src/HOLCF/Deflation.thy
author haftmann
Fri Jul 25 12:03:32 2008 +0200 (2008-07-25)
changeset 27681 8cedebf55539
parent 27401 4edc81f93e35
child 28611 983c1855a7af
permissions -rw-r--r--
dropped locale (open)
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(*  Title:      HOLCF/Deflation.thy
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    ID:         $Id$
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    Author:     Brian Huffman
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*)
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header {* Continuous Deflations and Embedding-Projection Pairs *}
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theory Deflation
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imports Cfun
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begin
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defaultsort cpo
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subsection {* Continuous deflations *}
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locale deflation =
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  fixes d :: "'a \<rightarrow> 'a"
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  assumes idem: "\<And>x. d\<cdot>(d\<cdot>x) = d\<cdot>x"
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  assumes less: "\<And>x. d\<cdot>x \<sqsubseteq> x"
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begin
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lemma less_ID: "d \<sqsubseteq> ID"
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by (rule less_cfun_ext, simp add: less)
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text {* The set of fixed points is the same as the range. *}
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lemma fixes_eq_range: "{x. d\<cdot>x = x} = range (\<lambda>x. d\<cdot>x)"
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by (auto simp add: eq_sym_conv idem)
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lemma range_eq_fixes: "range (\<lambda>x. d\<cdot>x) = {x. d\<cdot>x = x}"
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by (auto simp add: eq_sym_conv idem)
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text {*
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  The pointwise ordering on deflation functions coincides with
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  the subset ordering of their sets of fixed-points.
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*}
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lemma lessI:
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  assumes f: "\<And>x. d\<cdot>x = x \<Longrightarrow> f\<cdot>x = x" shows "d \<sqsubseteq> f"
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proof (rule less_cfun_ext)
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  fix x
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  from less have "f\<cdot>(d\<cdot>x) \<sqsubseteq> f\<cdot>x" by (rule monofun_cfun_arg)
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  also from idem have "f\<cdot>(d\<cdot>x) = d\<cdot>x" by (rule f)
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  finally show "d\<cdot>x \<sqsubseteq> f\<cdot>x" .
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qed
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lemma lessD: "\<lbrakk>f \<sqsubseteq> d; f\<cdot>x = x\<rbrakk> \<Longrightarrow> d\<cdot>x = x"
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proof (rule antisym_less)
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  from less show "d\<cdot>x \<sqsubseteq> x" .
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next
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  assume "f \<sqsubseteq> d"
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  hence "f\<cdot>x \<sqsubseteq> d\<cdot>x" by (rule monofun_cfun_fun)
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  also assume "f\<cdot>x = x"
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  finally show "x \<sqsubseteq> d\<cdot>x" .
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qed
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end
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lemma adm_deflation: "adm (\<lambda>d. deflation d)"
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by (simp add: deflation_def)
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lemma deflation_ID: "deflation ID"
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by (simp add: deflation.intro)
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lemma deflation_UU: "deflation \<bottom>"
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by (simp add: deflation.intro)
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lemma deflation_less_iff:
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  "\<lbrakk>deflation p; deflation q\<rbrakk> \<Longrightarrow> p \<sqsubseteq> q \<longleftrightarrow> (\<forall>x. p\<cdot>x = x \<longrightarrow> q\<cdot>x = x)"
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 apply safe
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  apply (simp add: deflation.lessD)
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 apply (simp add: deflation.lessI)
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done
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text {*
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  The composition of two deflations is equal to
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  the lesser of the two (if they are comparable).
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*}
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lemma deflation_less_comp1:
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  includes deflation f
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  includes deflation g
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  shows "f \<sqsubseteq> g \<Longrightarrow> f\<cdot>(g\<cdot>x) = f\<cdot>x"
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proof (rule antisym_less)
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  from g.less show "f\<cdot>(g\<cdot>x) \<sqsubseteq> f\<cdot>x" by (rule monofun_cfun_arg)
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next
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  assume "f \<sqsubseteq> g" hence "f\<cdot>x \<sqsubseteq> g\<cdot>x" by (rule monofun_cfun_fun)
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  hence "f\<cdot>(f\<cdot>x) \<sqsubseteq> f\<cdot>(g\<cdot>x)" by (rule monofun_cfun_arg)
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  also have "f\<cdot>(f\<cdot>x) = f\<cdot>x" by (rule f.idem)
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  finally show "f\<cdot>x \<sqsubseteq> f\<cdot>(g\<cdot>x)" .
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qed
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lemma deflation_less_comp2:
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  "\<lbrakk>deflation f; deflation g; f \<sqsubseteq> g\<rbrakk> \<Longrightarrow> g\<cdot>(f\<cdot>x) = f\<cdot>x"
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by (simp only: deflation.lessD deflation.idem)
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subsection {* Deflations with finite range *}
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lemma finite_range_imp_finite_fixes:
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  "finite (range f) \<Longrightarrow> finite {x. f x = x}"
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proof -
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  have "{x. f x = x} \<subseteq> range f"
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    by (clarify, erule subst, rule rangeI)
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  moreover assume "finite (range f)"
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  ultimately show "finite {x. f x = x}"
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    by (rule finite_subset)
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qed
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locale finite_deflation = deflation +
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  assumes finite_fixes: "finite {x. d\<cdot>x = x}"
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begin
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lemma finite_range: "finite (range (\<lambda>x. d\<cdot>x))"
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by (simp add: range_eq_fixes finite_fixes)
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lemma finite_image: "finite ((\<lambda>x. d\<cdot>x) ` A)"
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by (rule finite_subset [OF image_mono [OF subset_UNIV] finite_range])
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lemma compact: "compact (d\<cdot>x)"
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proof (rule compactI2)
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  fix Y :: "nat \<Rightarrow> 'a"
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  assume Y: "chain Y"
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  have "finite_chain (\<lambda>i. d\<cdot>(Y i))"
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  proof (rule finite_range_imp_finch)
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    show "chain (\<lambda>i. d\<cdot>(Y i))"
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      using Y by simp
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    have "range (\<lambda>i. d\<cdot>(Y i)) \<subseteq> range (\<lambda>x. d\<cdot>x)"
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      by clarsimp
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    thus "finite (range (\<lambda>i. d\<cdot>(Y i)))"
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      using finite_range by (rule finite_subset)
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  qed
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  hence "\<exists>j. (\<Squnion>i. d\<cdot>(Y i)) = d\<cdot>(Y j)"
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    by (simp add: finite_chain_def maxinch_is_thelub Y)
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  then obtain j where j: "(\<Squnion>i. d\<cdot>(Y i)) = d\<cdot>(Y j)" ..
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  assume "d\<cdot>x \<sqsubseteq> (\<Squnion>i. Y i)"
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  hence "d\<cdot>(d\<cdot>x) \<sqsubseteq> d\<cdot>(\<Squnion>i. Y i)"
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    by (rule monofun_cfun_arg)
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  hence "d\<cdot>x \<sqsubseteq> (\<Squnion>i. d\<cdot>(Y i))"
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    by (simp add: contlub_cfun_arg Y idem)
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  hence "d\<cdot>x \<sqsubseteq> d\<cdot>(Y j)"
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    using j by simp
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  hence "d\<cdot>x \<sqsubseteq> Y j"
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    using less by (rule trans_less)
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  thus "\<exists>j. d\<cdot>x \<sqsubseteq> Y j" ..
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qed
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end
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subsection {* Continuous embedding-projection pairs *}
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locale ep_pair =
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  fixes e :: "'a \<rightarrow> 'b" and p :: "'b \<rightarrow> 'a"
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  assumes e_inverse [simp]: "\<And>x. p\<cdot>(e\<cdot>x) = x"
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  and e_p_less: "\<And>y. e\<cdot>(p\<cdot>y) \<sqsubseteq> y"
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begin
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lemma e_less_iff [simp]: "e\<cdot>x \<sqsubseteq> e\<cdot>y \<longleftrightarrow> x \<sqsubseteq> y"
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proof
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  assume "e\<cdot>x \<sqsubseteq> e\<cdot>y"
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  hence "p\<cdot>(e\<cdot>x) \<sqsubseteq> p\<cdot>(e\<cdot>y)" by (rule monofun_cfun_arg)
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  thus "x \<sqsubseteq> y" by simp
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next
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  assume "x \<sqsubseteq> y"
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  thus "e\<cdot>x \<sqsubseteq> e\<cdot>y" by (rule monofun_cfun_arg)
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qed
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lemma e_eq_iff [simp]: "e\<cdot>x = e\<cdot>y \<longleftrightarrow> x = y"
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unfolding po_eq_conv e_less_iff ..
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lemma p_eq_iff:
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  "\<lbrakk>e\<cdot>(p\<cdot>x) = x; e\<cdot>(p\<cdot>y) = y\<rbrakk> \<Longrightarrow> p\<cdot>x = p\<cdot>y \<longleftrightarrow> x = y"
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by (safe, erule subst, erule subst, simp)
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lemma p_inverse: "(\<exists>x. y = e\<cdot>x) = (e\<cdot>(p\<cdot>y) = y)"
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by (auto, rule exI, erule sym)
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lemma e_less_iff_less_p: "e\<cdot>x \<sqsubseteq> y \<longleftrightarrow> x \<sqsubseteq> p\<cdot>y"
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proof
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  assume "e\<cdot>x \<sqsubseteq> y"
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  then have "p\<cdot>(e\<cdot>x) \<sqsubseteq> p\<cdot>y" by (rule monofun_cfun_arg)
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  then show "x \<sqsubseteq> p\<cdot>y" by simp
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next
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  assume "x \<sqsubseteq> p\<cdot>y"
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  then have "e\<cdot>x \<sqsubseteq> e\<cdot>(p\<cdot>y)" by (rule monofun_cfun_arg)
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  then show "e\<cdot>x \<sqsubseteq> y" using e_p_less by (rule trans_less)
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qed
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lemma compact_e_rev: "compact (e\<cdot>x) \<Longrightarrow> compact x"
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proof -
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  assume "compact (e\<cdot>x)"
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  hence "adm (\<lambda>y. \<not> e\<cdot>x \<sqsubseteq> y)" by (rule compactD)
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  hence "adm (\<lambda>y. \<not> e\<cdot>x \<sqsubseteq> e\<cdot>y)" by (rule adm_subst [OF cont_Rep_CFun2])
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  hence "adm (\<lambda>y. \<not> x \<sqsubseteq> y)" by simp
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  thus "compact x" by (rule compactI)
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qed
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lemma compact_e: "compact x \<Longrightarrow> compact (e\<cdot>x)"
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proof -
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  assume "compact x"
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  hence "adm (\<lambda>y. \<not> x \<sqsubseteq> y)" by (rule compactD)
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  hence "adm (\<lambda>y. \<not> x \<sqsubseteq> p\<cdot>y)" by (rule adm_subst [OF cont_Rep_CFun2])
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  hence "adm (\<lambda>y. \<not> e\<cdot>x \<sqsubseteq> y)" by (simp add: e_less_iff_less_p)
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  thus "compact (e\<cdot>x)" by (rule compactI)
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qed
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lemma compact_e_iff: "compact (e\<cdot>x) \<longleftrightarrow> compact x"
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by (rule iffI [OF compact_e_rev compact_e])
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text {* Deflations from ep-pairs *}
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lemma deflation_e_p: "deflation (e oo p)"
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by (simp add: deflation.intro e_p_less)
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lemma deflation_e_d_p:
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  includes deflation d
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  shows "deflation (e oo d oo p)"
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proof
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  fix x :: 'b
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  show "(e oo d oo p)\<cdot>((e oo d oo p)\<cdot>x) = (e oo d oo p)\<cdot>x"
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    by (simp add: idem)
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  show "(e oo d oo p)\<cdot>x \<sqsubseteq> x"
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    by (simp add: e_less_iff_less_p less)
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qed
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lemma finite_deflation_e_d_p:
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  includes finite_deflation d
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  shows "finite_deflation (e oo d oo p)"
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proof
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  fix x :: 'b
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  show "(e oo d oo p)\<cdot>((e oo d oo p)\<cdot>x) = (e oo d oo p)\<cdot>x"
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    by (simp add: idem)
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  show "(e oo d oo p)\<cdot>x \<sqsubseteq> x"
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    by (simp add: e_less_iff_less_p less)
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  have "finite ((\<lambda>x. e\<cdot>x) ` (\<lambda>x. d\<cdot>x) ` range (\<lambda>x. p\<cdot>x))"
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    by (simp add: finite_image)
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  hence "finite (range (\<lambda>x. (e oo d oo p)\<cdot>x))"
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    by (simp add: image_image)
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  thus "finite {x. (e oo d oo p)\<cdot>x = x}"
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    by (rule finite_range_imp_finite_fixes)
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qed
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lemma deflation_p_d_e:
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  includes deflation d
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  assumes d: "\<And>x. d\<cdot>x \<sqsubseteq> e\<cdot>(p\<cdot>x)"
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  shows "deflation (p oo d oo e)"
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 apply (default, simp_all)
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  apply (rule antisym_less)
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   apply (rule monofun_cfun_arg)
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   apply (rule trans_less [OF d])
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   apply (simp add: e_p_less)
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  apply (rule monofun_cfun_arg)
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  apply (rule rev_trans_less)
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  apply (rule monofun_cfun_arg)
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  apply (rule d)
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  apply (simp add: d.idem)
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 apply (rule sq_ord_less_eq_trans)
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  apply (rule monofun_cfun_arg)
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  apply (rule d.less)
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 apply (rule e_inverse)
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done
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lemma finite_deflation_p_d_e:
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  includes finite_deflation d
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  assumes d: "\<And>x. d\<cdot>x \<sqsubseteq> e\<cdot>(p\<cdot>x)"
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  shows "finite_deflation (p oo d oo e)"
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 apply (rule finite_deflation.intro)
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  apply (rule deflation_p_d_e)
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   apply (rule `deflation d`)
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  apply (rule d)
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 apply (rule finite_deflation_axioms.intro)
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 apply (rule finite_range_imp_finite_fixes)
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 apply (simp add: range_composition [where f="\<lambda>x. p\<cdot>x"])
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 apply (simp add: range_composition [where f="\<lambda>x. d\<cdot>x"])
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 apply (simp add: d.finite_image)
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done
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end
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subsection {* Uniqueness of ep-pairs *}
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lemma ep_pair_unique_e:
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  "\<lbrakk>ep_pair e1 p; ep_pair e2 p\<rbrakk> \<Longrightarrow> e1 = e2"
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 apply (rule ext_cfun)
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 apply (rule antisym_less)
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  apply (subgoal_tac "e1\<cdot>(p\<cdot>(e2\<cdot>x)) \<sqsubseteq> e2\<cdot>x")
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   apply (simp add: ep_pair.e_inverse)
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  apply (erule ep_pair.e_p_less)
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 apply (subgoal_tac "e2\<cdot>(p\<cdot>(e1\<cdot>x)) \<sqsubseteq> e1\<cdot>x")
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  apply (simp add: ep_pair.e_inverse)
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 apply (erule ep_pair.e_p_less)
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done
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lemma ep_pair_unique_p:
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  "\<lbrakk>ep_pair e p1; ep_pair e p2\<rbrakk> \<Longrightarrow> p1 = p2"
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 apply (rule ext_cfun)
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 apply (rule antisym_less)
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  apply (subgoal_tac "p2\<cdot>(e\<cdot>(p1\<cdot>x)) \<sqsubseteq> p2\<cdot>x")
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   apply (simp add: ep_pair.e_inverse)
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  apply (rule monofun_cfun_arg)
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  apply (erule ep_pair.e_p_less)
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 apply (subgoal_tac "p1\<cdot>(e\<cdot>(p2\<cdot>x)) \<sqsubseteq> p1\<cdot>x")
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  apply (simp add: ep_pair.e_inverse)
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 apply (rule monofun_cfun_arg)
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 apply (erule ep_pair.e_p_less)
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done
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subsection {* Composing ep-pairs *}
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lemma ep_pair_ID_ID: "ep_pair ID ID"
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by default simp_all
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lemma ep_pair_comp:
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  "\<lbrakk>ep_pair e1 p1; ep_pair e2 p2\<rbrakk>
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    \<Longrightarrow> ep_pair (e2 oo e1) (p1 oo p2)"
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 apply (rule ep_pair.intro)
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  apply (simp add: ep_pair.e_inverse)
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 apply (simp, rule trans_less)
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  apply (rule monofun_cfun_arg)
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  apply (erule ep_pair.e_p_less)
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 apply (erule ep_pair.e_p_less)
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done
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locale pcpo_ep_pair = ep_pair +
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  constrains e :: "'a::pcpo \<rightarrow> 'b::pcpo"
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  constrains p :: "'b::pcpo \<rightarrow> 'a::pcpo"
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begin
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lemma e_strict [simp]: "e\<cdot>\<bottom> = \<bottom>"
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proof -
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  have "\<bottom> \<sqsubseteq> p\<cdot>\<bottom>" by (rule minimal)
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  hence "e\<cdot>\<bottom> \<sqsubseteq> e\<cdot>(p\<cdot>\<bottom>)" by (rule monofun_cfun_arg)
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  also have "e\<cdot>(p\<cdot>\<bottom>) \<sqsubseteq> \<bottom>" by (rule e_p_less)
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  finally show "e\<cdot>\<bottom> = \<bottom>" by simp
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qed
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lemma e_defined_iff [simp]: "e\<cdot>x = \<bottom> \<longleftrightarrow> x = \<bottom>"
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by (rule e_eq_iff [where y="\<bottom>", unfolded e_strict])
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lemma e_defined: "x \<noteq> \<bottom> \<Longrightarrow> e\<cdot>x \<noteq> \<bottom>"
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by simp
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lemma p_strict [simp]: "p\<cdot>\<bottom> = \<bottom>"
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by (rule e_inverse [where x="\<bottom>", unfolded e_strict])
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lemmas stricts = e_strict p_strict
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end
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end