--- a/src/HOL/FixedPoint.thy Mon Oct 08 22:03:21 2007 +0200
+++ b/src/HOL/FixedPoint.thy Mon Oct 08 22:03:25 2007 +0200
@@ -1,273 +0,0 @@
-(* Title: HOL/FixedPoint.thy
- ID: $Id$
- Author: Lawrence C Paulson, Cambridge University Computer Laboratory
- Author: Stefan Berghofer, TU Muenchen
- Copyright 1992 University of Cambridge
-*)
-
-header {* Fixed Points and the Knaster-Tarski Theorem*}
-
-theory FixedPoint
-imports Lattices
-begin
-
-subsection {* Least and greatest fixed points *}
-
-definition
- lfp :: "('a\<Colon>complete_lattice \<Rightarrow> 'a) \<Rightarrow> 'a" where
- "lfp f = Inf {u. f u \<le> u}" --{*least fixed point*}
-
-definition
- gfp :: "('a\<Colon>complete_lattice \<Rightarrow> 'a) \<Rightarrow> 'a" where
- "gfp f = Sup {u. u \<le> f u}" --{*greatest fixed point*}
-
-
-subsection{* Proof of Knaster-Tarski Theorem using @{term lfp} *}
-
-text{*@{term "lfp f"} is the least upper bound of
- the set @{term "{u. f(u) \<le> u}"} *}
-
-lemma lfp_lowerbound: "f A \<le> A ==> lfp f \<le> A"
- by (auto simp add: lfp_def intro: Inf_lower)
-
-lemma lfp_greatest: "(!!u. f u \<le> u ==> A \<le> u) ==> A \<le> lfp f"
- by (auto simp add: lfp_def intro: Inf_greatest)
-
-lemma lfp_lemma2: "mono f ==> f (lfp f) \<le> lfp f"
- by (iprover intro: lfp_greatest order_trans monoD lfp_lowerbound)
-
-lemma lfp_lemma3: "mono f ==> lfp f \<le> f (lfp f)"
- by (iprover intro: lfp_lemma2 monoD lfp_lowerbound)
-
-lemma lfp_unfold: "mono f ==> lfp f = f (lfp f)"
- by (iprover intro: order_antisym lfp_lemma2 lfp_lemma3)
-
-lemma lfp_const: "lfp (\<lambda>x. t) = t"
- by (rule lfp_unfold) (simp add:mono_def)
-
-
-subsection {* General induction rules for least fixed points *}
-
-theorem lfp_induct:
- assumes mono: "mono f" and ind: "f (inf (lfp f) P) <= P"
- shows "lfp f <= P"
-proof -
- have "inf (lfp f) P <= lfp f" by (rule inf_le1)
- with mono have "f (inf (lfp f) P) <= f (lfp f)" ..
- also from mono have "f (lfp f) = lfp f" by (rule lfp_unfold [symmetric])
- finally have "f (inf (lfp f) P) <= lfp f" .
- from this and ind have "f (inf (lfp f) P) <= inf (lfp f) P" by (rule le_infI)
- hence "lfp f <= inf (lfp f) P" by (rule lfp_lowerbound)
- also have "inf (lfp f) P <= P" by (rule inf_le2)
- finally show ?thesis .
-qed
-
-lemma lfp_induct_set:
- assumes lfp: "a: lfp(f)"
- and mono: "mono(f)"
- and indhyp: "!!x. [| x: f(lfp(f) Int {x. P(x)}) |] ==> P(x)"
- shows "P(a)"
- by (rule lfp_induct [THEN subsetD, THEN CollectD, OF mono _ lfp])
- (auto simp: inf_set_eq intro: indhyp)
-
-lemma lfp_ordinal_induct:
- assumes mono: "mono f"
- and P_f: "!!S. P S ==> P(f S)"
- and P_Union: "!!M. !S:M. P S ==> P(Union M)"
- shows "P(lfp f)"
-proof -
- let ?M = "{S. S \<subseteq> lfp f & P S}"
- have "P (Union ?M)" using P_Union by simp
- also have "Union ?M = lfp f"
- proof
- show "Union ?M \<subseteq> lfp f" by blast
- hence "f (Union ?M) \<subseteq> f (lfp f)" by (rule mono [THEN monoD])
- hence "f (Union ?M) \<subseteq> lfp f" using mono [THEN lfp_unfold] by simp
- hence "f (Union ?M) \<in> ?M" using P_f P_Union by simp
- hence "f (Union ?M) \<subseteq> Union ?M" by (rule Union_upper)
- thus "lfp f \<subseteq> Union ?M" by (rule lfp_lowerbound)
- qed
- finally show ?thesis .
-qed
-
-
-text{*Definition forms of @{text lfp_unfold} and @{text lfp_induct},
- to control unfolding*}
-
-lemma def_lfp_unfold: "[| h==lfp(f); mono(f) |] ==> h = f(h)"
-by (auto intro!: lfp_unfold)
-
-lemma def_lfp_induct:
- "[| A == lfp(f); mono(f);
- f (inf A P) \<le> P
- |] ==> A \<le> P"
- by (blast intro: lfp_induct)
-
-lemma def_lfp_induct_set:
- "[| A == lfp(f); mono(f); a:A;
- !!x. [| x: f(A Int {x. P(x)}) |] ==> P(x)
- |] ==> P(a)"
- by (blast intro: lfp_induct_set)
-
-(*Monotonicity of lfp!*)
-lemma lfp_mono: "(!!Z. f Z \<le> g Z) ==> lfp f \<le> lfp g"
- by (rule lfp_lowerbound [THEN lfp_greatest], blast intro: order_trans)
-
-
-subsection {* Proof of Knaster-Tarski Theorem using @{term gfp} *}
-
-text{*@{term "gfp f"} is the greatest lower bound of
- the set @{term "{u. u \<le> f(u)}"} *}
-
-lemma gfp_upperbound: "X \<le> f X ==> X \<le> gfp f"
- by (auto simp add: gfp_def intro: Sup_upper)
-
-lemma gfp_least: "(!!u. u \<le> f u ==> u \<le> X) ==> gfp f \<le> X"
- by (auto simp add: gfp_def intro: Sup_least)
-
-lemma gfp_lemma2: "mono f ==> gfp f \<le> f (gfp f)"
- by (iprover intro: gfp_least order_trans monoD gfp_upperbound)
-
-lemma gfp_lemma3: "mono f ==> f (gfp f) \<le> gfp f"
- by (iprover intro: gfp_lemma2 monoD gfp_upperbound)
-
-lemma gfp_unfold: "mono f ==> gfp f = f (gfp f)"
- by (iprover intro: order_antisym gfp_lemma2 gfp_lemma3)
-
-
-subsection {* Coinduction rules for greatest fixed points *}
-
-text{*weak version*}
-lemma weak_coinduct: "[| a: X; X \<subseteq> f(X) |] ==> a : gfp(f)"
-by (rule gfp_upperbound [THEN subsetD], auto)
-
-lemma weak_coinduct_image: "!!X. [| a : X; g`X \<subseteq> f (g`X) |] ==> g a : gfp f"
-apply (erule gfp_upperbound [THEN subsetD])
-apply (erule imageI)
-done
-
-lemma coinduct_lemma:
- "[| X \<le> f (sup X (gfp f)); mono f |] ==> sup X (gfp f) \<le> f (sup X (gfp f))"
- apply (frule gfp_lemma2)
- apply (drule mono_sup)
- apply (rule le_supI)
- apply assumption
- apply (rule order_trans)
- apply (rule order_trans)
- apply assumption
- apply (rule sup_ge2)
- apply assumption
- done
-
-text{*strong version, thanks to Coen and Frost*}
-lemma coinduct_set: "[| mono(f); a: X; X \<subseteq> f(X Un gfp(f)) |] ==> a : gfp(f)"
-by (blast intro: weak_coinduct [OF _ coinduct_lemma, simplified sup_set_eq])
-
-lemma coinduct: "[| mono(f); X \<le> f (sup X (gfp f)) |] ==> X \<le> gfp(f)"
- apply (rule order_trans)
- apply (rule sup_ge1)
- apply (erule gfp_upperbound [OF coinduct_lemma])
- apply assumption
- done
-
-lemma gfp_fun_UnI2: "[| mono(f); a: gfp(f) |] ==> a: f(X Un gfp(f))"
-by (blast dest: gfp_lemma2 mono_Un)
-
-
-subsection {* Even Stronger Coinduction Rule, by Martin Coen *}
-
-text{* Weakens the condition @{term "X \<subseteq> f(X)"} to one expressed using both
- @{term lfp} and @{term gfp}*}
-
-lemma coinduct3_mono_lemma: "mono(f) ==> mono(%x. f(x) Un X Un B)"
-by (iprover intro: subset_refl monoI Un_mono monoD)
-
-lemma coinduct3_lemma:
- "[| X \<subseteq> f(lfp(%x. f(x) Un X Un gfp(f))); mono(f) |]
- ==> lfp(%x. f(x) Un X Un gfp(f)) \<subseteq> f(lfp(%x. f(x) Un X Un gfp(f)))"
-apply (rule subset_trans)
-apply (erule coinduct3_mono_lemma [THEN lfp_lemma3])
-apply (rule Un_least [THEN Un_least])
-apply (rule subset_refl, assumption)
-apply (rule gfp_unfold [THEN equalityD1, THEN subset_trans], assumption)
-apply (rule monoD, assumption)
-apply (subst coinduct3_mono_lemma [THEN lfp_unfold], auto)
-done
-
-lemma coinduct3:
- "[| mono(f); a:X; X \<subseteq> f(lfp(%x. f(x) Un X Un gfp(f))) |] ==> a : gfp(f)"
-apply (rule coinduct3_lemma [THEN [2] weak_coinduct])
-apply (rule coinduct3_mono_lemma [THEN lfp_unfold, THEN ssubst], auto)
-done
-
-
-text{*Definition forms of @{text gfp_unfold} and @{text coinduct},
- to control unfolding*}
-
-lemma def_gfp_unfold: "[| A==gfp(f); mono(f) |] ==> A = f(A)"
-by (auto intro!: gfp_unfold)
-
-lemma def_coinduct:
- "[| A==gfp(f); mono(f); X \<le> f(sup X A) |] ==> X \<le> A"
-by (iprover intro!: coinduct)
-
-lemma def_coinduct_set:
- "[| A==gfp(f); mono(f); a:X; X \<subseteq> f(X Un A) |] ==> a: A"
-by (auto intro!: coinduct_set)
-
-(*The version used in the induction/coinduction package*)
-lemma def_Collect_coinduct:
- "[| A == gfp(%w. Collect(P(w))); mono(%w. Collect(P(w)));
- a: X; !!z. z: X ==> P (X Un A) z |] ==>
- a : A"
-apply (erule def_coinduct_set, auto)
-done
-
-lemma def_coinduct3:
- "[| A==gfp(f); mono(f); a:X; X \<subseteq> f(lfp(%x. f(x) Un X Un A)) |] ==> a: A"
-by (auto intro!: coinduct3)
-
-text{*Monotonicity of @{term gfp}!*}
-lemma gfp_mono: "(!!Z. f Z \<le> g Z) ==> gfp f \<le> gfp g"
- by (rule gfp_upperbound [THEN gfp_least], blast intro: order_trans)
-
-ML
-{*
-val lfp_def = thm "lfp_def";
-val lfp_lowerbound = thm "lfp_lowerbound";
-val lfp_greatest = thm "lfp_greatest";
-val lfp_unfold = thm "lfp_unfold";
-val lfp_induct = thm "lfp_induct";
-val lfp_ordinal_induct = thm "lfp_ordinal_induct";
-val def_lfp_unfold = thm "def_lfp_unfold";
-val def_lfp_induct = thm "def_lfp_induct";
-val def_lfp_induct_set = thm "def_lfp_induct_set";
-val lfp_mono = thm "lfp_mono";
-val gfp_def = thm "gfp_def";
-val gfp_upperbound = thm "gfp_upperbound";
-val gfp_least = thm "gfp_least";
-val gfp_unfold = thm "gfp_unfold";
-val weak_coinduct = thm "weak_coinduct";
-val weak_coinduct_image = thm "weak_coinduct_image";
-val coinduct = thm "coinduct";
-val gfp_fun_UnI2 = thm "gfp_fun_UnI2";
-val coinduct3 = thm "coinduct3";
-val def_gfp_unfold = thm "def_gfp_unfold";
-val def_coinduct = thm "def_coinduct";
-val def_Collect_coinduct = thm "def_Collect_coinduct";
-val def_coinduct3 = thm "def_coinduct3";
-val gfp_mono = thm "gfp_mono";
-val le_funI = thm "le_funI";
-val le_boolI = thm "le_boolI";
-val le_boolI' = thm "le_boolI'";
-val inf_fun_eq = thm "inf_fun_eq";
-val inf_bool_eq = thm "inf_bool_eq";
-val le_funE = thm "le_funE";
-val le_funD = thm "le_funD";
-val le_boolE = thm "le_boolE";
-val le_boolD = thm "le_boolD";
-val le_bool_def = thm "le_bool_def";
-val le_fun_def = thm "le_fun_def";
-*}
-
-end