> Lconst(M): llist(A)";
by (rtac (singletonI RS llist_coinduct) 1);
by (safe_tac set_cs);
by (res_inst_tac [("P", "%u. u: ?A")] (Lconst RS ssubst) 1);
by (REPEAT (ares_tac [list_Fun_CONS_I, singletonI, UnI1] 1));
val Lconst_type = result();
goal LList.thy "Lconst(M) = LList_corec(M, %x.Inr(<x,x>))";
by (rtac (equals_LList_corec RS fun_cong) 1);
by (simp_tac sum_ss 1);
by (rtac Lconst 1);
val Lconst_eq_LList_corec = result();
(*Thus we could have used gfp in the definition of Lconst*)
goal LList.thy "gfp(%N. CONS(M, N)) = LList_corec(M, %x.Inr(<x,x>))";
by (rtac (equals_LList_corec RS fun_cong) 1);
by (simp_tac sum_ss 1);
by (rtac (Lconst_fun_mono RS gfp_Tarski) 1);
val gfp_Lconst_eq_LList_corec = result();
(*** Isomorphisms ***)
goal LList.thy "inj(Rep_llist)";
by (rtac inj_inverseI 1);
by (rtac Rep_llist_inverse 1);
val inj_Rep_llist = result();
goal LList.thy "inj_onto(Abs_llist,llist(range(Leaf)))";
by (rtac inj_onto_inverseI 1);
by (etac Abs_llist_inverse 1);
val inj_onto_Abs_llist = result();
(** Distinctness of constructors **)
goalw LList.thy [LNil_def,LCons_def] "~ LCons(x,xs) = LNil";
by (rtac (CONS_not_NIL RS (inj_onto_Abs_llist RS inj_onto_contraD)) 1);
by (REPEAT (resolve_tac (llist.intrs @ [rangeI, Rep_llist]) 1));
val LCons_not_LNil = result();
val LNil_not_LCons = standard (LCons_not_LNil RS not_sym);
val LCons_neq_LNil = standard (LCons_not_LNil RS notE);
val LNil_neq_LCons = sym RS LCons_neq_LNil;
(** llist constructors **)
goalw LList.thy [LNil_def]
"Rep_llist(LNil) = NIL";
by (rtac (llist.NIL_I RS Abs_llist_inverse) 1);
val Rep_llist_LNil = result();
goalw LList.thy [LCons_def]
"Rep_llist(LCons(x,l)) = CONS(Leaf(x),Rep_llist(l))";
by (REPEAT (resolve_tac [llist.CONS_I RS Abs_llist_inverse,
rangeI, Rep_llist] 1));
val Rep_llist_LCons = result();
(** Injectiveness of CONS and LCons **)
goalw LList.thy [CONS_def] "(CONS(M,N)=CONS(M',N')) = (M=M' & N=N')";
by (fast_tac (HOL_cs addSEs [Scons_inject, make_elim In1_inject]) 1);
val CONS_CONS_eq = result();
val CONS_inject = standard (CONS_CONS_eq RS iffD1 RS conjE);
(*For reasoning about abstract llist constructors*)
val llist_cs = set_cs addIs [Rep_llist]@llist.intrs
addSEs [CONS_neq_NIL,NIL_neq_CONS,CONS_inject]
addSDs [inj_onto_Abs_llist RS inj_ontoD,
inj_Rep_llist RS injD, Leaf_inject];
goalw LList.thy [LCons_def] "(LCons(x,xs)=LCons(y,ys)) = (x=y & xs=ys)";
by (fast_tac llist_cs 1);
val LCons_LCons_eq = result();
val LCons_inject = standard (LCons_LCons_eq RS iffD1 RS conjE);
val [major] = goal LList.thy "CONS(M,N): llist(A) ==> M: A & N: llist(A)";
by (rtac (major RS llist.elim) 1);
by (etac CONS_neq_NIL 1);
by (fast_tac llist_cs 1);
val CONS_D = result();
(****** Reasoning about llist(A) ******)
(*Don't use llist_ss, as it does case splits!*)
val List_case_ss = univ_ss addsimps [List_case_NIL, List_case_CONS];
(*A special case of list_equality for functions over lazy lists*)
val [Mlist,gMlist,NILcase,CONScase] = goal LList.thy
"[| M: llist(A); g(NIL): llist(A); \
\ f(NIL)=g(NIL); \
\ !!x l. [| x:A; l: llist(A) |] ==> \
\ <f(CONS(x,l)),g(CONS(x,l))> : \
\ LListD_Fun(diag(A), (%u.<f(u),g(u)>)``llist(A) Un \
\ diag(llist(A))) \
\ |] ==> f(M) = g(M)";
by (rtac llist_equalityI 1);
br (Mlist RS imageI) 1;
by (rtac subsetI 1);
by (etac imageE 1);
by (etac ssubst 1);
by (etac llist.elim 1);
by (etac ssubst 1);
by (stac NILcase 1);
br (gMlist RS LListD_Fun_diag_I) 1;
by (etac ssubst 1);
by (REPEAT (ares_tac [CONScase] 1));
val llist_fun_equalityI = result();
(*** The functional "Lmap" ***)
goal LList.thy "Lmap(f,NIL) = NIL";
by (rtac (Lmap_def RS def_LList_corec RS trans) 1);
by (simp_tac List_case_ss 1);
val Lmap_NIL = result();
goal LList.thy "Lmap(f, CONS(M,N)) = CONS(f(M), Lmap(f,N))";
by (rtac (Lmap_def RS def_LList_corec RS trans) 1);
by (simp_tac List_case_ss 1);
val Lmap_CONS = result();
(*Another type-checking proof by coinduction*)
val [major,minor] = goal LList.thy
"[| M: llist(A); !!x. x:A ==> f(x):B |] ==> Lmap(f,M): llist(B)";
by (rtac (major RS imageI RS llist_coinduct) 1);
by (safe_tac set_cs);
by (etac llist.elim 1);
by (ALLGOALS (asm_simp_tac (HOL_ss addsimps [Lmap_NIL,Lmap_CONS])));
by (REPEAT (ares_tac [list_Fun_NIL_I, list_Fun_CONS_I,
minor, imageI, UnI1] 1));
val Lmap_type = result();
(*This type checking rule synthesises a sufficiently large set for f*)
val [major] = goal LList.thy "M: llist(A) ==> Lmap(f,M): llist(f``A)";
by (rtac (major RS Lmap_type) 1);
by (etac imageI 1);
val Lmap_type2 = result();
(** Two easy results about Lmap **)
val [prem] = goalw LList.thy [o_def]
"M: llist(A) ==> Lmap(f o g, M) = Lmap(f, Lmap(g, M))";
by (rtac (prem RS imageI RS llist_equalityI) 1);
by (safe_tac set_cs);
by (etac llist.elim 1);
by (ALLGOALS (asm_simp_tac (HOL_ss addsimps [Lmap_NIL,Lmap_CONS])));
by (REPEAT (ares_tac [LListD_Fun_NIL_I, imageI, UnI1,
rangeI RS LListD_Fun_CONS_I] 1));
val Lmap_compose = result();
val [prem] = goal LList.thy "M: llist(A) ==> Lmap(%x.x, M) = M";
by (rtac (prem RS imageI RS llist_equalityI) 1);
by (safe_tac set_cs);
by (etac llist.elim 1);
by (ALLGOALS (asm_simp_tac (HOL_ss addsimps [Lmap_NIL,Lmap_CONS])));
by (REPEAT (ares_tac [LListD_Fun_NIL_I, imageI RS UnI1,
rangeI RS LListD_Fun_CONS_I] 1));
val Lmap_ident = result();
(*** Lappend -- its two arguments cause some complications! ***)
goalw LList.thy [Lappend_def] "Lappend(NIL,NIL) = NIL";
by (rtac (LList_corec RS trans) 1);
by (simp_tac List_case_ss 1);
val Lappend_NIL_NIL = result();
goalw LList.thy [Lappend_def]
"Lappend(NIL,CONS(N,N')) = CONS(N, Lappend(NIL,N'))";
by (rtac (LList_corec RS trans) 1);
by (simp_tac List_case_ss 1);
val Lappend_NIL_CONS = result();
goalw LList.thy [Lappend_def]
"Lappend(CONS(M,M'), N) = CONS(M, Lappend(M',N))";
by (rtac (LList_corec RS trans) 1);
by (simp_tac List_case_ss 1);
val Lappend_CONS = result();
val Lappend_ss =
List_case_ss addsimps [llist.NIL_I, Lappend_NIL_NIL, Lappend_NIL_CONS,
Lappend_CONS, LListD_Fun_CONS_I]
|> add_eqI;
goal LList.thy "!!M. M: llist(A) ==> Lappend(NIL,M) = M";
by (etac llist_fun_equalityI 1);
by (ALLGOALS (asm_simp_tac Lappend_ss));
val Lappend_NIL = result();
goal LList.thy "!!M. M: llist(A) ==> Lappend(M,NIL) = M";
by (etac llist_fun_equalityI 1);
by (ALLGOALS (asm_simp_tac Lappend_ss));
val Lappend_NIL2 = result();
(** Alternative type-checking proofs for Lappend **)
(*weak co-induction: bisimulation and case analysis on both variables*)
goal LList.thy
"!!M N. [| M: llist(A); N: llist(A) |] ==> Lappend(M,N): llist(A)";
by (res_inst_tac
[("X", "UN u:llist(A). UN v: llist(A). {Lappend(u,v)}")] llist_coinduct 1);
by (fast_tac set_cs 1);
by (safe_tac set_cs);
by (eres_inst_tac [("a", "u")] llist.elim 1);
by (eres_inst_tac [("a", "v")] llist.elim 1);
by (ALLGOALS
(asm_simp_tac Lappend_ss THEN'
fast_tac (set_cs addSIs [llist.NIL_I, list_Fun_NIL_I, list_Fun_CONS_I])));
val Lappend_type = result();
(*strong co-induction: bisimulation and case analysis on one variable*)
goal LList.thy
"!!M N. [| M: llist(A); N: llist(A) |] ==> Lappend(M,N): llist(A)";
by (res_inst_tac [("X", "(%u.Lappend(u,N))``llist(A)")] llist_coinduct 1);
be imageI 1;
br subsetI 1;
be imageE 1;
by (eres_inst_tac [("a", "u")] llist.elim 1);
by (asm_simp_tac (Lappend_ss addsimps [Lappend_NIL, list_Fun_llist_I]) 1);
by (asm_simp_tac Lappend_ss 1);
by (fast_tac (set_cs addSIs [list_Fun_CONS_I]) 1);
val Lappend_type = result();
(**** Lazy lists as the type 'a llist -- strongly typed versions of above ****)
(** llist_case: case analysis for 'a llist **)
val Rep_llist_simps =
[List_case_NIL, List_case_CONS,
Abs_llist_inverse, Rep_llist_inverse,
Rep_llist, rangeI, inj_Leaf, Inv_f_f]
@ llist.intrs;
val Rep_llist_ss = llist_ss addsimps Rep_llist_simps;
goalw LList.thy [llist_case_def,LNil_def] "llist_case(c, d, LNil) = c";
by (simp_tac Rep_llist_ss 1);
val llist_case_LNil = result();
goalw LList.thy [llist_case_def,LCons_def]
"llist_case(c, d, LCons(M,N)) = d(M,N)";
by (simp_tac Rep_llist_ss 1);
val llist_case_LCons = result();
(*Elimination is case analysis, not induction.*)
val [prem1,prem2] = goalw LList.thy [NIL_def,CONS_def]
"[| l=LNil ==> P; !!x l'. l=LCons(x,l') ==> P \
\ |] ==> P";
by (rtac (Rep_llist RS llist.elim) 1);
by (rtac (inj_Rep_llist RS injD RS prem1) 1);
by (stac Rep_llist_LNil 1);
by (assume_tac 1);
by (etac rangeE 1);
by (rtac (inj_Rep_llist RS injD RS prem2) 1);
by (asm_simp_tac (HOL_ss addsimps [Rep_llist_LCons]) 1);
by (etac (Abs_llist_inverse RS ssubst) 1);
by (rtac refl 1);
val llistE = result();
(** llist_corec: corecursion for 'a llist **)
goalw LList.thy [llist_corec_def,LNil_def,LCons_def]
"llist_corec(a,f) = sum_case(%u. LNil, \
\ split(%z w. LCons(z, llist_corec(w,f))), f(a))";
by (stac LList_corec 1);
by (res_inst_tac [("s","f(a)")] sumE 1);
by (asm_simp_tac (llist_ss addsimps [LList_corec_type2,Abs_llist_inverse]) 1);
by (res_inst_tac [("p","y")] PairE 1);
by (asm_simp_tac (llist_ss addsimps [LList_corec_type2,Abs_llist_inverse]) 1);
(*FIXME: correct case splits usd to be found automatically:
by (ASM_SIMP_TAC(llist_ss addsimps [LList_corec_type2,Abs_llist_inverse]) 1);*)
val llist_corec = result();
(*definitional version of same*)
val [rew] = goal LList.thy
"[| !!x. h(x) == llist_corec(x,f) |] ==> \
\ h(a) = sum_case(%u.LNil, split(%z w. LCons(z, h(w))), f(a))";
by (rewtac rew);
by (rtac llist_corec 1);
val def_llist_corec = result();
(**** Proofs about type 'a llist functions ****)
(*** Deriving llist_equalityI -- llist equality is a bisimulation ***)
goalw LList.thy [LListD_Fun_def]
"!!r A. r <= Sigma(llist(A), %x.llist(A)) ==> \
\ LListD_Fun(diag(A),r) <= Sigma(llist(A), %x.llist(A))";
by (stac llist_unfold 1);
by (simp_tac (HOL_ss addsimps [NIL_def, CONS_def]) 1);
by (fast_tac univ_cs 1);
val LListD_Fun_subset_Sigma_llist = result();
goal LList.thy
"prod_fun(Rep_llist,Rep_llist) `` r <= \
\ Sigma(llist(range(Leaf)), %x.llist(range(Leaf)))";
by (fast_tac (prod_cs addIs [Rep_llist]) 1);
val subset_Sigma_llist = result();
val [prem] = goal LList.thy
"r <= Sigma(llist(range(Leaf)), %x.llist(range(Leaf))) ==> \
\ prod_fun(Rep_llist o Abs_llist, Rep_llist o Abs_llist) `` r <= r";
by (safe_tac prod_cs);
by (rtac (prem RS subsetD RS SigmaE2) 1);
by (assume_tac 1);
by (asm_simp_tac (HOL_ss addsimps [o_def,prod_fun,Abs_llist_inverse]) 1);
val prod_fun_lemma = result();
goal LList.thy
"prod_fun(Rep_llist, Rep_llist) `` range(%x. <x, x>) = \
\ diag(llist(range(Leaf)))";
br equalityI 1;
by (fast_tac (univ_cs addIs [Rep_llist]) 1);
by (fast_tac (univ_cs addSEs [Abs_llist_inverse RS subst]) 1);
val prod_fun_range_eq_diag = result();
(** To show two llists are equal, exhibit a bisimulation!
[also admits true equality] **)
val [prem1,prem2] = goalw LList.thy [llistD_Fun_def]
"[| <l1,l2> : r; r <= llistD_Fun(r Un range(%x.<x,x>)) |] ==> l1=l2";
by (rtac (inj_Rep_llist RS injD) 1);
by (res_inst_tac [("r", "prod_fun(Rep_llist,Rep_llist)``r"),
("A", "range(Leaf)")]
llist_equalityI 1);
by (rtac (prem1 RS prod_fun_imageI) 1);
by (rtac (prem2 RS image_mono RS subset_trans) 1);
by (rtac (image_compose RS subst) 1);
by (rtac (prod_fun_compose RS subst) 1);
by (rtac (image_Un RS ssubst) 1);
by (stac prod_fun_range_eq_diag 1);
by (rtac (LListD_Fun_subset_Sigma_llist RS prod_fun_lemma) 1);
by (rtac (subset_Sigma_llist RS Un_least) 1);
by (rtac diag_subset_Sigma 1);
val llist_equalityI = result();
(** Rules to prove the 2nd premise of llist_equalityI **)
goalw LList.thy [llistD_Fun_def,LNil_def] "<LNil,LNil> : llistD_Fun(r)";
by (rtac (LListD_Fun_NIL_I RS prod_fun_imageI) 1);
val llistD_Fun_LNil_I = result();
val [prem] = goalw LList.thy [llistD_Fun_def,LCons_def]
"<l1,l2>:r ==> <LCons(x,l1), LCons(x,l2)> : llistD_Fun(r)";
by (rtac (rangeI RS LListD_Fun_CONS_I RS prod_fun_imageI) 1);
by (rtac (prem RS prod_fun_imageI) 1);
val llistD_Fun_LCons_I = result();
(*Utilise the "strong" part, i.e. gfp(f)*)
goalw LList.thy [llistD_Fun_def]
"!!l. <l,l> : llistD_Fun(r Un range(%x.<x,x>))";
br (Rep_llist_inverse RS subst) 1;
br prod_fun_imageI 1;
by (rtac (image_Un RS ssubst) 1);
by (stac prod_fun_range_eq_diag 1);
br (Rep_llist RS LListD_Fun_diag_I) 1;
val llistD_Fun_range_I = result();
(*A special case of list_equality for functions over lazy lists*)
val [prem1,prem2] = goal LList.thy
"[| f(LNil)=g(LNil); \
\ !!x l. <f(LCons(x,l)),g(LCons(x,l))> : \
\ llistD_Fun(range(%u. <f(u),g(u)>) Un range(%v. <v,v>)) \
\ |] ==> f(l) = (g(l :: 'a llist) :: 'b llist)";
by (res_inst_tac [("r", "range(%u. <f(u),g(u)>)")] llist_equalityI 1);
by (rtac rangeI 1);
by (rtac subsetI 1);
by (etac rangeE 1);
by (etac ssubst 1);
by (res_inst_tac [("l", "u")] llistE 1);
by (etac ssubst 1);
by (stac prem1 1);
by (rtac llistD_Fun_range_I 1);
by (etac ssubst 1);
by (rtac prem2 1);
val llist_fun_equalityI = result();
(*simpset for llist bisimulations*)
val llistD_simps = [llist_case_LNil, llist_case_LCons,
llistD_Fun_LNil_I, llistD_Fun_LCons_I];
(*Don't use llist_ss, as it does case splits!*)
val llistD_ss = univ_ss addsimps llistD_simps |> add_eqI;
(*** The functional "lmap" ***)
goal LList.thy "lmap(f,LNil) = LNil";
by (rtac (lmap_def RS def_llist_corec RS trans) 1);
by (simp_tac llistD_ss 1);
val lmap_LNil = result();
goal LList.thy "lmap(f, LCons(M,N)) = LCons(f(M), lmap(f,N))";
by (rtac (lmap_def RS def_llist_corec RS trans) 1);
by (simp_tac llistD_ss 1);
val lmap_LCons = result();
(** Two easy results about lmap **)
goal LList.thy "lmap(f o g, l) = lmap(f, lmap(g, l))";
by (res_inst_tac [("l","l")] llist_fun_equalityI 1);
by (ALLGOALS (simp_tac (llistD_ss addsimps [lmap_LNil, lmap_LCons])));
val lmap_compose = result();
goal LList.thy "lmap(%x.x, l) = l";
by (res_inst_tac [("l","l")] llist_fun_equalityI 1);
by (ALLGOALS (simp_tac (llistD_ss addsimps [lmap_LNil, lmap_LCons])));
val lmap_ident = result();
(*** iterates -- llist_fun_equalityI cannot be used! ***)
goal LList.thy "iterates(f,x) = LCons(x, iterates(f,f(x)))";
by (rtac (iterates_def RS def_llist_corec RS trans) 1);
by (simp_tac sum_ss 1);
val iterates = result();
goal LList.thy "lmap(f, iterates(f,x)) = iterates(f,f(x))";
by (res_inst_tac [("r", "range(%u.<lmap(f,iterates(f,u)),iterates(f,f(u))>)")]
llist_equalityI 1);
by (rtac rangeI 1);
by (safe_tac set_cs);
by (res_inst_tac [("x1", "f(u)")] (iterates RS ssubst) 1);
by (res_inst_tac [("x1", "u")] (iterates RS ssubst) 1);
by (simp_tac (llistD_ss addsimps [lmap_LCons]) 1);
val lmap_iterates = result();
goal LList.thy "iterates(f,x) = LCons(x, lmap(f, iterates(f,x)))";
br (lmap_iterates RS ssubst) 1;
br iterates 1;
val iterates_lmap = result();
(*** A rather complex proof about iterates -- cf Andy Pitts ***)
(** Two lemmas about natrec(n,x,%m.g), which is essentially (g^n)(x) **)
goal LList.thy
"nat_rec(n, LCons(b, l), %m. lmap(f)) = \
\ LCons(nat_rec(n, b, %m. f), nat_rec(n, l, %m. lmap(f)))";
by (nat_ind_tac "n" 1);
by (ALLGOALS (asm_simp_tac (nat_ss addsimps [lmap_LCons])));
val fun_power_lmap = result();
goal Nat.thy "nat_rec(n, g(x), %m. g) = nat_rec(Suc(n), x, %m. g)";
by (nat_ind_tac "n" 1);
by (ALLGOALS (asm_simp_tac nat_ss));
val fun_power_Suc = result();
val Pair_cong = read_instantiate_sg (sign_of Prod.thy)
[("f","Pair")] (standard(refl RS cong RS cong));
(*The bisimulation consists of {<lmap(f)^n (h(u)), lmap(f)^n (iterates(f,u))>}
for all u and all n::nat.*)
val [prem] = goal LList.thy
"(!!x. h(x) = LCons(x, lmap(f,h(x)))) ==> h = iterates(f)";
br ext 1;
by (res_inst_tac [("r",
"UN u. range(%n. <nat_rec(n, h(u), %m y.lmap(f,y)), \
\ nat_rec(n, iterates(f,u), %m y.lmap(f,y))>)")]
llist_equalityI 1);
by (REPEAT (resolve_tac [UN1_I, range_eqI, Pair_cong, nat_rec_0 RS sym] 1));
by (safe_tac set_cs);
by (stac iterates 1);
by (stac prem 1);
by (stac fun_power_lmap 1);
by (stac fun_power_lmap 1);
br llistD_Fun_LCons_I 1;
by (rtac (lmap_iterates RS subst) 1);
by (stac fun_power_Suc 1);
by (stac fun_power_Suc 1);
br (UN1_I RS UnI1) 1;
br rangeI 1;
val iterates_equality = result();
(*** lappend -- its two arguments cause some complications! ***)
goalw LList.thy [lappend_def] "lappend(LNil,LNil) = LNil";
by (rtac (llist_corec RS trans) 1);
by (simp_tac llistD_ss 1);
val lappend_LNil_LNil = result();
goalw LList.thy [lappend_def]
"lappend(LNil,LCons(l,l')) = LCons(l, lappend(LNil,l'))";
by (rtac (llist_corec RS trans) 1);
by (simp_tac llistD_ss 1);
val lappend_LNil_LCons = result();
goalw LList.thy [lappend_def]
"lappend(LCons(l,l'), N) = LCons(l, lappend(l',N))";
by (rtac (llist_corec RS trans) 1);
by (simp_tac llistD_ss 1);
val lappend_LCons = result();
goal LList.thy "lappend(LNil,l) = l";
by (res_inst_tac [("l","l")] llist_fun_equalityI 1);
by (ALLGOALS
(simp_tac (llistD_ss addsimps [lappend_LNil_LNil, lappend_LNil_LCons])));
val lappend_LNil = result();
goal LList.thy "lappend(l,LNil) = l";
by (res_inst_tac [("l","l")] llist_fun_equalityI 1);
by (ALLGOALS
(simp_tac (llistD_ss addsimps [lappend_LNil_LNil, lappend_LCons])));
val lappend_LNil2 = result();
(*The infinite first argument blocks the second*)
goal LList.thy "lappend(iterates(f,x), N) = iterates(f,x)";
by (res_inst_tac [("r", "range(%u.<lappend(iterates(f,u),N),iterates(f,u)>)")]
llist_equalityI 1);
by (rtac rangeI 1);
by (safe_tac set_cs);
by (stac iterates 1);
by (simp_tac (llistD_ss addsimps [lappend_LCons]) 1);
val lappend_iterates = result();
(** Two proofs that lmap distributes over lappend **)
(*Long proof requiring case analysis on both both arguments*)
goal LList.thy "lmap(f, lappend(l,n)) = lappend(lmap(f,l), lmap(f,n))";
by (res_inst_tac
[("r",
"UN n. range(%l.<lmap(f,lappend(l,n)), lappend(lmap(f,l),lmap(f,n))>)")]
llist_equalityI 1);
by (rtac UN1_I 1);
by (rtac rangeI 1);
by (safe_tac set_cs);
by (res_inst_tac [("l", "l")] llistE 1);
by (res_inst_tac [("l", "n")] llistE 1);
by (ALLGOALS (asm_simp_tac (llistD_ss addsimps
[lappend_LNil_LNil,lappend_LCons,lappend_LNil_LCons,
lmap_LNil,lmap_LCons])));
by (REPEAT_SOME (ares_tac [llistD_Fun_LCons_I, UN1_I RS UnI1, rangeI]));
by (rtac range_eqI 1);
by (rtac (refl RS Pair_cong) 1);
by (stac lmap_LNil 1);
by (rtac refl 1);
val lmap_lappend_distrib = result();
(*Shorter proof of theorem above using llist_equalityI as strong coinduction*)
goal LList.thy "lmap(f, lappend(l,n)) = lappend(lmap(f,l), lmap(f,n))";
by (res_inst_tac [("l","l")] llist_fun_equalityI 1);
by (simp_tac (llistD_ss addsimps [lappend_LNil, lmap_LNil])1);
by (simp_tac (llistD_ss addsimps [lappend_LCons, lmap_LCons]) 1);
val lmap_lappend_distrib = result();
(*Without strong coinduction, three case analyses might be needed*)
goal LList.thy "lappend(lappend(l1,l2) ,l3) = lappend(l1, lappend(l2,l3))";
by (res_inst_tac [("l","l1")] llist_fun_equalityI 1);
by (simp_tac (llistD_ss addsimps [lappend_LNil])1);
by (simp_tac (llistD_ss addsimps [lappend_LCons]) 1);
val lappend_assoc = result();