src/HOL/Probability/Caratheodory.thy
author hoelzl
Tue Mar 29 14:27:31 2011 +0200 (2011-03-29)
changeset 42145 8448713d48b7
parent 42067 66c8281349ec
child 42950 6e5c2a3c69da
permissions -rw-r--r--
proved caratheodory_empty_continuous
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(*  Title:      HOL/Probability/Caratheodory.thy
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    Author:     Lawrence C Paulson
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    Author:     Johannes Hölzl, TU München
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*)
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header {*Caratheodory Extension Theorem*}
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theory Caratheodory
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  imports Sigma_Algebra Extended_Real_Limits
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begin
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text {*
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  Originally from the Hurd/Coble measure theory development, translated by Lawrence Paulson.
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*}
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lemma suminf_extreal_2dimen:
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  fixes f:: "nat \<times> nat \<Rightarrow> extreal"
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  assumes pos: "\<And>p. 0 \<le> f p"
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  assumes "\<And>m. g m = (\<Sum>n. f (m,n))"
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  shows "(\<Sum>i. f (prod_decode i)) = suminf g"
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proof -
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  have g_def: "g = (\<lambda>m. (\<Sum>n. f (m,n)))"
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    using assms by (simp add: fun_eq_iff)
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  have reindex: "\<And>B. (\<Sum>x\<in>B. f (prod_decode x)) = setsum f (prod_decode ` B)"
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    by (simp add: setsum_reindex[OF inj_prod_decode] comp_def)
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  { fix n
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    let ?M = "\<lambda>f. Suc (Max (f ` prod_decode ` {..<n}))"
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    { fix a b x assume "x < n" and [symmetric]: "(a, b) = prod_decode x"
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      then have "a < ?M fst" "b < ?M snd"
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        by (auto intro!: Max_ge le_imp_less_Suc image_eqI) }
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    then have "setsum f (prod_decode ` {..<n}) \<le> setsum f ({..<?M fst} \<times> {..<?M snd})"
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      by (auto intro!: setsum_mono3 simp: pos)
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    then have "\<exists>a b. setsum f (prod_decode ` {..<n}) \<le> setsum f ({..<a} \<times> {..<b})" by auto }
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  moreover
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  { fix a b
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    let ?M = "prod_decode ` {..<Suc (Max (prod_encode ` ({..<a} \<times> {..<b})))}"
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    { fix a' b' assume "a' < a" "b' < b" then have "(a', b') \<in> ?M"
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        by (auto intro!: Max_ge le_imp_less_Suc image_eqI[where x="prod_encode (a', b')"]) }
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    then have "setsum f ({..<a} \<times> {..<b}) \<le> setsum f ?M"
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      by (auto intro!: setsum_mono3 simp: pos) }
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  ultimately
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  show ?thesis unfolding g_def using pos
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    by (auto intro!: SUPR_eq  simp: setsum_cartesian_product reindex le_SUPI2
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                     setsum_nonneg suminf_extreal_eq_SUPR SUPR_pair
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                     SUPR_extreal_setsum[symmetric] incseq_setsumI setsum_nonneg)
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qed
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subsection {* Measure Spaces *}
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record 'a measure_space = "'a algebra" +
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  measure :: "'a set \<Rightarrow> extreal"
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definition positive where "positive M f \<longleftrightarrow> f {} = (0::extreal) \<and> (\<forall>A\<in>sets M. 0 \<le> f A)"
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definition additive where "additive M f \<longleftrightarrow>
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  (\<forall>x \<in> sets M. \<forall>y \<in> sets M. x \<inter> y = {} \<longrightarrow> f (x \<union> y) = f x + f y)"
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definition countably_additive :: "('a, 'b) algebra_scheme \<Rightarrow> ('a set \<Rightarrow> extreal) \<Rightarrow> bool" where
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  "countably_additive M f \<longleftrightarrow> (\<forall>A. range A \<subseteq> sets M \<longrightarrow> disjoint_family A \<longrightarrow> (\<Union>i. A i) \<in> sets M \<longrightarrow>
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    (\<Sum>i. f (A i)) = f (\<Union>i. A i))"
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definition increasing where "increasing M f \<longleftrightarrow>
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  (\<forall>x \<in> sets M. \<forall>y \<in> sets M. x \<subseteq> y \<longrightarrow> f x \<le> f y)"
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definition subadditive where "subadditive M f \<longleftrightarrow>
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  (\<forall>x \<in> sets M. \<forall>y \<in> sets M. x \<inter> y = {} \<longrightarrow> f (x \<union> y) \<le> f x + f y)"
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definition countably_subadditive where "countably_subadditive M f \<longleftrightarrow>
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  (\<forall>A. range A \<subseteq> sets M \<longrightarrow> disjoint_family A \<longrightarrow> (\<Union>i. A i) \<in> sets M \<longrightarrow>
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    (f (\<Union>i. A i) \<le> (\<Sum>i. f (A i))))"
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definition lambda_system where "lambda_system M f = {l \<in> sets M.
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  \<forall>x \<in> sets M. f (l \<inter> x) + f ((space M - l) \<inter> x) = f x}"
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definition outer_measure_space where "outer_measure_space M f \<longleftrightarrow>
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  positive M f \<and> increasing M f \<and> countably_subadditive M f"
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definition measure_set where "measure_set M f X = {r.
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  \<exists>A. range A \<subseteq> sets M \<and> disjoint_family A \<and> X \<subseteq> (\<Union>i. A i) \<and> (\<Sum>i. f (A i)) = r}"
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locale measure_space = sigma_algebra M for M :: "('a, 'b) measure_space_scheme" +
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  assumes measure_positive: "positive M (measure M)"
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      and ca: "countably_additive M (measure M)"
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abbreviation (in measure_space) "\<mu> \<equiv> measure M"
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lemma (in measure_space)
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  shows empty_measure[simp, intro]: "\<mu> {} = 0"
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  and positive_measure[simp, intro!]: "\<And>A. A \<in> sets M \<Longrightarrow> 0 \<le> \<mu> A"
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  using measure_positive unfolding positive_def by auto
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lemma increasingD:
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  "increasing M f \<Longrightarrow> x \<subseteq> y \<Longrightarrow> x\<in>sets M \<Longrightarrow> y\<in>sets M \<Longrightarrow> f x \<le> f y"
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  by (auto simp add: increasing_def)
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lemma subadditiveD:
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  "subadditive M f \<Longrightarrow> x \<inter> y = {} \<Longrightarrow> x \<in> sets M \<Longrightarrow> y \<in> sets M
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    \<Longrightarrow> f (x \<union> y) \<le> f x + f y"
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  by (auto simp add: subadditive_def)
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lemma additiveD:
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  "additive M f \<Longrightarrow> x \<inter> y = {} \<Longrightarrow> x \<in> sets M \<Longrightarrow> y \<in> sets M
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    \<Longrightarrow> f (x \<union> y) = f x + f y"
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  by (auto simp add: additive_def)
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lemma countably_additiveI:
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  assumes "\<And>A x. range A \<subseteq> sets M \<Longrightarrow> disjoint_family A \<Longrightarrow> (\<Union>i. A i) \<in> sets M
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    \<Longrightarrow> (\<Sum>i. f (A i)) = f (\<Union>i. A i)"
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  shows "countably_additive M f"
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  using assms by (simp add: countably_additive_def)
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section "Extend binary sets"
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lemma LIMSEQ_binaryset:
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  assumes f: "f {} = 0"
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  shows  "(\<lambda>n. \<Sum>i<n. f (binaryset A B i)) ----> f A + f B"
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proof -
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  have "(\<lambda>n. \<Sum>i < Suc (Suc n). f (binaryset A B i)) = (\<lambda>n. f A + f B)"
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    proof
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      fix n
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      show "(\<Sum>i < Suc (Suc n). f (binaryset A B i)) = f A + f B"
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        by (induct n)  (auto simp add: binaryset_def f)
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    qed
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  moreover
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  have "... ----> f A + f B" by (rule LIMSEQ_const)
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  ultimately
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  have "(\<lambda>n. \<Sum>i< Suc (Suc n). f (binaryset A B i)) ----> f A + f B"
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    by metis
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  hence "(\<lambda>n. \<Sum>i< n+2. f (binaryset A B i)) ----> f A + f B"
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    by simp
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  thus ?thesis by (rule LIMSEQ_offset [where k=2])
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qed
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lemma binaryset_sums:
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  assumes f: "f {} = 0"
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  shows  "(\<lambda>n. f (binaryset A B n)) sums (f A + f B)"
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    by (simp add: sums_def LIMSEQ_binaryset [where f=f, OF f] atLeast0LessThan)
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lemma suminf_binaryset_eq:
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  fixes f :: "'a set \<Rightarrow> 'b::{comm_monoid_add, t2_space}"
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  shows "f {} = 0 \<Longrightarrow> (\<Sum>n. f (binaryset A B n)) = f A + f B"
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  by (metis binaryset_sums sums_unique)
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subsection {* Lambda Systems *}
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lemma (in algebra) lambda_system_eq:
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  shows "lambda_system M f = {l \<in> sets M.
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    \<forall>x \<in> sets M. f (x \<inter> l) + f (x - l) = f x}"
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proof -
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  have [simp]: "!!l x. l \<in> sets M \<Longrightarrow> x \<in> sets M \<Longrightarrow> (space M - l) \<inter> x = x - l"
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    by (metis Int_Diff Int_absorb1 Int_commute sets_into_space)
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  show ?thesis
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    by (auto simp add: lambda_system_def) (metis Int_commute)+
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qed
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lemma (in algebra) lambda_system_empty:
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  "positive M f \<Longrightarrow> {} \<in> lambda_system M f"
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  by (auto simp add: positive_def lambda_system_eq)
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lemma lambda_system_sets:
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  "x \<in> lambda_system M f \<Longrightarrow> x \<in> sets M"
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  by (simp add: lambda_system_def)
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lemma (in algebra) lambda_system_Compl:
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  fixes f:: "'a set \<Rightarrow> extreal"
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  assumes x: "x \<in> lambda_system M f"
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  shows "space M - x \<in> lambda_system M f"
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proof -
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  have "x \<subseteq> space M"
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    by (metis sets_into_space lambda_system_sets x)
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  hence "space M - (space M - x) = x"
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    by (metis double_diff equalityE)
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  with x show ?thesis
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    by (force simp add: lambda_system_def ac_simps)
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qed
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lemma (in algebra) lambda_system_Int:
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  fixes f:: "'a set \<Rightarrow> extreal"
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  assumes xl: "x \<in> lambda_system M f" and yl: "y \<in> lambda_system M f"
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  shows "x \<inter> y \<in> lambda_system M f"
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proof -
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  from xl yl show ?thesis
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  proof (auto simp add: positive_def lambda_system_eq Int)
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    fix u
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    assume x: "x \<in> sets M" and y: "y \<in> sets M" and u: "u \<in> sets M"
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       and fx: "\<forall>z\<in>sets M. f (z \<inter> x) + f (z - x) = f z"
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       and fy: "\<forall>z\<in>sets M. f (z \<inter> y) + f (z - y) = f z"
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    have "u - x \<inter> y \<in> sets M"
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      by (metis Diff Diff_Int Un u x y)
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    moreover
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    have "(u - (x \<inter> y)) \<inter> y = u \<inter> y - x" by blast
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    moreover
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    have "u - x \<inter> y - y = u - y" by blast
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    ultimately
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    have ey: "f (u - x \<inter> y) = f (u \<inter> y - x) + f (u - y)" using fy
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      by force
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    have "f (u \<inter> (x \<inter> y)) + f (u - x \<inter> y)
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          = (f (u \<inter> (x \<inter> y)) + f (u \<inter> y - x)) + f (u - y)"
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      by (simp add: ey ac_simps)
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    also have "... =  (f ((u \<inter> y) \<inter> x) + f (u \<inter> y - x)) + f (u - y)"
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      by (simp add: Int_ac)
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    also have "... = f (u \<inter> y) + f (u - y)"
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      using fx [THEN bspec, of "u \<inter> y"] Int y u
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      by force
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    also have "... = f u"
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      by (metis fy u)
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    finally show "f (u \<inter> (x \<inter> y)) + f (u - x \<inter> y) = f u" .
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  qed
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qed
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lemma (in algebra) lambda_system_Un:
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  fixes f:: "'a set \<Rightarrow> extreal"
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  assumes xl: "x \<in> lambda_system M f" and yl: "y \<in> lambda_system M f"
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  shows "x \<union> y \<in> lambda_system M f"
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proof -
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  have "(space M - x) \<inter> (space M - y) \<in> sets M"
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    by (metis Diff_Un Un compl_sets lambda_system_sets xl yl)
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  moreover
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  have "x \<union> y = space M - ((space M - x) \<inter> (space M - y))"
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    by auto  (metis subsetD lambda_system_sets sets_into_space xl yl)+
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  ultimately show ?thesis
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    by (metis lambda_system_Compl lambda_system_Int xl yl)
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qed
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lemma (in algebra) lambda_system_algebra:
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  "positive M f \<Longrightarrow> algebra (M\<lparr>sets := lambda_system M f\<rparr>)"
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  apply (auto simp add: algebra_iff_Un)
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  apply (metis lambda_system_sets set_mp sets_into_space)
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  apply (metis lambda_system_empty)
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  apply (metis lambda_system_Compl)
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  apply (metis lambda_system_Un)
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  done
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lemma (in algebra) lambda_system_strong_additive:
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  assumes z: "z \<in> sets M" and disj: "x \<inter> y = {}"
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      and xl: "x \<in> lambda_system M f" and yl: "y \<in> lambda_system M f"
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  shows "f (z \<inter> (x \<union> y)) = f (z \<inter> x) + f (z \<inter> y)"
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proof -
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  have "z \<inter> x = (z \<inter> (x \<union> y)) \<inter> x" using disj by blast
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  moreover
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  have "z \<inter> y = (z \<inter> (x \<union> y)) - x" using disj by blast
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  moreover
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  have "(z \<inter> (x \<union> y)) \<in> sets M"
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    by (metis Int Un lambda_system_sets xl yl z)
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  ultimately show ?thesis using xl yl
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    by (simp add: lambda_system_eq)
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qed
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lemma (in algebra) lambda_system_additive:
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     "additive (M (|sets := lambda_system M f|)) f"
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proof (auto simp add: additive_def)
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  fix x and y
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  assume disj: "x \<inter> y = {}"
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     and xl: "x \<in> lambda_system M f" and yl: "y \<in> lambda_system M f"
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  hence  "x \<in> sets M" "y \<in> sets M" by (blast intro: lambda_system_sets)+
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  thus "f (x \<union> y) = f x + f y"
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    using lambda_system_strong_additive [OF top disj xl yl]
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    by (simp add: Un)
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qed
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lemma (in ring_of_sets) disjointed_additive:
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  assumes f: "positive M f" "additive M f" and A: "range A \<subseteq> sets M" "incseq A"
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  shows "(\<Sum>i\<le>n. f (disjointed A i)) = f (A n)"
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proof (induct n)
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  case (Suc n)
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  then have "(\<Sum>i\<le>Suc n. f (disjointed A i)) = f (A n) + f (disjointed A (Suc n))"
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    by simp
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  also have "\<dots> = f (A n \<union> disjointed A (Suc n))"
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    using A by (subst f(2)[THEN additiveD]) (auto simp: disjointed_incseq)
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  also have "A n \<union> disjointed A (Suc n) = A (Suc n)"
hoelzl@42145
   271
    using `incseq A` by (auto dest: incseq_SucD simp: disjointed_incseq)
hoelzl@42145
   272
  finally show ?case .
hoelzl@42145
   273
qed simp
hoelzl@42145
   274
hoelzl@42145
   275
lemma (in ring_of_sets) countably_subadditive_subadditive:
hoelzl@41689
   276
  assumes f: "positive M f" and cs: "countably_subadditive M f"
paulson@33271
   277
  shows  "subadditive M f"
hoelzl@35582
   278
proof (auto simp add: subadditive_def)
paulson@33271
   279
  fix x y
paulson@33271
   280
  assume x: "x \<in> sets M" and y: "y \<in> sets M" and "x \<inter> y = {}"
paulson@33271
   281
  hence "disjoint_family (binaryset x y)"
hoelzl@35582
   282
    by (auto simp add: disjoint_family_on_def binaryset_def)
hoelzl@35582
   283
  hence "range (binaryset x y) \<subseteq> sets M \<longrightarrow>
hoelzl@35582
   284
         (\<Union>i. binaryset x y i) \<in> sets M \<longrightarrow>
hoelzl@41981
   285
         f (\<Union>i. binaryset x y i) \<le> (\<Sum> n. f (binaryset x y n))"
hoelzl@41981
   286
    using cs by (auto simp add: countably_subadditive_def)
hoelzl@35582
   287
  hence "{x,y,{}} \<subseteq> sets M \<longrightarrow> x \<union> y \<in> sets M \<longrightarrow>
hoelzl@41981
   288
         f (x \<union> y) \<le> (\<Sum> n. f (binaryset x y n))"
paulson@33271
   289
    by (simp add: range_binaryset_eq UN_binaryset_eq)
hoelzl@38656
   290
  thus "f (x \<union> y) \<le>  f x + f y" using f x y
hoelzl@41981
   291
    by (auto simp add: Un o_def suminf_binaryset_eq positive_def)
paulson@33271
   292
qed
paulson@33271
   293
hoelzl@42145
   294
lemma (in ring_of_sets) additive_sum:
paulson@33271
   295
  fixes A:: "nat \<Rightarrow> 'a set"
hoelzl@41981
   296
  assumes f: "positive M f" and ad: "additive M f" and "finite S"
paulson@33271
   297
      and A: "range A \<subseteq> sets M"
hoelzl@41981
   298
      and disj: "disjoint_family_on A S"
hoelzl@41981
   299
  shows  "(\<Sum>i\<in>S. f (A i)) = f (\<Union>i\<in>S. A i)"
hoelzl@41981
   300
using `finite S` disj proof induct
hoelzl@41981
   301
  case empty show ?case using f by (simp add: positive_def)
paulson@33271
   302
next
hoelzl@41981
   303
  case (insert s S)
hoelzl@41981
   304
  then have "A s \<inter> (\<Union>i\<in>S. A i) = {}"
hoelzl@41981
   305
    by (auto simp add: disjoint_family_on_def neq_iff)
hoelzl@38656
   306
  moreover
hoelzl@41981
   307
  have "A s \<in> sets M" using A by blast
hoelzl@41981
   308
  moreover have "(\<Union>i\<in>S. A i) \<in> sets M"
hoelzl@41981
   309
    using A `finite S` by auto
hoelzl@38656
   310
  moreover
hoelzl@41981
   311
  ultimately have "f (A s \<union> (\<Union>i\<in>S. A i)) = f (A s) + f(\<Union>i\<in>S. A i)"
hoelzl@38656
   312
    using ad UNION_in_sets A by (auto simp add: additive_def)
hoelzl@41981
   313
  with insert show ?case using ad disjoint_family_on_mono[of S "insert s S" A]
hoelzl@41981
   314
    by (auto simp add: additive_def subset_insertI)
paulson@33271
   315
qed
paulson@33271
   316
hoelzl@38656
   317
lemma (in algebra) increasing_additive_bound:
hoelzl@41981
   318
  fixes A:: "nat \<Rightarrow> 'a set" and  f :: "'a set \<Rightarrow> extreal"
hoelzl@41689
   319
  assumes f: "positive M f" and ad: "additive M f"
paulson@33271
   320
      and inc: "increasing M f"
paulson@33271
   321
      and A: "range A \<subseteq> sets M"
paulson@33271
   322
      and disj: "disjoint_family A"
hoelzl@41981
   323
  shows  "(\<Sum>i. f (A i)) \<le> f (space M)"
hoelzl@41981
   324
proof (safe intro!: suminf_bound)
hoelzl@38656
   325
  fix N
hoelzl@41981
   326
  note disj_N = disjoint_family_on_mono[OF _ disj, of "{..<N}"]
hoelzl@41981
   327
  have "(\<Sum>i<N. f (A i)) = f (\<Union>i\<in>{..<N}. A i)"
hoelzl@41981
   328
    by (rule additive_sum [OF f ad _ A]) (auto simp: disj_N)
paulson@33271
   329
  also have "... \<le> f (space M)" using space_closed A
hoelzl@41981
   330
    by (intro increasingD[OF inc] finite_UN) auto
hoelzl@41981
   331
  finally show "(\<Sum>i<N. f (A i)) \<le> f (space M)" by simp
hoelzl@41981
   332
qed (insert f A, auto simp: positive_def)
paulson@33271
   333
paulson@33271
   334
lemma lambda_system_increasing:
hoelzl@41689
   335
 "increasing M f \<Longrightarrow> increasing (M (|sets := lambda_system M f|)) f"
hoelzl@38656
   336
  by (simp add: increasing_def lambda_system_def)
paulson@33271
   337
hoelzl@41689
   338
lemma lambda_system_positive:
hoelzl@41689
   339
  "positive M f \<Longrightarrow> positive (M (|sets := lambda_system M f|)) f"
hoelzl@41689
   340
  by (simp add: positive_def lambda_system_def)
hoelzl@41689
   341
paulson@33271
   342
lemma (in algebra) lambda_system_strong_sum:
hoelzl@41981
   343
  fixes A:: "nat \<Rightarrow> 'a set" and f :: "'a set \<Rightarrow> extreal"
hoelzl@41689
   344
  assumes f: "positive M f" and a: "a \<in> sets M"
paulson@33271
   345
      and A: "range A \<subseteq> lambda_system M f"
paulson@33271
   346
      and disj: "disjoint_family A"
paulson@33271
   347
  shows  "(\<Sum>i = 0..<n. f (a \<inter>A i)) = f (a \<inter> (\<Union>i\<in>{0..<n}. A i))"
paulson@33271
   348
proof (induct n)
hoelzl@38656
   349
  case 0 show ?case using f by (simp add: positive_def)
paulson@33271
   350
next
hoelzl@38656
   351
  case (Suc n)
paulson@33271
   352
  have 2: "A n \<inter> UNION {0..<n} A = {}" using disj
hoelzl@38656
   353
    by (force simp add: disjoint_family_on_def neq_iff)
paulson@33271
   354
  have 3: "A n \<in> lambda_system M f" using A
paulson@33271
   355
    by blast
hoelzl@42065
   356
  interpret l: algebra "M\<lparr>sets := lambda_system M f\<rparr>"
hoelzl@42065
   357
    using f by (rule lambda_system_algebra)
paulson@33271
   358
  have 4: "UNION {0..<n} A \<in> lambda_system M f"
hoelzl@42065
   359
    using A l.UNION_in_sets by simp
paulson@33271
   360
  from Suc.hyps show ?case
paulson@33271
   361
    by (simp add: atLeastLessThanSuc lambda_system_strong_additive [OF a 2 3 4])
paulson@33271
   362
qed
paulson@33271
   363
paulson@33271
   364
lemma (in sigma_algebra) lambda_system_caratheodory:
paulson@33271
   365
  assumes oms: "outer_measure_space M f"
paulson@33271
   366
      and A: "range A \<subseteq> lambda_system M f"
paulson@33271
   367
      and disj: "disjoint_family A"
hoelzl@41981
   368
  shows  "(\<Union>i. A i) \<in> lambda_system M f \<and> (\<Sum>i. f (A i)) = f (\<Union>i. A i)"
paulson@33271
   369
proof -
hoelzl@41689
   370
  have pos: "positive M f" and inc: "increasing M f"
hoelzl@38656
   371
   and csa: "countably_subadditive M f"
paulson@33271
   372
    by (metis oms outer_measure_space_def)+
paulson@33271
   373
  have sa: "subadditive M f"
hoelzl@38656
   374
    by (metis countably_subadditive_subadditive csa pos)
hoelzl@38656
   375
  have A': "range A \<subseteq> sets (M(|sets := lambda_system M f|))" using A
paulson@33271
   376
    by simp
hoelzl@42065
   377
  interpret ls: algebra "M\<lparr>sets := lambda_system M f\<rparr>"
hoelzl@42065
   378
    using pos by (rule lambda_system_algebra)
paulson@33271
   379
  have A'': "range A \<subseteq> sets M"
paulson@33271
   380
     by (metis A image_subset_iff lambda_system_sets)
hoelzl@38656
   381
paulson@33271
   382
  have U_in: "(\<Union>i. A i) \<in> sets M"
huffman@37032
   383
    by (metis A'' countable_UN)
hoelzl@41981
   384
  have U_eq: "f (\<Union>i. A i) = (\<Sum>i. f (A i))"
hoelzl@41689
   385
  proof (rule antisym)
hoelzl@41981
   386
    show "f (\<Union>i. A i) \<le> (\<Sum>i. f (A i))"
hoelzl@41981
   387
      using csa[unfolded countably_subadditive_def] A'' disj U_in by auto
hoelzl@41981
   388
    have *: "\<And>i. 0 \<le> f (A i)" using pos A'' unfolding positive_def by auto
hoelzl@41981
   389
    have dis: "\<And>N. disjoint_family_on A {..<N}" by (intro disjoint_family_on_mono[OF _ disj]) auto
hoelzl@41981
   390
    show "(\<Sum>i. f (A i)) \<le> f (\<Union>i. A i)"
hoelzl@42065
   391
      using ls.additive_sum [OF lambda_system_positive[OF pos] lambda_system_additive _ A' dis]
hoelzl@41981
   392
      using A''
hoelzl@41981
   393
      by (intro suminf_bound[OF _ *]) (auto intro!: increasingD[OF inc] allI countable_UN)
hoelzl@41689
   394
  qed
paulson@33271
   395
  {
hoelzl@38656
   396
    fix a
hoelzl@38656
   397
    assume a [iff]: "a \<in> sets M"
paulson@33271
   398
    have "f (a \<inter> (\<Union>i. A i)) + f (a - (\<Union>i. A i)) = f a"
paulson@33271
   399
    proof -
paulson@33271
   400
      show ?thesis
paulson@33271
   401
      proof (rule antisym)
wenzelm@33536
   402
        have "range (\<lambda>i. a \<inter> A i) \<subseteq> sets M" using A''
wenzelm@33536
   403
          by blast
hoelzl@38656
   404
        moreover
wenzelm@33536
   405
        have "disjoint_family (\<lambda>i. a \<inter> A i)" using disj
hoelzl@38656
   406
          by (auto simp add: disjoint_family_on_def)
hoelzl@38656
   407
        moreover
wenzelm@33536
   408
        have "a \<inter> (\<Union>i. A i) \<in> sets M"
wenzelm@33536
   409
          by (metis Int U_in a)
hoelzl@38656
   410
        ultimately
hoelzl@41981
   411
        have "f (a \<inter> (\<Union>i. A i)) \<le> (\<Sum>i. f (a \<inter> A i))"
hoelzl@41981
   412
          using csa[unfolded countably_subadditive_def, rule_format, of "(\<lambda>i. a \<inter> A i)"]
hoelzl@38656
   413
          by (simp add: o_def)
hoelzl@38656
   414
        hence "f (a \<inter> (\<Union>i. A i)) + f (a - (\<Union>i. A i)) \<le>
hoelzl@41981
   415
            (\<Sum>i. f (a \<inter> A i)) + f (a - (\<Union>i. A i))"
hoelzl@38656
   416
          by (rule add_right_mono)
hoelzl@38656
   417
        moreover
hoelzl@41981
   418
        have "(\<Sum>i. f (a \<inter> A i)) + f (a - (\<Union>i. A i)) \<le> f a"
hoelzl@41981
   419
          proof (intro suminf_bound_add allI)
wenzelm@33536
   420
            fix n
wenzelm@33536
   421
            have UNION_in: "(\<Union>i\<in>{0..<n}. A i) \<in> sets M"
hoelzl@38656
   422
              by (metis A'' UNION_in_sets)
wenzelm@33536
   423
            have le_fa: "f (UNION {0..<n} A \<inter> a) \<le> f a" using A''
huffman@37032
   424
              by (blast intro: increasingD [OF inc] A'' UNION_in_sets)
wenzelm@33536
   425
            have ls: "(\<Union>i\<in>{0..<n}. A i) \<in> lambda_system M f"
hoelzl@42065
   426
              using ls.UNION_in_sets by (simp add: A)
hoelzl@38656
   427
            hence eq_fa: "f a = f (a \<inter> (\<Union>i\<in>{0..<n}. A i)) + f (a - (\<Union>i\<in>{0..<n}. A i))"
huffman@37032
   428
              by (simp add: lambda_system_eq UNION_in)
wenzelm@33536
   429
            have "f (a - (\<Union>i. A i)) \<le> f (a - (\<Union>i\<in>{0..<n}. A i))"
hoelzl@38656
   430
              by (blast intro: increasingD [OF inc] UNION_eq_Union_image
huffman@37032
   431
                               UNION_in U_in)
hoelzl@41981
   432
            thus "(\<Sum>i<n. f (a \<inter> A i)) + f (a - (\<Union>i. A i)) \<le> f a"
hoelzl@38656
   433
              by (simp add: lambda_system_strong_sum pos A disj eq_fa add_left_mono atLeast0LessThan[symmetric])
hoelzl@41981
   434
          next
hoelzl@41981
   435
            have "\<And>i. a \<inter> A i \<in> sets M" using A'' by auto
hoelzl@41981
   436
            then show "\<And>i. 0 \<le> f (a \<inter> A i)" using pos[unfolded positive_def] by auto
hoelzl@41981
   437
            have "\<And>i. a - (\<Union>i. A i) \<in> sets M" using A'' by auto
hoelzl@41981
   438
            then have "\<And>i. 0 \<le> f (a - (\<Union>i. A i))" using pos[unfolded positive_def] by auto
hoelzl@41981
   439
            then show "f (a - (\<Union>i. A i)) \<noteq> -\<infinity>" by auto
wenzelm@33536
   440
          qed
hoelzl@38656
   441
        ultimately show "f (a \<inter> (\<Union>i. A i)) + f (a - (\<Union>i. A i)) \<le> f a"
hoelzl@38656
   442
          by (rule order_trans)
paulson@33271
   443
      next
hoelzl@38656
   444
        have "f a \<le> f (a \<inter> (\<Union>i. A i) \<union> (a - (\<Union>i. A i)))"
huffman@37032
   445
          by (blast intro:  increasingD [OF inc] U_in)
wenzelm@33536
   446
        also have "... \<le>  f (a \<inter> (\<Union>i. A i)) + f (a - (\<Union>i. A i))"
huffman@37032
   447
          by (blast intro: subadditiveD [OF sa] U_in)
wenzelm@33536
   448
        finally show "f a \<le> f (a \<inter> (\<Union>i. A i)) + f (a - (\<Union>i. A i))" .
paulson@33271
   449
        qed
paulson@33271
   450
     qed
paulson@33271
   451
  }
paulson@33271
   452
  thus  ?thesis
hoelzl@38656
   453
    by (simp add: lambda_system_eq sums_iff U_eq U_in)
paulson@33271
   454
qed
paulson@33271
   455
paulson@33271
   456
lemma (in sigma_algebra) caratheodory_lemma:
paulson@33271
   457
  assumes oms: "outer_measure_space M f"
hoelzl@41689
   458
  shows "measure_space \<lparr> space = space M, sets = lambda_system M f, measure = f \<rparr>"
hoelzl@41689
   459
    (is "measure_space ?M")
paulson@33271
   460
proof -
hoelzl@41689
   461
  have pos: "positive M f"
paulson@33271
   462
    by (metis oms outer_measure_space_def)
hoelzl@41689
   463
  have alg: "algebra ?M"
hoelzl@38656
   464
    using lambda_system_algebra [of f, OF pos]
hoelzl@42065
   465
    by (simp add: algebra_iff_Un)
hoelzl@42065
   466
  then
hoelzl@41689
   467
  have "sigma_algebra ?M"
paulson@33271
   468
    using lambda_system_caratheodory [OF oms]
hoelzl@38656
   469
    by (simp add: sigma_algebra_disjoint_iff)
hoelzl@38656
   470
  moreover
hoelzl@41689
   471
  have "measure_space_axioms ?M"
paulson@33271
   472
    using pos lambda_system_caratheodory [OF oms]
hoelzl@38656
   473
    by (simp add: measure_space_axioms_def positive_def lambda_system_sets
hoelzl@38656
   474
                  countably_additive_def o_def)
hoelzl@38656
   475
  ultimately
paulson@33271
   476
  show ?thesis
hoelzl@42065
   477
    by (simp add: measure_space_def)
paulson@33271
   478
qed
paulson@33271
   479
hoelzl@42066
   480
lemma (in ring_of_sets) additive_increasing:
hoelzl@41689
   481
  assumes posf: "positive M f" and addf: "additive M f"
paulson@33271
   482
  shows "increasing M f"
hoelzl@38656
   483
proof (auto simp add: increasing_def)
paulson@33271
   484
  fix x y
paulson@33271
   485
  assume xy: "x \<in> sets M" "y \<in> sets M" "x \<subseteq> y"
hoelzl@41981
   486
  then have "y - x \<in> sets M" by auto
hoelzl@41981
   487
  then have "0 \<le> f (y-x)" using posf[unfolded positive_def] by auto
hoelzl@41981
   488
  then have "f x + 0 \<le> f x + f (y-x)" by (intro add_left_mono) auto
paulson@33271
   489
  also have "... = f (x \<union> (y-x))" using addf
huffman@37032
   490
    by (auto simp add: additive_def) (metis Diff_disjoint Un_Diff_cancel Diff xy(1,2))
paulson@33271
   491
  also have "... = f y"
huffman@37032
   492
    by (metis Un_Diff_cancel Un_absorb1 xy(3))
hoelzl@41981
   493
  finally show "f x \<le> f y" by simp
paulson@33271
   494
qed
paulson@33271
   495
hoelzl@42066
   496
lemma (in ring_of_sets) countably_additive_additive:
hoelzl@41689
   497
  assumes posf: "positive M f" and ca: "countably_additive M f"
paulson@33271
   498
  shows "additive M f"
hoelzl@38656
   499
proof (auto simp add: additive_def)
paulson@33271
   500
  fix x y
paulson@33271
   501
  assume x: "x \<in> sets M" and y: "y \<in> sets M" and "x \<inter> y = {}"
paulson@33271
   502
  hence "disjoint_family (binaryset x y)"
hoelzl@38656
   503
    by (auto simp add: disjoint_family_on_def binaryset_def)
hoelzl@38656
   504
  hence "range (binaryset x y) \<subseteq> sets M \<longrightarrow>
hoelzl@38656
   505
         (\<Union>i. binaryset x y i) \<in> sets M \<longrightarrow>
hoelzl@41981
   506
         f (\<Union>i. binaryset x y i) = (\<Sum> n. f (binaryset x y n))"
paulson@33271
   507
    using ca
hoelzl@38656
   508
    by (simp add: countably_additive_def)
hoelzl@38656
   509
  hence "{x,y,{}} \<subseteq> sets M \<longrightarrow> x \<union> y \<in> sets M \<longrightarrow>
hoelzl@41981
   510
         f (x \<union> y) = (\<Sum>n. f (binaryset x y n))"
paulson@33271
   511
    by (simp add: range_binaryset_eq UN_binaryset_eq)
paulson@33271
   512
  thus "f (x \<union> y) = f x + f y" using posf x y
hoelzl@41981
   513
    by (auto simp add: Un suminf_binaryset_eq positive_def)
hoelzl@38656
   514
qed
hoelzl@38656
   515
hoelzl@39096
   516
lemma inf_measure_nonempty:
hoelzl@41689
   517
  assumes f: "positive M f" and b: "b \<in> sets M" and a: "a \<subseteq> b" "{} \<in> sets M"
hoelzl@39096
   518
  shows "f b \<in> measure_set M f a"
hoelzl@39096
   519
proof -
hoelzl@41981
   520
  let ?A = "\<lambda>i::nat. (if i = 0 then b else {})"
hoelzl@41981
   521
  have "(\<Sum>i. f (?A i)) = (\<Sum>i<1::nat. f (?A i))"
hoelzl@41981
   522
    by (rule suminf_finite) (simp add: f[unfolded positive_def])
hoelzl@39096
   523
  also have "... = f b"
hoelzl@39096
   524
    by simp
hoelzl@41981
   525
  finally show ?thesis using assms
hoelzl@41981
   526
    by (auto intro!: exI [of _ ?A]
hoelzl@39096
   527
             simp: measure_set_def disjoint_family_on_def split_if_mem2 comp_def)
hoelzl@39096
   528
qed
hoelzl@39096
   529
hoelzl@42066
   530
lemma (in ring_of_sets) inf_measure_agrees:
hoelzl@41689
   531
  assumes posf: "positive M f" and ca: "countably_additive M f"
hoelzl@38656
   532
      and s: "s \<in> sets M"
paulson@33271
   533
  shows "Inf (measure_set M f s) = f s"
hoelzl@41981
   534
  unfolding Inf_extreal_def
hoelzl@38656
   535
proof (safe intro!: Greatest_equality)
paulson@33271
   536
  fix z
paulson@33271
   537
  assume z: "z \<in> measure_set M f s"
hoelzl@38656
   538
  from this obtain A where
paulson@33271
   539
    A: "range A \<subseteq> sets M" and disj: "disjoint_family A"
hoelzl@41981
   540
    and "s \<subseteq> (\<Union>x. A x)" and si: "(\<Sum>i. f (A i)) = z"
hoelzl@38656
   541
    by (auto simp add: measure_set_def comp_def)
paulson@33271
   542
  hence seq: "s = (\<Union>i. A i \<inter> s)" by blast
paulson@33271
   543
  have inc: "increasing M f"
paulson@33271
   544
    by (metis additive_increasing ca countably_additive_additive posf)
hoelzl@41981
   545
  have sums: "(\<Sum>i. f (A i \<inter> s)) = f (\<Union>i. A i \<inter> s)"
hoelzl@41981
   546
    proof (rule ca[unfolded countably_additive_def, rule_format])
paulson@33271
   547
      show "range (\<lambda>n. A n \<inter> s) \<subseteq> sets M" using A s
wenzelm@33536
   548
        by blast
paulson@33271
   549
      show "disjoint_family (\<lambda>n. A n \<inter> s)" using disj
hoelzl@35582
   550
        by (auto simp add: disjoint_family_on_def)
paulson@33271
   551
      show "(\<Union>i. A i \<inter> s) \<in> sets M" using A s
wenzelm@33536
   552
        by (metis UN_extend_simps(4) s seq)
paulson@33271
   553
    qed
hoelzl@41981
   554
  hence "f s = (\<Sum>i. f (A i \<inter> s))"
huffman@37032
   555
    using seq [symmetric] by (simp add: sums_iff)
hoelzl@41981
   556
  also have "... \<le> (\<Sum>i. f (A i))"
hoelzl@41981
   557
    proof (rule suminf_le_pos)
hoelzl@41981
   558
      fix n show "f (A n \<inter> s) \<le> f (A n)" using A s
hoelzl@38656
   559
        by (force intro: increasingD [OF inc])
hoelzl@41981
   560
      fix N have "A N \<inter> s \<in> sets M"  using A s by auto
hoelzl@41981
   561
      then show "0 \<le> f (A N \<inter> s)" using posf unfolding positive_def by auto
paulson@33271
   562
    qed
hoelzl@38656
   563
  also have "... = z" by (rule si)
paulson@33271
   564
  finally show "f s \<le> z" .
paulson@33271
   565
next
paulson@33271
   566
  fix y
hoelzl@38656
   567
  assume y: "\<forall>u \<in> measure_set M f s. y \<le> u"
paulson@33271
   568
  thus "y \<le> f s"
hoelzl@41689
   569
    by (blast intro: inf_measure_nonempty [of _ f, OF posf s subset_refl])
paulson@33271
   570
qed
paulson@33271
   571
hoelzl@41981
   572
lemma measure_set_pos:
hoelzl@41981
   573
  assumes posf: "positive M f" "r \<in> measure_set M f X"
hoelzl@41981
   574
  shows "0 \<le> r"
hoelzl@41981
   575
proof -
hoelzl@41981
   576
  obtain A where "range A \<subseteq> sets M" and r: "r = (\<Sum>i. f (A i))"
hoelzl@41981
   577
    using `r \<in> measure_set M f X` unfolding measure_set_def by auto
hoelzl@41981
   578
  then show "0 \<le> r" using posf unfolding r positive_def
hoelzl@41981
   579
    by (intro suminf_0_le) auto
hoelzl@41981
   580
qed
hoelzl@41981
   581
hoelzl@41981
   582
lemma inf_measure_pos:
hoelzl@41981
   583
  assumes posf: "positive M f"
hoelzl@41981
   584
  shows "0 \<le> Inf (measure_set M f X)"
hoelzl@41981
   585
proof (rule complete_lattice_class.Inf_greatest)
hoelzl@41981
   586
  fix r assume "r \<in> measure_set M f X" with posf show "0 \<le> r"
hoelzl@41981
   587
    by (rule measure_set_pos)
hoelzl@41981
   588
qed
hoelzl@41981
   589
hoelzl@41689
   590
lemma inf_measure_empty:
hoelzl@41981
   591
  assumes posf: "positive M f" and "{} \<in> sets M"
paulson@33271
   592
  shows "Inf (measure_set M f {}) = 0"
paulson@33271
   593
proof (rule antisym)
paulson@33271
   594
  show "Inf (measure_set M f {}) \<le> 0"
hoelzl@41689
   595
    by (metis complete_lattice_class.Inf_lower `{} \<in> sets M`
hoelzl@41689
   596
              inf_measure_nonempty[OF posf] subset_refl posf[unfolded positive_def])
hoelzl@41981
   597
qed (rule inf_measure_pos[OF posf])
paulson@33271
   598
hoelzl@42066
   599
lemma (in ring_of_sets) inf_measure_positive:
hoelzl@41981
   600
  assumes p: "positive M f" and "{} \<in> sets M"
hoelzl@41981
   601
  shows "positive M (\<lambda>x. Inf (measure_set M f x))"
hoelzl@41981
   602
proof (unfold positive_def, intro conjI ballI)
hoelzl@41981
   603
  show "Inf (measure_set M f {}) = 0" using inf_measure_empty[OF assms] by auto
hoelzl@41981
   604
  fix A assume "A \<in> sets M"
hoelzl@41981
   605
qed (rule inf_measure_pos[OF p])
paulson@33271
   606
hoelzl@42066
   607
lemma (in ring_of_sets) inf_measure_increasing:
hoelzl@41689
   608
  assumes posf: "positive M f"
hoelzl@41689
   609
  shows "increasing \<lparr> space = space M, sets = Pow (space M) \<rparr>
paulson@33271
   610
                    (\<lambda>x. Inf (measure_set M f x))"
hoelzl@38656
   611
apply (auto simp add: increasing_def)
hoelzl@38656
   612
apply (rule complete_lattice_class.Inf_greatest)
hoelzl@38656
   613
apply (rule complete_lattice_class.Inf_lower)
huffman@37032
   614
apply (clarsimp simp add: measure_set_def, rule_tac x=A in exI, blast)
paulson@33271
   615
done
paulson@33271
   616
hoelzl@42066
   617
lemma (in ring_of_sets) inf_measure_le:
hoelzl@41689
   618
  assumes posf: "positive M f" and inc: "increasing M f"
hoelzl@41981
   619
      and x: "x \<in> {r . \<exists>A. range A \<subseteq> sets M \<and> s \<subseteq> (\<Union>i. A i) \<and> (\<Sum>i. f (A i)) = r}"
paulson@33271
   620
  shows "Inf (measure_set M f s) \<le> x"
paulson@33271
   621
proof -
hoelzl@38656
   622
  obtain A where A: "range A \<subseteq> sets M" and ss: "s \<subseteq> (\<Union>i. A i)"
hoelzl@41981
   623
             and xeq: "(\<Sum>i. f (A i)) = x"
hoelzl@41981
   624
    using x by auto
paulson@33271
   625
  have dA: "range (disjointed A) \<subseteq> sets M"
paulson@33271
   626
    by (metis A range_disjointed_sets)
hoelzl@41981
   627
  have "\<forall>n. f (disjointed A n) \<le> f (A n)"
hoelzl@38656
   628
    by (metis increasingD [OF inc] UNIV_I dA image_subset_iff disjointed_subset A comp_def)
hoelzl@41981
   629
  moreover have "\<forall>i. 0 \<le> f (disjointed A i)"
hoelzl@41981
   630
    using posf dA unfolding positive_def by auto
hoelzl@41981
   631
  ultimately have sda: "(\<Sum>i. f (disjointed A i)) \<le> (\<Sum>i. f (A i))"
hoelzl@41981
   632
    by (blast intro!: suminf_le_pos)
hoelzl@41981
   633
  hence ley: "(\<Sum>i. f (disjointed A i)) \<le> x"
hoelzl@38656
   634
    by (metis xeq)
hoelzl@41981
   635
  hence y: "(\<Sum>i. f (disjointed A i)) \<in> measure_set M f s"
paulson@33271
   636
    apply (auto simp add: measure_set_def)
hoelzl@38656
   637
    apply (rule_tac x="disjointed A" in exI)
hoelzl@38656
   638
    apply (simp add: disjoint_family_disjointed UN_disjointed_eq ss dA comp_def)
paulson@33271
   639
    done
paulson@33271
   640
  show ?thesis
hoelzl@38656
   641
    by (blast intro: y order_trans [OF _ ley] posf complete_lattice_class.Inf_lower)
paulson@33271
   642
qed
paulson@33271
   643
hoelzl@42066
   644
lemma (in ring_of_sets) inf_measure_close:
hoelzl@41981
   645
  fixes e :: extreal
hoelzl@42066
   646
  assumes posf: "positive M f" and e: "0 < e" and ss: "s \<subseteq> (space M)" and "Inf (measure_set M f s) \<noteq> \<infinity>"
hoelzl@38656
   647
  shows "\<exists>A. range A \<subseteq> sets M \<and> disjoint_family A \<and> s \<subseteq> (\<Union>i. A i) \<and>
hoelzl@41981
   648
               (\<Sum>i. f (A i)) \<le> Inf (measure_set M f s) + e"
hoelzl@42066
   649
proof -
hoelzl@42066
   650
  from `Inf (measure_set M f s) \<noteq> \<infinity>` have fin: "\<bar>Inf (measure_set M f s)\<bar> \<noteq> \<infinity>"
hoelzl@41981
   651
    using inf_measure_pos[OF posf, of s] by auto
hoelzl@38656
   652
  obtain l where "l \<in> measure_set M f s" "l \<le> Inf (measure_set M f s) + e"
hoelzl@41981
   653
    using Inf_extreal_close[OF fin e] by auto
hoelzl@38656
   654
  thus ?thesis
hoelzl@38656
   655
    by (auto intro!: exI[of _ l] simp: measure_set_def comp_def)
paulson@33271
   656
qed
paulson@33271
   657
hoelzl@42066
   658
lemma (in ring_of_sets) inf_measure_countably_subadditive:
hoelzl@41689
   659
  assumes posf: "positive M f" and inc: "increasing M f"
paulson@33271
   660
  shows "countably_subadditive (| space = space M, sets = Pow (space M) |)
paulson@33271
   661
                  (\<lambda>x. Inf (measure_set M f x))"
hoelzl@42066
   662
proof (simp add: countably_subadditive_def, safe)
hoelzl@42066
   663
  fix A :: "nat \<Rightarrow> 'a set"
hoelzl@42066
   664
  let "?outer B" = "Inf (measure_set M f B)"
hoelzl@38656
   665
  assume A: "range A \<subseteq> Pow (space M)"
hoelzl@38656
   666
     and disj: "disjoint_family A"
hoelzl@38656
   667
     and sb: "(\<Union>i. A i) \<subseteq> space M"
hoelzl@42066
   668
hoelzl@42066
   669
  { fix e :: extreal assume e: "0 < e" and "\<forall>i. ?outer (A i) \<noteq> \<infinity>"
hoelzl@42066
   670
    hence "\<exists>BB. \<forall>n. range (BB n) \<subseteq> sets M \<and> disjoint_family (BB n) \<and>
hoelzl@42066
   671
        A n \<subseteq> (\<Union>i. BB n i) \<and> (\<Sum>i. f (BB n i)) \<le> ?outer (A n) + e * (1/2)^(Suc n)"
hoelzl@42066
   672
      apply (safe intro!: choice inf_measure_close [of f, OF posf])
hoelzl@42066
   673
      using e sb by (auto simp: extreal_zero_less_0_iff one_extreal_def)
hoelzl@42066
   674
    then obtain BB
hoelzl@42066
   675
      where BB: "\<And>n. (range (BB n) \<subseteq> sets M)"
hoelzl@38656
   676
      and disjBB: "\<And>n. disjoint_family (BB n)"
hoelzl@38656
   677
      and sbBB: "\<And>n. A n \<subseteq> (\<Union>i. BB n i)"
hoelzl@42066
   678
      and BBle: "\<And>n. (\<Sum>i. f (BB n i)) \<le> ?outer (A n) + e * (1/2)^(Suc n)"
hoelzl@42066
   679
      by auto blast
hoelzl@42066
   680
    have sll: "(\<Sum>n. \<Sum>i. (f (BB n i))) \<le> (\<Sum>n. ?outer (A n)) + e"
hoelzl@38656
   681
    proof -
hoelzl@41981
   682
      have sum_eq_1: "(\<Sum>n. e*(1/2) ^ Suc n) = e"
hoelzl@41981
   683
        using suminf_half_series_extreal e
hoelzl@41981
   684
        by (simp add: extreal_zero_le_0_iff zero_le_divide_extreal suminf_cmult_extreal)
hoelzl@41981
   685
      have "\<And>n i. 0 \<le> f (BB n i)" using posf[unfolded positive_def] BB by auto
hoelzl@41981
   686
      then have "\<And>n. 0 \<le> (\<Sum>i. f (BB n i))" by (rule suminf_0_le)
hoelzl@42066
   687
      then have "(\<Sum>n. \<Sum>i. (f (BB n i))) \<le> (\<Sum>n. ?outer (A n) + e*(1/2) ^ Suc n)"
hoelzl@41981
   688
        by (rule suminf_le_pos[OF BBle])
hoelzl@42066
   689
      also have "... = (\<Sum>n. ?outer (A n)) + e"
hoelzl@41981
   690
        using sum_eq_1 inf_measure_pos[OF posf] e
hoelzl@41981
   691
        by (subst suminf_add_extreal) (auto simp add: extreal_zero_le_0_iff)
hoelzl@38656
   692
      finally show ?thesis .
hoelzl@38656
   693
    qed
hoelzl@42066
   694
    def C \<equiv> "(split BB) o prod_decode"
hoelzl@42066
   695
    have C: "!!n. C n \<in> sets M"
hoelzl@42066
   696
      apply (rule_tac p="prod_decode n" in PairE)
hoelzl@42066
   697
      apply (simp add: C_def)
hoelzl@42066
   698
      apply (metis BB subsetD rangeI)
hoelzl@42066
   699
      done
hoelzl@42066
   700
    have sbC: "(\<Union>i. A i) \<subseteq> (\<Union>i. C i)"
hoelzl@38656
   701
    proof (auto simp add: C_def)
hoelzl@38656
   702
      fix x i
hoelzl@38656
   703
      assume x: "x \<in> A i"
hoelzl@38656
   704
      with sbBB [of i] obtain j where "x \<in> BB i j"
hoelzl@38656
   705
        by blast
hoelzl@38656
   706
      thus "\<exists>i. x \<in> split BB (prod_decode i)"
hoelzl@38656
   707
        by (metis prod_encode_inverse prod.cases)
hoelzl@38656
   708
    qed
hoelzl@42066
   709
    have "(f \<circ> C) = (f \<circ> (\<lambda>(x, y). BB x y)) \<circ> prod_decode"
hoelzl@42066
   710
      by (rule ext)  (auto simp add: C_def)
hoelzl@42066
   711
    moreover have "suminf ... = (\<Sum>n. \<Sum>i. f (BB n i))" using BBle
hoelzl@42066
   712
      using BB posf[unfolded positive_def]
hoelzl@42066
   713
      by (force intro!: suminf_extreal_2dimen simp: o_def)
hoelzl@42066
   714
    ultimately have Csums: "(\<Sum>i. f (C i)) = (\<Sum>n. \<Sum>i. f (BB n i))" by (simp add: o_def)
hoelzl@42066
   715
    have "?outer (\<Union>i. A i) \<le> (\<Sum>n. \<Sum>i. f (BB n i))"
hoelzl@42066
   716
      apply (rule inf_measure_le [OF posf(1) inc], auto)
hoelzl@42066
   717
      apply (rule_tac x="C" in exI)
hoelzl@42066
   718
      apply (auto simp add: C sbC Csums)
hoelzl@42066
   719
      done
hoelzl@42066
   720
    also have "... \<le> (\<Sum>n. ?outer (A n)) + e" using sll
hoelzl@42066
   721
      by blast
hoelzl@42066
   722
    finally have "?outer (\<Union>i. A i) \<le> (\<Sum>n. ?outer (A n)) + e" . }
hoelzl@42066
   723
  note for_finite_Inf = this
hoelzl@42066
   724
hoelzl@42066
   725
  show "?outer (\<Union>i. A i) \<le> (\<Sum>n. ?outer (A n))"
hoelzl@42066
   726
  proof cases
hoelzl@42066
   727
    assume "\<forall>i. ?outer (A i) \<noteq> \<infinity>"
hoelzl@42066
   728
    with for_finite_Inf show ?thesis
hoelzl@42066
   729
      by (intro extreal_le_epsilon) auto
hoelzl@42066
   730
  next
hoelzl@42066
   731
    assume "\<not> (\<forall>i. ?outer (A i) \<noteq> \<infinity>)"
hoelzl@42066
   732
    then have "\<exists>i. ?outer (A i) = \<infinity>"
hoelzl@42066
   733
      by auto
hoelzl@42066
   734
    then have "(\<Sum>n. ?outer (A n)) = \<infinity>"
hoelzl@42066
   735
      using suminf_PInfty[OF inf_measure_pos, OF posf]
hoelzl@42066
   736
      by metis
hoelzl@42066
   737
    then show ?thesis by simp
hoelzl@42066
   738
  qed
paulson@33271
   739
qed
paulson@33271
   740
hoelzl@42066
   741
lemma (in ring_of_sets) inf_measure_outer:
hoelzl@41689
   742
  "\<lbrakk> positive M f ; increasing M f \<rbrakk>
hoelzl@41689
   743
   \<Longrightarrow> outer_measure_space \<lparr> space = space M, sets = Pow (space M) \<rparr>
paulson@33271
   744
                          (\<lambda>x. Inf (measure_set M f x))"
hoelzl@41981
   745
  using inf_measure_pos[of M f]
hoelzl@38656
   746
  by (simp add: outer_measure_space_def inf_measure_empty
hoelzl@38656
   747
                inf_measure_increasing inf_measure_countably_subadditive positive_def)
paulson@33271
   748
hoelzl@42066
   749
lemma (in ring_of_sets) algebra_subset_lambda_system:
hoelzl@41689
   750
  assumes posf: "positive M f" and inc: "increasing M f"
paulson@33271
   751
      and add: "additive M f"
hoelzl@42066
   752
  shows "sets M \<subseteq> lambda_system \<lparr> space = space M, sets = Pow (space M) \<rparr>
paulson@33271
   753
                                (\<lambda>x. Inf (measure_set M f x))"
hoelzl@38656
   754
proof (auto dest: sets_into_space
hoelzl@38656
   755
            simp add: algebra.lambda_system_eq [OF algebra_Pow])
paulson@33271
   756
  fix x s
paulson@33271
   757
  assume x: "x \<in> sets M"
paulson@33271
   758
     and s: "s \<subseteq> space M"
hoelzl@38656
   759
  have [simp]: "!!x. x \<in> sets M \<Longrightarrow> s \<inter> (space M - x) = s-x" using s
paulson@33271
   760
    by blast
paulson@33271
   761
  have "Inf (measure_set M f (s\<inter>x)) + Inf (measure_set M f (s-x))
paulson@33271
   762
        \<le> Inf (measure_set M f s)"
hoelzl@42066
   763
  proof cases
hoelzl@42066
   764
    assume "Inf (measure_set M f s) = \<infinity>" then show ?thesis by simp
hoelzl@42066
   765
  next
hoelzl@42066
   766
    assume fin: "Inf (measure_set M f s) \<noteq> \<infinity>"
hoelzl@42066
   767
    then have "measure_set M f s \<noteq> {}"
hoelzl@42066
   768
      by (auto simp: top_extreal_def)
hoelzl@42066
   769
    show ?thesis
hoelzl@42066
   770
    proof (rule complete_lattice_class.Inf_greatest)
hoelzl@42066
   771
      fix r assume "r \<in> measure_set M f s"
hoelzl@42066
   772
      then obtain A where A: "disjoint_family A" "range A \<subseteq> sets M" "s \<subseteq> (\<Union>i. A i)"
hoelzl@42066
   773
        and r: "r = (\<Sum>i. f (A i))" unfolding measure_set_def by auto
hoelzl@42066
   774
      have "Inf (measure_set M f (s \<inter> x)) \<le> (\<Sum>i. f (A i \<inter> x))"
hoelzl@42066
   775
        unfolding measure_set_def
hoelzl@42066
   776
      proof (safe intro!: complete_lattice_class.Inf_lower exI[of _ "\<lambda>i. A i \<inter> x"])
hoelzl@42066
   777
        from A(1) show "disjoint_family (\<lambda>i. A i \<inter> x)"
hoelzl@42066
   778
          by (rule disjoint_family_on_bisimulation) auto
hoelzl@42066
   779
      qed (insert x A, auto)
hoelzl@42066
   780
      moreover
hoelzl@42066
   781
      have "Inf (measure_set M f (s - x)) \<le> (\<Sum>i. f (A i - x))"
hoelzl@42066
   782
        unfolding measure_set_def
hoelzl@42066
   783
      proof (safe intro!: complete_lattice_class.Inf_lower exI[of _ "\<lambda>i. A i - x"])
hoelzl@42066
   784
        from A(1) show "disjoint_family (\<lambda>i. A i - x)"
hoelzl@42066
   785
          by (rule disjoint_family_on_bisimulation) auto
hoelzl@42066
   786
      qed (insert x A, auto)
hoelzl@42066
   787
      ultimately have "Inf (measure_set M f (s \<inter> x)) + Inf (measure_set M f (s - x)) \<le>
hoelzl@42066
   788
          (\<Sum>i. f (A i \<inter> x)) + (\<Sum>i. f (A i - x))" by (rule add_mono)
hoelzl@42066
   789
      also have "\<dots> = (\<Sum>i. f (A i \<inter> x) + f (A i - x))"
hoelzl@42066
   790
        using A(2) x posf by (subst suminf_add_extreal) (auto simp: positive_def)
hoelzl@42066
   791
      also have "\<dots> = (\<Sum>i. f (A i))"
hoelzl@42066
   792
        using A x
hoelzl@42066
   793
        by (subst add[THEN additiveD, symmetric])
hoelzl@42066
   794
           (auto intro!: arg_cong[where f=suminf] arg_cong[where f=f])
hoelzl@42066
   795
      finally show "Inf (measure_set M f (s \<inter> x)) + Inf (measure_set M f (s - x)) \<le> r"
hoelzl@42066
   796
        using r by simp
paulson@33271
   797
    qed
hoelzl@42066
   798
  qed
hoelzl@38656
   799
  moreover
paulson@33271
   800
  have "Inf (measure_set M f s)
paulson@33271
   801
       \<le> Inf (measure_set M f (s\<inter>x)) + Inf (measure_set M f (s-x))"
hoelzl@42145
   802
  proof -
paulson@33271
   803
    have "Inf (measure_set M f s) = Inf (measure_set M f ((s\<inter>x) \<union> (s-x)))"
paulson@33271
   804
      by (metis Un_Diff_Int Un_commute)
hoelzl@38656
   805
    also have "... \<le> Inf (measure_set M f (s\<inter>x)) + Inf (measure_set M f (s-x))"
hoelzl@38656
   806
      apply (rule subadditiveD)
hoelzl@42145
   807
      apply (rule ring_of_sets.countably_subadditive_subadditive [OF ring_of_sets_Pow])
hoelzl@41981
   808
      apply (simp add: positive_def inf_measure_empty[OF posf] inf_measure_pos[OF posf])
hoelzl@41689
   809
      apply (rule inf_measure_countably_subadditive)
hoelzl@41689
   810
      using s by (auto intro!: posf inc)
paulson@33271
   811
    finally show ?thesis .
hoelzl@42145
   812
  qed
hoelzl@38656
   813
  ultimately
paulson@33271
   814
  show "Inf (measure_set M f (s\<inter>x)) + Inf (measure_set M f (s-x))
paulson@33271
   815
        = Inf (measure_set M f s)"
paulson@33271
   816
    by (rule order_antisym)
paulson@33271
   817
qed
paulson@33271
   818
paulson@33271
   819
lemma measure_down:
hoelzl@41689
   820
  "measure_space N \<Longrightarrow> sigma_algebra M \<Longrightarrow> sets M \<subseteq> sets N \<Longrightarrow> measure N = measure M \<Longrightarrow> measure_space M"
hoelzl@38656
   821
  by (simp add: measure_space_def measure_space_axioms_def positive_def
hoelzl@38656
   822
                countably_additive_def)
paulson@33271
   823
     blast
paulson@33271
   824
hoelzl@42066
   825
theorem (in ring_of_sets) caratheodory:
hoelzl@41689
   826
  assumes posf: "positive M f" and ca: "countably_additive M f"
hoelzl@41981
   827
  shows "\<exists>\<mu> :: 'a set \<Rightarrow> extreal. (\<forall>s \<in> sets M. \<mu> s = f s) \<and>
hoelzl@41689
   828
            measure_space \<lparr> space = space M, sets = sets (sigma M), measure = \<mu> \<rparr>"
hoelzl@41689
   829
proof -
hoelzl@41689
   830
  have inc: "increasing M f"
hoelzl@41689
   831
    by (metis additive_increasing ca countably_additive_additive posf)
hoelzl@41689
   832
  let ?infm = "(\<lambda>x. Inf (measure_set M f x))"
hoelzl@41689
   833
  def ls \<equiv> "lambda_system (|space = space M, sets = Pow (space M)|) ?infm"
hoelzl@41689
   834
  have mls: "measure_space \<lparr>space = space M, sets = ls, measure = ?infm\<rparr>"
hoelzl@41689
   835
    using sigma_algebra.caratheodory_lemma
hoelzl@41689
   836
            [OF sigma_algebra_Pow  inf_measure_outer [OF posf inc]]
hoelzl@41689
   837
    by (simp add: ls_def)
hoelzl@41689
   838
  hence sls: "sigma_algebra (|space = space M, sets = ls, measure = ?infm|)"
hoelzl@41689
   839
    by (simp add: measure_space_def)
hoelzl@41689
   840
  have "sets M \<subseteq> ls"
hoelzl@41689
   841
    by (simp add: ls_def)
hoelzl@41689
   842
       (metis ca posf inc countably_additive_additive algebra_subset_lambda_system)
hoelzl@41689
   843
  hence sgs_sb: "sigma_sets (space M) (sets M) \<subseteq> ls"
hoelzl@41689
   844
    using sigma_algebra.sigma_sets_subset [OF sls, of "sets M"]
hoelzl@41689
   845
    by simp
hoelzl@41689
   846
  have "measure_space \<lparr> space = space M, sets = sets (sigma M), measure = ?infm \<rparr>"
hoelzl@41689
   847
    unfolding sigma_def
hoelzl@41689
   848
    by (rule measure_down [OF mls], rule sigma_algebra_sigma_sets)
hoelzl@41689
   849
       (simp_all add: sgs_sb space_closed)
hoelzl@41689
   850
  thus ?thesis using inf_measure_agrees [OF posf ca]
hoelzl@41689
   851
    by (intro exI[of _ ?infm]) auto
hoelzl@41689
   852
qed
paulson@33271
   853
hoelzl@42145
   854
subsubsection {*Alternative instances of caratheodory*}
hoelzl@42145
   855
hoelzl@42145
   856
lemma sums_def2:
hoelzl@42145
   857
  "f sums x \<longleftrightarrow> (\<lambda>n. (\<Sum>i\<le>n. f i)) ----> x"
hoelzl@42145
   858
  unfolding sums_def
hoelzl@42145
   859
  apply (subst LIMSEQ_Suc_iff[symmetric])
hoelzl@42145
   860
  unfolding atLeastLessThanSuc_atLeastAtMost atLeast0AtMost ..
hoelzl@42145
   861
hoelzl@42145
   862
lemma (in ring_of_sets) countably_additive_iff_continuous_from_below:
hoelzl@42145
   863
  assumes f: "positive M f" "additive M f"
hoelzl@42145
   864
  shows "countably_additive M f \<longleftrightarrow>
hoelzl@42145
   865
    (\<forall>A. range A \<subseteq> sets M \<longrightarrow> incseq A \<longrightarrow> (\<Union>i. A i) \<in> sets M \<longrightarrow> (\<lambda>i. f (A i)) ----> f (\<Union>i. A i))"
hoelzl@42145
   866
  unfolding countably_additive_def
hoelzl@42145
   867
proof safe
hoelzl@42145
   868
  assume count_sum: "\<forall>A. range A \<subseteq> sets M \<longrightarrow> disjoint_family A \<longrightarrow> UNION UNIV A \<in> sets M \<longrightarrow> (\<Sum>i. f (A i)) = f (UNION UNIV A)"
hoelzl@42145
   869
  fix A :: "nat \<Rightarrow> 'a set" assume A: "range A \<subseteq> sets M" "incseq A" "(\<Union>i. A i) \<in> sets M"
hoelzl@42145
   870
  then have dA: "range (disjointed A) \<subseteq> sets M" by (auto simp: range_disjointed_sets)
hoelzl@42145
   871
  with count_sum[THEN spec, of "disjointed A"] A(3)
hoelzl@42145
   872
  have f_UN: "(\<Sum>i. f (disjointed A i)) = f (\<Union>i. A i)"
hoelzl@42145
   873
    by (auto simp: UN_disjointed_eq disjoint_family_disjointed)
hoelzl@42145
   874
  moreover have "(\<lambda>n. (\<Sum>i=0..<n. f (disjointed A i))) ----> (\<Sum>i. f (disjointed A i))"
hoelzl@42145
   875
    using f(1)[unfolded positive_def] dA
hoelzl@42145
   876
    by (auto intro!: summable_sumr_LIMSEQ_suminf summable_extreal_pos)
hoelzl@42145
   877
  from LIMSEQ_Suc[OF this]
hoelzl@42145
   878
  have "(\<lambda>n. (\<Sum>i\<le>n. f (disjointed A i))) ----> (\<Sum>i. f (disjointed A i))"
hoelzl@42145
   879
    unfolding atLeastLessThanSuc_atLeastAtMost atLeast0AtMost .
hoelzl@42145
   880
  moreover have "\<And>n. (\<Sum>i\<le>n. f (disjointed A i)) = f (A n)"
hoelzl@42145
   881
    using disjointed_additive[OF f A(1,2)] .
hoelzl@42145
   882
  ultimately show "(\<lambda>i. f (A i)) ----> f (\<Union>i. A i)" by simp
hoelzl@42145
   883
next
hoelzl@42145
   884
  assume cont: "\<forall>A. range A \<subseteq> sets M \<longrightarrow> incseq A \<longrightarrow> (\<Union>i. A i) \<in> sets M \<longrightarrow> (\<lambda>i. f (A i)) ----> f (\<Union>i. A i)"
hoelzl@42145
   885
  fix A :: "nat \<Rightarrow> 'a set" assume A: "range A \<subseteq> sets M" "disjoint_family A" "(\<Union>i. A i) \<in> sets M"
hoelzl@42145
   886
  have *: "(\<Union>n. (\<Union>i\<le>n. A i)) = (\<Union>i. A i)" by auto
hoelzl@42145
   887
  have "(\<lambda>n. f (\<Union>i\<le>n. A i)) ----> f (\<Union>i. A i)"
hoelzl@42145
   888
  proof (unfold *[symmetric], intro cont[rule_format])
hoelzl@42145
   889
    show "range (\<lambda>i. \<Union> i\<le>i. A i) \<subseteq> sets M" "(\<Union>i. \<Union> i\<le>i. A i) \<in> sets M"
hoelzl@42145
   890
      using A * by auto
hoelzl@42145
   891
  qed (force intro!: incseq_SucI)
hoelzl@42145
   892
  moreover have "\<And>n. f (\<Union>i\<le>n. A i) = (\<Sum>i\<le>n. f (A i))"
hoelzl@42145
   893
    using A
hoelzl@42145
   894
    by (intro additive_sum[OF f, of _ A, symmetric])
hoelzl@42145
   895
       (auto intro: disjoint_family_on_mono[where B=UNIV])
hoelzl@42145
   896
  ultimately
hoelzl@42145
   897
  have "(\<lambda>i. f (A i)) sums f (\<Union>i. A i)"
hoelzl@42145
   898
    unfolding sums_def2 by simp
hoelzl@42145
   899
  from sums_unique[OF this]
hoelzl@42145
   900
  show "(\<Sum>i. f (A i)) = f (\<Union>i. A i)" by simp
hoelzl@42145
   901
qed
hoelzl@42145
   902
hoelzl@42145
   903
lemma uminus_extreal_add_uminus_uminus:
hoelzl@42145
   904
  fixes a b :: extreal shows "a \<noteq> \<infinity> \<Longrightarrow> b \<noteq> \<infinity> \<Longrightarrow> - (- a + - b) = a + b"
hoelzl@42145
   905
  by (cases rule: extreal2_cases[of a b]) auto
hoelzl@42145
   906
hoelzl@42145
   907
lemma INFI_extreal_add:
hoelzl@42145
   908
  assumes "decseq f" "decseq g" and fin: "\<And>i. f i \<noteq> \<infinity>" "\<And>i. g i \<noteq> \<infinity>"
hoelzl@42145
   909
  shows "(INF i. f i + g i) = INFI UNIV f + INFI UNIV g"
hoelzl@42145
   910
proof -
hoelzl@42145
   911
  have INF_less: "(INF i. f i) < \<infinity>" "(INF i. g i) < \<infinity>"
hoelzl@42145
   912
    using assms unfolding INF_less_iff by auto
hoelzl@42145
   913
  { fix i from fin[of i] have "- ((- f i) + (- g i)) = f i + g i"
hoelzl@42145
   914
      by (rule uminus_extreal_add_uminus_uminus) }
hoelzl@42145
   915
  then have "(INF i. f i + g i) = (INF i. - ((- f i) + (- g i)))"
hoelzl@42145
   916
    by simp
hoelzl@42145
   917
  also have "\<dots> = INFI UNIV f + INFI UNIV g"
hoelzl@42145
   918
    unfolding extreal_INFI_uminus
hoelzl@42145
   919
    using assms INF_less
hoelzl@42145
   920
    by (subst SUPR_extreal_add)
hoelzl@42145
   921
       (auto simp: extreal_SUPR_uminus intro!: uminus_extreal_add_uminus_uminus)
hoelzl@42145
   922
  finally show ?thesis .
hoelzl@42145
   923
qed
hoelzl@42145
   924
hoelzl@42145
   925
lemma (in ring_of_sets) continuous_from_above_iff_empty_continuous:
hoelzl@42145
   926
  assumes f: "positive M f" "additive M f"
hoelzl@42145
   927
  shows "(\<forall>A. range A \<subseteq> sets M \<longrightarrow> decseq A \<longrightarrow> (\<Inter>i. A i) \<in> sets M \<longrightarrow> (\<forall>i. f (A i) \<noteq> \<infinity>) \<longrightarrow> (\<lambda>i. f (A i)) ----> f (\<Inter>i. A i))
hoelzl@42145
   928
     \<longleftrightarrow> (\<forall>A. range A \<subseteq> sets M \<longrightarrow> decseq A \<longrightarrow> (\<Inter>i. A i) = {} \<longrightarrow> (\<forall>i. f (A i) \<noteq> \<infinity>) \<longrightarrow> (\<lambda>i. f (A i)) ----> 0)"
hoelzl@42145
   929
proof safe
hoelzl@42145
   930
  assume cont: "(\<forall>A. range A \<subseteq> sets M \<longrightarrow> decseq A \<longrightarrow> (\<Inter>i. A i) \<in> sets M \<longrightarrow> (\<forall>i. f (A i) \<noteq> \<infinity>) \<longrightarrow> (\<lambda>i. f (A i)) ----> f (\<Inter>i. A i))"
hoelzl@42145
   931
  fix A :: "nat \<Rightarrow> 'a set" assume A: "range A \<subseteq> sets M" "decseq A" "(\<Inter>i. A i) = {}" "\<forall>i. f (A i) \<noteq> \<infinity>"
hoelzl@42145
   932
  with cont[THEN spec, of A] show "(\<lambda>i. f (A i)) ----> 0"
hoelzl@42145
   933
    using `positive M f`[unfolded positive_def] by auto
hoelzl@42145
   934
next
hoelzl@42145
   935
  assume cont: "\<forall>A. range A \<subseteq> sets M \<longrightarrow> decseq A \<longrightarrow> (\<Inter>i. A i) = {} \<longrightarrow> (\<forall>i. f (A i) \<noteq> \<infinity>) \<longrightarrow> (\<lambda>i. f (A i)) ----> 0"
hoelzl@42145
   936
  fix A :: "nat \<Rightarrow> 'a set" assume A: "range A \<subseteq> sets M" "decseq A" "(\<Inter>i. A i) \<in> sets M" "\<forall>i. f (A i) \<noteq> \<infinity>"
hoelzl@42145
   937
hoelzl@42145
   938
  have f_mono: "\<And>a b. a \<in> sets M \<Longrightarrow> b \<in> sets M \<Longrightarrow> a \<subseteq> b \<Longrightarrow> f a \<le> f b"
hoelzl@42145
   939
    using additive_increasing[OF f] unfolding increasing_def by simp
hoelzl@42145
   940
hoelzl@42145
   941
  have decseq_fA: "decseq (\<lambda>i. f (A i))"
hoelzl@42145
   942
    using A by (auto simp: decseq_def intro!: f_mono)
hoelzl@42145
   943
  have decseq: "decseq (\<lambda>i. A i - (\<Inter>i. A i))"
hoelzl@42145
   944
    using A by (auto simp: decseq_def)
hoelzl@42145
   945
  then have decseq_f: "decseq (\<lambda>i. f (A i - (\<Inter>i. A i)))"
hoelzl@42145
   946
    using A unfolding decseq_def by (auto intro!: f_mono Diff)
hoelzl@42145
   947
  have "f (\<Inter>x. A x) \<le> f (A 0)"
hoelzl@42145
   948
    using A by (auto intro!: f_mono)
hoelzl@42145
   949
  then have f_Int_fin: "f (\<Inter>x. A x) \<noteq> \<infinity>"
hoelzl@42145
   950
    using A by auto
hoelzl@42145
   951
  { fix i
hoelzl@42145
   952
    have "f (A i - (\<Inter>i. A i)) \<le> f (A i)" using A by (auto intro!: f_mono)
hoelzl@42145
   953
    then have "f (A i - (\<Inter>i. A i)) \<noteq> \<infinity>"
hoelzl@42145
   954
      using A by auto }
hoelzl@42145
   955
  note f_fin = this
hoelzl@42145
   956
  have "(\<lambda>i. f (A i - (\<Inter>i. A i))) ----> 0"
hoelzl@42145
   957
  proof (intro cont[rule_format, OF _ decseq _ f_fin])
hoelzl@42145
   958
    show "range (\<lambda>i. A i - (\<Inter>i. A i)) \<subseteq> sets M" "(\<Inter>i. A i - (\<Inter>i. A i)) = {}"
hoelzl@42145
   959
      using A by auto
hoelzl@42145
   960
  qed
hoelzl@42145
   961
  from INF_Lim_extreal[OF decseq_f this]
hoelzl@42145
   962
  have "(INF n. f (A n - (\<Inter>i. A i))) = 0" .
hoelzl@42145
   963
  moreover have "(INF n. f (\<Inter>i. A i)) = f (\<Inter>i. A i)"
hoelzl@42145
   964
    by auto
hoelzl@42145
   965
  ultimately have "(INF n. f (A n - (\<Inter>i. A i)) + f (\<Inter>i. A i)) = 0 + f (\<Inter>i. A i)"
hoelzl@42145
   966
    using A(4) f_fin f_Int_fin
hoelzl@42145
   967
    by (subst INFI_extreal_add) (auto simp: decseq_f)
hoelzl@42145
   968
  moreover {
hoelzl@42145
   969
    fix n
hoelzl@42145
   970
    have "f (A n - (\<Inter>i. A i)) + f (\<Inter>i. A i) = f ((A n - (\<Inter>i. A i)) \<union> (\<Inter>i. A i))"
hoelzl@42145
   971
      using A by (subst f(2)[THEN additiveD]) auto
hoelzl@42145
   972
    also have "(A n - (\<Inter>i. A i)) \<union> (\<Inter>i. A i) = A n"
hoelzl@42145
   973
      by auto
hoelzl@42145
   974
    finally have "f (A n - (\<Inter>i. A i)) + f (\<Inter>i. A i) = f (A n)" . }
hoelzl@42145
   975
  ultimately have "(INF n. f (A n)) = f (\<Inter>i. A i)"
hoelzl@42145
   976
    by simp
hoelzl@42145
   977
  with LIMSEQ_extreal_INFI[OF decseq_fA]
hoelzl@42145
   978
  show "(\<lambda>i. f (A i)) ----> f (\<Inter>i. A i)" by simp
hoelzl@42145
   979
qed
hoelzl@42145
   980
hoelzl@42145
   981
lemma positiveD1: "positive M f \<Longrightarrow> f {} = 0" by (auto simp: positive_def)
hoelzl@42145
   982
lemma positiveD2: "positive M f \<Longrightarrow> A \<in> sets M \<Longrightarrow> 0 \<le> f A" by (auto simp: positive_def)
hoelzl@42145
   983
hoelzl@42145
   984
lemma (in ring_of_sets) empty_continuous_imp_continuous_from_below:
hoelzl@42145
   985
  assumes f: "positive M f" "additive M f" "\<forall>A\<in>sets M. f A \<noteq> \<infinity>"
hoelzl@42145
   986
  assumes cont: "\<forall>A. range A \<subseteq> sets M \<longrightarrow> decseq A \<longrightarrow> (\<Inter>i. A i) = {} \<longrightarrow> (\<lambda>i. f (A i)) ----> 0"
hoelzl@42145
   987
  assumes A: "range A \<subseteq> sets M" "incseq A" "(\<Union>i. A i) \<in> sets M"
hoelzl@42145
   988
  shows "(\<lambda>i. f (A i)) ----> f (\<Union>i. A i)"
hoelzl@42145
   989
proof -
hoelzl@42145
   990
  have "\<forall>A\<in>sets M. \<exists>x. f A = extreal x"
hoelzl@42145
   991
  proof
hoelzl@42145
   992
    fix A assume "A \<in> sets M" with f show "\<exists>x. f A = extreal x"
hoelzl@42145
   993
      unfolding positive_def by (cases "f A") auto
hoelzl@42145
   994
  qed
hoelzl@42145
   995
  from bchoice[OF this] guess f' .. note f' = this[rule_format]
hoelzl@42145
   996
  from A have "(\<lambda>i. f ((\<Union>i. A i) - A i)) ----> 0"
hoelzl@42145
   997
    by (intro cont[rule_format]) (auto simp: decseq_def incseq_def)
hoelzl@42145
   998
  moreover
hoelzl@42145
   999
  { fix i
hoelzl@42145
  1000
    have "f ((\<Union>i. A i) - A i) + f (A i) = f ((\<Union>i. A i) - A i \<union> A i)"
hoelzl@42145
  1001
      using A by (intro f(2)[THEN additiveD, symmetric]) auto
hoelzl@42145
  1002
    also have "(\<Union>i. A i) - A i \<union> A i = (\<Union>i. A i)"
hoelzl@42145
  1003
      by auto
hoelzl@42145
  1004
    finally have "f' (\<Union>i. A i) - f' (A i) = f' ((\<Union>i. A i) - A i)"
hoelzl@42145
  1005
      using A by (subst (asm) (1 2 3) f') auto
hoelzl@42145
  1006
    then have "f ((\<Union>i. A i) - A i) = extreal (f' (\<Union>i. A i) - f' (A i))"
hoelzl@42145
  1007
      using A f' by auto }
hoelzl@42145
  1008
  ultimately have "(\<lambda>i. f' (\<Union>i. A i) - f' (A i)) ----> 0"
hoelzl@42145
  1009
    by (simp add: zero_extreal_def)
hoelzl@42145
  1010
  then have "(\<lambda>i. f' (A i)) ----> f' (\<Union>i. A i)"
hoelzl@42145
  1011
    by (rule LIMSEQ_diff_approach_zero2[OF LIMSEQ_const])
hoelzl@42145
  1012
  then show "(\<lambda>i. f (A i)) ----> f (\<Union>i. A i)"
hoelzl@42145
  1013
    using A by (subst (1 2) f') auto
hoelzl@42145
  1014
qed
hoelzl@42145
  1015
hoelzl@42145
  1016
lemma (in ring_of_sets) empty_continuous_imp_countably_additive:
hoelzl@42145
  1017
  assumes f: "positive M f" "additive M f" and fin: "\<forall>A\<in>sets M. f A \<noteq> \<infinity>"
hoelzl@42145
  1018
  assumes cont: "\<And>A. range A \<subseteq> sets M \<Longrightarrow> decseq A \<Longrightarrow> (\<Inter>i. A i) = {} \<Longrightarrow> (\<lambda>i. f (A i)) ----> 0"
hoelzl@42145
  1019
  shows "countably_additive M f"
hoelzl@42145
  1020
  using countably_additive_iff_continuous_from_below[OF f]
hoelzl@42145
  1021
  using empty_continuous_imp_continuous_from_below[OF f fin] cont
hoelzl@42145
  1022
  by blast
hoelzl@42145
  1023
hoelzl@42145
  1024
lemma (in ring_of_sets) caratheodory_empty_continuous:
hoelzl@42145
  1025
  assumes f: "positive M f" "additive M f" and fin: "\<And>A. A \<in> sets M \<Longrightarrow> f A \<noteq> \<infinity>"
hoelzl@42145
  1026
  assumes cont: "\<And>A. range A \<subseteq> sets M \<Longrightarrow> decseq A \<Longrightarrow> (\<Inter>i. A i) = {} \<Longrightarrow> (\<lambda>i. f (A i)) ----> 0"
hoelzl@42145
  1027
  shows "\<exists>\<mu> :: 'a set \<Rightarrow> extreal. (\<forall>s \<in> sets M. \<mu> s = f s) \<and>
hoelzl@42145
  1028
            measure_space \<lparr> space = space M, sets = sets (sigma M), measure = \<mu> \<rparr>"
hoelzl@42145
  1029
proof (intro caratheodory empty_continuous_imp_countably_additive f)
hoelzl@42145
  1030
  show "\<forall>A\<in>sets M. f A \<noteq> \<infinity>" using fin by auto
hoelzl@42145
  1031
qed (rule cont)
hoelzl@42145
  1032
paulson@33271
  1033
end