(* Title: CCL/Fix.thy ID: $Id$ Author: Martin Coen Copyright 1993 University of Cambridge *) header {* Tentative attempt at including fixed point induction; justified by Smith *} theory Fix imports Type begin consts idgen :: "[i]=>i" INCL :: "[i=>o]=>o" defs idgen_def: "idgen(f) == lam t. case(t,true,false,%x y.,%u. lam x. f ` u(x))" axioms INCL_def: "INCL(%x. P(x)) == (ALL f.(ALL n:Nat. P(f^n`bot)) --> P(fix(f)))" po_INCL: "INCL(%x. a(x) [= b(x))" INCL_subst: "INCL(P) ==> INCL(%x. P((g::i=>i)(x)))" subsection {* Fixed Point Induction *} lemma fix_ind: assumes base: "P(bot)" and step: "!!x. P(x) ==> P(f(x))" and incl: "INCL(P)" shows "P(fix(f))" apply (rule incl [unfolded INCL_def, rule_format]) apply (rule Nat_ind [THEN ballI], assumption) apply simp_all apply (rule base) apply (erule step) done subsection {* Inclusive Predicates *} lemma inclXH: "INCL(P) <-> (ALL f. (ALL n:Nat. P(f ^ n ` bot)) --> P(fix(f)))" by (simp add: INCL_def) lemma inclI: "[| !!f. ALL n:Nat. P(f^n`bot) ==> P(fix(f)) |] ==> INCL(%x. P(x))" unfolding inclXH by blast lemma inclD: "[| INCL(P); !!n. n:Nat ==> P(f^n`bot) |] ==> P(fix(f))" unfolding inclXH by blast lemma inclE: "[| INCL(P); (ALL n:Nat. P(f^n`bot))-->P(fix(f)) ==> R |] ==> R" by (blast dest: inclD) subsection {* Lemmas for Inclusive Predicates *} lemma npo_INCL: "INCL(%x.~ a(x) [= t)" apply (rule inclI) apply (drule bspec) apply (rule zeroT) apply (erule contrapos) apply (rule po_trans) prefer 2 apply assumption apply (subst napplyBzero) apply (rule po_cong, rule po_bot) done lemma conj_INCL: "[| INCL(P); INCL(Q) |] ==> INCL(%x. P(x) & Q(x))" by (blast intro!: inclI dest!: inclD) lemma all_INCL: "[| !!a. INCL(P(a)) |] ==> INCL(%x. ALL a. P(a,x))" by (blast intro!: inclI dest!: inclD) lemma ball_INCL: "[| !!a. a:A ==> INCL(P(a)) |] ==> INCL(%x. ALL a:A. P(a,x))" by (blast intro!: inclI dest!: inclD) lemma eq_INCL: "INCL(%x. a(x) = (b(x)::'a::prog))" apply (simp add: eq_iff) apply (rule conj_INCL po_INCL)+ done subsection {* Derivation of Reachability Condition *} (* Fixed points of idgen *) lemma fix_idgenfp: "idgen(fix(idgen)) = fix(idgen)" apply (rule fixB [symmetric]) done lemma id_idgenfp: "idgen(lam x. x) = lam x. x" apply (simp add: idgen_def) apply (rule term_case [THEN allI]) apply simp_all done (* All fixed points are lam-expressions *) lemma idgenfp_lam: "idgen(d) = d ==> d = lam x. ?f(x)" apply (unfold idgen_def) apply (erule ssubst) apply (rule refl) done (* Lemmas for rewriting fixed points of idgen *) lemma l_lemma: "[| a = b; a ` t = u |] ==> b ` t = u" by (simp add: idgen_def) lemma idgen_lemmas: "idgen(d) = d ==> d ` bot = bot" "idgen(d) = d ==> d ` true = true" "idgen(d) = d ==> d ` false = false" "idgen(d) = d ==> d ` = " "idgen(d) = d ==> d ` (lam x. f(x)) = lam x. d ` f(x)" by (erule l_lemma, simp add: idgen_def)+ (* Proof of Reachability law - show that fix and lam x.x both give LEAST fixed points of idgen and hence are they same *) lemma po_eta: "[| ALL x. t ` x [= u ` x; EX f. t=lam x. f(x); EX f. u=lam x. f(x) |] ==> t [= u" apply (drule cond_eta)+ apply (erule ssubst) apply (erule ssubst) apply (rule po_lam [THEN iffD2]) apply simp done lemma po_eta_lemma: "idgen(d) = d ==> d = lam x. ?f(x)" apply (unfold idgen_def) apply (erule sym) done lemma lemma1: "idgen(d) = d ==> {p. EX a b. p= & (EX t. a=fix(idgen) ` t & b = d ` t)} <= POgen({p. EX a b. p= & (EX t. a=fix(idgen) ` t & b = d ` t)})" apply clarify apply (rule_tac t = t in term_case) apply (simp_all add: POgenXH idgen_lemmas idgen_lemmas [OF fix_idgenfp]) apply blast apply fast done lemma fix_least_idgen: "idgen(d) = d ==> fix(idgen) [= d" apply (rule allI [THEN po_eta]) apply (rule lemma1 [THEN [2] po_coinduct]) apply (blast intro: po_eta_lemma fix_idgenfp)+ done lemma lemma2: "idgen(d) = d ==> {p. EX a b. p= & b = d ` a} <= POgen({p. EX a b. p= & b = d ` a})" apply clarify apply (rule_tac t = a in term_case) apply (simp_all add: POgenXH idgen_lemmas) apply fast done lemma id_least_idgen: "idgen(d) = d ==> lam x. x [= d" apply (rule allI [THEN po_eta]) apply (rule lemma2 [THEN [2] po_coinduct]) apply simp apply (fast intro: po_eta_lemma fix_idgenfp)+ done lemma reachability: "fix(idgen) = lam x. x" apply (fast intro: eq_iff [THEN iffD2] id_idgenfp [THEN fix_least_idgen] fix_idgenfp [THEN id_least_idgen]) done (********) lemma id_apply: "f = lam x. x ==> f`t = t" apply (erule ssubst) apply (rule applyB) done lemma term_ind: assumes 1: "P(bot)" and 2: "P(true)" and 3: "P(false)" and 4: "!!x y.[| P(x); P(y) |] ==> P()" and 5: "!!u.(!!x. P(u(x))) ==> P(lam x. u(x))" and 6: "INCL(P)" shows "P(t)" apply (rule reachability [THEN id_apply, THEN subst]) apply (rule_tac x = t in spec) apply (rule fix_ind) apply (unfold idgen_def) apply (rule allI) apply (subst applyBbot) apply (rule 1) apply (rule allI) apply (rule applyB [THEN ssubst]) apply (rule_tac t = "xa" in term_case) apply simp_all apply (fast intro: assms INCL_subst all_INCL)+ done end