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Datei: Hilbert_Choice.thy Sprache: Isabelle

Original von: Isabelle^©

(*  Title:      HOL/Hilbert_Choice.thy
    Author:     Lawrence C Paulson, Tobias Nipkow
    Author:     Viorel Preoteasa (Results about complete distributive lattices)
    Copyright   2001  University of Cambridge
*)

section \<open>Hilbert's Epsilon-Operator and the Axiom of Choice\<close>

theory Hilbert_Choice
  imports Wellfounded
  keywords "specification" :: thy_goal_defn
begin

subsection \<open>Hilbert's epsilon\<close>

axiomatization Eps :: "('a \ bool) \ 'a"
  where someI: "P x \ P (Eps P)"

syntax (epsilon)
  "_Eps" :: "pttrn \ bool \ 'a" ("(3\_./ _)" [0, 10] 10)
syntax (input)
  "_Eps" :: "pttrn \ bool \ 'a" ("(3@ _./ _)" [0, 10] 10)
syntax
  "_Eps" :: "pttrn \ bool \ 'a" ("(3SOME _./ _)" [0, 10] 10)
translations
  "SOME x. P" \<rightleftharpoons> "CONST Eps (\<lambda>x. P)"

print_translation \<open>
  [(\<^const_syntax>\<open>Eps\<close>, fn _ => fn [Abs abs] =>
      let val (x, t) = Syntax_Trans.atomic_abs_tr' abs
      in Syntax.const \<^syntax_const>\<open>_Eps\<close> $ x $ t end)]
\<close> \<comment> \<open>to avoid eta-contraction of body\<close>

definition inv_into :: "'a set \ ('a \ 'b) \ ('b \ 'a)" where
"inv_into A f = (\x. SOME y. y \ A \ f y = x)"

lemma inv_into_def2: "inv_into A f x = (SOME y. y \ A \ f y = x)"
by(simp add: inv_into_def)

abbreviation inv :: "('a \ 'b) \ ('b \ 'a)" where
"inv \ inv_into UNIV"

subsection \<open>Hilbert's Epsilon-operator\<close>

lemma Eps_cong:
  assumes "\x. P x = Q x"
  shows "Eps P = Eps Q"
  using ext[of P Q, OF assms] by simp

text \<open>
  Easier to use than \<open>someI\<close> if the witness comes from an
  existential formula.
\<close>
lemma someI_ex [elim?]: "\x. P x \ P (SOME x. P x)"
  by (elim exE someI)

lemma some_eq_imp:
  assumes "Eps P = a" "P b" shows "P a"
  using assms someI_ex by force

text \<open>
  Easier to use than \<open>someI\<close> because the conclusion has only one
  occurrence of \<^term>\<open>P\<close>.
\<close>
lemma someI2: "P a \ (\x. P x \ Q x) \ Q (SOME x. P x)"
  by (blast intro: someI)

text \<open>
  Easier to use than \<open>someI2\<close> if the witness comes from an
  existential formula.
\<close>
lemma someI2_ex: "\a. P a \ (\x. P x \ Q x) \ Q (SOME x. P x)"
  by (blast intro: someI2)

lemma someI2_bex: "\a\A. P a \ (\x. x \ A \ P x \ Q x) \ Q (SOME x. x \ A \ P x)"
  by (blast intro: someI2)

lemma some_equality [intro]: "P a \ (\x. P x \ x = a) \ (SOME x. P x) = a"
  by (blast intro: someI2)

lemma some1_equality: "\!x. P x \ P a \ (SOME x. P x) = a"
  by blast

lemma some_eq_ex: "P (SOME x. P x) \ (\x. P x)"
  by (blast intro: someI)

lemma some_in_eq: "(SOME x. x \ A) \ A \ A \ {}"
  unfolding ex_in_conv[symmetric] by (rule some_eq_ex)

lemma some_eq_trivial [simp]: "(SOME y. y = x) = x"
  by (rule some_equality) (rule refl)

lemma some_sym_eq_trivial [simp]: "(SOME y. x = y) = x"
  by (iprover intro: some_equality)

subsection \<open>Axiom of Choice, Proved Using the Description Operator\<close>

lemma choice: "\x. \y. Q x y \ \f. \x. Q x (f x)"
  by (fast elim: someI)

lemma bchoice: "\x\S. \y. Q x y \ \f. \x\S. Q x (f x)"
  by (fast elim: someI)

lemma choice_iff: "(\x. \y. Q x y) \ (\f. \x. Q x (f x))"
  by (fast elim: someI)

lemma choice_iff': "(\x. P x \ (\y. Q x y)) \ (\f. \x. P x \ Q x (f x))"
  by (fast elim: someI)

lemma bchoice_iff: "(\x\S. \y. Q x y) \ (\f. \x\S. Q x (f x))"
  by (fast elim: someI)

lemma bchoice_iff': "(\x\S. P x \ (\y. Q x y)) \ (\f. \x\S. P x \ Q x (f x))"
  by (fast elim: someI)

lemma dependent_nat_choice:
  assumes 1: "\x. P 0 x"
    and 2: "\x n. P n x \ \y. P (Suc n) y \ Q n x y"
  shows "\f. \n. P n (f n) \ Q n (f n) (f (Suc n))"
proof (intro exI allI conjI)
  fix n
  define f where "f = rec_nat (SOME x. P 0 x) (\n x. SOME y. P (Suc n) y \ Q n x y)"
  then have "P 0 (f 0)" "\n. P n (f n) \ P (Suc n) (f (Suc n)) \ Q n (f n) (f (Suc n))"
    using someI_ex[OF 1] someI_ex[OF 2] by simp_all
  then show "P n (f n)" "Q n (f n) (f (Suc n))"
    by (induct n) auto
qed

lemma finite_subset_Union:
  assumes "finite A" "A \ \\"
  obtains \<F> where "finite \<F>" "\<F> \<subseteq> \<B>" "A \<subseteq> \<Union>\<F>"
proof -
  have "\x\A. \B\\. x\B"
    using assms by blast
  then obtain f where f: "\x. x \ A \ f x \ \ \ x \ f x"
    by (auto simp add: bchoice_iff Bex_def)
  show thesis
  proof
    show "finite (f ` A)"
      using assms by auto
  qed (use f in auto)
qed

subsection \<open>Function Inverse\<close>

lemma inv_def: "inv f = (\y. SOME x. f x = y)"
  by (simp add: inv_into_def)

lemma inv_into_into: "x \ f ` A \ inv_into A f x \ A"
  by (simp add: inv_into_def) (fast intro: someI2)

lemma inv_identity [simp]: "inv (\a. a) = (\a. a)"
  by (simp add: inv_def)

lemma inv_id [simp]: "inv id = id"
  by (simp add: id_def)

lemma inv_into_f_f [simp]: "inj_on f A \ x \ A \ inv_into A f (f x) = x"
  by (simp add: inv_into_def inj_on_def) (blast intro: someI2)

lemma inv_f_f: "inj f \ inv f (f x) = x"
  by simp

lemma f_inv_into_f: "y \ f`A \ f (inv_into A f y) = y"
  by (simp add: inv_into_def) (fast intro: someI2)

lemma inv_into_f_eq: "inj_on f A \ x \ A \ f x = y \ inv_into A f y = x"
  by (erule subst) (fast intro: inv_into_f_f)

lemma inv_f_eq: "inj f \ f x = y \ inv f y = x"
  by (simp add:inv_into_f_eq)

lemma inj_imp_inv_eq: "inj f \ \x. f (g x) = x \ inv f = g"
  by (blast intro: inv_into_f_eq)

text \<open>But is it useful?\<close>
lemma inj_transfer:
  assumes inj: "inj f"
    and minor: "\y. y \ range f \ P (inv f y)"
  shows "P x"
proof -
  have "f x \ range f" by auto
  then have "P(inv f (f x))" by (rule minor)
  then show "P x" by (simp add: inv_into_f_f [OF inj])
qed

lemma inj_iff: "inj f \ inv f \ f = id"
  by (simp add: o_def fun_eq_iff) (blast intro: inj_on_inverseI inv_into_f_f)

lemma inv_o_cancel[simp]: "inj f \ inv f \ f = id"
  by (simp add: inj_iff)

lemma o_inv_o_cancel[simp]: "inj f \ g \ inv f \ f = g"
  by (simp add: comp_assoc)

lemma inv_into_image_cancel[simp]: "inj_on f A \ S \ A \ inv_into A f ` f ` S = S"
  by (fastforce simp: image_def)

lemma inj_imp_surj_inv: "inj f \ surj (inv f)"
  by (blast intro!: surjI inv_into_f_f)

lemma surj_f_inv_f: "surj f \ f (inv f y) = y"
  by (simp add: f_inv_into_f)

lemma bij_inv_eq_iff: "bij p \ x = inv p y \ p x = y"
  using surj_f_inv_f[of p] by (auto simp add: bij_def)

lemma inv_into_injective:
  assumes eq: "inv_into A f x = inv_into A f y"
    and x: "x \ f`A"
    and y: "y \ f`A"
  shows "x = y"
proof -
  from eq have "f (inv_into A f x) = f (inv_into A f y)"
    by simp
  with x y show ?thesis
    by (simp add: f_inv_into_f)
qed

lemma inj_on_inv_into: "B \ f`A \ inj_on (inv_into A f) B"
  by (blast intro: inj_onI dest: inv_into_injective injD)

lemma inj_imp_bij_betw_inv: "inj f \ bij_betw (inv f) (f ` M) M"
  by (simp add: bij_betw_def image_subsetI inj_on_inv_into)

lemma bij_betw_inv_into: "bij_betw f A B \ bij_betw (inv_into A f) B A"
  by (auto simp add: bij_betw_def inj_on_inv_into)

lemma surj_imp_inj_inv: "surj f \ inj (inv f)"
  by (simp add: inj_on_inv_into)

lemma surj_iff: "surj f \ f \ inv f = id"
  by (auto intro!: surjI simp: surj_f_inv_f fun_eq_iff[where 'b='a])

lemma surj_iff_all: "surj f \ (\x. f (inv f x) = x)"
  by (simp add: o_def surj_iff fun_eq_iff)

lemma surj_imp_inv_eq:
  assumes "surj f" and gf: "\x. g (f x) = x"
  shows "inv f = g"
proof (rule ext)
  fix x
  have "g (f (inv f x)) = inv f x"
    by (rule gf)
  then show "inv f x = g x"
    by (simp add: surj_f_inv_f \<open>surj f\<close>)
qed

lemma bij_imp_bij_inv: "bij f \ bij (inv f)"
  by (simp add: bij_def inj_imp_surj_inv surj_imp_inj_inv)

lemma inv_equality: "(\x. g (f x) = x) \ (\y. f (g y) = y) \ inv f = g"
  by (rule ext) (auto simp add: inv_into_def)

lemma inv_inv_eq: "bij f \ inv (inv f) = f"
  by (rule inv_equality) (auto simp add: bij_def surj_f_inv_f)

text \<open>
  \<open>bij (inv f)\<close> implies little about \<open>f\<close>. Consider \<open>f :: bool \<Rightarrow> bool\<close> such
  that \<open>f True = f False = True\<close>. Then it ia consistent with axiom \<open>someI\<close>
  that \<open>inv f\<close> could be any function at all, including the identity function.
  If \<open>inv f = id\<close> then \<open>inv f\<close> is a bijection, but \<open>inj f\<close>, \<open>surj f\<close> and \<open>inv
  (inv f) = f\<close> all fail.
\<close>

lemma inv_into_comp:
  "inj_on f (g ` A) \ inj_on g A \ x \ f ` g ` A \
    inv_into A (f \<circ> g) x = (inv_into A g \<circ> inv_into (g ` A) f) x"
  by (auto simp: f_inv_into_f inv_into_into intro: inv_into_f_eq comp_inj_on)

lemma o_inv_distrib: "bij f \ bij g \ inv (f \ g) = inv g \ inv f"
  by (rule inv_equality) (auto simp add: bij_def surj_f_inv_f)

lemma image_f_inv_f: "surj f \ f ` (inv f ` A) = A"
  by (simp add: surj_f_inv_f image_comp comp_def)

lemma image_inv_f_f: "inj f \ inv f ` (f ` A) = A"
  by simp

lemma bij_image_Collect_eq:
  assumes "bij f"
  shows "f ` Collect P = {y. P (inv f y)}"
proof
  show "f ` Collect P \ {y. P (inv f y)}"
    using assms by (force simp add: bij_is_inj)
  show "{y. P (inv f y)} \ f ` Collect P"
    using assms by (blast intro: bij_is_surj [THEN surj_f_inv_f, symmetric])
qed

lemma bij_vimage_eq_inv_image:
  assumes "bij f"
  shows "f -` A = inv f ` A"
proof
  show "f -` A \ inv f ` A"
    using assms by (blast intro: bij_is_inj [THEN inv_into_f_f, symmetric])
  show "inv f ` A \ f -` A"
    using assms by (auto simp add: bij_is_surj [THEN surj_f_inv_f])
qed

lemma inv_fn_o_fn_is_id:
  fixes f::"'a \ 'a"
  assumes "bij f"
  shows "((inv f)^^n) o (f^^n) = (\x. x)"
proof -
  have "((inv f)^^n)((f^^n) x) = x" for x n
  proof (induction n)
    case (Suc n)
    have *: "(inv f) (f y) = y" for y
      by (simp add: assms bij_is_inj)
    have "(inv f ^^ Suc n) ((f ^^ Suc n) x) = (inv f^^n) (inv f (f ((f^^n) x)))"
      by (simp add: funpow_swap1)
    also have "... = (inv f^^n) ((f^^n) x)"
      using * by auto
    also have "... = x" using Suc.IH by auto
    finally show ?case by simp
  qed (auto)
  then show ?thesis unfolding o_def by blast
qed

lemma fn_o_inv_fn_is_id:
  fixes f::"'a \ 'a"
  assumes "bij f"
  shows "(f^^n) o ((inv f)^^n) = (\x. x)"
proof -
  have "(f^^n) (((inv f)^^n) x) = x" for x n
  proof (induction n)
    case (Suc n)
    have *: "f(inv f y) = y" for y
      using bij_inv_eq_iff[OF assms] by auto
    have "(f ^^ Suc n) ((inv f ^^ Suc n) x) = (f^^n) (f (inv f ((inv f^^n) x)))"
      by (simp add: funpow_swap1)
    also have "... = (f^^n) ((inv f^^n) x)"
      using * by auto
    also have "... = x" using Suc.IH by auto
    finally show ?case by simp
  qed (auto)
  then show ?thesis unfolding o_def by blast
qed

lemma inv_fn:
  fixes f::"'a \ 'a"
  assumes "bij f"
  shows "inv (f^^n) = ((inv f)^^n)"
proof -
  have "inv (f^^n) x = ((inv f)^^n) x" for x
  proof (rule inv_into_f_eq)
    show "inj (f ^^ n)"
      by (simp add: inj_fn[OF bij_is_inj [OF assms]])
    show "(f ^^ n) ((inv f ^^ n) x) = x"
      using fn_o_inv_fn_is_id[OF assms, THEN fun_cong] by force
  qed auto
  then show ?thesis by auto
qed

lemma mono_inv:
  fixes f::"'a::linorder \ 'b::linorder"
  assumes "mono f" "bij f"
  shows "mono (inv f)"
proof
  fix x y::'b assume "x \ y"
  from \<open>bij f\<close> obtain a b where x: "x = f a" and y: "y = f b" by(fastforce simp: bij_def surj_def)
  show "inv f x \ inv f y"
  proof (rule le_cases)
    assume "a \ b"
    thus ?thesis using  \<open>bij f\<close> x y by(simp add: bij_def inv_f_f)
  next
    assume "b \ a"
    hence "f b \ f a" by(rule monoD[OF \mono f\])
    hence "y \ x" using x y by simp
    hence "x = y" using \<open>x \<le> y\<close> by auto
    thus ?thesis by simp
  qed
qed

lemma strict_mono_inv_on_range:
  fixes f :: "'a::linorder \ 'b::order"
  assumes "strict_mono f"
  shows "strict_mono_on (inv f) (range f)"
proof (clarsimp simp: strict_mono_on_def)
  fix x y
  assume "f x < f y"
  then show "inv f (f x) < inv f (f y)"
    using assms strict_mono_imp_inj_on strict_mono_less by fastforce
qed

lemma mono_bij_Inf:
  fixes f :: "'a::complete_linorder \ 'b::complete_linorder"
  assumes "mono f" "bij f"
  shows "f (Inf A) = Inf (f`A)"
proof -
  have "surj f" using \<open>bij f\<close> by (auto simp: bij_betw_def)
  have *: "(inv f) (Inf (f`A)) \ Inf ((inv f)`(f`A))"
    using mono_Inf[OF mono_inv[OF assms], of "f`A"] by simp
  have "Inf (f`A) \ f (Inf ((inv f)`(f`A)))"
    using monoD[OF \<open>mono f\<close> *] by(simp add: surj_f_inv_f[OF \<open>surj f\<close>])
  also have "... = f(Inf A)"
    using assms by (simp add: bij_is_inj)
  finally show ?thesis using mono_Inf[OF assms(1), of A] by auto
qed

lemma finite_fun_UNIVD1:
  assumes fin: "finite (UNIV :: ('a \ 'b) set)"
    and card: "card (UNIV :: 'b set) \ Suc 0"
  shows "finite (UNIV :: 'a set)"
proof -
  let ?UNIV_b = "UNIV :: 'b set"
  from fin have "finite ?UNIV_b"
    by (rule finite_fun_UNIVD2)
  with card have "card ?UNIV_b \ Suc (Suc 0)"
    by (cases "card ?UNIV_b") (auto simp: card_eq_0_iff)
  then have "card ?UNIV_b = Suc (Suc (card ?UNIV_b - Suc (Suc 0)))"
    by simp
  then obtain b1 b2 :: 'b where b1b2: "b1 \ b2"
    by (auto simp: card_Suc_eq)
  from fin have fin': "finite (range (\f :: 'a \ 'b. inv f b1))"
    by (rule finite_imageI)
  have "UNIV = range (\f :: 'a \ 'b. inv f b1)"
  proof (rule UNIV_eq_I)
    fix x :: 'a
    from b1b2 have "x = inv (\y. if y = x then b1 else b2) b1"
      by (simp add: inv_into_def)
    then show "x \ range (\f::'a \ 'b. inv f b1)"
      by blast
  qed
  with fin' show ?thesis
    by simp
qed

text \<open>
  Every infinite set contains a countable subset. More precisely we
  show that a set \<open>S\<close> is infinite if and only if there exists an
  injective function from the naturals into \<open>S\<close>.

  The ``only if'' direction is harder because it requires the
  construction of a sequence of pairwise different elements of an
  infinite set \<open>S\<close>. The idea is to construct a sequence of
  non-empty and infinite subsets of \<open>S\<close> obtained by successively
  removing elements of \<open>S\<close>.
\<close>

lemma infinite_countable_subset:
  assumes inf: "\ finite S"
  shows "\f::nat \ 'a. inj f \ range f \ S"
  \<comment> \<open>Courtesy of Stephan Merz\<close>
proof -
  define Sseq where "Sseq = rec_nat S (\n T. T - {SOME e. e \ T})"
  define pick where "pick n = (SOME e. e \ Sseq n)" for n
  have *: "Sseq n \ S" "\ finite (Sseq n)" for n
    by (induct n) (auto simp: Sseq_def inf)
  then have **: "\n. pick n \ Sseq n"
    unfolding pick_def by (subst (asm) finite.simps) (auto simp add: ex_in_conv intro: someI_ex)
  with * have "range pick \ S" by auto
  moreover have "pick n \ pick (n + Suc m)" for m n
  proof -
    have "pick n \ Sseq (n + Suc m)"
      by (induct m) (auto simp add: Sseq_def pick_def)
    with ** show ?thesis by auto
  qed
  then have "inj pick"
    by (intro linorder_injI) (auto simp add: less_iff_Suc_add)
  ultimately show ?thesis by blast
qed

lemma infinite_iff_countable_subset: "\ finite S \ (\f::nat \ 'a. inj f \ range f \ S)"
  \<comment> \<open>Courtesy of Stephan Merz\<close>
  using finite_imageD finite_subset infinite_UNIV_char_0 infinite_countable_subset by auto

lemma image_inv_into_cancel:
  assumes surj: "f`A = A'"
    and sub: "B' \ A'"
  shows "f `((inv_into A f)`B') = B'"
  using assms
proof (auto simp: f_inv_into_f)
  let ?f' = "inv_into A f"
  fix a'
  assume *: "a' \ B'"
  with sub have "a' \ A'" by auto
  with surj have "a' = f (?f' a')"
    by (auto simp: f_inv_into_f)
  with * show "a' \ f ` (?f' ` B')" by blast
qed

lemma inv_into_inv_into_eq:
  assumes "bij_betw f A A'"
    and a: "a \ A"
  shows "inv_into A' (inv_into A f) a = f a"
proof -
  let ?f' = "inv_into A f"
  let ?f'' = "inv_into A' ?f'"
  from assms have *: "bij_betw ?f' A' A"
    by (auto simp: bij_betw_inv_into)
  with a obtain a' where a': "a' \ A'" "?f' a' = a"
    unfolding bij_betw_def by force
  with a * have "?f'' a = a'"
    by (auto simp: f_inv_into_f bij_betw_def)
  moreover from assms a' have "f a = a'"
    by (auto simp: bij_betw_def)
  ultimately show "?f'' a = f a" by simp
qed

lemma inj_on_iff_surj:
  assumes "A \ {}"
  shows "(\f. inj_on f A \ f ` A \ A') \ (\g. g ` A' = A)"
proof safe
  fix f
  assume inj: "inj_on f A" and incl: "f ` A \ A'"
  let ?phi = "\a' a. a \ A \ f a = a'"
  let ?csi = "\a. a \ A"
  let ?g = "\a'. if a' \ f ` A then (SOME a. ?phi a' a) else (SOME a. ?csi a)"
  have "?g ` A' = A"
  proof
    show "?g ` A' \ A"
    proof clarify
      fix a'
      assume *: "a' \ A'"
      show "?g a' \ A"
      proof (cases "a' \ f ` A")
        case True
        then obtain a where "?phi a' a" by blast
        then have "?phi a' (SOME a. ?phi a' a)"
          using someI[of "?phi a'" a] by blast
        with True show ?thesis by auto
      next
        case False
        with assms have "?csi (SOME a. ?csi a)"
          using someI_ex[of ?csi] by blast
        with False show ?thesis by auto
      qed
    qed
  next
    show "A \ ?g ` A'"
    proof -
      have "?g (f a) = a \ f a \ A'" if a: "a \ A" for a
      proof -
        let ?b = "SOME aa. ?phi (f a) aa"
        from a have "?phi (f a) a" by auto
        then have *: "?phi (f a) ?b"
          using someI[of "?phi(f a)" a] by blast
        then have "?g (f a) = ?b" using a by auto
        moreover from inj * a have "a = ?b"
          by (auto simp add: inj_on_def)
        ultimately have "?g(f a) = a" by simp
        with incl a show ?thesis by auto
      qed
      then show ?thesis by force
    qed
  qed
  then show "\g. g ` A' = A" by blast
next
  fix g
  let ?f = "inv_into A' g"
  have "inj_on ?f (g ` A')"
    by (auto simp: inj_on_inv_into)
  moreover have "?f (g a') \ A'" if a': "a' \ A'" for a'
  proof -
    let ?phi = "\ b'. b' \ A' \ g b' = g a'"
    from a' have "?phi a'" by auto
    then have "?phi (SOME b'. ?phi b')"
      using someI[of ?phi] by blast
    then show ?thesis by (auto simp: inv_into_def)
  qed
  ultimately show "\f. inj_on f (g ` A') \ f ` g ` A' \ A'"
    by auto
qed

lemma Ex_inj_on_UNION_Sigma:
  "\f. (inj_on f (\i \ I. A i) \ f ` (\i \ I. A i) \ (SIGMA i : I. A i))"
proof
  let ?phi = "\a i. i \ I \ a \ A i"
  let ?sm = "\a. SOME i. ?phi a i"
  let ?f = "\a. (?sm a, a)"
  have "inj_on ?f (\i \ I. A i)"
    by (auto simp: inj_on_def)
  moreover
  have "?sm a \ I \ a \ A(?sm a)" if "i \ I" and "a \ A i" for i a
    using that someI[of "?phi a" i] by auto
  then have "?f ` (\i \ I. A i) \ (SIGMA i : I. A i)"
    by auto
  ultimately show "inj_on ?f (\i \ I. A i) \ ?f ` (\i \ I. A i) \ (SIGMA i : I. A i)"
    by auto
qed

lemma inv_unique_comp:
  assumes fg: "f \ g = id"
    and gf: "g \ f = id"
  shows "inv f = g"
  using fg gf inv_equality[of g f] by (auto simp add: fun_eq_iff)

lemma subset_image_inj:
  "S \ f ` T \ (\U. U \ T \ inj_on f U \ S = f ` U)"
proof safe
  show "\U\T. inj_on f U \ S = f ` U"
    if "S \ f ` T"
  proof -
    from that [unfolded subset_image_iff subset_iff]
    obtain g where g: "\x. x \ S \ g x \ T \ x = f (g x)"
      by (auto simp add: image_iff Bex_def choice_iff')
    show ?thesis
    proof (intro exI conjI)
      show "g ` S \ T"
        by (simp add: g image_subsetI)
      show "inj_on f (g ` S)"
        using g by (auto simp: inj_on_def)
      show "S = f ` (g ` S)"
        using g image_subset_iff by auto
    qed
  qed
qed blast

subsection \<open>Other Consequences of Hilbert's Epsilon\<close>

text \<open>Hilbert's Epsilon and the \<^term>\<open>split\<close> Operator\<close>

text \<open>Looping simprule!\<close>
lemma split_paired_Eps: "(SOME x. P x) = (SOME (a, b). P (a, b))"
  by simp

lemma Eps_case_prod: "Eps (case_prod P) = (SOME xy. P (fst xy) (snd xy))"
  by (simp add: split_def)

lemma Eps_case_prod_eq [simp]: "(SOME (x', y'). x = x' \ y = y') = (x, y)"
  by blast

text \<open>A relation is wellfounded iff it has no infinite descending chain.\<close>
lemma wf_iff_no_infinite_down_chain: "wf r \ (\f. \i. (f (Suc i), f i) \ r)"
  (is "_ \ \ ?ex")
proof
  assume "wf r"
  show "\ ?ex"
  proof
    assume ?ex
    then obtain f where f: "(f (Suc i), f i) \ r" for i
      by blast
    from \<open>wf r\<close> have minimal: "x \<in> Q \<Longrightarrow> \<exists>z\<in>Q. \<forall>y. (y, z) \<in> r \<longrightarrow> y \<notin> Q" for x Q
      by (auto simp: wf_eq_minimal)
    let ?Q = "{w. \i. w = f i}"
    fix n
    have "f n \ ?Q" by blast
    from minimal [OF this] obtain j where "(y, f j) \ r \ y \ ?Q" for y by blast
    with this [OF \<open>(f (Suc j), f j) \<in> r\<close>] have "f (Suc j) \<notin> ?Q" by simp
    then show False by blast
  qed
next
  assume "\ ?ex"
  then show "wf r"
  proof (rule contrapos_np)
    assume "\ wf r"
    then obtain Q x where x: "x \ Q" and rec: "z \ Q \ \y. (y, z) \ r \ y \ Q" for z
      by (auto simp add: wf_eq_minimal)
    obtain descend :: "nat \ 'a"
      where descend_0: "descend 0 = x"
        and descend_Suc: "descend (Suc n) = (SOME y. y \ Q \ (y, descend n) \ r)" for n
      by (rule that [of "rec_nat x (\_ rec. (SOME y. y \ Q \ (y, rec) \ r))"]) simp_all
    have descend_Q: "descend n \ Q" for n
    proof (induct n)
      case 0
      with x show ?case by (simp only: descend_0)
    next
      case Suc
      then show ?case by (simp only: descend_Suc) (rule someI2_ex; use rec in blast)
    qed
    have "(descend (Suc i), descend i) \ r" for i
      by (simp only: descend_Suc) (rule someI2_ex; use descend_Q rec in blast)
    then show "\f. \i. (f (Suc i), f i) \ r" by blast
  qed
qed

lemma wf_no_infinite_down_chainE:
  assumes "wf r"
  obtains k where "(f (Suc k), f k) \ r"
  using assms wf_iff_no_infinite_down_chain[of r] by blast

text \<open>A dynamically-scoped fact for TFL\<close>
lemma tfl_some: "\P x. P x \ P (Eps P)"
  by (blast intro: someI)

subsection \<open>An aside: bounded accessible part\<close>

text \<open>Finite monotone eventually stable sequences\<close>

lemma finite_mono_remains_stable_implies_strict_prefix:
  fixes f :: "nat \ 'a::order"
  assumes S: "finite (range f)" "mono f"
    and eq: "\n. f n = f (Suc n) \ f (Suc n) = f (Suc (Suc n))"
  shows "\N. (\n\N. \m\N. m < n \ f m < f n) \ (\n\N. f N = f n)"
  using assms
proof -
  have "\n. f n = f (Suc n)"
  proof (rule ccontr)
    assume "\ ?thesis"
    then have "\n. f n \ f (Suc n)" by auto
    with \<open>mono f\<close> have "\<And>n. f n < f (Suc n)"
      by (auto simp: le_less mono_iff_le_Suc)
    with lift_Suc_mono_less_iff[of f] have *: "\n m. n < m \ f n < f m"
      by auto
    have "inj f"
    proof (intro injI)
      fix x y
      assume "f x = f y"
      then show "x = y"
        by (cases x y rule: linorder_cases) (auto dest: *)
    qed
    with \<open>finite (range f)\<close> have "finite (UNIV::nat set)"
      by (rule finite_imageD)
    then show False by simp
  qed
  then obtain n where n: "f n = f (Suc n)" ..
  define N where "N = (LEAST n. f n = f (Suc n))"
  have N: "f N = f (Suc N)"
    unfolding N_def using n by (rule LeastI)
  show ?thesis
  proof (intro exI[of _ N] conjI allI impI)
    fix n
    assume "N \ n"
    then have "\m. N \ m \ m \ n \ f m = f N"
    proof (induct rule: dec_induct)
      case base
      then show ?case by simp
    next
      case (step n)
      then show ?case
        using eq [rule_format, of "n - 1"] N
        by (cases n) (auto simp add: le_Suc_eq)
    qed
    from this[of n] \<open>N \<le> n\<close> show "f N = f n" by auto
  next
    fix n m :: nat
    assume "m < n" "n \ N"
    then show "f m < f n"
    proof (induct rule: less_Suc_induct)
      case (1 i)
      then have "i < N" by simp
      then have "f i \ f (Suc i)"
        unfolding N_def by (rule not_less_Least)
      with \<open>mono f\<close> show ?case by (simp add: mono_iff_le_Suc less_le)
    next
      case 2
      then show ?case by simp
    qed
  qed
qed

lemma finite_mono_strict_prefix_implies_finite_fixpoint:
  fixes f :: "nat \ 'a set"
  assumes S: "\i. f i \ S" "finite S"
    and ex: "\N. (\n\N. \m\N. m < n \ f m \ f n) \ (\n\N. f N = f n)"
  shows "f (card S) = (\n. f n)"
proof -
  from ex obtain N where inj: "\n m. n \ N \ m \ N \ m < n \ f m \ f n"
    and eq: "\n\N. f N = f n"
    by atomize auto
  have "i \ N \ i \ card (f i)" for i
  proof (induct i)
    case 0
    then show ?case by simp
  next
    case (Suc i)
    with inj [of "Suc i" i] have "(f i) \ (f (Suc i))" by auto
    moreover have "finite (f (Suc i))" using S by (rule finite_subset)
    ultimately have "card (f i) < card (f (Suc i))" by (intro psubset_card_mono)
    with Suc inj show ?case by auto
  qed
  then have "N \ card (f N)" by simp
  also have "\ \ card S" using S by (intro card_mono)
  finally have \<section>: "f (card S) = f N" using eq by auto
  moreover have "\ (range f) \ f N"
  proof clarify
    fix x n
    assume "x \ f n"
    with eq inj [of N] show "x \ f N"
      by (cases "n < N") (auto simp: not_less)
  qed
  ultimately show ?thesis
    by auto
qed

subsection \<open>More on injections, bijections, and inverses\<close>

locale bijection =
  fixes f :: "'a \ 'a"
  assumes bij: "bij f"
begin

lemma bij_inv: "bij (inv f)"
  using bij by (rule bij_imp_bij_inv)

lemma surj [simp]: "surj f"
  using bij by (rule bij_is_surj)

lemma inj: "inj f"
  using bij by (rule bij_is_inj)

lemma surj_inv [simp]: "surj (inv f)"
  using inj by (rule inj_imp_surj_inv)

lemma inj_inv: "inj (inv f)"
  using surj by (rule surj_imp_inj_inv)

lemma eqI: "f a = f b \ a = b"
  using inj by (rule injD)

lemma eq_iff [simp]: "f a = f b \ a = b"
  by (auto intro: eqI)

lemma eq_invI: "inv f a = inv f b \ a = b"
  using inj_inv by (rule injD)

lemma eq_inv_iff [simp]: "inv f a = inv f b \ a = b"
  by (auto intro: eq_invI)

lemma inv_left [simp]: "inv f (f a) = a"
  using inj by (simp add: inv_f_eq)

lemma inv_comp_left [simp]: "inv f \ f = id"
  by (simp add: fun_eq_iff)

lemma inv_right [simp]: "f (inv f a) = a"
  using surj by (simp add: surj_f_inv_f)

lemma inv_comp_right [simp]: "f \ inv f = id"
  by (simp add: fun_eq_iff)

lemma inv_left_eq_iff [simp]: "inv f a = b \ f b = a"
  by auto

lemma inv_right_eq_iff [simp]: "b = inv f a \ f b = a"
  by auto

end

lemma infinite_imp_bij_betw:
  assumes infinite: "\ finite A"
  shows "\h. bij_betw h A (A - {a})"
proof (cases "a \ A")
  case False
  then have "A - {a} = A" by blast
  then show ?thesis
    using bij_betw_id[of A] by auto
next
  case True
  with infinite have "\ finite (A - {a})" by auto
  with infinite_iff_countable_subset[of "A - {a}"]
  obtain f :: "nat \ 'a" where "inj f" and f: "f ` UNIV \ A - {a}" by blast
  define g where "g n = (if n = 0 then a else f (Suc n))" for n
  define A' where "A' = g ` UNIV"
  have *: "\y. f y \ a" using f by blast
  have 3: "inj_on g UNIV \ g ` UNIV \ A \ a \ g ` UNIV"
    using \<open>inj f\<close> f * unfolding inj_on_def g_def
    by (auto simp add: True image_subset_iff)
  then have 4: "bij_betw g UNIV A' \ a \ A' \ A' \ A"
    using inj_on_imp_bij_betw[of g] by (auto simp: A'_def)
  then have 5: "bij_betw (inv g) A' UNIV"
    by (auto simp add: bij_betw_inv_into)
  from 3 obtain n where n: "g n = a" by auto
  have 6: "bij_betw g (UNIV - {n}) (A' - {a})"
    by (rule bij_betw_subset) (use 3 4 n in \<open>auto simp: image_set_diff A'_def\<close>)
  define v where "v m = (if m < n then m else Suc m)" for m
  have "m < n \ m = n" if "\k. k < n \ m \ Suc k" for m
    using that [of "m-1"] by auto
  then have 7: "bij_betw v UNIV (UNIV - {n})"
    unfolding bij_betw_def inj_on_def v_def by auto
  define h' where "h' = g \<circ> v \<circ> (inv g)"
  with 5 6 7 have 8: "bij_betw h' A' (A' - {a})"
    by (auto simp add: bij_betw_trans)
  define h where "h b = (if b \ A' then h' b else b)" for b
  with 8 have "bij_betw h A' (A' - {a})"
    using bij_betw_cong[of A' h] by auto
  moreover
  have "\b \ A - A'. h b = b" by (auto simp: h_def)
  then have "bij_betw h (A - A') (A - A')"
    using bij_betw_cong[of "A - A'" h id] bij_betw_id[of "A - A'"] by auto
  moreover
  from 4 have "(A' \ (A - A') = {} \ A' \ (A - A') = A) \
    ((A' - {a}) \ (A - A') = {} \ (A' - {a}) \ (A - A') = A - {a})"
    by blast
  ultimately have "bij_betw h A (A - {a})"
    using bij_betw_combine[of h A' "A' - {a}" "A - A'" "A - A'"] by simp
  then show ?thesis by blast
qed

lemma infinite_imp_bij_betw2:
  assumes "\ finite A"
  shows "\h. bij_betw h A (A \ {a})"
proof (cases "a \ A")
  case True
  then have "A \ {a} = A" by blast
  then show ?thesis using bij_betw_id[of A] by auto
next
  case False
  let ?A' = "A \ {a}"
  from False have "A = ?A' - {a}" by blast
  moreover from assms have "\ finite ?A'" by auto
  ultimately obtain f where "bij_betw f ?A' A"
    using infinite_imp_bij_betw[of ?A' a] by auto
  then have "bij_betw (inv_into ?A' f) A ?A'" by (rule bij_betw_inv_into)
  then show ?thesis by auto
qed

lemma bij_betw_inv_into_left: "bij_betw f A A' \ a \ A \ inv_into A f (f a) = a"
  unfolding bij_betw_def by clarify (rule inv_into_f_f)

lemma bij_betw_inv_into_right: "bij_betw f A A' \ a' \ A' \ f (inv_into A f a') = a'"
  unfolding bij_betw_def using f_inv_into_f by force

lemma bij_betw_inv_into_subset:
  "bij_betw f A A' \ B \ A \ f ` B = B' \ bij_betw (inv_into A f) B' B"
  by (auto simp: bij_betw_def intro: inj_on_inv_into)

subsection \<open>Specification package -- Hilbertized version\<close>

lemma exE_some: "Ex P \ c \ Eps P \ P c"
  by (simp only: someI_ex)

ML_file \<open>Tools/choice_specification.ML\<close>

subsection \<open>Complete Distributive Lattices -- Properties depending on Hilbert Choice\<close>

context complete_distrib_lattice
begin

lemma Sup_Inf: "\ (Inf ` A) = \ (Sup ` {f ` A |f. \B\A. f B \ B})"
proof (rule antisym)
  show "\ (Inf ` A) \ \ (Sup ` {f ` A |f. \B\A. f B \ B})"
    using Inf_lower2 Sup_upper
    by (fastforce simp add: intro: Sup_least INF_greatest)
next
  show "\ (Sup ` {f ` A |f. \B\A. f B \ B}) \ \ (Inf ` A)"
  proof (simp add:  Inf_Sup, rule SUP_least, simp, safe)
    fix f
    assume "\Y. (\f. Y = f ` A \ (\Y\A. f Y \ Y)) \ f Y \ Y"
    then have B: "\ F . (\ Y \ A . F Y \ Y) \ \ Z \ A . f (F ` A) = F Z"
      by auto
    show "\(f ` {f ` A |f. \Y\A. f Y \ Y}) \ \(Inf ` A)"
    proof (cases "\ Z \ A . \(f ` {f ` A |f. \Y\A. f Y \ Y}) \ Inf Z")
      case True
      from this obtain Z where [simp]: "Z \ A" and A: "\(f ` {f ` A |f. \Y\A. f Y \ Y}) \ Inf Z"
        by blast
      have B: "... \ $Inf ` A)"
        by (simp add: SUP_upper)
      from A and B show ?thesis
        by simp
    next
      case False
      then have X: "\ Z . Z \ A \ \ x . x \ Z \ \ \(f ` {f ` A |f. \Y\A. f Y \ Y}) \ x"
        using Inf_greatest by blast
      define F where "F = (\ Z . SOME x . x \ Z \ \ \(f ` {f ` A |f. \Y\A. f Y \ Y}) \ x)"
      have C: "\Y. Y \ A \ F Y \ Y"
        using X by (simp add: F_def, rule someI2_ex, auto)
      have E: "\Y. Y \ A \ \ \(f ` {f ` A |f. \Y\A. f Y \ Y}) \ F Y"
        using X by (simp add: F_def, rule someI2_ex, auto)
      from C and B obtain  Z where D: "Z \ A " and Y: "f (F ` A) = F Z"
        by blast
      from E and D have W: "\ \(f ` {f ` A |f. \Y\A. f Y \ Y}) \ F Z"
        by simp
      have "\(f ` {f ` A |f. \Y\A. f Y \ Y}) \ f (F ` A)"
        using C by (blast intro: INF_lower)
      with W Y show ?thesis
        by simp
    qed
  qed
qed

lemma dual_complete_distrib_lattice:
  "class.complete_distrib_lattice Sup Inf sup ($ (>) inf \ \"
  by (simp add: class.complete_distrib_lattice.intro [OF dual_complete_lattice]
                class.complete_distrib_lattice_axioms_def Sup_Inf)

lemma sup_Inf: "a \ \B = $($ a ` B)"
proof (rule antisym)
  show "a \ \B \ $($ a ` B)"
    using Inf_lower sup.mono by (fastforce intro: INF_greatest)
next
  have "$($ a ` B) \ $Sup ` {{f {a}, f B} |f. f {a} = a \ f B \ B})"
    by (rule INF_greatest, auto simp add: INF_lower)
  also have "... = \(Inf ` {{a}, B})"
    by (unfold Sup_Inf, simp)
  finally show "\(($ a ` B) \ a \ \B"
    by simp
qed

lemma inf_Sup: "a \ \B = $($ a ` B)"
  using dual_complete_distrib_lattice
  by (rule complete_distrib_lattice.sup_Inf)

lemma INF_SUP: "(\y. \x. P x y) = (\f. \x. P (f x) x)"
proof (rule antisym)
  show "(SUP x. INF y. P (x y) y) \ (INF y. SUP x. P x y)"
    by (rule SUP_least, rule INF_greatest, rule SUP_upper2, simp_all, rule INF_lower2, simp, blast)
next
  have "(INF y. SUP x. ((P x y))) \ Inf (Sup ` {{P x y | x . True} | y . True })" (is "?A \ ?B")
  proof (rule INF_greatest, clarsimp)
    fix y
    have "?A \ (SUP x. P x y)"
      by (rule INF_lower, simp)
    also have "... \ Sup {uu. \x. uu = P x y}"
      by (simp add: full_SetCompr_eq)
    finally show "?A \ Sup {uu. \x. uu = P x y}"
      by simp
  qed
  also have "... \ (SUP x. INF y. P (x y) y)"
  proof (subst Inf_Sup, rule SUP_least, clarsimp)
    fix f
    assume A: "\Y. (\y. Y = {uu. \x. uu = P x y}) \ f Y \ Y"

    have " \(f ` {uu. \y. uu = {uu. \x. uu = P x y}}) \
      (\<Sqinter>y. P (SOME x. f {P x y |x. True} = P x y) y)"
    proof (rule INF_greatest, clarsimp)
      fix y
        have "(INF x\{uu. \y. uu = {uu. \x. uu = P x y}}. f x) \ f {uu. \x. uu = P x y}"
          by (rule INF_lower, blast)
        also have "... \ P (SOME x. f {uu . \x. uu = P x y} = P x y) y"
          by (rule someI2_ex) (use A in auto)
        finally show "\(f ` {uu. \y. uu = {uu. \x. uu = P x y}}) \
          P (SOME x. f {uu. \<exists>x. uu = P x y} = P x y) y"
          by simp
      qed
      also have "... \ (SUP x. INF y. P (x y) y)"
        by (rule SUP_upper, simp)
      finally show "$f ` {uu. \y. uu = {uu. \x. uu = P x y}}) \ (\x. \y. P (x y) y)"
        by simp
    qed
  finally show "(INF y. SUP x. P x y) \ (SUP x. INF y. P (x y) y)"
    by simp
qed

lemma INF_SUP_set: "(\B\A. \(g ` B)) = (\B\{f ` A |f. \C\A. f C \ C}. \(g ` B))"
                    (is "_ = (\B\?F. _)")
proof (rule antisym)
  have "\ ((g \ f) ` A) \ \ (g ` B)" if "\B. B \ A \ f B \ B" "B \ A" for f B
    using that by (auto intro: SUP_upper2 INF_lower2)
  then show "(\x\?F. \a\x. g a) \ (\x\A. \a\x. g a)"
    by (auto intro!: SUP_least INF_greatest simp add: image_comp)
next
  show "(\x\A. \a\x. g a) \ (\x\?F. \a\x. g a)"
  proof (cases "{} \ A")
    case True
    then show ?thesis
      by (rule INF_lower2) simp_all
  next
    case False
    {fix x
      have "(\x\A. \x\x. g x) \ (\u. if x \ A then if u \ x then g u else \ else $"
      proof (cases "x \ A")
        case True
        then show ?thesis
          by (intro INF_lower2 SUP_least SUP_upper2) auto
      qed auto
    }
    then have "(\Y\A. \a\Y. g a) \ (\Y. \y. if Y \ A then if y \ Y then g y else \ else \)"
      by (rule INF_greatest)
    also have "... = (\x. \Y. if Y \ A then if x Y \ Y then g (x Y) else \ else \)"
      by (simp only: INF_SUP)
    also have "... \ (\x\?F. \a\x. g a)"
    proof (rule SUP_least)
      show "(\B. if B \ A then if x B \ B then g (x B) else \ else \)
               \<le> (\<Squnion>x\<in>?F. \<Sqinter>x\<in>x. g x)" for x
      proof -
        define G where "G \ \Y. if x Y \ Y then x Y else (SOME x. x \Y)"
        have "\Y\A. G Y \ Y"
          using False some_in_eq G_def by auto
        then have A: "G ` A \ ?F"
          by blast
        show "(\Y. if Y \ A then if x Y \ Y then g (x Y) else \ else \) \ (\x\?F. \x\x. g x)"
          by (fastforce simp: G_def intro: SUP_upper2 [OF A] INF_greatest INF_lower2)
      qed
    qed
    finally show ?thesis by simp
  qed
qed

lemma SUP_INF: "(\y. \x. P x y) = (\x. \y. P (x y) y)"
  using dual_complete_distrib_lattice
  by (rule complete_distrib_lattice.INF_SUP)

lemma SUP_INF_set: "(\x\A. \ (g ` x)) = (\x\{f ` A |f. \Y\A. f Y \ Y}. \ (g ` x))"
  using dual_complete_distrib_lattice
  by (rule complete_distrib_lattice.INF_SUP_set)

end

(*properties of the former complete_distrib_lattice*)
context complete_distrib_lattice
begin

lemma sup_INF: "a \ (\b\B. f b) = (\b\B. a \ f b)"
  by (simp add: sup_Inf image_comp)

lemma inf_SUP: "a \ (\b\B. f b) = (\b\B. a \ f b)"
  by (simp add: inf_Sup image_comp)

lemma Inf_sup: "\B \ a = (\b\B. b \ a)"
  by (simp add: sup_Inf sup_commute)

lemma Sup_inf: "\B \ a = (\b\B. b \ a)"
  by (simp add: inf_Sup inf_commute)

lemma INF_sup: "(\b\B. f b) \ a = (\b\B. f b \ a)"
  by (simp add: sup_INF sup_commute)

lemma SUP_inf: "(\b\B. f b) \ a = (\b\B. f b \ a)"
  by (simp add: inf_SUP inf_commute)

lemma Inf_sup_eq_top_iff: "(\B \ a = \) \ (\b\B. b \ a = \)"
  by (simp only: Inf_sup INF_top_conv)

lemma Sup_inf_eq_bot_iff: "(\B \ a = \) \ (\b\B. b \ a = \)"
  by (simp only: Sup_inf SUP_bot_conv)

lemma INF_sup_distrib2: "(\a\A. f a) \ (\b\B. g b) = (\a\A. \b\B. f a \ g b)"
  by (subst INF_commute) (simp add: sup_INF INF_sup)

lemma SUP_inf_distrib2: "(\a\A. f a) \ (\b\B. g b) = (\a\A. \b\B. f a \ g b)"
  by (subst SUP_commute) (simp add: inf_SUP SUP_inf)

end

context complete_boolean_algebra
begin

lemma dual_complete_boolean_algebra:
  "class.complete_boolean_algebra Sup Inf sup (\) (>) inf \ \ (\x y. x \ - y) uminus"
  by (rule class.complete_boolean_algebra.intro,
      rule dual_complete_distrib_lattice,
      rule dual_boolean_algebra)
end

instantiation set :: (type) complete_distrib_lattice
begin
instance proof (standard, clarsimp)
  fix A :: "(('a set) set) set"
  fix x::'a
  assume A: "\\~~\A. \X\\~~. x \ X"~~~~
  define F where "F \ \Y. SOME X. Y \ A \ X \ Y \ x \ X"
  have "(\S \ F ` A. x \ S)"
    using A unfolding F_def by (fastforce intro: someI2_ex)
  moreover have "\Y\A. F Y \ Y"
    using A unfolding F_def by (fastforce intro: someI2_ex)
  then have "\f. F ` A = f ` A \ (\Y\A. f Y \ Y)"
    by blast
  ultimately show "\X. (\f. X = f ` A \ (\Y\A. f Y \ Y)) \ (\S\X. x \ S)"
    by auto
qed
end

instance set :: (type) complete_boolean_algebra ..

instantiation "fun" :: (type, complete_distrib_lattice) complete_distrib_lattice
begin
instance by standard (simp add: le_fun_def INF_SUP_set image_comp)
end

instance "fun" :: (type, complete_boolean_algebra) complete_boolean_algebra ..

context complete_linorder
begin

subclass complete_distrib_lattice
proof (standard, rule ccontr)
  fix A :: "'a set set"
  let ?F = "{f ` A |f. \Y\A. f Y \ Y}"
  assume "\ \(Sup ` A) \ \(Inf ` ?F)"
  then have C: "\(Sup ` A) > \(Inf ` ?F)"
    by (simp add: not_le)
  show False
  proof (cases "\ z . \(Sup ` A) > z \ z > \(Inf ` ?F)")
    case True
    then obtain z where A: "z < \(Sup ` A)" and X: "z > \(Inf ` ?F)"
      by blast
    then have B: "\Y. Y \ A \ \k \Y . z < k"
      using local.less_Sup_iff by(force dest: less_INF_D)

    define G where "G \ \Y. SOME k . k \ Y \ z < k"
    have E: "\Y. Y \ A \ G Y \ Y"
      using B unfolding G_def by (fastforce intro: someI2_ex)
    have "z \ Inf (G ` A)"
    proof (rule INF_greatest)
      show  "\Y. Y \ A \ z \ G Y"
        using B unfolding G_def by (fastforce intro: someI2_ex)
    qed
    also have "... \ \(Inf ` ?F)"
      by (rule SUP_upper) (use E in blast)
    finally have "z \ \(Inf ` ?F)"
      by simp

    with X show ?thesis
      using local.not_less by blast
  next
    case False
    have B: "\Y. Y \ A \ \ k \Y . \(Inf ` ?F) < k"
      using C local.less_Sup_iff by(force dest: less_INF_D)
    define G where "G \ \ Y . SOME k . k \ Y \ \(Inf ` ?F) < k"
    have E: "\Y. Y \ A \ G Y \ Y"
      using B unfolding G_def by (fastforce intro: someI2_ex)
    have "\Y. Y \ A \ \(Sup ` A) \ G Y"
      using B False local.leI unfolding G_def by (fastforce intro: someI2_ex)
    then have "\(Sup ` A) \ Inf (G ` A)"
      by (simp add: local.INF_greatest)
    also have "Inf (G ` A) \ \(Inf ` ?F)"
      by (rule SUP_upper) (use E in blast)
    finally have "\(Sup ` A) \ \(Inf ` ?F)"
      by simp
    with C show ?thesis
      using not_less by blast
  qed
qed
end

end

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