(* Title: HOL/Induct/LList.thy
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Shares NIL, CONS, List_case with List.thy
Still needs flatten function -- hard because it need
bounds on the amount of lookahead required.
Could try (but would it work for the gfp analogue of term?)
LListD_Fun_def "LListD_Fun(A) == (%Z. diag({Numb(0)}) <++> diag(A) <**> Z)"
A nice but complex example would be [ML for the Working Programmer, page 176]
from(1) = enumerate (Lmap (Lmap(pack), makeqq(from(1),from(1))))
Previous definition of llistD_Fun was explicit:
llistD_Fun_def
"llistD_Fun(r) ==
{(LNil,LNil)} Un
(UN x. (split(%l1 l2.(LCons(x,l1),LCons(x,l2))))`r)"
*)
header {*Definition of type llist by a greatest fixed point*}
theory LList = Main + SList:
consts
llist :: "'a item set => 'a item set"
LListD :: "('a item * 'a item)set => ('a item * 'a item)set"
coinductive "llist(A)"
intros
NIL_I: "NIL \<in> llist(A)"
CONS_I: "[| a \<in> A; M \<in> llist(A) |] ==> CONS a M \<in> llist(A)"
coinductive "LListD(r)"
intros
NIL_I: "(NIL, NIL) \<in> LListD(r)"
CONS_I: "[| (a,b) \<in> r; (M,N) \<in> LListD(r) |]
==> (CONS a M, CONS b N) \<in> LListD(r)"
typedef (LList)
'a llist = "llist(range Leaf) :: 'a item set"
by (blast intro: llist.NIL_I)
constdefs
list_Fun :: "['a item set, 'a item set] => 'a item set"
--{*Now used exclusively for abbreviating the coinduction rule*}
"list_Fun A X == {z. z = NIL | (\<exists>M a. z = CONS a M & a \<in> A & M \<in> X)}"
LListD_Fun ::
"[('a item * 'a item)set, ('a item * 'a item)set] =>
('a item * 'a item)set"
"LListD_Fun r X ==
{z. z = (NIL, NIL) |
(\<exists>M N a b. z = (CONS a M, CONS b N) & (a, b) \<in> r & (M, N) \<in> X)}"
LNil :: "'a llist"
--{*abstract constructor*}
"LNil == Abs_LList NIL"
LCons :: "['a, 'a llist] => 'a llist"
--{*abstract constructor*}
"LCons x xs == Abs_LList(CONS (Leaf x) (Rep_LList xs))"
llist_case :: "['b, ['a, 'a llist]=>'b, 'a llist] => 'b"
"llist_case c d l ==
List_case c (%x y. d (inv Leaf x) (Abs_LList y)) (Rep_LList l)"
LList_corec_fun :: "[nat, 'a=> ('b item * 'a) option, 'a] => 'b item"
"LList_corec_fun k f ==
nat_rec (%x. {})
(%j r x. case f x of None => NIL
| Some(z,w) => CONS z (r w))
k"
LList_corec :: "['a, 'a => ('b item * 'a) option] => 'b item"
"LList_corec a f == \<Union>k. LList_corec_fun k f a"
llist_corec :: "['a, 'a => ('b * 'a) option] => 'b llist"
"llist_corec a f ==
Abs_LList(LList_corec a
(%z. case f z of None => None
| Some(v,w) => Some(Leaf(v), w)))"
llistD_Fun :: "('a llist * 'a llist)set => ('a llist * 'a llist)set"
"llistD_Fun(r) ==
prod_fun Abs_LList Abs_LList `
LListD_Fun (diag(range Leaf))
(prod_fun Rep_LList Rep_LList ` r)"
text{* The case syntax for type @{text "'a llist"} *}
translations
"case p of LNil => a | LCons x l => b" == "llist_case a (%x l. b) p"
subsubsection{* Sample function definitions. Item-based ones start with @{text L} *}
constdefs
Lmap :: "('a item => 'b item) => ('a item => 'b item)"
"Lmap f M == LList_corec M (List_case None (%x M'. Some((f(x), M'))))"
lmap :: "('a=>'b) => ('a llist => 'b llist)"
"lmap f l == llist_corec l (%z. case z of LNil => None
| LCons y z => Some(f(y), z))"
iterates :: "['a => 'a, 'a] => 'a llist"
"iterates f a == llist_corec a (%x. Some((x, f(x))))"
Lconst :: "'a item => 'a item"
"Lconst(M) == lfp(%N. CONS M N)"
Lappend :: "['a item, 'a item] => 'a item"
"Lappend M N == LList_corec (M,N)
(split(List_case (List_case None (%N1 N2. Some((N1, (NIL,N2)))))
(%M1 M2 N. Some((M1, (M2,N))))))"
lappend :: "['a llist, 'a llist] => 'a llist"
"lappend l n == llist_corec (l,n)
(split(llist_case (llist_case None (%n1 n2. Some((n1, (LNil,n2)))))
(%l1 l2 n. Some((l1, (l2,n))))))"
text{*Append generates its result by applying f, where
f((NIL,NIL)) = None
f((NIL, CONS N1 N2)) = Some((N1, (NIL,N2))
f((CONS M1 M2, N)) = Some((M1, (M2,N))
*}
text{*
SHOULD @{text LListD_Fun_CONS_I}, etc., be equations (for rewriting)?
*}
lemmas UN1_I = UNIV_I [THEN UN_I, standard]
subsubsection{* Simplification *}
declare option.split [split]
text{*This justifies using llist in other recursive type definitions*}
lemma llist_mono: "A<=B ==> llist(A) <= llist(B)"
apply (unfold llist.defs )
apply (rule gfp_mono)
apply (assumption | rule basic_monos)+
done
lemma llist_unfold: "llist(A) = usum {Numb(0)} (uprod A (llist A))"
by (fast intro!: llist.intros [unfolded NIL_def CONS_def]
elim: llist.cases [unfolded NIL_def CONS_def])
subsection{* Type checking by coinduction *}
text {*
{\dots} using @{text list_Fun} THE COINDUCTIVE DEFINITION PACKAGE
COULD DO THIS!
*}
lemma llist_coinduct:
"[| M \<in> X; X <= list_Fun A (X Un llist(A)) |] ==> M \<in> llist(A)"
apply (unfold list_Fun_def)
apply (erule llist.coinduct)
apply (erule subsetD [THEN CollectD], assumption)
done
lemma list_Fun_NIL_I [iff]: "NIL \<in> list_Fun A X"
by (unfold list_Fun_def NIL_def, fast)
lemma list_Fun_CONS_I [intro!,simp]:
"[| M \<in> A; N \<in> X |] ==> CONS M N \<in> list_Fun A X"
apply (unfold list_Fun_def CONS_def, fast)
done
text{*Utilise the ``strong'' part, i.e. @{text "gfp(f)"}*}
lemma list_Fun_llist_I: "M \<in> llist(A) ==> M \<in> list_Fun A (X Un llist(A))"
apply (unfold llist.defs list_Fun_def)
apply (rule gfp_fun_UnI2)
apply (rule monoI, blast)
apply assumption
done
subsection{* @{text LList_corec} satisfies the desired recurion equation *}
text{*A continuity result?*}
lemma CONS_UN1: "CONS M (\<Union>x. f(x)) = (\<Union>x. CONS M (f x))"
apply (unfold CONS_def)
apply (simp add: In1_UN1 Scons_UN1_y)
done
lemma CONS_mono: "[| M<=M'; N<=N' |] ==> CONS M N <= CONS M' N'"
apply (unfold CONS_def)
apply (assumption | rule In1_mono Scons_mono)+
done
declare LList_corec_fun_def [THEN def_nat_rec_0, simp]
LList_corec_fun_def [THEN def_nat_rec_Suc, simp]
subsubsection{* The directions of the equality are proved separately *}
lemma LList_corec_subset1:
"LList_corec a f <=
(case f a of None => NIL | Some(z,w) => CONS z (LList_corec w f))"
apply (unfold LList_corec_def)
apply (rule UN_least)
apply (case_tac "k")
apply (simp_all (no_asm_simp))
apply (rule allI impI subset_refl [THEN CONS_mono] UNIV_I [THEN UN_upper])+
done
lemma LList_corec_subset2:
"(case f a of None => NIL | Some(z,w) => CONS z (LList_corec w f)) <=
LList_corec a f"
apply (unfold LList_corec_def)
apply (simp add: CONS_UN1, safe)
apply (rule_tac a="Suc(?k)" in UN_I, simp, simp)+
done
text{*the recursion equation for @{text LList_corec} -- NOT SUITABLE FOR REWRITING!*}
lemma LList_corec:
"LList_corec a f =
(case f a of None => NIL | Some(z,w) => CONS z (LList_corec w f))"
by (rule equalityI LList_corec_subset1 LList_corec_subset2)+
text{*definitional version of same*}
lemma def_LList_corec:
"[| !!x. h(x) == LList_corec x f |]
==> h(a) = (case f a of None => NIL | Some(z,w) => CONS z (h w))"
by (simp add: LList_corec)
text{*A typical use of co-induction to show membership in the @{text gfp}.
Bisimulation is @{text "range(%x. LList_corec x f)"} *}
lemma LList_corec_type: "LList_corec a f \<in> llist UNIV"
apply (rule_tac X = "range (%x. LList_corec x ?g) " in llist_coinduct)
apply (rule rangeI, safe)
apply (subst LList_corec, simp)
done
subsection{* @{text llist} equality as a @{text gfp}; the bisimulation principle *}
text{*This theorem is actually used, unlike the many similar ones in ZF*}
lemma LListD_unfold: "LListD r = dsum (diag {Numb 0}) (dprod r (LListD r))"
by (fast intro!: LListD.intros [unfolded NIL_def CONS_def]
elim: LListD.cases [unfolded NIL_def CONS_def])
lemma LListD_implies_ntrunc_equality [rule_format]:
"\<forall>M N. (M,N) \<in> LListD(diag A) --> ntrunc k M = ntrunc k N"
apply (induct_tac "k" rule: nat_less_induct)
apply (safe del: equalityI)
apply (erule LListD.cases)
apply (safe del: equalityI)
apply (case_tac "n", simp)
apply (rename_tac "n'")
apply (case_tac "n'")
apply (simp_all add: CONS_def less_Suc_eq)
done
text{*The domain of the @{text LListD} relation*}
lemma Domain_LListD:
"Domain (LListD(diag A)) <= llist(A)"
apply (unfold llist.defs NIL_def CONS_def)
apply (rule gfp_upperbound)
txt{*avoids unfolding @{text LListD} on the rhs*}
apply (rule_tac P = "%x. Domain x <= ?B" in LListD_unfold [THEN ssubst], simp)
apply blast
done
text{*This inclusion justifies the use of coinduction to show @{text "M = N"}*}
lemma LListD_subset_diag: "LListD(diag A) <= diag(llist(A))"
apply (rule subsetI)
apply (rule_tac p = "x" in PairE, safe)
apply (rule diag_eqI)
apply (rule LListD_implies_ntrunc_equality [THEN ntrunc_equality], assumption)
apply (erule DomainI [THEN Domain_LListD [THEN subsetD]])
done
subsubsection{* Coinduction, using @{text LListD_Fun} *}
text {* THE COINDUCTIVE DEFINITION PACKAGE COULD DO THIS! *}
lemma LListD_Fun_mono: "A<=B ==> LListD_Fun r A <= LListD_Fun r B"
apply (unfold LListD_Fun_def)
apply (assumption | rule basic_monos)+
done
lemma LListD_coinduct:
"[| M \<in> X; X <= LListD_Fun r (X Un LListD(r)) |] ==> M \<in> LListD(r)"
apply (unfold LListD_Fun_def)
apply (erule LListD.coinduct)
apply (erule subsetD [THEN CollectD], assumption)
done
lemma LListD_Fun_NIL_I: "(NIL,NIL) \<in> LListD_Fun r s"
by (unfold LListD_Fun_def NIL_def, fast)
lemma LListD_Fun_CONS_I:
"[| x\<in>A; (M,N):s |] ==> (CONS x M, CONS x N) \<in> LListD_Fun (diag A) s"
apply (unfold LListD_Fun_def CONS_def, blast)
done
text{*Utilise the "strong" part, i.e. @{text "gfp(f)"}*}
lemma LListD_Fun_LListD_I:
"M \<in> LListD(r) ==> M \<in> LListD_Fun r (X Un LListD(r))"
apply (unfold LListD.defs LListD_Fun_def)
apply (rule gfp_fun_UnI2)
apply (rule monoI, blast)
apply assumption
done
text{*This converse inclusion helps to strengthen @{text LList_equalityI}*}
lemma diag_subset_LListD: "diag(llist(A)) <= LListD(diag A)"
apply (rule subsetI)
apply (erule LListD_coinduct)
apply (rule subsetI)
apply (erule diagE)
apply (erule ssubst)
apply (erule llist.cases)
apply (simp_all add: diagI LListD_Fun_NIL_I LListD_Fun_CONS_I)
done
lemma LListD_eq_diag: "LListD(diag A) = diag(llist(A))"
apply (rule equalityI LListD_subset_diag diag_subset_LListD)+
done
lemma LListD_Fun_diag_I: "M \<in> llist(A) ==> (M,M) \<in> LListD_Fun (diag A) (X Un diag(llist(A)))"
apply (rule LListD_eq_diag [THEN subst])
apply (rule LListD_Fun_LListD_I)
apply (simp add: LListD_eq_diag diagI)
done
subsubsection{* To show two LLists are equal, exhibit a bisimulation!
[also admits true equality]
Replace @{text A} by some particular set, like @{text "{x. True}"}??? *}
lemma LList_equalityI:
"[| (M,N) \<in> r; r <= LListD_Fun (diag A) (r Un diag(llist(A))) |]
==> M=N"
apply (rule LListD_subset_diag [THEN subsetD, THEN diagE])
apply (erule LListD_coinduct)
apply (simp add: LListD_eq_diag, safe)
done
subsection{* Finality of @{text "llist(A)"}: Uniqueness of functions defined by corecursion *}
text{*We must remove @{text Pair_eq} because it may turn an instance of reflexivity
@{text "(h1 b, h2 b) = (h1 ?x17, h2 ?x17)"} into a conjunction!
(or strengthen the Solver?)
*}
declare Pair_eq [simp del]
text{*abstract proof using a bisimulation*}
lemma LList_corec_unique:
"[| !!x. h1(x) = (case f x of None => NIL | Some(z,w) => CONS z (h1 w));
!!x. h2(x) = (case f x of None => NIL | Some(z,w) => CONS z (h2 w)) |]
==> h1=h2"
apply (rule ext)
txt{*next step avoids an unknown (and flexflex pair) in simplification*}
apply (rule_tac A = "UNIV" and r = "range(%u. (h1 u, h2 u))"
in LList_equalityI)
apply (rule rangeI, safe)
apply (simp add: LListD_Fun_NIL_I UNIV_I [THEN LListD_Fun_CONS_I])
done
lemma equals_LList_corec:
"[| !!x. h(x) = (case f x of None => NIL | Some(z,w) => CONS z (h w)) |]
==> h = (%x. LList_corec x f)"
by (simp add: LList_corec_unique LList_corec)
subsubsection{*Obsolete proof of @{text LList_corec_unique}:
complete induction, not coinduction *}
lemma ntrunc_one_CONS [simp]: "ntrunc (Suc 0) (CONS M N) = {}"
by (simp add: CONS_def ntrunc_one_In1)
lemma ntrunc_CONS [simp]:
"ntrunc (Suc(Suc(k))) (CONS M N) = CONS (ntrunc k M) (ntrunc k N)"
by (simp add: CONS_def)
lemma
assumes prem1:
"!!x. h1 x = (case f x of None => NIL | Some(z,w) => CONS z (h1 w))"
and prem2:
"!!x. h2 x = (case f x of None => NIL | Some(z,w) => CONS z (h2 w))"
shows "h1=h2"
apply (rule ntrunc_equality [THEN ext])
apply (rule_tac x = "x" in spec)
apply (induct_tac "k" rule: nat_less_induct)
apply (rename_tac "n")
apply (rule allI)
apply (subst prem1)
apply (subst prem2, simp)
apply (intro strip)
apply (case_tac "n")
apply (rename_tac [2] "m")
apply (case_tac [2] "m")
apply simp_all
done
subsection{*Lconst: defined directly by @{text lfp} *}
text{*But it could be defined by corecursion.*}
lemma Lconst_fun_mono: "mono(CONS(M))"
apply (rule monoI subset_refl CONS_mono)+
apply assumption
done
text{* @{text "Lconst(M) = CONS M (Lconst M)"} *}
lemmas Lconst = Lconst_fun_mono [THEN Lconst_def [THEN def_lfp_unfold]]
text{*A typical use of co-induction to show membership in the gfp.
The containing set is simply the singleton @{text "{Lconst(M)}"}. *}
lemma Lconst_type: "M\<in>A ==> Lconst(M): llist(A)"
apply (rule singletonI [THEN llist_coinduct], safe)
apply (rule_tac P = "%u. u \<in> ?A" in Lconst [THEN ssubst])
apply (assumption | rule list_Fun_CONS_I singletonI UnI1)+
done
lemma Lconst_eq_LList_corec: "Lconst(M) = LList_corec M (%x. Some(x,x))"
apply (rule equals_LList_corec [THEN fun_cong], simp)
apply (rule Lconst)
done
text{*Thus we could have used gfp in the definition of Lconst*}
lemma gfp_Lconst_eq_LList_corec: "gfp(%N. CONS M N) = LList_corec M (%x. Some(x,x))"
apply (rule equals_LList_corec [THEN fun_cong], simp)
apply (rule Lconst_fun_mono [THEN gfp_unfold])
done
subsection{* Isomorphisms *}
lemma LListI: "x \<in> llist (range Leaf) ==> x \<in> LList"
by (unfold LList_def, simp)
lemma LListD: "x \<in> LList ==> x \<in> llist (range Leaf)"
by (unfold LList_def, simp)
subsubsection{* Distinctness of constructors *}
lemma LCons_not_LNil [iff]: "~ LCons x xs = LNil"
apply (unfold LNil_def LCons_def)
apply (subst Abs_LList_inject)
apply (rule llist.intros CONS_not_NIL rangeI LListI Rep_LList [THEN LListD])+
done
lemmas LNil_not_LCons [iff] = LCons_not_LNil [THEN not_sym, standard]
subsubsection{* llist constructors *}
lemma Rep_LList_LNil: "Rep_LList LNil = NIL"
apply (unfold LNil_def)
apply (rule llist.NIL_I [THEN LListI, THEN Abs_LList_inverse])
done
lemma Rep_LList_LCons: "Rep_LList(LCons x l) = CONS (Leaf x) (Rep_LList l)"
apply (unfold LCons_def)
apply (rule llist.CONS_I [THEN LListI, THEN Abs_LList_inverse]
rangeI Rep_LList [THEN LListD])+
done
subsubsection{* Injectiveness of @{text CONS} and @{text LCons} *}
lemma CONS_CONS_eq2: "(CONS M N=CONS M' N') = (M=M' & N=N')"
apply (unfold CONS_def)
apply (fast elim!: Scons_inject)
done
lemmas CONS_inject = CONS_CONS_eq [THEN iffD1, THEN conjE, standard]
text{*For reasoning about abstract llist constructors*}
declare Rep_LList [THEN LListD, intro] LListI [intro]
declare llist.intros [intro]
lemma LCons_LCons_eq [iff]: "(LCons x xs=LCons y ys) = (x=y & xs=ys)"
apply (unfold LCons_def)
apply (subst Abs_LList_inject)
apply (auto simp add: Rep_LList_inject)
done
lemma CONS_D2: "CONS M N \<in> llist(A) ==> M \<in> A & N \<in> llist(A)"
apply (erule llist.cases)
apply (erule CONS_neq_NIL, fast)
done
subsection{* Reasoning about @{text "llist(A)"} *}
text{*A special case of @{text list_equality} for functions over lazy lists*}
lemma LList_fun_equalityI:
"[| M \<in> llist(A); g(NIL): llist(A);
f(NIL)=g(NIL);
!!x l. [| x\<in>A; l \<in> llist(A) |] ==>
(f(CONS x l),g(CONS x l)) \<in>
LListD_Fun (diag A) ((%u.(f(u),g(u)))`llist(A) Un
diag(llist(A)))
|] ==> f(M) = g(M)"
apply (rule LList_equalityI)
apply (erule imageI)
apply (rule image_subsetI)
apply (erule_tac aa=x in llist.cases)
apply (erule ssubst, erule ssubst, erule LListD_Fun_diag_I, blast)
done
subsection{* The functional @{text Lmap} *}
lemma Lmap_NIL [simp]: "Lmap f NIL = NIL"
by (rule Lmap_def [THEN def_LList_corec, THEN trans], simp)
lemma Lmap_CONS [simp]: "Lmap f (CONS M N) = CONS (f M) (Lmap f N)"
by (rule Lmap_def [THEN def_LList_corec, THEN trans], simp)
text{*Another type-checking proof by coinduction*}
lemma Lmap_type:
"[| M \<in> llist(A); !!x. x\<in>A ==> f(x):B |] ==> Lmap f M \<in> llist(B)"
apply (erule imageI [THEN llist_coinduct], safe)
apply (erule llist.cases, simp_all)
done
text{*This type checking rule synthesises a sufficiently large set for @{text f}*}
lemma Lmap_type2: "M \<in> llist(A) ==> Lmap f M \<in> llist(f`A)"
apply (erule Lmap_type)
apply (erule imageI)
done
subsubsection{* Two easy results about @{text Lmap} *}
lemma Lmap_compose: "M \<in> llist(A) ==> Lmap (f o g) M = Lmap f (Lmap g M)"
apply (unfold o_def)
apply (drule imageI)
apply (erule LList_equalityI, safe)
apply (erule llist.cases, simp_all)
apply (rule LListD_Fun_NIL_I imageI UnI1 rangeI [THEN LListD_Fun_CONS_I])+
apply assumption
done
lemma Lmap_ident: "M \<in> llist(A) ==> Lmap (%x. x) M = M"
apply (drule imageI)
apply (erule LList_equalityI, safe)
apply (erule llist.cases, simp_all)
apply (rule LListD_Fun_NIL_I imageI UnI1 rangeI [THEN LListD_Fun_CONS_I])+
apply assumption
done
subsection{* @{text Lappend} -- its two arguments cause some complications! *}
lemma Lappend_NIL_NIL [simp]: "Lappend NIL NIL = NIL"
apply (unfold Lappend_def)
apply (rule LList_corec [THEN trans], simp)
done
lemma Lappend_NIL_CONS [simp]:
"Lappend NIL (CONS N N') = CONS N (Lappend NIL N')"
apply (unfold Lappend_def)
apply (rule LList_corec [THEN trans], simp)
done
lemma Lappend_CONS [simp]:
"Lappend (CONS M M') N = CONS M (Lappend M' N)"
apply (unfold Lappend_def)
apply (rule LList_corec [THEN trans], simp)
done
declare llist.intros [simp] LListD_Fun_CONS_I [simp]
range_eqI [simp] image_eqI [simp]
lemma Lappend_NIL [simp]: "M \<in> llist(A) ==> Lappend NIL M = M"
by (erule LList_fun_equalityI, simp_all)
lemma Lappend_NIL2: "M \<in> llist(A) ==> Lappend M NIL = M"
by (erule LList_fun_equalityI, simp_all)
subsubsection{* Alternative type-checking proofs for @{text Lappend} *}
text{*weak co-induction: bisimulation and case analysis on both variables*}
lemma Lappend_type: "[| M \<in> llist(A); N \<in> llist(A) |] ==> Lappend M N \<in> llist(A)"
apply (rule_tac X = "\<Union>u\<in>llist (A) . \<Union>v \<in> llist (A) . {Lappend u v}" in llist_coinduct)
apply fast
apply safe
apply (erule_tac aa = "u" in llist.cases)
apply (erule_tac aa = "v" in llist.cases, simp_all)
apply blast
done
text{*strong co-induction: bisimulation and case analysis on one variable*}
lemma Lappend_type': "[| M \<in> llist(A); N \<in> llist(A) |] ==> Lappend M N \<in> llist(A)"
apply (rule_tac X = " (%u. Lappend u N) `llist (A) " in llist_coinduct)
apply (erule imageI)
apply (rule image_subsetI)
apply (erule_tac aa = "x" in llist.cases)
apply (simp add: list_Fun_llist_I, simp)
done
subsection{* Lazy lists as the type @{text "'a llist"} -- strongly typed versions of above *}
subsubsection{* @{text llist_case}: case analysis for @{text "'a llist"} *}
declare LListI [THEN Abs_LList_inverse, simp]
declare Rep_LList_inverse [simp]
declare Rep_LList [THEN LListD, simp]
declare rangeI [simp] inj_Leaf [simp]
lemma llist_case_LNil [simp]: "llist_case c d LNil = c"
by (unfold llist_case_def LNil_def, simp)
lemma llist_case_LCons [simp]:
"llist_case c d (LCons M N) = d M N"
apply (unfold llist_case_def LCons_def, simp)
done
text{*Elimination is case analysis, not induction.*}
lemma llistE: "[| l=LNil ==> P; !!x l'. l=LCons x l' ==> P |] ==> P"
apply (rule Rep_LList [THEN LListD, THEN llist.cases])
apply (simp add: Rep_LList_LNil [symmetric] Rep_LList_inject)
apply blast
apply (erule LListI [THEN Rep_LList_cases], clarify)
apply (simp add: Rep_LList_LCons [symmetric] Rep_LList_inject, blast)
done
subsubsection{* @{text llist_corec}: corecursion for @{text "'a llist"} *}
text{*Lemma for the proof of @{text llist_corec}*}
lemma LList_corec_type2:
"LList_corec a
(%z. case f z of None => None | Some(v,w) => Some(Leaf(v),w))
\<in> llist(range Leaf)"
apply (rule_tac X = "range (%x. LList_corec x ?g) " in llist_coinduct)
apply (rule rangeI, safe)
apply (subst LList_corec, force)
done
lemma llist_corec:
"llist_corec a f =
(case f a of None => LNil | Some(z,w) => LCons z (llist_corec w f))"
apply (unfold llist_corec_def LNil_def LCons_def)
apply (subst LList_corec)
apply (case_tac "f a")
apply (simp add: LList_corec_type2)
apply (force simp add: LList_corec_type2)
done
text{*definitional version of same*}
lemma def_llist_corec:
"[| !!x. h(x) == llist_corec x f |] ==>
h(a) = (case f a of None => LNil | Some(z,w) => LCons z (h w))"
by (simp add: llist_corec)
subsection{* Proofs about type @{text "'a llist"} functions *}
subsection{* Deriving @{text llist_equalityI} -- @{text llist} equality is a bisimulation *}
lemma LListD_Fun_subset_Times_llist:
"r <= (llist A) <*> (llist A)
==> LListD_Fun (diag A) r <= (llist A) <*> (llist A)"
by (auto simp add: LListD_Fun_def)
lemma subset_Times_llist:
"prod_fun Rep_LList Rep_LList ` r <=
(llist(range Leaf)) <*> (llist(range Leaf))"
by (blast intro: Rep_LList [THEN LListD])
lemma prod_fun_lemma:
"r <= (llist(range Leaf)) <*> (llist(range Leaf))
==> prod_fun (Rep_LList o Abs_LList) (Rep_LList o Abs_LList) ` r <= r"
apply safe
apply (erule subsetD [THEN SigmaE2], assumption)
apply (simp add: LListI [THEN Abs_LList_inverse])
done
lemma prod_fun_range_eq_diag:
"prod_fun Rep_LList Rep_LList ` range(%x. (x, x)) =
diag(llist(range Leaf))"
apply (rule equalityI, blast)
apply (fast elim: LListI [THEN Abs_LList_inverse, THEN subst])
done
text{*Used with @{text lfilter}*}
lemma llistD_Fun_mono:
"A<=B ==> llistD_Fun A <= llistD_Fun B"
apply (unfold llistD_Fun_def prod_fun_def, auto)
apply (rule image_eqI)
prefer 2 apply (blast intro: rev_subsetD [OF _ LListD_Fun_mono], force)
done
subsubsection{* To show two llists are equal, exhibit a bisimulation!
[also admits true equality] *}
lemma llist_equalityI:
"[| (l1,l2) \<in> r; r <= llistD_Fun(r Un range(%x.(x,x))) |] ==> l1=l2"
apply (unfold llistD_Fun_def)
apply (rule Rep_LList_inject [THEN iffD1])
apply (rule_tac r = "prod_fun Rep_LList Rep_LList `r" and A = "range (Leaf) " in LList_equalityI)
apply (erule prod_fun_imageI)
apply (erule image_mono [THEN subset_trans])
apply (rule image_compose [THEN subst])
apply (rule prod_fun_compose [THEN subst])
apply (subst image_Un)
apply (subst prod_fun_range_eq_diag)
apply (rule LListD_Fun_subset_Times_llist [THEN prod_fun_lemma])
apply (rule subset_Times_llist [THEN Un_least])
apply (rule diag_subset_Times)
done
subsubsection{* Rules to prove the 2nd premise of @{text llist_equalityI} *}
lemma llistD_Fun_LNil_I [simp]: "(LNil,LNil) \<in> llistD_Fun(r)"
apply (unfold llistD_Fun_def LNil_def)
apply (rule LListD_Fun_NIL_I [THEN prod_fun_imageI])
done
lemma llistD_Fun_LCons_I [simp]:
"(l1,l2):r ==> (LCons x l1, LCons x l2) \<in> llistD_Fun(r)"
apply (unfold llistD_Fun_def LCons_def)
apply (rule rangeI [THEN LListD_Fun_CONS_I, THEN prod_fun_imageI])
apply (erule prod_fun_imageI)
done
text{*Utilise the "strong" part, i.e. @{text "gfp(f)"}*}
lemma llistD_Fun_range_I: "(l,l) \<in> llistD_Fun(r Un range(%x.(x,x)))"
apply (unfold llistD_Fun_def)
apply (rule Rep_LList_inverse [THEN subst])
apply (rule prod_fun_imageI)
apply (subst image_Un)
apply (subst prod_fun_range_eq_diag)
apply (rule Rep_LList [THEN LListD, THEN LListD_Fun_diag_I])
done
text{*A special case of @{text list_equality} for functions over lazy lists*}
lemma llist_fun_equalityI:
"[| f(LNil)=g(LNil);
!!x l. (f(LCons x l),g(LCons x l))
\<in> llistD_Fun(range(%u. (f(u),g(u))) Un range(%v. (v,v)))
|] ==> f(l) = (g(l :: 'a llist) :: 'b llist)"
apply (rule_tac r = "range (%u. (f (u),g (u))) " in llist_equalityI)
apply (rule rangeI, clarify)
apply (rule_tac l = "u" in llistE)
apply (simp_all add: llistD_Fun_range_I)
done
subsection{* The functional @{text lmap} *}
lemma lmap_LNil [simp]: "lmap f LNil = LNil"
by (rule lmap_def [THEN def_llist_corec, THEN trans], simp)
lemma lmap_LCons [simp]: "lmap f (LCons M N) = LCons (f M) (lmap f N)"
by (rule lmap_def [THEN def_llist_corec, THEN trans], simp)
subsubsection{* Two easy results about @{text lmap} *}
lemma lmap_compose [simp]: "lmap (f o g) l = lmap f (lmap g l)"
by (rule_tac l = "l" in llist_fun_equalityI, simp_all)
lemma lmap_ident [simp]: "lmap (%x. x) l = l"
by (rule_tac l = "l" in llist_fun_equalityI, simp_all)
subsection{* iterates -- @{text llist_fun_equalityI} cannot be used! *}
lemma iterates: "iterates f x = LCons x (iterates f (f x))"
by (rule iterates_def [THEN def_llist_corec, THEN trans], simp)
lemma lmap_iterates [simp]: "lmap f (iterates f x) = iterates f (f x)"
apply (rule_tac r = "range (%u. (lmap f (iterates f u),iterates f (f u))) " in llist_equalityI)
apply (rule rangeI, safe)
apply (rule_tac x1 = "f (u) " in iterates [THEN ssubst])
apply (rule_tac x1 = "u" in iterates [THEN ssubst], simp)
done
lemma iterates_lmap: "iterates f x = LCons x (lmap f (iterates f x))"
apply (subst lmap_iterates)
apply (rule iterates)
done
subsection{* A rather complex proof about iterates -- cf Andy Pitts *}
subsubsection{* Two lemmas about @{text "natrec n x (%m. g)"}, which is essentially
@{text "(g^n)(x)"} *}
lemma fun_power_lmap: "nat_rec (LCons b l) (%m. lmap(f)) n =
LCons (nat_rec b (%m. f) n) (nat_rec l (%m. lmap(f)) n)"
apply (induct_tac "n", simp_all)
done
lemma fun_power_Suc: "nat_rec (g x) (%m. g) n = nat_rec x (%m. g) (Suc n)"
by (induct_tac "n", simp_all)
lemmas Pair_cong = refl [THEN cong, THEN cong, of concl: Pair]
text{*The bisimulation consists of @{text "{(lmap(f)^n (h(u)), lmap(f)^n (iterates(f,u)))}"}
for all @{text u} and all @{text "n::nat"}.*}
lemma iterates_equality:
"(!!x. h(x) = LCons x (lmap f (h x))) ==> h = iterates(f)"
apply (rule ext)
apply (rule_tac
r = "\<Union>u. range (%n. (nat_rec (h u) (%m y. lmap f y) n,
nat_rec (iterates f u) (%m y. lmap f y) n))"
in llist_equalityI)
apply (rule UN1_I range_eqI Pair_cong nat_rec_0 [symmetric])+
apply clarify
apply (subst iterates, atomize)
apply (drule_tac x=u in spec)
apply (erule ssubst)
apply (subst fun_power_lmap)
apply (subst fun_power_lmap)
apply (rule llistD_Fun_LCons_I)
apply (rule lmap_iterates [THEN subst])
apply (subst fun_power_Suc)
apply (subst fun_power_Suc, blast)
done
subsection{* @{text lappend} -- its two arguments cause some complications! *}
lemma lappend_LNil_LNil [simp]: "lappend LNil LNil = LNil"
apply (unfold lappend_def)
apply (rule llist_corec [THEN trans], simp)
done
lemma lappend_LNil_LCons [simp]:
"lappend LNil (LCons l l') = LCons l (lappend LNil l')"
apply (unfold lappend_def)
apply (rule llist_corec [THEN trans], simp)
done
lemma lappend_LCons [simp]:
"lappend (LCons l l') N = LCons l (lappend l' N)"
apply (unfold lappend_def)
apply (rule llist_corec [THEN trans], simp)
done
lemma lappend_LNil [simp]: "lappend LNil l = l"
by (rule_tac l = "l" in llist_fun_equalityI, simp_all)
lemma lappend_LNil2 [simp]: "lappend l LNil = l"
by (rule_tac l = "l" in llist_fun_equalityI, simp_all)
text{*The infinite first argument blocks the second*}
lemma lappend_iterates [simp]: "lappend (iterates f x) N = iterates f x"
apply (rule_tac r = "range (%u. (lappend (iterates f u) N,iterates f u))"
in llist_equalityI)
apply (rule rangeI)
apply (safe)
apply (simplesubst iterates, simp) --{*two redexes*}
done
subsubsection{* Two proofs that @{text lmap} distributes over lappend *}
text{*Long proof requiring case analysis on both both arguments*}
lemma lmap_lappend_distrib:
"lmap f (lappend l n) = lappend (lmap f l) (lmap f n)"
apply (rule_tac r = "\<Union>n. range (%l. (lmap f (lappend l n),
lappend (lmap f l) (lmap f n)))"
in llist_equalityI)
apply (rule UN1_I)
apply (rule rangeI, safe)
apply (rule_tac l = "l" in llistE)
apply (rule_tac l = "n" in llistE, simp_all)
apply (blast intro: llistD_Fun_LCons_I)
done
text{*Shorter proof of theorem above using @{text llist_equalityI} as strong coinduction*}
lemma lmap_lappend_distrib':
"lmap f (lappend l n) = lappend (lmap f l) (lmap f n)"
apply (rule_tac l = "l" in llist_fun_equalityI, simp)
apply simp
done
text{*Without strong coinduction, three case analyses might be needed*}
lemma lappend_assoc': "lappend (lappend l1 l2) l3 = lappend l1 (lappend l2 l3)"
apply (rule_tac l = "l1" in llist_fun_equalityI, simp)
apply simp
done
end