src/HOLCF/Bifinite.thy
author huffman
Mon May 11 08:28:09 2009 -0700 (2009-05-11)
changeset 31095 b79d140f6d0b
parent 31076 99fe356cbbc2
child 31113 15cf300a742f
permissions -rw-r--r--
simplify fixrec proofs for mutually-recursive definitions; generate better fixpoint induction rules
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(*  Title:      HOLCF/Bifinite.thy
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    Author:     Brian Huffman
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*)
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header {* Bifinite domains and approximation *}
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theory Bifinite
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imports Deflation
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begin
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subsection {* Omega-profinite and bifinite domains *}
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class profinite =
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  fixes approx :: "nat \<Rightarrow> 'a \<rightarrow> 'a"
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  assumes chain_approx [simp]: "chain approx"
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  assumes lub_approx_app [simp]: "(\<Squnion>i. approx i\<cdot>x) = x"
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  assumes approx_idem: "approx i\<cdot>(approx i\<cdot>x) = approx i\<cdot>x"
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  assumes finite_fixes_approx: "finite {x. approx i\<cdot>x = x}"
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class bifinite = profinite + pcpo
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lemma approx_below: "approx i\<cdot>x \<sqsubseteq> x"
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proof -
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  have "chain (\<lambda>i. approx i\<cdot>x)" by simp
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  hence "approx i\<cdot>x \<sqsubseteq> (\<Squnion>i. approx i\<cdot>x)" by (rule is_ub_thelub)
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  thus "approx i\<cdot>x \<sqsubseteq> x" by simp
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qed
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lemma finite_deflation_approx: "finite_deflation (approx i)"
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proof
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  fix x :: 'a
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  show "approx i\<cdot>(approx i\<cdot>x) = approx i\<cdot>x"
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    by (rule approx_idem)
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  show "approx i\<cdot>x \<sqsubseteq> x"
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    by (rule approx_below)
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  show "finite {x. approx i\<cdot>x = x}"
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    by (rule finite_fixes_approx)
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qed
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interpretation approx: finite_deflation "approx i"
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by (rule finite_deflation_approx)
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lemma (in deflation) deflation: "deflation d" ..
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lemma deflation_approx: "deflation (approx i)"
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by (rule approx.deflation)
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lemma lub_approx [simp]: "(\<Squnion>i. approx i) = (\<Lambda> x. x)"
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by (rule ext_cfun, simp add: contlub_cfun_fun)
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lemma approx_strict [simp]: "approx i\<cdot>\<bottom> = \<bottom>"
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by (rule UU_I, rule approx_below)
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lemma approx_approx1:
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  "i \<le> j \<Longrightarrow> approx i\<cdot>(approx j\<cdot>x) = approx i\<cdot>x"
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apply (rule deflation_below_comp1 [OF deflation_approx deflation_approx])
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apply (erule chain_mono [OF chain_approx])
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done
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lemma approx_approx2:
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  "j \<le> i \<Longrightarrow> approx i\<cdot>(approx j\<cdot>x) = approx j\<cdot>x"
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apply (rule deflation_below_comp2 [OF deflation_approx deflation_approx])
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apply (erule chain_mono [OF chain_approx])
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done
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lemma approx_approx [simp]:
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  "approx i\<cdot>(approx j\<cdot>x) = approx (min i j)\<cdot>x"
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apply (rule_tac x=i and y=j in linorder_le_cases)
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apply (simp add: approx_approx1 min_def)
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apply (simp add: approx_approx2 min_def)
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done
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lemma finite_image_approx: "finite ((\<lambda>x. approx n\<cdot>x) ` A)"
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by (rule approx.finite_image)
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lemma finite_range_approx: "finite (range (\<lambda>x. approx i\<cdot>x))"
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by (rule approx.finite_range)
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lemma compact_approx [simp]: "compact (approx n\<cdot>x)"
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by (rule approx.compact)
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lemma profinite_compact_eq_approx: "compact x \<Longrightarrow> \<exists>i. approx i\<cdot>x = x"
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by (rule admD2, simp_all)
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lemma profinite_compact_iff: "compact x \<longleftrightarrow> (\<exists>n. approx n\<cdot>x = x)"
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 apply (rule iffI)
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  apply (erule profinite_compact_eq_approx)
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 apply (erule exE)
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 apply (erule subst)
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 apply (rule compact_approx)
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done
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lemma approx_induct:
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  assumes adm: "adm P" and P: "\<And>n x. P (approx n\<cdot>x)"
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  shows "P x"
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proof -
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  have "P (\<Squnion>n. approx n\<cdot>x)"
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    by (rule admD [OF adm], simp, simp add: P)
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  thus "P x" by simp
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qed
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lemma profinite_below_ext: "(\<And>i. approx i\<cdot>x \<sqsubseteq> approx i\<cdot>y) \<Longrightarrow> x \<sqsubseteq> y"
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apply (subgoal_tac "(\<Squnion>i. approx i\<cdot>x) \<sqsubseteq> (\<Squnion>i. approx i\<cdot>y)", simp)
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apply (rule lub_mono, simp, simp, simp)
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done
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subsection {* Instance for continuous function space *}
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lemma finite_range_cfun_lemma:
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  assumes a: "finite (range (\<lambda>x. a\<cdot>x))"
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  assumes b: "finite (range (\<lambda>y. b\<cdot>y))"
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  shows "finite (range (\<lambda>f. \<Lambda> x. b\<cdot>(f\<cdot>(a\<cdot>x))))"  (is "finite (range ?h)")
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proof (rule finite_imageD)
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  let ?f = "\<lambda>g. range (\<lambda>x. (a\<cdot>x, g\<cdot>x))"
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  show "finite (?f ` range ?h)"
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  proof (rule finite_subset)
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    let ?B = "Pow (range (\<lambda>x. a\<cdot>x) \<times> range (\<lambda>y. b\<cdot>y))"
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    show "?f ` range ?h \<subseteq> ?B"
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      by clarsimp
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    show "finite ?B"
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      by (simp add: a b)
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  qed
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  show "inj_on ?f (range ?h)"
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  proof (rule inj_onI, rule ext_cfun, clarsimp)
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    fix x f g
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    assume "range (\<lambda>x. (a\<cdot>x, b\<cdot>(f\<cdot>(a\<cdot>x)))) = range (\<lambda>x. (a\<cdot>x, b\<cdot>(g\<cdot>(a\<cdot>x))))"
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    hence "range (\<lambda>x. (a\<cdot>x, b\<cdot>(f\<cdot>(a\<cdot>x)))) \<subseteq> range (\<lambda>x. (a\<cdot>x, b\<cdot>(g\<cdot>(a\<cdot>x))))"
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      by (rule equalityD1)
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    hence "(a\<cdot>x, b\<cdot>(f\<cdot>(a\<cdot>x))) \<in> range (\<lambda>x. (a\<cdot>x, b\<cdot>(g\<cdot>(a\<cdot>x))))"
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      by (simp add: subset_eq)
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    then obtain y where "(a\<cdot>x, b\<cdot>(f\<cdot>(a\<cdot>x))) = (a\<cdot>y, b\<cdot>(g\<cdot>(a\<cdot>y)))"
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      by (rule rangeE)
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    thus "b\<cdot>(f\<cdot>(a\<cdot>x)) = b\<cdot>(g\<cdot>(a\<cdot>x))"
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      by clarsimp
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  qed
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qed
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instantiation "->" :: (profinite, profinite) profinite
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begin
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definition
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  approx_cfun_def:
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    "approx = (\<lambda>n. \<Lambda> f x. approx n\<cdot>(f\<cdot>(approx n\<cdot>x)))"
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instance proof
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  show "chain (approx :: nat \<Rightarrow> ('a \<rightarrow> 'b) \<rightarrow> ('a \<rightarrow> 'b))"
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    unfolding approx_cfun_def by simp
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next
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  fix x :: "'a \<rightarrow> 'b"
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  show "(\<Squnion>i. approx i\<cdot>x) = x"
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    unfolding approx_cfun_def
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    by (simp add: lub_distribs eta_cfun)
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next
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  fix i :: nat and x :: "'a \<rightarrow> 'b"
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  show "approx i\<cdot>(approx i\<cdot>x) = approx i\<cdot>x"
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    unfolding approx_cfun_def by simp
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next
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  fix i :: nat
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  show "finite {x::'a \<rightarrow> 'b. approx i\<cdot>x = x}"
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    apply (rule finite_range_imp_finite_fixes)
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    apply (simp add: approx_cfun_def)
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    apply (intro finite_range_cfun_lemma finite_range_approx)
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    done
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qed
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end
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instance "->" :: (profinite, bifinite) bifinite ..
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lemma approx_cfun: "approx n\<cdot>f\<cdot>x = approx n\<cdot>(f\<cdot>(approx n\<cdot>x))"
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by (simp add: approx_cfun_def)
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end