(* 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 ‹Hilbert's Epsilon-Operator and the Axiom of Choice› theory Hilbert_Choice imports Wellfounded keywords "specification" :: thy_goal begin subsection ‹Hilbert's epsilon› axiomatization Eps :: "('a ⇒ bool) ⇒ 'a" where someI: "P x ⟹ P (Eps P)" syntax (epsilon) "_Eps" :: "pttrn ⇒ bool ⇒ 'a" ("(3ϵ_./ _)" [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" ⇌ "CONST Eps (λx. P)" print_translation ‹ [(@{const_syntax Eps}, fn _ => fn [Abs abs] => let val (x, t) = Syntax_Trans.atomic_abs_tr' abs in Syntax.const @{syntax_const "_Eps"} $ x $ t end)] › ― ‹to avoid eta-contraction of body› definition inv_into :: "'a set ⇒ ('a ⇒ 'b) ⇒ ('b ⇒ 'a)" where "inv_into A f = (λx. 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 ‹Hilbert's Epsilon-operator› text ‹ Easier to apply than ‹someI› if the witness comes from an existential formula. › lemma someI_ex [elim?]: "∃x. P x ⟹ P (SOME x. P x)" apply (erule exE) apply (erule someI) done text ‹ Easier to apply than ‹someI› because the conclusion has only one occurrence of @{term P}. › lemma someI2: "P a ⟹ (⋀x. P x ⟹ Q x) ⟹ Q (SOME x. P x)" by (blast intro: someI) text ‹ Easier to apply than ‹someI2› if the witness comes from an existential formula. › 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" apply (rule some_equality) apply (rule refl) apply (erule sym) done subsection ‹Axiom of Choice, Proved Using the Description Operator› 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) (λn 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 subsection ‹Function Inverse› lemma inv_def: "inv f = (λy. 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 (λa. a) = (λa. 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 ‹But is it useful?› 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 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: "surj f ⟹ ∀x. g (f x) = x ⟹ inv f = g" apply (rule ext) apply (drule_tac x = "inv f x" in spec) apply (simp add: surj_f_inv_f) done 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 ‹ ‹bij (inv f)› implies little about ‹f›. Consider ‹f :: bool ⇒ bool› such that ‹f True = f False = True›. Then it ia consistent with axiom ‹someI› that ‹inv f› could be any function at all, including the identity function. If ‹inv f = id› then ‹inv f› is a bijection, but ‹inj f›, ‹surj f› and ‹inv (inv f) = f› all fail. › lemma inv_into_comp: "inj_on f (g ` A) ⟹ inj_on g A ⟹ x ∈ f ` g ` A ⟹ inv_into A (f ∘ g) x = (inv_into A g ∘ inv_into (g ` A) f) x" apply (rule inv_into_f_eq) apply (fast intro: comp_inj_on) apply (simp add: inv_into_into) apply (simp add: f_inv_into_f inv_into_into) done 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: "bij f ⟹ f ` Collect P = {y. P (inv f y)}" apply auto apply (force simp add: bij_is_inj) apply (blast intro: bij_is_surj [THEN surj_f_inv_f, symmetric]) done lemma bij_vimage_eq_inv_image: "bij f ⟹ f -` A = inv f ` A" apply (auto simp add: bij_is_surj [THEN surj_f_inv_f]) apply (blast intro: bij_is_inj [THEN inv_into_f_f, symmetric]) done lemma inv_fn_o_fn_is_id: fixes f::"'a ⇒ 'a" assumes "bij f" shows "((inv f)^^n) o (f^^n) = (λx. 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) = (λx. 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 apply (rule inv_into_f_eq, auto simp add: inj_fn[OF bij_is_inj[OF assms]]) using fn_o_inv_fn_is_id[OF assms, of n, THEN fun_cong] by (simp) 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 ‹bij f› 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 ‹bij f› 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 ‹x ≤ y› by auto thus ?thesis by simp qed 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 ‹bij f› 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 ‹mono f› *] by(simp add: surj_f_inv_f[OF ‹surj f›]) 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 (λf :: 'a ⇒ 'b. inv f b1))" by (rule finite_imageI) have "UNIV = range (λf :: 'a ⇒ 'b. inv f b1)" proof (rule UNIV_eq_I) fix x :: 'a from b1b2 have "x = inv (λy. if y = x then b1 else b2) b1" by (simp add: inv_into_def) then show "x ∈ range (λf::'a ⇒ 'b. inv f b1)" by blast qed with fin' show ?thesis by simp qed text ‹ Every infinite set contains a countable subset. More precisely we show that a set ‹S› is infinite if and only if there exists an injective function from the naturals into ‹S›. The ``only if'' direction is harder because it requires the construction of a sequence of pairwise different elements of an infinite set ‹S›. The idea is to construct a sequence of non-empty and infinite subsets of ‹S› obtained by successively removing elements of ‹S›. › lemma infinite_countable_subset: assumes inf: "¬ finite S" shows "∃f::nat ⇒ 'a. inj f ∧ range f ⊆ S" ― ‹Courtesy of Stephan Merz› proof - define Sseq where "Sseq = rec_nat S (λn 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)" ― ‹Courtesy of Stephan Merz› 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 = "λa' a. a ∈ A ∧ f a = a'" let ?csi = "λa. a ∈ A" let ?g = "λa'. 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 = "λ 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 = "λa i. i ∈ I ∧ a ∈ A i" let ?sm = "λa. SOME i. ?phi a i" let ?f = "λa. (?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) subsection ‹Other Consequences of Hilbert's Epsilon› text ‹Hilbert's Epsilon and the @{term split} Operator› text ‹Looping simprule!› 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 ‹A relation is wellfounded iff it has no infinite descending chain.› 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 ‹wf r› have minimal: "x ∈ Q ⟹ ∃z∈Q. ∀y. (y, z) ∈ r ⟶ y ∉ 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 ‹(f (Suc j), f j) ∈ r›] have "f (Suc j) ∉ ?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 (λ_ 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 ‹A dynamically-scoped fact for TFL› lemma tfl_some: "∀P x. P x ⟶ P (Eps P)" by (blast intro: someI) subsection ‹An aside: bounded accessible part› text ‹Finite monotone eventually stable sequences› 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 ‹mono f› have "⋀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 ‹finite (range f)› 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] ‹N ≤ n› 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 ‹mono f› 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 "f (card S) = f N" using eq by auto then show ?thesis using eq inj [of N] apply auto apply (case_tac "n < N") apply (auto simp: not_less) done qed subsection ‹More on injections, bijections, and inverses› 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 1: "inj f" and 2: "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 2 by blast have 3: "inj_on g UNIV ∧ g ` UNIV ⊆ A ∧ a ∈ g ` UNIV" apply (auto simp add: True g_def [abs_def]) apply (unfold inj_on_def) apply (intro ballI impI) apply (case_tac "x = 0") apply (auto simp add: 2) proof - fix y assume "a = (if y = 0 then a else f (Suc y))" then show "y = 0" by (cases "y = 0") (use * in auto) next fix x y assume "f (Suc x) = (if y = 0 then a else f (Suc y))" with 1 * show "x = y" by (cases "y = 0") (auto simp: inj_on_def) next fix n from 2 show "f (Suc n) ∈ A" by blast qed 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 ‹auto simp: image_set_diff A'_def›) define v where "v m = (if m < n then m else Suc m)" for m have 7: "bij_betw v UNIV (UNIV - {n})" proof (unfold bij_betw_def inj_on_def, intro conjI, clarify) fix m1 m2 assume "v m1 = v m2" then show "m1 = m2" apply (cases "m1 < n") apply (cases "m2 < n") apply (auto simp: inj_on_def v_def [abs_def]) apply (cases "m2 < n") apply auto done next show "v ` UNIV = UNIV - {n}" proof (auto simp: v_def [abs_def]) fix m assume "m ≠ n" assume *: "m ∉ Suc ` {m'. ¬ m' < n}" have False if "n ≤ m" proof - from ‹m ≠ n› that have **: "Suc n ≤ m" by auto from Suc_le_D [OF this] obtain m' where m': "m = Suc m'" .. with ** have "n ≤ m'" by auto with m' * show ?thesis by auto qed then show "m < n" by force qed qed define h' where "h' = g ∘ v ∘ (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 then have "∀b ∈ A'. h b = h' b" by simp 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 ‹Specification package -- Hilbertized version› lemma exE_some: "Ex P ⟹ c ≡ Eps P ⟹ P c" by (simp only: someI_ex) ML_file "Tools/choice_specification.ML" subsection ‹Complete Distributive Lattices -- Properties depending on Hilbert Choice› context complete_distrib_lattice begin lemma Sup_Inf: "Sup (Inf ` A) = Inf (Sup ` {f ` A | f . (∀ Y ∈ A . f Y ∈ Y)})" proof (rule antisym) show "SUPREMUM A Inf ≤ INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Sup" apply (rule Sup_least, rule INF_greatest) using Inf_lower2 Sup_upper by auto next show "INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Sup ≤ SUPREMUM A Inf" 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" from this have B: "⋀ F . (∀ Y ∈ A . F Y ∈ Y) ⟹ ∃ Z ∈ A . f (F ` A) = F Z" by auto show "INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} f ≤ SUPREMUM A Inf" proof (cases "∃ Z ∈ A . INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} f ≤ Inf Z") case True from this obtain Z where [simp]: "Z ∈ A" and A: "INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} f ≤ Inf Z" by blast have B: "... ≤ SUPREMUM A Inf" by (simp add: SUP_upper) from A and B show ?thesis by simp next case False from this have X: "⋀ Z . Z ∈ A ⟹ ∃ x . x ∈ Z ∧ ¬ INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} f ≤ x" using Inf_greatest by blast define F where "F = (λ Z . SOME x . x ∈ Z ∧ ¬ INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} f ≤ 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 ⟹ ¬ INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} f ≤ 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: "¬ INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} f ≤ F Z" by simp have "INFIMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} f ≤ f (F ` A)" apply (rule INF_lower) using C by blast from this and W and Y show ?thesis by simp qed qed qed lemma dual_complete_distrib_lattice: "class.complete_distrib_lattice Sup Inf sup (≥) (>) inf ⊤ ⊥" apply (rule class.complete_distrib_lattice.intro) apply (fact dual_complete_lattice) by (simp add: class.complete_distrib_lattice_axioms_def Sup_Inf) lemma sup_Inf: "a ⊔ Inf B = (INF b:B. a ⊔ b)" proof (rule antisym) show "a ⊔ Inf B ≤ (INF b:B. a ⊔ b)" apply (rule INF_greatest) using Inf_lower sup.mono by fastforce next have "(INF b:B. a ⊔ b) ≤ INFIMUM {{f {a}, f B} |f. f {a} = a ∧ f B ∈ B} Sup" by (rule INF_greatest, auto simp add: INF_lower) also have "... = SUPREMUM {{a}, B} Inf" by (unfold Sup_Inf, simp) finally show "(INF b:B. a ⊔ b) ≤ a ⊔ Inf B" by simp qed lemma inf_Sup: "a ⊓ Sup B = (SUP b:B. a ⊓ b)" using dual_complete_distrib_lattice by (rule complete_distrib_lattice.sup_Inf) lemma INF_SUP: "(INF y. SUP x. ((P x y)::'a)) = (SUP x. INF y. P (x y) y)" 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 "(INF x:{uu. ∃y. uu = {uu. ∃x. uu = P x y}}. f x) ≤ (INF y. P ((λ y. SOME x . f ({P x y | x. True}) = P x y) 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" apply (rule someI2_ex) using A by auto finally show "(INF x:{uu. ∃y. uu = {uu. ∃x. uu = P x y}}. f x) ≤ P (SOME x. f {uu . ∃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 "(INF x:{uu. ∃y. uu = {uu. ∃x. uu = P x y}}. f x) ≤ (SUP x. INF 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: "(INF x:A. SUP a:x. (g a)) = (SUP x:{f ` A |f. ∀Y∈A. f Y ∈ Y}. INF a:x. g a)" proof (rule antisym) have [simp]: "⋀f xa. ∀Y∈A. f Y ∈ Y ⟹ xa ∈ A ⟹ (⨅x∈A. g (f x)) ≤ g (f xa)" by (rule INF_lower2, blast+) have B: "⋀f xa. ∀Y∈A. f Y ∈ Y ⟹ xa ∈ A ⟹ f xa ∈ xa" by blast have A: "⋀f xa. ∀Y∈A. f Y ∈ Y ⟹ xa ∈ A ⟹ (⨅x∈A. g (f x)) ≤ SUPREMUM xa g" by (rule SUP_upper2, rule B, simp_all, simp) show "(⨆x∈{f ` A |f. ∀Y∈A. f Y ∈ Y}. ⨅a∈x. g a) ≤ (⨅x∈A. ⨆a∈x. g a)" apply (rule SUP_least, simp, safe, rule INF_greatest, simp) by (rule A) next show "(⨅x∈A. ⨆a∈x. g a) ≤ (⨆x∈{f ` A |f. ∀Y∈A. f Y ∈ Y}. ⨅a∈x. g a)" proof (cases "{} ∈ A") case True then show ?thesis by (rule INF_lower2, simp_all) next case False have [simp]: "⋀x xa xb. xb ∈ A ⟹ x xb ∈ xb ⟹ (⨅xa. if xa ∈ A then if x xa ∈ xa then g (x xa) else ⊥ else ⊤) ≤ g (x xb)" by (rule INF_lower2, auto) have [simp]: " ⋀x xa y. y ∈ A ⟹ x y ∉ y ⟹ (⨅xa. if xa ∈ A then if x xa ∈ xa then g (x xa) else ⊥ else ⊤) ≤ g (SOME x. x ∈ y)" by (rule INF_lower2, auto) have [simp]: "⋀x. (⨅xa. if xa ∈ A then if x xa ∈ xa then g (x xa) else ⊥ else ⊤) ≤ (⨆x∈{f ` A |f. ∀Y∈A. f Y ∈ Y}. ⨅x∈x. g x)" proof - fix x define F where "F = (λ (y::'b set) . if x y ∈ y then x y else (SOME x . x ∈y))" have B: "(∀Y∈A. F Y ∈ Y)" using False some_in_eq F_def by auto have A: "F ` A ∈ {f ` A |f. ∀Y∈A. f Y ∈ Y}" using B by blast show "(⨅xa. if xa ∈ A then if x xa ∈ xa then g (x xa) else ⊥ else ⊤) ≤ (⨆x∈{f ` A |f. ∀Y∈A. f Y ∈ Y}. ⨅x∈x. g x)" using A apply (rule SUP_upper2) by (simp add: F_def, rule INF_greatest, auto) qed {fix x have "(⨅x∈A. ⨆x∈x. g x) ≤ (⨆xa. if x ∈ A then if xa ∈ x then g xa else ⊥ else ⊤)" proof (cases "x ∈ A") case True then show ?thesis apply (rule INF_lower2, simp_all) by (rule SUP_least, rule SUP_upper2, auto) next case False then show ?thesis by simp qed } from this have "(⨅x∈A. ⨆a∈x. g a) ≤ (⨅x. ⨆xa. if x ∈ A then if xa ∈ x then g xa else ⊥ else ⊤)" by (rule INF_greatest) also have "... = (⨆x. ⨅xa. if xa ∈ A then if x xa ∈ xa then g (x xa) else ⊥ else ⊤)" by (simp add: INF_SUP) also have "... ≤ (⨆x∈{f ` A |f. ∀Y∈A. f Y ∈ Y}. ⨅a∈x. g a)" by (rule SUP_least, simp) finally show ?thesis by simp qed qed lemma SUP_INF: "(SUP y. INF x. ((P x y)::'a)) = (INF x. SUP y. P (x y) y)" using dual_complete_distrib_lattice by (rule complete_distrib_lattice.INF_SUP) lemma SUP_INF_set: "(SUP x:A. INF a:x. (g a)) = (INF x:{f ` A |f. ∀Y∈A. f Y ∈ Y}. SUP a:x. g a)" 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) lemma inf_SUP: "a ⊓ (⨆b∈B. f b) = (⨆b∈B. a ⊓ f b)" by (simp add: inf_Sup) 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 ⊤ ⊥ (λx 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 define F where "F = (λ Y . (SOME X . (Y ∈ A ∧ X ∈ Y ∧ x ∈ X)))" assume A: "∀xa∈A. ∃X∈xa. x ∈ X" from this have B: " (∀xa ∈ F ` A. x ∈ xa)" apply (safe, simp add: F_def) by (rule someI2_ex, auto) have C: "(∀Y∈A. F Y ∈ Y)" apply (simp add: F_def, safe) apply (rule someI2_ex) using A by auto have "(∃f. F ` A = f ` A ∧ (∀Y∈A. f Y ∈ Y))" using C by blast from B and this show "∃X. (∃f. X = f ` A ∧ (∀Y∈A. f Y ∈ Y)) ∧ (∀xa∈X. x ∈ xa)" 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) end instance "fun" :: (type, complete_boolean_algebra) complete_boolean_algebra .. context complete_linorder begin subclass complete_distrib_lattice proof (standard, rule ccontr) fix A assume "¬ INFIMUM A Sup ≤ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf" from this have C: "INFIMUM A Sup > SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf" using local.not_le by blast show "False" proof (cases "∃ z . INFIMUM A Sup > z ∧ z > SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf") case True from this obtain z where A: "z < INFIMUM A Sup" and X: "SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf < z" by blast from A have "⋀ Y . Y ∈ A ⟹ z < Sup Y" by (simp add: less_INF_D) from this have B: "⋀ Y . Y ∈ A ⟹ ∃ k ∈Y . z < k" using local.less_Sup_iff by blast define F where "F = (λ Y . SOME k . k ∈ Y ∧ z < k)" have D: "⋀ Y . Y ∈ A ⟹ z < F Y" using B apply (simp add: F_def) by (rule someI2_ex, auto) have E: "⋀ Y . Y ∈ A ⟹ F Y ∈ Y" using B apply (simp add: F_def) by (rule someI2_ex, auto) have "z ≤ Inf (F ` A)" by (simp add: D local.INF_greatest local.order.strict_implies_order) also have "... ≤ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf" apply (rule SUP_upper, safe) using E by blast finally have "z ≤ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf" by simp from X and this show ?thesis using local.not_less by blast next case False from this have A: "⋀ z . INFIMUM A Sup ≤ z ∨ z ≤ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf" using local.le_less_linear by blast from C have "⋀ Y . Y ∈ A ⟹ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf < Sup Y" by (simp add: less_INF_D) from this have B: "⋀ Y . Y ∈ A ⟹ ∃ k ∈Y . SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf < k" using local.less_Sup_iff by blast define F where "F = (λ Y . SOME k . k ∈ Y ∧ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf < k)" have D: "⋀ Y . Y ∈ A ⟹ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf < F Y" using B apply (simp add: F_def) by (rule someI2_ex, auto) have E: "⋀ Y . Y ∈ A ⟹ F Y ∈ Y" using B apply (simp add: F_def) by (rule someI2_ex, auto) have "⋀ Y . Y ∈ A ⟹ INFIMUM A Sup ≤ F Y" using D False local.leI by blast from this have "INFIMUM A Sup ≤ Inf (F ` A)" by (simp add: local.INF_greatest) also have "Inf (F ` A) ≤ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf" apply (rule SUP_upper, safe) using E by blast finally have "INFIMUM A Sup ≤ SUPREMUM {f ` A |f. ∀Y∈A. f Y ∈ Y} Inf" by simp from C and this show ?thesis using not_less by blast qed qed end end