src/HOL/Library/Countable_Set.thy
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add various lemmas
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(*  Title:      HOL/Library/Countable_Set.thy
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    Author:     Johannes Hölzl
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    Author:     Andrei Popescu
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*)
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header {* Countable sets *}
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theory Countable_Set
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imports Countable Infinite_Set
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begin
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subsection {* Predicate for countable sets *}
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definition countable :: "'a set \<Rightarrow> bool" where
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  "countable S \<longleftrightarrow> (\<exists>f::'a \<Rightarrow> nat. inj_on f S)"
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lemma countableE:
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  assumes S: "countable S" obtains f :: "'a \<Rightarrow> nat" where "inj_on f S"
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  using S by (auto simp: countable_def)
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lemma countableI: "inj_on (f::'a \<Rightarrow> nat) S \<Longrightarrow> countable S"
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  by (auto simp: countable_def)
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lemma countableI': "inj_on (f::'a \<Rightarrow> 'b::countable) S \<Longrightarrow> countable S"
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  using comp_inj_on[of f S to_nat] by (auto intro: countableI)
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lemma countableE_bij:
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  assumes S: "countable S" obtains f :: "nat \<Rightarrow> 'a" and C :: "nat set" where "bij_betw f C S"
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  using S by (blast elim: countableE dest: inj_on_imp_bij_betw bij_betw_inv)
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lemma countableI_bij: "bij_betw f (C::nat set) S \<Longrightarrow> countable S"
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  by (blast intro: countableI bij_betw_inv_into bij_betw_imp_inj_on)
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lemma countable_finite: "finite S \<Longrightarrow> countable S"
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  by (blast dest: finite_imp_inj_to_nat_seg countableI)
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lemma countableI_bij1: "bij_betw f A B \<Longrightarrow> countable A \<Longrightarrow> countable B"
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  by (blast elim: countableE_bij intro: bij_betw_trans countableI_bij)
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lemma countableI_bij2: "bij_betw f B A \<Longrightarrow> countable A \<Longrightarrow> countable B"
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  by (blast elim: countableE_bij intro: bij_betw_trans bij_betw_inv_into countableI_bij)
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lemma countable_iff_bij[simp]: "bij_betw f A B \<Longrightarrow> countable A \<longleftrightarrow> countable B"
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  by (blast intro: countableI_bij1 countableI_bij2)
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lemma countable_subset: "A \<subseteq> B \<Longrightarrow> countable B \<Longrightarrow> countable A"
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  by (auto simp: countable_def intro: subset_inj_on)
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lemma countableI_type[intro, simp]: "countable (A:: 'a :: countable set)"
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  using countableI[of to_nat A] by auto
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subsection {* Enumerate a countable set *}
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lemma countableE_infinite:
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  assumes "countable S" "infinite S"
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  obtains e :: "'a \<Rightarrow> nat" where "bij_betw e S UNIV"
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proof -
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  obtain f :: "'a \<Rightarrow> nat" where "inj_on f S"
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    using `countable S` by (rule countableE)
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  then have "bij_betw f S (f`S)"
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    unfolding bij_betw_def by simp
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  moreover
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  from `inj_on f S` `infinite S` have inf_fS: "infinite (f`S)"
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    by (auto dest: finite_imageD)
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  then have "bij_betw (the_inv_into UNIV (enumerate (f`S))) (f`S) UNIV"
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    by (intro bij_betw_the_inv_into bij_enumerate)
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  ultimately have "bij_betw (the_inv_into UNIV (enumerate (f`S)) \<circ> f) S UNIV"
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    by (rule bij_betw_trans)
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  then show thesis ..
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qed
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lemma countable_enum_cases:
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  assumes "countable S"
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  obtains (finite) f :: "'a \<Rightarrow> nat" where "finite S" "bij_betw f S {..<card S}"
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        | (infinite) f :: "'a \<Rightarrow> nat" where "infinite S" "bij_betw f S UNIV"
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  using ex_bij_betw_finite_nat[of S] countableE_infinite `countable S`
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  by (cases "finite S") (auto simp add: atLeast0LessThan)
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definition to_nat_on :: "'a set \<Rightarrow> 'a \<Rightarrow> nat" where
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  "to_nat_on S = (SOME f. if finite S then bij_betw f S {..< card S} else bij_betw f S UNIV)"
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definition from_nat_into :: "'a set \<Rightarrow> nat \<Rightarrow> 'a" where
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  "from_nat_into S n = (if n \<in> to_nat_on S ` S then inv_into S (to_nat_on S) n else SOME s. s\<in>S)"
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lemma to_nat_on_finite: "finite S \<Longrightarrow> bij_betw (to_nat_on S) S {..< card S}"
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  using ex_bij_betw_finite_nat unfolding to_nat_on_def
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  by (intro someI2_ex[where Q="\<lambda>f. bij_betw f S {..<card S}"]) (auto simp add: atLeast0LessThan)
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lemma to_nat_on_infinite: "countable S \<Longrightarrow> infinite S \<Longrightarrow> bij_betw (to_nat_on S) S UNIV"
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  using countableE_infinite unfolding to_nat_on_def
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  by (intro someI2_ex[where Q="\<lambda>f. bij_betw f S UNIV"]) auto
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lemma bij_betw_from_nat_into_finite: "finite S \<Longrightarrow> bij_betw (from_nat_into S) {..< card S} S"
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  unfolding from_nat_into_def[abs_def]
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  using to_nat_on_finite[of S]
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  apply (subst bij_betw_cong)
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  apply (split split_if)
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  apply (simp add: bij_betw_def)
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  apply (auto cong: bij_betw_cong
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              intro: bij_betw_inv_into to_nat_on_finite)
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  done
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lemma bij_betw_from_nat_into: "countable S \<Longrightarrow> infinite S \<Longrightarrow> bij_betw (from_nat_into S) UNIV S"
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  unfolding from_nat_into_def[abs_def]
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  using to_nat_on_infinite[of S, unfolded bij_betw_def]
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  by (auto cong: bij_betw_cong intro: bij_betw_inv_into to_nat_on_infinite)
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lemma inj_on_to_nat_on[intro]: "countable A \<Longrightarrow> inj_on (to_nat_on A) A"
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  using to_nat_on_infinite[of A] to_nat_on_finite[of A]
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  by (cases "finite A") (auto simp: bij_betw_def)
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lemma to_nat_on_inj[simp]:
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  "countable A \<Longrightarrow> a \<in> A \<Longrightarrow> b \<in> A \<Longrightarrow> to_nat_on A a = to_nat_on A b \<longleftrightarrow> a = b"
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  using inj_on_to_nat_on[of A] by (auto dest: inj_onD)
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lemma from_nat_into_to_nat_on[simp]: "countable A \<Longrightarrow> a \<in> A \<Longrightarrow> from_nat_into A (to_nat_on A a) = a"
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  by (auto simp: from_nat_into_def intro!: inv_into_f_f)
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lemma subset_range_from_nat_into: "countable A \<Longrightarrow> A \<subseteq> range (from_nat_into A)"
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  by (auto intro: from_nat_into_to_nat_on[symmetric])
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lemma from_nat_into: "A \<noteq> {} \<Longrightarrow> from_nat_into A n \<in> A"
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  unfolding from_nat_into_def by (metis equals0I inv_into_into someI_ex)
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lemma range_from_nat_into_subset: "A \<noteq> {} \<Longrightarrow> range (from_nat_into A) \<subseteq> A"
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  using from_nat_into[of A] by auto
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lemma range_from_nat_into[simp]: "A \<noteq> {} \<Longrightarrow> countable A \<Longrightarrow> range (from_nat_into A) = A"
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  by (metis equalityI range_from_nat_into_subset subset_range_from_nat_into)
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lemma image_to_nat_on: "countable A \<Longrightarrow> infinite A \<Longrightarrow> to_nat_on A ` A = UNIV"
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  using to_nat_on_infinite[of A] by (simp add: bij_betw_def)
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lemma to_nat_on_surj: "countable A \<Longrightarrow> infinite A \<Longrightarrow> \<exists>a\<in>A. to_nat_on A a = n"
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  by (metis (no_types) image_iff iso_tuple_UNIV_I image_to_nat_on)
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lemma to_nat_on_from_nat_into[simp]: "n \<in> to_nat_on A ` A \<Longrightarrow> to_nat_on A (from_nat_into A n) = n"
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  by (simp add: f_inv_into_f from_nat_into_def)
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lemma to_nat_on_from_nat_into_infinite[simp]:
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  "countable A \<Longrightarrow> infinite A \<Longrightarrow> to_nat_on A (from_nat_into A n) = n"
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   142
  by (metis image_iff to_nat_on_surj to_nat_on_from_nat_into)
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   143
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   144
lemma from_nat_into_inj:
50148
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   145
  "countable A \<Longrightarrow> m \<in> to_nat_on A ` A \<Longrightarrow> n \<in> to_nat_on A ` A \<Longrightarrow>
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   146
    from_nat_into A m = from_nat_into A n \<longleftrightarrow> m = n"
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   147
  by (subst to_nat_on_inj[symmetric, of A]) auto
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diff changeset
   148
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   149
lemma from_nat_into_inj_infinite[simp]:
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   150
  "countable A \<Longrightarrow> infinite A \<Longrightarrow> from_nat_into A m = from_nat_into A n \<longleftrightarrow> m = n"
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diff changeset
   151
  using image_to_nat_on[of A] from_nat_into_inj[of A m n] by simp
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   152
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   153
lemma eq_from_nat_into_iff:
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   154
  "countable A \<Longrightarrow> x \<in> A \<Longrightarrow> i \<in> to_nat_on A ` A \<Longrightarrow> x = from_nat_into A i \<longleftrightarrow> i = to_nat_on A x"
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parents: 50144
diff changeset
   155
  by auto
50144
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hoelzl
parents: 50134
diff changeset
   156
885deccc264e renamed BNF/Countable_Set to Countable_Type and moved its generic stuff to Library/Countable_Set
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diff changeset
   157
lemma from_nat_into_surj: "countable A \<Longrightarrow> a \<in> A \<Longrightarrow> \<exists>n. from_nat_into A n = a"
885deccc264e renamed BNF/Countable_Set to Countable_Type and moved its generic stuff to Library/Countable_Set
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parents: 50134
diff changeset
   158
  by (rule exI[of _ "to_nat_on A a"]) simp
885deccc264e renamed BNF/Countable_Set to Countable_Type and moved its generic stuff to Library/Countable_Set
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diff changeset
   159
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diff changeset
   160
lemma from_nat_into_inject[simp]:
50148
b8cff6a8fda2 Countable_Set: tuned lemma names; more generic lemmas
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diff changeset
   161
  "A \<noteq> {} \<Longrightarrow> countable A \<Longrightarrow> B \<noteq> {} \<Longrightarrow> countable B \<Longrightarrow> from_nat_into A = from_nat_into B \<longleftrightarrow> A = B"
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parents: 50144
diff changeset
   162
  by (metis range_from_nat_into)
50144
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diff changeset
   163
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   164
lemma inj_on_from_nat_into: "inj_on from_nat_into ({A. A \<noteq> {} \<and> countable A})"
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parents: 50144
diff changeset
   165
  unfolding inj_on_def by auto
50144
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diff changeset
   166
50134
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   167
subsection {* Closure properties of countability *}
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parents:
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   168
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   169
lemma countable_SIGMA[intro, simp]:
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parents:
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   170
  "countable I \<Longrightarrow> (\<And>i. i \<in> I \<Longrightarrow> countable (A i)) \<Longrightarrow> countable (SIGMA i : I. A i)"
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parents:
diff changeset
   171
  by (intro countableI'[of "\<lambda>(i, a). (to_nat_on I i, to_nat_on (A i) a)"]) (auto simp: inj_on_def)
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parents:
diff changeset
   172
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   173
lemma countable_image[intro, simp]:
355a4cac5440 tuned proofs -- less guessing;
wenzelm
parents: 51542
diff changeset
   174
  assumes "countable A"
355a4cac5440 tuned proofs -- less guessing;
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parents: 51542
diff changeset
   175
  shows "countable (f`A)"
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13211e07d931 add Countable_Set theory
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parents:
diff changeset
   176
proof -
53381
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parents: 51542
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   177
  obtain g :: "'a \<Rightarrow> nat" where "inj_on g A"
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parents: 51542
diff changeset
   178
    using assms by (rule countableE)
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parents:
diff changeset
   179
  moreover have "inj_on (inv_into A f) (f`A)" "inv_into A f ` f ` A \<subseteq> A"
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hoelzl
parents:
diff changeset
   180
    by (auto intro: inj_on_inv_into inv_into_into)
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parents:
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   181
  ultimately show ?thesis
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   182
    by (blast dest: comp_inj_on subset_inj_on intro: countableI)
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   183
qed
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   184
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   185
lemma countable_UN[intro, simp]:
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   186
  fixes I :: "'i set" and A :: "'i => 'a set"
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   187
  assumes I: "countable I"
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   188
  assumes A: "\<And>i. i \<in> I \<Longrightarrow> countable (A i)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   189
  shows "countable (\<Union>i\<in>I. A i)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   190
proof -
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   191
  have "(\<Union>i\<in>I. A i) = snd ` (SIGMA i : I. A i)" by (auto simp: image_iff)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   192
  then show ?thesis by (simp add: assms)
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   193
qed
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   194
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   195
lemma countable_Un[intro]: "countable A \<Longrightarrow> countable B \<Longrightarrow> countable (A \<union> B)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   196
  by (rule countable_UN[of "{True, False}" "\<lambda>True \<Rightarrow> A | False \<Rightarrow> B", simplified])
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   197
     (simp split: bool.split)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   198
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   199
lemma countable_Un_iff[simp]: "countable (A \<union> B) \<longleftrightarrow> countable A \<and> countable B"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   200
  by (metis countable_Un countable_subset inf_sup_ord(3,4))
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   201
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   202
lemma countable_Plus[intro, simp]:
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   203
  "countable A \<Longrightarrow> countable B \<Longrightarrow> countable (A <+> B)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   204
  by (simp add: Plus_def)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   205
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   206
lemma countable_empty[intro, simp]: "countable {}"
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   207
  by (blast intro: countable_finite)
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   208
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   209
lemma countable_insert[intro, simp]: "countable A \<Longrightarrow> countable (insert a A)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   210
  using countable_Un[of "{a}" A] by (auto simp: countable_finite)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   211
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   212
lemma countable_Int1[intro, simp]: "countable A \<Longrightarrow> countable (A \<inter> B)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   213
  by (force intro: countable_subset)
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   214
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   215
lemma countable_Int2[intro, simp]: "countable B \<Longrightarrow> countable (A \<inter> B)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   216
  by (blast intro: countable_subset)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   217
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   218
lemma countable_INT[intro, simp]: "i \<in> I \<Longrightarrow> countable (A i) \<Longrightarrow> countable (\<Inter>i\<in>I. A i)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   219
  by (blast intro: countable_subset)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   220
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   221
lemma countable_Diff[intro, simp]: "countable A \<Longrightarrow> countable (A - B)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   222
  by (blast intro: countable_subset)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   223
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   224
lemma countable_vimage: "B \<subseteq> range f \<Longrightarrow> countable (f -` B) \<Longrightarrow> countable B"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   225
  by (metis Int_absorb2 assms countable_image image_vimage_eq)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   226
13211e07d931 add Countable_Set theory
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parents:
diff changeset
   227
lemma surj_countable_vimage: "surj f \<Longrightarrow> countable (f -` B) \<Longrightarrow> countable B"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   228
  by (metis countable_vimage top_greatest)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   229
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885deccc264e renamed BNF/Countable_Set to Countable_Type and moved its generic stuff to Library/Countable_Set
hoelzl
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diff changeset
   230
lemma countable_Collect[simp]: "countable A \<Longrightarrow> countable {a \<in> A. \<phi> a}"
885deccc264e renamed BNF/Countable_Set to Countable_Type and moved its generic stuff to Library/Countable_Set
hoelzl
parents: 50134
diff changeset
   231
  by (metis Collect_conj_eq Int_absorb Int_commute Int_def countable_Int1)
885deccc264e renamed BNF/Countable_Set to Countable_Type and moved its generic stuff to Library/Countable_Set
hoelzl
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diff changeset
   232
54410
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diff changeset
   233
lemma countable_Image:
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hoelzl
parents: 53381
diff changeset
   234
  assumes "\<And>y. y \<in> Y \<Longrightarrow> countable (X `` {y})"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   235
  assumes "countable Y"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   236
  shows "countable (X `` Y)"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   237
proof -
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   238
  have "countable (X `` (\<Union>y\<in>Y. {y}))"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   239
    unfolding Image_UN by (intro countable_UN assms)
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   240
  then show ?thesis by simp
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   241
qed
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   242
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   243
lemma countable_relpow:
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   244
  fixes X :: "'a rel"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   245
  assumes Image_X: "\<And>Y. countable Y \<Longrightarrow> countable (X `` Y)"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   246
  assumes Y: "countable Y"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   247
  shows "countable ((X ^^ i) `` Y)"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   248
  using Y by (induct i arbitrary: Y) (auto simp: relcomp_Image Image_X)
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   249
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
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diff changeset
   250
lemma countable_rtrancl:
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   251
  "(\<And>Y. countable Y \<Longrightarrow> countable (X `` Y)) \<Longrightarrow> countable Y \<Longrightarrow> countable (X^* `` Y)"
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   252
  unfolding rtrancl_is_UN_relpow UN_Image by (intro countable_UN countableI_type countable_relpow)
0a578fb7fb73 countability of the image of a reflexive transitive closure
hoelzl
parents: 53381
diff changeset
   253
50134
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parents:
diff changeset
   254
lemma countable_lists[intro, simp]:
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hoelzl
parents:
diff changeset
   255
  assumes A: "countable A" shows "countable (lists A)"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   256
proof -
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   257
  have "countable (lists (range (from_nat_into A)))"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   258
    by (auto simp: lists_image)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   259
  with A show ?thesis
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   260
    by (auto dest: subset_range_from_nat_into countable_subset lists_mono)
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   261
qed
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   262
50245
dea9363887a6 based countable topological basis on Countable_Set
immler
parents: 50148
diff changeset
   263
lemma Collect_finite_eq_lists: "Collect finite = set ` lists UNIV"
dea9363887a6 based countable topological basis on Countable_Set
immler
parents: 50148
diff changeset
   264
  using finite_list by auto
dea9363887a6 based countable topological basis on Countable_Set
immler
parents: 50148
diff changeset
   265
dea9363887a6 based countable topological basis on Countable_Set
immler
parents: 50148
diff changeset
   266
lemma countable_Collect_finite: "countable (Collect (finite::'a::countable set\<Rightarrow>bool))"
dea9363887a6 based countable topological basis on Countable_Set
immler
parents: 50148
diff changeset
   267
  by (simp add: Collect_finite_eq_lists)
dea9363887a6 based countable topological basis on Countable_Set
immler
parents: 50148
diff changeset
   268
50936
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   269
lemma countable_rat: "countable \<rat>"
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   270
  unfolding Rats_def by auto
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   271
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   272
lemma Collect_finite_subset_eq_lists: "{A. finite A \<and> A \<subseteq> T} = set ` lists T"
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   273
  using finite_list by (auto simp: lists_eq_set)
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   274
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   275
lemma countable_Collect_finite_subset:
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   276
  "countable T \<Longrightarrow> countable {A. finite A \<and> A \<subseteq> T}"
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   277
  unfolding Collect_finite_subset_eq_lists by auto
b28f258ebc1a countablility of finite subsets and rational numbers
hoelzl
parents: 50245
diff changeset
   278
50134
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parents:
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   279
subsection {* Misc lemmas *}
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parents:
diff changeset
   280
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parents:
diff changeset
   281
lemma countable_all:
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parents:
diff changeset
   282
  assumes S: "countable S"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   283
  shows "(\<forall>s\<in>S. P s) \<longleftrightarrow> (\<forall>n::nat. from_nat_into S n \<in> S \<longrightarrow> P (from_nat_into S n))"
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   284
  using S[THEN subset_range_from_nat_into] by auto
13211e07d931 add Countable_Set theory
hoelzl
parents:
diff changeset
   285
57025
e7fd64f82876 add various lemmas
hoelzl
parents: 54410
diff changeset
   286
lemma finite_sequence_to_countable_set:
e7fd64f82876 add various lemmas
hoelzl
parents: 54410
diff changeset
   287
   assumes "countable X" obtains F where "\<And>i. F i \<subseteq> X" "\<And>i. F i \<subseteq> F (Suc i)" "\<And>i. finite (F i)" "(\<Union>i. F i) = X"
e7fd64f82876 add various lemmas
hoelzl
parents: 54410
diff changeset
   288
proof -  show thesis
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    apply (rule that[of "\<lambda>i. if X = {} then {} else from_nat_into X ` {..i}"])
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    apply (auto simp: image_iff Ball_def intro: from_nat_into split: split_if_asm)
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  proof -
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    fix x n assume "x \<in> X" "\<forall>i m. m \<le> i \<longrightarrow> x \<noteq> from_nat_into X m"
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    with from_nat_into_surj[OF `countable X` `x \<in> X`]
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    show False
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      by auto
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  qed
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qed
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50134
13211e07d931 add Countable_Set theory
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end