(* Title: HOL/Probability/Independent_Family.thy
Author: Johannes Hölzl, TU München
Author: Sudeep Kanav, TU München
*)
header {* Independent families of events, event sets, and random variables *}
theory Independent_Family
imports Probability_Measure Infinite_Product_Measure
begin
definition (in prob_space)
"indep_sets F I \<longleftrightarrow> (\<forall>i\<in>I. F i \<subseteq> events) \<and>
(\<forall>J\<subseteq>I. J \<noteq> {} \<longrightarrow> finite J \<longrightarrow> (\<forall>A\<in>Pi J F. prob (\<Inter>j\<in>J. A j) = (\<Prod>j\<in>J. prob (A j))))"
definition (in prob_space)
"indep_set A B \<longleftrightarrow> indep_sets (case_bool A B) UNIV"
definition (in prob_space)
indep_events_def_alt: "indep_events A I \<longleftrightarrow> indep_sets (\<lambda>i. {A i}) I"
lemma (in prob_space) indep_events_def:
"indep_events A I \<longleftrightarrow> (A`I \<subseteq> events) \<and>
(\<forall>J\<subseteq>I. J \<noteq> {} \<longrightarrow> finite J \<longrightarrow> prob (\<Inter>j\<in>J. A j) = (\<Prod>j\<in>J. prob (A j)))"
unfolding indep_events_def_alt indep_sets_def
apply (simp add: Ball_def Pi_iff image_subset_iff_funcset)
apply (intro conj_cong refl arg_cong[where f=All] ext imp_cong)
apply auto
done
definition (in prob_space)
"indep_event A B \<longleftrightarrow> indep_events (case_bool A B) UNIV"
lemma (in prob_space) indep_sets_cong:
"I = J \<Longrightarrow> (\<And>i. i \<in> I \<Longrightarrow> F i = G i) \<Longrightarrow> indep_sets F I \<longleftrightarrow> indep_sets G J"
by (simp add: indep_sets_def, intro conj_cong all_cong imp_cong ball_cong) blast+
lemma (in prob_space) indep_events_finite_index_events:
"indep_events F I \<longleftrightarrow> (\<forall>J\<subseteq>I. J \<noteq> {} \<longrightarrow> finite J \<longrightarrow> indep_events F J)"
by (auto simp: indep_events_def)
lemma (in prob_space) indep_sets_finite_index_sets:
"indep_sets F I \<longleftrightarrow> (\<forall>J\<subseteq>I. J \<noteq> {} \<longrightarrow> finite J \<longrightarrow> indep_sets F J)"
proof (intro iffI allI impI)
assume *: "\<forall>J\<subseteq>I. J \<noteq> {} \<longrightarrow> finite J \<longrightarrow> indep_sets F J"
show "indep_sets F I" unfolding indep_sets_def
proof (intro conjI ballI allI impI)
fix i assume "i \<in> I"
with *[THEN spec, of "{i}"] show "F i \<subseteq> events"
by (auto simp: indep_sets_def)
qed (insert *, auto simp: indep_sets_def)
qed (auto simp: indep_sets_def)
lemma (in prob_space) indep_sets_mono_index:
"J \<subseteq> I \<Longrightarrow> indep_sets F I \<Longrightarrow> indep_sets F J"
unfolding indep_sets_def by auto
lemma (in prob_space) indep_sets_mono_sets:
assumes indep: "indep_sets F I"
assumes mono: "\<And>i. i\<in>I \<Longrightarrow> G i \<subseteq> F i"
shows "indep_sets G I"
proof -
have "(\<forall>i\<in>I. F i \<subseteq> events) \<Longrightarrow> (\<forall>i\<in>I. G i \<subseteq> events)"
using mono by auto
moreover have "\<And>A J. J \<subseteq> I \<Longrightarrow> A \<in> (\<Pi> j\<in>J. G j) \<Longrightarrow> A \<in> (\<Pi> j\<in>J. F j)"
using mono by (auto simp: Pi_iff)
ultimately show ?thesis
using indep by (auto simp: indep_sets_def)
qed
lemma (in prob_space) indep_sets_mono:
assumes indep: "indep_sets F I"
assumes mono: "J \<subseteq> I" "\<And>i. i\<in>J \<Longrightarrow> G i \<subseteq> F i"
shows "indep_sets G J"
apply (rule indep_sets_mono_sets)
apply (rule indep_sets_mono_index)
apply (fact +)
done
lemma (in prob_space) indep_setsI:
assumes "\<And>i. i \<in> I \<Longrightarrow> F i \<subseteq> events"
and "\<And>A J. J \<noteq> {} \<Longrightarrow> J \<subseteq> I \<Longrightarrow> finite J \<Longrightarrow> (\<forall>j\<in>J. A j \<in> F j) \<Longrightarrow> prob (\<Inter>j\<in>J. A j) = (\<Prod>j\<in>J. prob (A j))"
shows "indep_sets F I"
using assms unfolding indep_sets_def by (auto simp: Pi_iff)
lemma (in prob_space) indep_setsD:
assumes "indep_sets F I" and "J \<subseteq> I" "J \<noteq> {}" "finite J" "\<forall>j\<in>J. A j \<in> F j"
shows "prob (\<Inter>j\<in>J. A j) = (\<Prod>j\<in>J. prob (A j))"
using assms unfolding indep_sets_def by auto
lemma (in prob_space) indep_setI:
assumes ev: "A \<subseteq> events" "B \<subseteq> events"
and indep: "\<And>a b. a \<in> A \<Longrightarrow> b \<in> B \<Longrightarrow> prob (a \<inter> b) = prob a * prob b"
shows "indep_set A B"
unfolding indep_set_def
proof (rule indep_setsI)
fix F J assume "J \<noteq> {}" "J \<subseteq> UNIV"
and F: "\<forall>j\<in>J. F j \<in> (case j of True \<Rightarrow> A | False \<Rightarrow> B)"
have "J \<in> Pow UNIV" by auto
with F `J \<noteq> {}` indep[of "F True" "F False"]
show "prob (\<Inter>j\<in>J. F j) = (\<Prod>j\<in>J. prob (F j))"
unfolding UNIV_bool Pow_insert by (auto simp: ac_simps)
qed (auto split: bool.split simp: ev)
lemma (in prob_space) indep_setD:
assumes indep: "indep_set A B" and ev: "a \<in> A" "b \<in> B"
shows "prob (a \<inter> b) = prob a * prob b"
using indep[unfolded indep_set_def, THEN indep_setsD, of UNIV "case_bool a b"] ev
by (simp add: ac_simps UNIV_bool)
lemma (in prob_space)
assumes indep: "indep_set A B"
shows indep_setD_ev1: "A \<subseteq> events"
and indep_setD_ev2: "B \<subseteq> events"
using indep unfolding indep_set_def indep_sets_def UNIV_bool by auto
lemma (in prob_space) indep_sets_dynkin:
assumes indep: "indep_sets F I"
shows "indep_sets (\<lambda>i. dynkin (space M) (F i)) I"
(is "indep_sets ?F I")
proof (subst indep_sets_finite_index_sets, intro allI impI ballI)
fix J assume "finite J" "J \<subseteq> I" "J \<noteq> {}"
with indep have "indep_sets F J"
by (subst (asm) indep_sets_finite_index_sets) auto
{ fix J K assume "indep_sets F K"
let ?G = "\<lambda>S i. if i \<in> S then ?F i else F i"
assume "finite J" "J \<subseteq> K"
then have "indep_sets (?G J) K"
proof induct
case (insert j J)
moreover def G \<equiv> "?G J"
ultimately have G: "indep_sets G K" "\<And>i. i \<in> K \<Longrightarrow> G i \<subseteq> events" and "j \<in> K"
by (auto simp: indep_sets_def)
let ?D = "{E\<in>events. indep_sets (G(j := {E})) K }"
{ fix X assume X: "X \<in> events"
assume indep: "\<And>J A. J \<noteq> {} \<Longrightarrow> J \<subseteq> K \<Longrightarrow> finite J \<Longrightarrow> j \<notin> J \<Longrightarrow> (\<forall>i\<in>J. A i \<in> G i)
\<Longrightarrow> prob ((\<Inter>i\<in>J. A i) \<inter> X) = prob X * (\<Prod>i\<in>J. prob (A i))"
have "indep_sets (G(j := {X})) K"
proof (rule indep_setsI)
fix i assume "i \<in> K" then show "(G(j:={X})) i \<subseteq> events"
using G X by auto
next
fix A J assume J: "J \<noteq> {}" "J \<subseteq> K" "finite J" "\<forall>i\<in>J. A i \<in> (G(j := {X})) i"
show "prob (\<Inter>j\<in>J. A j) = (\<Prod>j\<in>J. prob (A j))"
proof cases
assume "j \<in> J"
with J have "A j = X" by auto
show ?thesis
proof cases
assume "J = {j}" then show ?thesis by simp
next
assume "J \<noteq> {j}"
have "prob (\<Inter>i\<in>J. A i) = prob ((\<Inter>i\<in>J-{j}. A i) \<inter> X)"
using `j \<in> J` `A j = X` by (auto intro!: arg_cong[where f=prob] split: split_if_asm)
also have "\<dots> = prob X * (\<Prod>i\<in>J-{j}. prob (A i))"
proof (rule indep)
show "J - {j} \<noteq> {}" "J - {j} \<subseteq> K" "finite (J - {j})" "j \<notin> J - {j}"
using J `J \<noteq> {j}` `j \<in> J` by auto
show "\<forall>i\<in>J - {j}. A i \<in> G i"
using J by auto
qed
also have "\<dots> = prob (A j) * (\<Prod>i\<in>J-{j}. prob (A i))"
using `A j = X` by simp
also have "\<dots> = (\<Prod>i\<in>J. prob (A i))"
unfolding setprod.insert_remove[OF `finite J`, symmetric, of "\<lambda>i. prob (A i)"]
using `j \<in> J` by (simp add: insert_absorb)
finally show ?thesis .
qed
next
assume "j \<notin> J"
with J have "\<forall>i\<in>J. A i \<in> G i" by (auto split: split_if_asm)
with J show ?thesis
by (intro indep_setsD[OF G(1)]) auto
qed
qed }
note indep_sets_insert = this
have "dynkin_system (space M) ?D"
proof (rule dynkin_systemI', simp_all cong del: indep_sets_cong, safe)
show "indep_sets (G(j := {{}})) K"
by (rule indep_sets_insert) auto
next
fix X assume X: "X \<in> events" and G': "indep_sets (G(j := {X})) K"
show "indep_sets (G(j := {space M - X})) K"
proof (rule indep_sets_insert)
fix J A assume J: "J \<noteq> {}" "J \<subseteq> K" "finite J" "j \<notin> J" and A: "\<forall>i\<in>J. A i \<in> G i"
then have A_sets: "\<And>i. i\<in>J \<Longrightarrow> A i \<in> events"
using G by auto
have "prob ((\<Inter>j\<in>J. A j) \<inter> (space M - X)) =
prob ((\<Inter>j\<in>J. A j) - (\<Inter>i\<in>insert j J. (A(j := X)) i))"
using A_sets sets.sets_into_space[of _ M] X `J \<noteq> {}`
by (auto intro!: arg_cong[where f=prob] split: split_if_asm)
also have "\<dots> = prob (\<Inter>j\<in>J. A j) - prob (\<Inter>i\<in>insert j J. (A(j := X)) i)"
using J `J \<noteq> {}` `j \<notin> J` A_sets X sets.sets_into_space
by (auto intro!: finite_measure_Diff sets.finite_INT split: split_if_asm)
finally have "prob ((\<Inter>j\<in>J. A j) \<inter> (space M - X)) =
prob (\<Inter>j\<in>J. A j) - prob (\<Inter>i\<in>insert j J. (A(j := X)) i)" .
moreover {
have "prob (\<Inter>j\<in>J. A j) = (\<Prod>j\<in>J. prob (A j))"
using J A `finite J` by (intro indep_setsD[OF G(1)]) auto
then have "prob (\<Inter>j\<in>J. A j) = prob (space M) * (\<Prod>i\<in>J. prob (A i))"
using prob_space by simp }
moreover {
have "prob (\<Inter>i\<in>insert j J. (A(j := X)) i) = (\<Prod>i\<in>insert j J. prob ((A(j := X)) i))"
using J A `j \<in> K` by (intro indep_setsD[OF G']) auto
then have "prob (\<Inter>i\<in>insert j J. (A(j := X)) i) = prob X * (\<Prod>i\<in>J. prob (A i))"
using `finite J` `j \<notin> J` by (auto intro!: setprod.cong) }
ultimately have "prob ((\<Inter>j\<in>J. A j) \<inter> (space M - X)) = (prob (space M) - prob X) * (\<Prod>i\<in>J. prob (A i))"
by (simp add: field_simps)
also have "\<dots> = prob (space M - X) * (\<Prod>i\<in>J. prob (A i))"
using X A by (simp add: finite_measure_compl)
finally show "prob ((\<Inter>j\<in>J. A j) \<inter> (space M - X)) = prob (space M - X) * (\<Prod>i\<in>J. prob (A i))" .
qed (insert X, auto)
next
fix F :: "nat \<Rightarrow> 'a set" assume disj: "disjoint_family F" and "range F \<subseteq> ?D"
then have F: "\<And>i. F i \<in> events" "\<And>i. indep_sets (G(j:={F i})) K" by auto
show "indep_sets (G(j := {\<Union>k. F k})) K"
proof (rule indep_sets_insert)
fix J A assume J: "j \<notin> J" "J \<noteq> {}" "J \<subseteq> K" "finite J" and A: "\<forall>i\<in>J. A i \<in> G i"
then have A_sets: "\<And>i. i\<in>J \<Longrightarrow> A i \<in> events"
using G by auto
have "prob ((\<Inter>j\<in>J. A j) \<inter> (\<Union>k. F k)) = prob (\<Union>k. (\<Inter>i\<in>insert j J. (A(j := F k)) i))"
using `J \<noteq> {}` `j \<notin> J` `j \<in> K` by (auto intro!: arg_cong[where f=prob] split: split_if_asm)
moreover have "(\<lambda>k. prob (\<Inter>i\<in>insert j J. (A(j := F k)) i)) sums prob (\<Union>k. (\<Inter>i\<in>insert j J. (A(j := F k)) i))"
proof (rule finite_measure_UNION)
show "disjoint_family (\<lambda>k. \<Inter>i\<in>insert j J. (A(j := F k)) i)"
using disj by (rule disjoint_family_on_bisimulation) auto
show "range (\<lambda>k. \<Inter>i\<in>insert j J. (A(j := F k)) i) \<subseteq> events"
using A_sets F `finite J` `J \<noteq> {}` `j \<notin> J` by (auto intro!: sets.Int)
qed
moreover { fix k
from J A `j \<in> K` have "prob (\<Inter>i\<in>insert j J. (A(j := F k)) i) = prob (F k) * (\<Prod>i\<in>J. prob (A i))"
by (subst indep_setsD[OF F(2)]) (auto intro!: setprod.cong split: split_if_asm)
also have "\<dots> = prob (F k) * prob (\<Inter>i\<in>J. A i)"
using J A `j \<in> K` by (subst indep_setsD[OF G(1)]) auto
finally have "prob (\<Inter>i\<in>insert j J. (A(j := F k)) i) = prob (F k) * prob (\<Inter>i\<in>J. A i)" . }
ultimately have "(\<lambda>k. prob (F k) * prob (\<Inter>i\<in>J. A i)) sums (prob ((\<Inter>j\<in>J. A j) \<inter> (\<Union>k. F k)))"
by simp
moreover
have "(\<lambda>k. prob (F k) * prob (\<Inter>i\<in>J. A i)) sums (prob (\<Union>k. F k) * prob (\<Inter>i\<in>J. A i))"
using disj F(1) by (intro finite_measure_UNION sums_mult2) auto
then have "(\<lambda>k. prob (F k) * prob (\<Inter>i\<in>J. A i)) sums (prob (\<Union>k. F k) * (\<Prod>i\<in>J. prob (A i)))"
using J A `j \<in> K` by (subst indep_setsD[OF G(1), symmetric]) auto
ultimately
show "prob ((\<Inter>j\<in>J. A j) \<inter> (\<Union>k. F k)) = prob (\<Union>k. F k) * (\<Prod>j\<in>J. prob (A j))"
by (auto dest!: sums_unique)
qed (insert F, auto)
qed (insert sets.sets_into_space, auto)
then have mono: "dynkin (space M) (G j) \<subseteq> {E \<in> events. indep_sets (G(j := {E})) K}"
proof (rule dynkin_system.dynkin_subset, safe)
fix X assume "X \<in> G j"
then show "X \<in> events" using G `j \<in> K` by auto
from `indep_sets G K`
show "indep_sets (G(j := {X})) K"
by (rule indep_sets_mono_sets) (insert `X \<in> G j`, auto)
qed
have "indep_sets (G(j:=?D)) K"
proof (rule indep_setsI)
fix i assume "i \<in> K" then show "(G(j := ?D)) i \<subseteq> events"
using G(2) by auto
next
fix A J assume J: "J\<noteq>{}" "J \<subseteq> K" "finite J" and A: "\<forall>i\<in>J. A i \<in> (G(j := ?D)) i"
show "prob (\<Inter>j\<in>J. A j) = (\<Prod>j\<in>J. prob (A j))"
proof cases
assume "j \<in> J"
with A have indep: "indep_sets (G(j := {A j})) K" by auto
from J A show ?thesis
by (intro indep_setsD[OF indep]) auto
next
assume "j \<notin> J"
with J A have "\<forall>i\<in>J. A i \<in> G i" by (auto split: split_if_asm)
with J show ?thesis
by (intro indep_setsD[OF G(1)]) auto
qed
qed
then have "indep_sets (G(j := dynkin (space M) (G j))) K"
by (rule indep_sets_mono_sets) (insert mono, auto)
then show ?case
by (rule indep_sets_mono_sets) (insert `j \<in> K` `j \<notin> J`, auto simp: G_def)
qed (insert `indep_sets F K`, simp) }
from this[OF `indep_sets F J` `finite J` subset_refl]
show "indep_sets ?F J"
by (rule indep_sets_mono_sets) auto
qed
lemma (in prob_space) indep_sets_sigma:
assumes indep: "indep_sets F I"
assumes stable: "\<And>i. i \<in> I \<Longrightarrow> Int_stable (F i)"
shows "indep_sets (\<lambda>i. sigma_sets (space M) (F i)) I"
proof -
from indep_sets_dynkin[OF indep]
show ?thesis
proof (rule indep_sets_mono_sets, subst sigma_eq_dynkin, simp_all add: stable)
fix i assume "i \<in> I"
with indep have "F i \<subseteq> events" by (auto simp: indep_sets_def)
with sets.sets_into_space show "F i \<subseteq> Pow (space M)" by auto
qed
qed
lemma (in prob_space) indep_sets_sigma_sets_iff:
assumes "\<And>i. i \<in> I \<Longrightarrow> Int_stable (F i)"
shows "indep_sets (\<lambda>i. sigma_sets (space M) (F i)) I \<longleftrightarrow> indep_sets F I"
proof
assume "indep_sets F I" then show "indep_sets (\<lambda>i. sigma_sets (space M) (F i)) I"
by (rule indep_sets_sigma) fact
next
assume "indep_sets (\<lambda>i. sigma_sets (space M) (F i)) I" then show "indep_sets F I"
by (rule indep_sets_mono_sets) (intro subsetI sigma_sets.Basic)
qed
definition (in prob_space)
indep_vars_def2: "indep_vars M' X I \<longleftrightarrow>
(\<forall>i\<in>I. random_variable (M' i) (X i)) \<and>
indep_sets (\<lambda>i. { X i -` A \<inter> space M | A. A \<in> sets (M' i)}) I"
definition (in prob_space)
"indep_var Ma A Mb B \<longleftrightarrow> indep_vars (case_bool Ma Mb) (case_bool A B) UNIV"
lemma (in prob_space) indep_vars_def:
"indep_vars M' X I \<longleftrightarrow>
(\<forall>i\<in>I. random_variable (M' i) (X i)) \<and>
indep_sets (\<lambda>i. sigma_sets (space M) { X i -` A \<inter> space M | A. A \<in> sets (M' i)}) I"
unfolding indep_vars_def2
apply (rule conj_cong[OF refl])
apply (rule indep_sets_sigma_sets_iff[symmetric])
apply (auto simp: Int_stable_def)
apply (rule_tac x="A \<inter> Aa" in exI)
apply auto
done
lemma (in prob_space) indep_var_eq:
"indep_var S X T Y \<longleftrightarrow>
(random_variable S X \<and> random_variable T Y) \<and>
indep_set
(sigma_sets (space M) { X -` A \<inter> space M | A. A \<in> sets S})
(sigma_sets (space M) { Y -` A \<inter> space M | A. A \<in> sets T})"
unfolding indep_var_def indep_vars_def indep_set_def UNIV_bool
by (intro arg_cong2[where f="op \<and>"] arg_cong2[where f=indep_sets] ext)
(auto split: bool.split)
lemma (in prob_space) indep_sets2_eq:
"indep_set A B \<longleftrightarrow> A \<subseteq> events \<and> B \<subseteq> events \<and> (\<forall>a\<in>A. \<forall>b\<in>B. prob (a \<inter> b) = prob a * prob b)"
unfolding indep_set_def
proof (intro iffI ballI conjI)
assume indep: "indep_sets (case_bool A B) UNIV"
{ fix a b assume "a \<in> A" "b \<in> B"
with indep_setsD[OF indep, of UNIV "case_bool a b"]
show "prob (a \<inter> b) = prob a * prob b"
unfolding UNIV_bool by (simp add: ac_simps) }
from indep show "A \<subseteq> events" "B \<subseteq> events"
unfolding indep_sets_def UNIV_bool by auto
next
assume *: "A \<subseteq> events \<and> B \<subseteq> events \<and> (\<forall>a\<in>A. \<forall>b\<in>B. prob (a \<inter> b) = prob a * prob b)"
show "indep_sets (case_bool A B) UNIV"
proof (rule indep_setsI)
fix i show "(case i of True \<Rightarrow> A | False \<Rightarrow> B) \<subseteq> events"
using * by (auto split: bool.split)
next
fix J X assume "J \<noteq> {}" "J \<subseteq> UNIV" and X: "\<forall>j\<in>J. X j \<in> (case j of True \<Rightarrow> A | False \<Rightarrow> B)"
then have "J = {True} \<or> J = {False} \<or> J = {True,False}"
by (auto simp: UNIV_bool)
then show "prob (\<Inter>j\<in>J. X j) = (\<Prod>j\<in>J. prob (X j))"
using X * by auto
qed
qed
lemma (in prob_space) indep_set_sigma_sets:
assumes "indep_set A B"
assumes A: "Int_stable A" and B: "Int_stable B"
shows "indep_set (sigma_sets (space M) A) (sigma_sets (space M) B)"
proof -
have "indep_sets (\<lambda>i. sigma_sets (space M) (case i of True \<Rightarrow> A | False \<Rightarrow> B)) UNIV"
proof (rule indep_sets_sigma)
show "indep_sets (case_bool A B) UNIV"
by (rule `indep_set A B`[unfolded indep_set_def])
fix i show "Int_stable (case i of True \<Rightarrow> A | False \<Rightarrow> B)"
using A B by (cases i) auto
qed
then show ?thesis
unfolding indep_set_def
by (rule indep_sets_mono_sets) (auto split: bool.split)
qed
lemma (in prob_space) indep_sets_collect_sigma:
fixes I :: "'j \<Rightarrow> 'i set" and J :: "'j set" and E :: "'i \<Rightarrow> 'a set set"
assumes indep: "indep_sets E (\<Union>j\<in>J. I j)"
assumes Int_stable: "\<And>i j. j \<in> J \<Longrightarrow> i \<in> I j \<Longrightarrow> Int_stable (E i)"
assumes disjoint: "disjoint_family_on I J"
shows "indep_sets (\<lambda>j. sigma_sets (space M) (\<Union>i\<in>I j. E i)) J"
proof -
let ?E = "\<lambda>j. {\<Inter>k\<in>K. E' k| E' K. finite K \<and> K \<noteq> {} \<and> K \<subseteq> I j \<and> (\<forall>k\<in>K. E' k \<in> E k) }"
from indep have E: "\<And>j i. j \<in> J \<Longrightarrow> i \<in> I j \<Longrightarrow> E i \<subseteq> events"
unfolding indep_sets_def by auto
{ fix j
let ?S = "sigma_sets (space M) (\<Union>i\<in>I j. E i)"
assume "j \<in> J"
from E[OF this] interpret S: sigma_algebra "space M" ?S
using sets.sets_into_space[of _ M] by (intro sigma_algebra_sigma_sets) auto
have "sigma_sets (space M) (\<Union>i\<in>I j. E i) = sigma_sets (space M) (?E j)"
proof (rule sigma_sets_eqI)
fix A assume "A \<in> (\<Union>i\<in>I j. E i)"
then guess i ..
then show "A \<in> sigma_sets (space M) (?E j)"
by (auto intro!: sigma_sets.intros(2-) exI[of _ "{i}"] exI[of _ "\<lambda>i. A"])
next
fix A assume "A \<in> ?E j"
then obtain E' K where "finite K" "K \<noteq> {}" "K \<subseteq> I j" "\<And>k. k \<in> K \<Longrightarrow> E' k \<in> E k"
and A: "A = (\<Inter>k\<in>K. E' k)"
by auto
then have "A \<in> ?S" unfolding A
by (safe intro!: S.finite_INT) auto
then show "A \<in> sigma_sets (space M) (\<Union>i\<in>I j. E i)"
by simp
qed }
moreover have "indep_sets (\<lambda>j. sigma_sets (space M) (?E j)) J"
proof (rule indep_sets_sigma)
show "indep_sets ?E J"
proof (intro indep_setsI)
fix j assume "j \<in> J" with E show "?E j \<subseteq> events" by (force intro!: sets.finite_INT)
next
fix K A assume K: "K \<noteq> {}" "K \<subseteq> J" "finite K"
and "\<forall>j\<in>K. A j \<in> ?E j"
then have "\<forall>j\<in>K. \<exists>E' L. A j = (\<Inter>l\<in>L. E' l) \<and> finite L \<and> L \<noteq> {} \<and> L \<subseteq> I j \<and> (\<forall>l\<in>L. E' l \<in> E l)"
by simp
from bchoice[OF this] guess E' ..
from bchoice[OF this] obtain L
where A: "\<And>j. j\<in>K \<Longrightarrow> A j = (\<Inter>l\<in>L j. E' j l)"
and L: "\<And>j. j\<in>K \<Longrightarrow> finite (L j)" "\<And>j. j\<in>K \<Longrightarrow> L j \<noteq> {}" "\<And>j. j\<in>K \<Longrightarrow> L j \<subseteq> I j"
and E': "\<And>j l. j\<in>K \<Longrightarrow> l \<in> L j \<Longrightarrow> E' j l \<in> E l"
by auto
{ fix k l j assume "k \<in> K" "j \<in> K" "l \<in> L j" "l \<in> L k"
have "k = j"
proof (rule ccontr)
assume "k \<noteq> j"
with disjoint `K \<subseteq> J` `k \<in> K` `j \<in> K` have "I k \<inter> I j = {}"
unfolding disjoint_family_on_def by auto
with L(2,3)[OF `j \<in> K`] L(2,3)[OF `k \<in> K`]
show False using `l \<in> L k` `l \<in> L j` by auto
qed }
note L_inj = this
def k \<equiv> "\<lambda>l. (SOME k. k \<in> K \<and> l \<in> L k)"
{ fix x j l assume *: "j \<in> K" "l \<in> L j"
have "k l = j" unfolding k_def
proof (rule some_equality)
fix k assume "k \<in> K \<and> l \<in> L k"
with * L_inj show "k = j" by auto
qed (insert *, simp) }
note k_simp[simp] = this
let ?E' = "\<lambda>l. E' (k l) l"
have "prob (\<Inter>j\<in>K. A j) = prob (\<Inter>l\<in>(\<Union>k\<in>K. L k). ?E' l)"
by (auto simp: A intro!: arg_cong[where f=prob])
also have "\<dots> = (\<Prod>l\<in>(\<Union>k\<in>K. L k). prob (?E' l))"
using L K E' by (intro indep_setsD[OF indep]) (simp_all add: UN_mono)
also have "\<dots> = (\<Prod>j\<in>K. \<Prod>l\<in>L j. prob (E' j l))"
using K L L_inj by (subst setprod.UNION_disjoint) auto
also have "\<dots> = (\<Prod>j\<in>K. prob (A j))"
using K L E' by (auto simp add: A intro!: setprod.cong indep_setsD[OF indep, symmetric]) blast
finally show "prob (\<Inter>j\<in>K. A j) = (\<Prod>j\<in>K. prob (A j))" .
qed
next
fix j assume "j \<in> J"
show "Int_stable (?E j)"
proof (rule Int_stableI)
fix a assume "a \<in> ?E j" then obtain Ka Ea
where a: "a = (\<Inter>k\<in>Ka. Ea k)" "finite Ka" "Ka \<noteq> {}" "Ka \<subseteq> I j" "\<And>k. k\<in>Ka \<Longrightarrow> Ea k \<in> E k" by auto
fix b assume "b \<in> ?E j" then obtain Kb Eb
where b: "b = (\<Inter>k\<in>Kb. Eb k)" "finite Kb" "Kb \<noteq> {}" "Kb \<subseteq> I j" "\<And>k. k\<in>Kb \<Longrightarrow> Eb k \<in> E k" by auto
let ?A = "\<lambda>k. (if k \<in> Ka \<inter> Kb then Ea k \<inter> Eb k else if k \<in> Kb then Eb k else if k \<in> Ka then Ea k else {})"
have "a \<inter> b = INTER (Ka \<union> Kb) ?A"
by (simp add: a b set_eq_iff) auto
with a b `j \<in> J` Int_stableD[OF Int_stable] show "a \<inter> b \<in> ?E j"
by (intro CollectI exI[of _ "Ka \<union> Kb"] exI[of _ ?A]) auto
qed
qed
ultimately show ?thesis
by (simp cong: indep_sets_cong)
qed
lemma (in prob_space) indep_vars_restrict:
assumes ind: "indep_vars M' X I" and K: "\<And>j. j \<in> L \<Longrightarrow> K j \<subseteq> I" and J: "disjoint_family_on K L"
shows "indep_vars (\<lambda>j. PiM (K j) M') (\<lambda>j \<omega>. restrict (\<lambda>i. X i \<omega>) (K j)) L"
unfolding indep_vars_def
proof safe
fix j assume "j \<in> L" then show "random_variable (Pi\<^sub>M (K j) M') (\<lambda>\<omega>. \<lambda>i\<in>K j. X i \<omega>)"
using K ind by (auto simp: indep_vars_def intro!: measurable_restrict)
next
have X: "\<And>i. i \<in> I \<Longrightarrow> X i \<in> measurable M (M' i)"
using ind by (auto simp: indep_vars_def)
let ?proj = "\<lambda>j S. {(\<lambda>\<omega>. \<lambda>i\<in>K j. X i \<omega>) -` A \<inter> space M |A. A \<in> S}"
let ?UN = "\<lambda>j. sigma_sets (space M) (\<Union>i\<in>K j. { X i -` A \<inter> space M| A. A \<in> sets (M' i) })"
show "indep_sets (\<lambda>i. sigma_sets (space M) (?proj i (sets (Pi\<^sub>M (K i) M')))) L"
proof (rule indep_sets_mono_sets)
fix j assume j: "j \<in> L"
have "sigma_sets (space M) (?proj j (sets (Pi\<^sub>M (K j) M'))) =
sigma_sets (space M) (sigma_sets (space M) (?proj j (prod_algebra (K j) M')))"
using j K X[THEN measurable_space] unfolding sets_PiM
by (subst sigma_sets_vimage_commute) (auto simp add: Pi_iff)
also have "\<dots> = sigma_sets (space M) (?proj j (prod_algebra (K j) M'))"
by (rule sigma_sets_sigma_sets_eq) auto
also have "\<dots> \<subseteq> ?UN j"
proof (rule sigma_sets_mono, safe del: disjE elim!: prod_algebraE)
fix J E assume J: "finite J" "J \<noteq> {} \<or> K j = {}" "J \<subseteq> K j" and E: "\<forall>i. i \<in> J \<longrightarrow> E i \<in> sets (M' i)"
show "(\<lambda>\<omega>. \<lambda>i\<in>K j. X i \<omega>) -` prod_emb (K j) M' J (Pi\<^sub>E J E) \<inter> space M \<in> ?UN j"
proof cases
assume "K j = {}" with J show ?thesis
by (auto simp add: sigma_sets_empty_eq prod_emb_def)
next
assume "K j \<noteq> {}" with J have "J \<noteq> {}"
by auto
{ interpret sigma_algebra "space M" "?UN j"
by (rule sigma_algebra_sigma_sets) auto
have "\<And>A. (\<And>i. i \<in> J \<Longrightarrow> A i \<in> ?UN j) \<Longrightarrow> INTER J A \<in> ?UN j"
using `finite J` `J \<noteq> {}` by (rule finite_INT) blast }
note INT = this
from `J \<noteq> {}` J K E[rule_format, THEN sets.sets_into_space] j
have "(\<lambda>\<omega>. \<lambda>i\<in>K j. X i \<omega>) -` prod_emb (K j) M' J (Pi\<^sub>E J E) \<inter> space M
= (\<Inter>i\<in>J. X i -` E i \<inter> space M)"
apply (subst prod_emb_PiE[OF _ ])
apply auto []
apply auto []
apply (auto simp add: Pi_iff intro!: X[THEN measurable_space])
apply (erule_tac x=i in ballE)
apply auto
done
also have "\<dots> \<in> ?UN j"
apply (rule INT)
apply (rule sigma_sets.Basic)
using `J \<subseteq> K j` E
apply auto
done
finally show ?thesis .
qed
qed
finally show "sigma_sets (space M) (?proj j (sets (Pi\<^sub>M (K j) M'))) \<subseteq> ?UN j" .
next
show "indep_sets ?UN L"
proof (rule indep_sets_collect_sigma)
show "indep_sets (\<lambda>i. {X i -` A \<inter> space M |A. A \<in> sets (M' i)}) (\<Union>j\<in>L. K j)"
proof (rule indep_sets_mono_index)
show "indep_sets (\<lambda>i. {X i -` A \<inter> space M |A. A \<in> sets (M' i)}) I"
using ind unfolding indep_vars_def2 by auto
show "(\<Union>l\<in>L. K l) \<subseteq> I"
using K by auto
qed
next
fix l i assume "l \<in> L" "i \<in> K l"
show "Int_stable {X i -` A \<inter> space M |A. A \<in> sets (M' i)}"
apply (auto simp: Int_stable_def)
apply (rule_tac x="A \<inter> Aa" in exI)
apply auto
done
qed fact
qed
qed
lemma (in prob_space) indep_var_restrict:
assumes ind: "indep_vars M' X I" and AB: "A \<inter> B = {}" "A \<subseteq> I" "B \<subseteq> I"
shows "indep_var (PiM A M') (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) A) (PiM B M') (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) B)"
proof -
have *:
"case_bool (Pi\<^sub>M A M') (Pi\<^sub>M B M') = (\<lambda>b. PiM (case_bool A B b) M')"
"case_bool (\<lambda>\<omega>. \<lambda>i\<in>A. X i \<omega>) (\<lambda>\<omega>. \<lambda>i\<in>B. X i \<omega>) = (\<lambda>b \<omega>. \<lambda>i\<in>case_bool A B b. X i \<omega>)"
by (simp_all add: fun_eq_iff split: bool.split)
show ?thesis
unfolding indep_var_def * using AB
by (intro indep_vars_restrict[OF ind]) (auto simp: disjoint_family_on_def split: bool.split)
qed
lemma (in prob_space) indep_vars_subset:
assumes "indep_vars M' X I" "J \<subseteq> I"
shows "indep_vars M' X J"
using assms unfolding indep_vars_def indep_sets_def
by auto
lemma (in prob_space) indep_vars_cong:
"I = J \<Longrightarrow> (\<And>i. i \<in> I \<Longrightarrow> X i = Y i) \<Longrightarrow> (\<And>i. i \<in> I \<Longrightarrow> M' i = N' i) \<Longrightarrow> indep_vars M' X I \<longleftrightarrow> indep_vars N' Y J"
unfolding indep_vars_def2 by (intro conj_cong indep_sets_cong) auto
definition (in prob_space) tail_events where
"tail_events A = (\<Inter>n. sigma_sets (space M) (UNION {n..} A))"
lemma (in prob_space) tail_events_sets:
assumes A: "\<And>i::nat. A i \<subseteq> events"
shows "tail_events A \<subseteq> events"
proof
fix X assume X: "X \<in> tail_events A"
let ?A = "(\<Inter>n. sigma_sets (space M) (UNION {n..} A))"
from X have "\<And>n::nat. X \<in> sigma_sets (space M) (UNION {n..} A)" by (auto simp: tail_events_def)
from this[of 0] have "X \<in> sigma_sets (space M) (UNION UNIV A)" by simp
then show "X \<in> events"
by induct (insert A, auto)
qed
lemma (in prob_space) sigma_algebra_tail_events:
assumes "\<And>i::nat. sigma_algebra (space M) (A i)"
shows "sigma_algebra (space M) (tail_events A)"
unfolding tail_events_def
proof (simp add: sigma_algebra_iff2, safe)
let ?A = "(\<Inter>n. sigma_sets (space M) (UNION {n..} A))"
interpret A: sigma_algebra "space M" "A i" for i by fact
{ fix X x assume "X \<in> ?A" "x \<in> X"
then have "\<And>n. X \<in> sigma_sets (space M) (UNION {n..} A)" by auto
from this[of 0] have "X \<in> sigma_sets (space M) (UNION UNIV A)" by simp
then have "X \<subseteq> space M"
by induct (insert A.sets_into_space, auto)
with `x \<in> X` show "x \<in> space M" by auto }
{ fix F :: "nat \<Rightarrow> 'a set" and n assume "range F \<subseteq> ?A"
then show "(UNION UNIV F) \<in> sigma_sets (space M) (UNION {n..} A)"
by (intro sigma_sets.Union) auto }
qed (auto intro!: sigma_sets.Compl sigma_sets.Empty)
lemma (in prob_space) kolmogorov_0_1_law:
fixes A :: "nat \<Rightarrow> 'a set set"
assumes "\<And>i::nat. sigma_algebra (space M) (A i)"
assumes indep: "indep_sets A UNIV"
and X: "X \<in> tail_events A"
shows "prob X = 0 \<or> prob X = 1"
proof -
have A: "\<And>i. A i \<subseteq> events"
using indep unfolding indep_sets_def by simp
let ?D = "{D \<in> events. prob (X \<inter> D) = prob X * prob D}"
interpret A: sigma_algebra "space M" "A i" for i by fact
interpret T: sigma_algebra "space M" "tail_events A"
by (rule sigma_algebra_tail_events) fact
have "X \<subseteq> space M" using T.space_closed X by auto
have X_in: "X \<in> events"
using tail_events_sets A X by auto
interpret D: dynkin_system "space M" ?D
proof (rule dynkin_systemI)
fix D assume "D \<in> ?D" then show "D \<subseteq> space M"
using sets.sets_into_space by auto
next
show "space M \<in> ?D"
using prob_space `X \<subseteq> space M` by (simp add: Int_absorb2)
next
fix A assume A: "A \<in> ?D"
have "prob (X \<inter> (space M - A)) = prob (X - (X \<inter> A))"
using `X \<subseteq> space M` by (auto intro!: arg_cong[where f=prob])
also have "\<dots> = prob X - prob (X \<inter> A)"
using X_in A by (intro finite_measure_Diff) auto
also have "\<dots> = prob X * prob (space M) - prob X * prob A"
using A prob_space by auto
also have "\<dots> = prob X * prob (space M - A)"
using X_in A sets.sets_into_space
by (subst finite_measure_Diff) (auto simp: field_simps)
finally show "space M - A \<in> ?D"
using A `X \<subseteq> space M` by auto
next
fix F :: "nat \<Rightarrow> 'a set" assume dis: "disjoint_family F" and "range F \<subseteq> ?D"
then have F: "range F \<subseteq> events" "\<And>i. prob (X \<inter> F i) = prob X * prob (F i)"
by auto
have "(\<lambda>i. prob (X \<inter> F i)) sums prob (\<Union>i. X \<inter> F i)"
proof (rule finite_measure_UNION)
show "range (\<lambda>i. X \<inter> F i) \<subseteq> events"
using F X_in by auto
show "disjoint_family (\<lambda>i. X \<inter> F i)"
using dis by (rule disjoint_family_on_bisimulation) auto
qed
with F have "(\<lambda>i. prob X * prob (F i)) sums prob (X \<inter> (\<Union>i. F i))"
by simp
moreover have "(\<lambda>i. prob X * prob (F i)) sums (prob X * prob (\<Union>i. F i))"
by (intro sums_mult finite_measure_UNION F dis)
ultimately have "prob (X \<inter> (\<Union>i. F i)) = prob X * prob (\<Union>i. F i)"
by (auto dest!: sums_unique)
with F show "(\<Union>i. F i) \<in> ?D"
by auto
qed
{ fix n
have "indep_sets (\<lambda>b. sigma_sets (space M) (\<Union>m\<in>case_bool {..n} {Suc n..} b. A m)) UNIV"
proof (rule indep_sets_collect_sigma)
have *: "(\<Union>b. case b of True \<Rightarrow> {..n} | False \<Rightarrow> {Suc n..}) = UNIV" (is "?U = _")
by (simp split: bool.split add: set_eq_iff) (metis not_less_eq_eq)
with indep show "indep_sets A ?U" by simp
show "disjoint_family (case_bool {..n} {Suc n..})"
unfolding disjoint_family_on_def by (auto split: bool.split)
fix m
show "Int_stable (A m)"
unfolding Int_stable_def using A.Int by auto
qed
also have "(\<lambda>b. sigma_sets (space M) (\<Union>m\<in>case_bool {..n} {Suc n..} b. A m)) =
case_bool (sigma_sets (space M) (\<Union>m\<in>{..n}. A m)) (sigma_sets (space M) (\<Union>m\<in>{Suc n..}. A m))"
by (auto intro!: ext split: bool.split)
finally have indep: "indep_set (sigma_sets (space M) (\<Union>m\<in>{..n}. A m)) (sigma_sets (space M) (\<Union>m\<in>{Suc n..}. A m))"
unfolding indep_set_def by simp
have "sigma_sets (space M) (\<Union>m\<in>{..n}. A m) \<subseteq> ?D"
proof (simp add: subset_eq, rule)
fix D assume D: "D \<in> sigma_sets (space M) (\<Union>m\<in>{..n}. A m)"
have "X \<in> sigma_sets (space M) (\<Union>m\<in>{Suc n..}. A m)"
using X unfolding tail_events_def by simp
from indep_setD[OF indep D this] indep_setD_ev1[OF indep] D
show "D \<in> events \<and> prob (X \<inter> D) = prob X * prob D"
by (auto simp add: ac_simps)
qed }
then have "(\<Union>n. sigma_sets (space M) (\<Union>m\<in>{..n}. A m)) \<subseteq> ?D" (is "?A \<subseteq> _")
by auto
note `X \<in> tail_events A`
also {
have "\<And>n. sigma_sets (space M) (\<Union>i\<in>{n..}. A i) \<subseteq> sigma_sets (space M) ?A"
by (intro sigma_sets_subseteq UN_mono) auto
then have "tail_events A \<subseteq> sigma_sets (space M) ?A"
unfolding tail_events_def by auto }
also have "sigma_sets (space M) ?A = dynkin (space M) ?A"
proof (rule sigma_eq_dynkin)
{ fix B n assume "B \<in> sigma_sets (space M) (\<Union>m\<in>{..n}. A m)"
then have "B \<subseteq> space M"
by induct (insert A sets.sets_into_space[of _ M], auto) }
then show "?A \<subseteq> Pow (space M)" by auto
show "Int_stable ?A"
proof (rule Int_stableI)
fix a assume "a \<in> ?A" then guess n .. note a = this
fix b assume "b \<in> ?A" then guess m .. note b = this
interpret Amn: sigma_algebra "space M" "sigma_sets (space M) (\<Union>i\<in>{..max m n}. A i)"
using A sets.sets_into_space[of _ M] by (intro sigma_algebra_sigma_sets) auto
have "sigma_sets (space M) (\<Union>i\<in>{..n}. A i) \<subseteq> sigma_sets (space M) (\<Union>i\<in>{..max m n}. A i)"
by (intro sigma_sets_subseteq UN_mono) auto
with a have "a \<in> sigma_sets (space M) (\<Union>i\<in>{..max m n}. A i)" by auto
moreover
have "sigma_sets (space M) (\<Union>i\<in>{..m}. A i) \<subseteq> sigma_sets (space M) (\<Union>i\<in>{..max m n}. A i)"
by (intro sigma_sets_subseteq UN_mono) auto
with b have "b \<in> sigma_sets (space M) (\<Union>i\<in>{..max m n}. A i)" by auto
ultimately have "a \<inter> b \<in> sigma_sets (space M) (\<Union>i\<in>{..max m n}. A i)"
using Amn.Int[of a b] by simp
then show "a \<inter> b \<in> (\<Union>n. sigma_sets (space M) (\<Union>i\<in>{..n}. A i))" by auto
qed
qed
also have "dynkin (space M) ?A \<subseteq> ?D"
using `?A \<subseteq> ?D` by (auto intro!: D.dynkin_subset)
finally show ?thesis by auto
qed
lemma (in prob_space) borel_0_1_law:
fixes F :: "nat \<Rightarrow> 'a set"
assumes F2: "indep_events F UNIV"
shows "prob (\<Inter>n. \<Union>m\<in>{n..}. F m) = 0 \<or> prob (\<Inter>n. \<Union>m\<in>{n..}. F m) = 1"
proof (rule kolmogorov_0_1_law[of "\<lambda>i. sigma_sets (space M) { F i }"])
have F1: "range F \<subseteq> events"
using F2 by (simp add: indep_events_def subset_eq)
{ fix i show "sigma_algebra (space M) (sigma_sets (space M) {F i})"
using sigma_algebra_sigma_sets[of "{F i}" "space M"] F1 sets.sets_into_space
by auto }
show "indep_sets (\<lambda>i. sigma_sets (space M) {F i}) UNIV"
proof (rule indep_sets_sigma)
show "indep_sets (\<lambda>i. {F i}) UNIV"
unfolding indep_events_def_alt[symmetric] by fact
fix i show "Int_stable {F i}"
unfolding Int_stable_def by simp
qed
let ?Q = "\<lambda>n. \<Union>i\<in>{n..}. F i"
show "(\<Inter>n. \<Union>m\<in>{n..}. F m) \<in> tail_events (\<lambda>i. sigma_sets (space M) {F i})"
unfolding tail_events_def
proof
fix j
interpret S: sigma_algebra "space M" "sigma_sets (space M) (\<Union>i\<in>{j..}. sigma_sets (space M) {F i})"
using order_trans[OF F1 sets.space_closed]
by (intro sigma_algebra_sigma_sets) (simp add: sigma_sets_singleton subset_eq)
have "(\<Inter>n. ?Q n) = (\<Inter>n\<in>{j..}. ?Q n)"
by (intro decseq_SucI INT_decseq_offset UN_mono) auto
also have "\<dots> \<in> sigma_sets (space M) (\<Union>i\<in>{j..}. sigma_sets (space M) {F i})"
using order_trans[OF F1 sets.space_closed]
by (safe intro!: S.countable_INT S.countable_UN)
(auto simp: sigma_sets_singleton intro!: sigma_sets.Basic bexI)
finally show "(\<Inter>n. ?Q n) \<in> sigma_sets (space M) (\<Union>i\<in>{j..}. sigma_sets (space M) {F i})"
by simp
qed
qed
lemma (in prob_space) indep_sets_finite:
assumes I: "I \<noteq> {}" "finite I"
and F: "\<And>i. i \<in> I \<Longrightarrow> F i \<subseteq> events" "\<And>i. i \<in> I \<Longrightarrow> space M \<in> F i"
shows "indep_sets F I \<longleftrightarrow> (\<forall>A\<in>Pi I F. prob (\<Inter>j\<in>I. A j) = (\<Prod>j\<in>I. prob (A j)))"
proof
assume *: "indep_sets F I"
from I show "\<forall>A\<in>Pi I F. prob (\<Inter>j\<in>I. A j) = (\<Prod>j\<in>I. prob (A j))"
by (intro indep_setsD[OF *] ballI) auto
next
assume indep: "\<forall>A\<in>Pi I F. prob (\<Inter>j\<in>I. A j) = (\<Prod>j\<in>I. prob (A j))"
show "indep_sets F I"
proof (rule indep_setsI[OF F(1)])
fix A J assume J: "J \<noteq> {}" "J \<subseteq> I" "finite J"
assume A: "\<forall>j\<in>J. A j \<in> F j"
let ?A = "\<lambda>j. if j \<in> J then A j else space M"
have "prob (\<Inter>j\<in>I. ?A j) = prob (\<Inter>j\<in>J. A j)"
using subset_trans[OF F(1) sets.space_closed] J A
by (auto intro!: arg_cong[where f=prob] split: split_if_asm) blast
also
from A F have "(\<lambda>j. if j \<in> J then A j else space M) \<in> Pi I F" (is "?A \<in> _")
by (auto split: split_if_asm)
with indep have "prob (\<Inter>j\<in>I. ?A j) = (\<Prod>j\<in>I. prob (?A j))"
by auto
also have "\<dots> = (\<Prod>j\<in>J. prob (A j))"
unfolding if_distrib setprod.If_cases[OF `finite I`]
using prob_space `J \<subseteq> I` by (simp add: Int_absorb1 setprod.neutral_const)
finally show "prob (\<Inter>j\<in>J. A j) = (\<Prod>j\<in>J. prob (A j))" ..
qed
qed
lemma (in prob_space) indep_vars_finite:
fixes I :: "'i set"
assumes I: "I \<noteq> {}" "finite I"
and M': "\<And>i. i \<in> I \<Longrightarrow> sets (M' i) = sigma_sets (space (M' i)) (E i)"
and rv: "\<And>i. i \<in> I \<Longrightarrow> random_variable (M' i) (X i)"
and Int_stable: "\<And>i. i \<in> I \<Longrightarrow> Int_stable (E i)"
and space: "\<And>i. i \<in> I \<Longrightarrow> space (M' i) \<in> E i" and closed: "\<And>i. i \<in> I \<Longrightarrow> E i \<subseteq> Pow (space (M' i))"
shows "indep_vars M' X I \<longleftrightarrow>
(\<forall>A\<in>(\<Pi> i\<in>I. E i). prob (\<Inter>j\<in>I. X j -` A j \<inter> space M) = (\<Prod>j\<in>I. prob (X j -` A j \<inter> space M)))"
proof -
from rv have X: "\<And>i. i \<in> I \<Longrightarrow> X i \<in> space M \<rightarrow> space (M' i)"
unfolding measurable_def by simp
{ fix i assume "i\<in>I"
from closed[OF `i \<in> I`]
have "sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> sets (M' i)}
= sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> E i}"
unfolding sigma_sets_vimage_commute[OF X, OF `i \<in> I`, symmetric] M'[OF `i \<in> I`]
by (subst sigma_sets_sigma_sets_eq) auto }
note sigma_sets_X = this
{ fix i assume "i\<in>I"
have "Int_stable {X i -` A \<inter> space M |A. A \<in> E i}"
proof (rule Int_stableI)
fix a assume "a \<in> {X i -` A \<inter> space M |A. A \<in> E i}"
then obtain A where "a = X i -` A \<inter> space M" "A \<in> E i" by auto
moreover
fix b assume "b \<in> {X i -` A \<inter> space M |A. A \<in> E i}"
then obtain B where "b = X i -` B \<inter> space M" "B \<in> E i" by auto
moreover
have "(X i -` A \<inter> space M) \<inter> (X i -` B \<inter> space M) = X i -` (A \<inter> B) \<inter> space M" by auto
moreover note Int_stable[OF `i \<in> I`]
ultimately
show "a \<inter> b \<in> {X i -` A \<inter> space M |A. A \<in> E i}"
by (auto simp del: vimage_Int intro!: exI[of _ "A \<inter> B"] dest: Int_stableD)
qed }
note indep_sets_X = indep_sets_sigma_sets_iff[OF this]
{ fix i assume "i \<in> I"
{ fix A assume "A \<in> E i"
with M'[OF `i \<in> I`] have "A \<in> sets (M' i)" by auto
moreover
from rv[OF `i\<in>I`] have "X i \<in> measurable M (M' i)" by auto
ultimately
have "X i -` A \<inter> space M \<in> sets M" by (auto intro: measurable_sets) }
with X[OF `i\<in>I`] space[OF `i\<in>I`]
have "{X i -` A \<inter> space M |A. A \<in> E i} \<subseteq> events"
"space M \<in> {X i -` A \<inter> space M |A. A \<in> E i}"
by (auto intro!: exI[of _ "space (M' i)"]) }
note indep_sets_finite_X = indep_sets_finite[OF I this]
have "(\<forall>A\<in>\<Pi> i\<in>I. {X i -` A \<inter> space M |A. A \<in> E i}. prob (INTER I A) = (\<Prod>j\<in>I. prob (A j))) =
(\<forall>A\<in>\<Pi> i\<in>I. E i. prob ((\<Inter>j\<in>I. X j -` A j) \<inter> space M) = (\<Prod>x\<in>I. prob (X x -` A x \<inter> space M)))"
(is "?L = ?R")
proof safe
fix A assume ?L and A: "A \<in> (\<Pi> i\<in>I. E i)"
from `?L`[THEN bspec, of "\<lambda>i. X i -` A i \<inter> space M"] A `I \<noteq> {}`
show "prob ((\<Inter>j\<in>I. X j -` A j) \<inter> space M) = (\<Prod>x\<in>I. prob (X x -` A x \<inter> space M))"
by (auto simp add: Pi_iff)
next
fix A assume ?R and A: "A \<in> (\<Pi> i\<in>I. {X i -` A \<inter> space M |A. A \<in> E i})"
from A have "\<forall>i\<in>I. \<exists>B. A i = X i -` B \<inter> space M \<and> B \<in> E i" by auto
from bchoice[OF this] obtain B where B: "\<forall>i\<in>I. A i = X i -` B i \<inter> space M"
"B \<in> (\<Pi> i\<in>I. E i)" by auto
from `?R`[THEN bspec, OF B(2)] B(1) `I \<noteq> {}`
show "prob (INTER I A) = (\<Prod>j\<in>I. prob (A j))"
by simp
qed
then show ?thesis using `I \<noteq> {}`
by (simp add: rv indep_vars_def indep_sets_X sigma_sets_X indep_sets_finite_X cong: indep_sets_cong)
qed
lemma (in prob_space) indep_vars_compose:
assumes "indep_vars M' X I"
assumes rv: "\<And>i. i \<in> I \<Longrightarrow> Y i \<in> measurable (M' i) (N i)"
shows "indep_vars N (\<lambda>i. Y i \<circ> X i) I"
unfolding indep_vars_def
proof
from rv `indep_vars M' X I`
show "\<forall>i\<in>I. random_variable (N i) (Y i \<circ> X i)"
by (auto simp: indep_vars_def)
have "indep_sets (\<lambda>i. sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> sets (M' i)}) I"
using `indep_vars M' X I` by (simp add: indep_vars_def)
then show "indep_sets (\<lambda>i. sigma_sets (space M) {(Y i \<circ> X i) -` A \<inter> space M |A. A \<in> sets (N i)}) I"
proof (rule indep_sets_mono_sets)
fix i assume "i \<in> I"
with `indep_vars M' X I` have X: "X i \<in> space M \<rightarrow> space (M' i)"
unfolding indep_vars_def measurable_def by auto
{ fix A assume "A \<in> sets (N i)"
then have "\<exists>B. (Y i \<circ> X i) -` A \<inter> space M = X i -` B \<inter> space M \<and> B \<in> sets (M' i)"
by (intro exI[of _ "Y i -` A \<inter> space (M' i)"])
(auto simp: vimage_comp intro!: measurable_sets rv `i \<in> I` funcset_mem[OF X]) }
then show "sigma_sets (space M) {(Y i \<circ> X i) -` A \<inter> space M |A. A \<in> sets (N i)} \<subseteq>
sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> sets (M' i)}"
by (intro sigma_sets_subseteq) (auto simp: vimage_comp)
qed
qed
lemma (in prob_space) indep_var_compose:
assumes "indep_var M1 X1 M2 X2" "Y1 \<in> measurable M1 N1" "Y2 \<in> measurable M2 N2"
shows "indep_var N1 (Y1 \<circ> X1) N2 (Y2 \<circ> X2)"
proof -
have "indep_vars (case_bool N1 N2) (\<lambda>b. case_bool Y1 Y2 b \<circ> case_bool X1 X2 b) UNIV"
using assms
by (intro indep_vars_compose[where M'="case_bool M1 M2"])
(auto simp: indep_var_def split: bool.split)
also have "(\<lambda>b. case_bool Y1 Y2 b \<circ> case_bool X1 X2 b) = case_bool (Y1 \<circ> X1) (Y2 \<circ> X2)"
by (simp add: fun_eq_iff split: bool.split)
finally show ?thesis
unfolding indep_var_def .
qed
lemma (in prob_space) indep_vars_Min:
fixes X :: "'i \<Rightarrow> 'a \<Rightarrow> real"
assumes I: "finite I" "i \<notin> I" and indep: "indep_vars (\<lambda>_. borel) X (insert i I)"
shows "indep_var borel (X i) borel (\<lambda>\<omega>. Min ((\<lambda>i. X i \<omega>)`I))"
proof -
have "indep_var
borel ((\<lambda>f. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) {i}))
borel ((\<lambda>f. Min (f`I)) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) I))"
using I by (intro indep_var_compose[OF indep_var_restrict[OF indep]] borel_measurable_Min) auto
also have "((\<lambda>f. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) {i})) = X i"
by auto
also have "((\<lambda>f. Min (f`I)) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) I)) = (\<lambda>\<omega>. Min ((\<lambda>i. X i \<omega>)`I))"
by (auto cong: rev_conj_cong)
finally show ?thesis
unfolding indep_var_def .
qed
lemma (in prob_space) indep_vars_setsum:
fixes X :: "'i \<Rightarrow> 'a \<Rightarrow> real"
assumes I: "finite I" "i \<notin> I" and indep: "indep_vars (\<lambda>_. borel) X (insert i I)"
shows "indep_var borel (X i) borel (\<lambda>\<omega>. \<Sum>i\<in>I. X i \<omega>)"
proof -
have "indep_var
borel ((\<lambda>f. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) {i}))
borel ((\<lambda>f. \<Sum>i\<in>I. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) I))"
using I by (intro indep_var_compose[OF indep_var_restrict[OF indep]] ) auto
also have "((\<lambda>f. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) {i})) = X i"
by auto
also have "((\<lambda>f. \<Sum>i\<in>I. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) I)) = (\<lambda>\<omega>. \<Sum>i\<in>I. X i \<omega>)"
by (auto cong: rev_conj_cong)
finally show ?thesis .
qed
lemma (in prob_space) indep_vars_setprod:
fixes X :: "'i \<Rightarrow> 'a \<Rightarrow> real"
assumes I: "finite I" "i \<notin> I" and indep: "indep_vars (\<lambda>_. borel) X (insert i I)"
shows "indep_var borel (X i) borel (\<lambda>\<omega>. \<Prod>i\<in>I. X i \<omega>)"
proof -
have "indep_var
borel ((\<lambda>f. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) {i}))
borel ((\<lambda>f. \<Prod>i\<in>I. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) I))"
using I by (intro indep_var_compose[OF indep_var_restrict[OF indep]] ) auto
also have "((\<lambda>f. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) {i})) = X i"
by auto
also have "((\<lambda>f. \<Prod>i\<in>I. f i) \<circ> (\<lambda>\<omega>. restrict (\<lambda>i. X i \<omega>) I)) = (\<lambda>\<omega>. \<Prod>i\<in>I. X i \<omega>)"
by (auto cong: rev_conj_cong)
finally show ?thesis .
qed
lemma (in prob_space) indep_varsD_finite:
assumes X: "indep_vars M' X I"
assumes I: "I \<noteq> {}" "finite I" "\<And>i. i \<in> I \<Longrightarrow> A i \<in> sets (M' i)"
shows "prob (\<Inter>i\<in>I. X i -` A i \<inter> space M) = (\<Prod>i\<in>I. prob (X i -` A i \<inter> space M))"
proof (rule indep_setsD)
show "indep_sets (\<lambda>i. sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> sets (M' i)}) I"
using X by (auto simp: indep_vars_def)
show "I \<subseteq> I" "I \<noteq> {}" "finite I" using I by auto
show "\<forall>i\<in>I. X i -` A i \<inter> space M \<in> sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> sets (M' i)}"
using I by auto
qed
lemma (in prob_space) indep_varsD:
assumes X: "indep_vars M' X I"
assumes I: "J \<noteq> {}" "finite J" "J \<subseteq> I" "\<And>i. i \<in> J \<Longrightarrow> A i \<in> sets (M' i)"
shows "prob (\<Inter>i\<in>J. X i -` A i \<inter> space M) = (\<Prod>i\<in>J. prob (X i -` A i \<inter> space M))"
proof (rule indep_setsD)
show "indep_sets (\<lambda>i. sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> sets (M' i)}) I"
using X by (auto simp: indep_vars_def)
show "\<forall>i\<in>J. X i -` A i \<inter> space M \<in> sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> sets (M' i)}"
using I by auto
qed fact+
lemma (in prob_space) indep_vars_iff_distr_eq_PiM:
fixes I :: "'i set" and X :: "'i \<Rightarrow> 'a \<Rightarrow> 'b"
assumes "I \<noteq> {}"
assumes rv: "\<And>i. random_variable (M' i) (X i)"
shows "indep_vars M' X I \<longleftrightarrow>
distr M (\<Pi>\<^sub>M i\<in>I. M' i) (\<lambda>x. \<lambda>i\<in>I. X i x) = (\<Pi>\<^sub>M i\<in>I. distr M (M' i) (X i))"
proof -
let ?P = "\<Pi>\<^sub>M i\<in>I. M' i"
let ?X = "\<lambda>x. \<lambda>i\<in>I. X i x"
let ?D = "distr M ?P ?X"
have X: "random_variable ?P ?X" by (intro measurable_restrict rv)
interpret D: prob_space ?D by (intro prob_space_distr X)
let ?D' = "\<lambda>i. distr M (M' i) (X i)"
let ?P' = "\<Pi>\<^sub>M i\<in>I. distr M (M' i) (X i)"
interpret D': prob_space "?D' i" for i by (intro prob_space_distr rv)
interpret P: product_prob_space ?D' I ..
show ?thesis
proof
assume "indep_vars M' X I"
show "?D = ?P'"
proof (rule measure_eqI_generator_eq)
show "Int_stable (prod_algebra I M')"
by (rule Int_stable_prod_algebra)
show "prod_algebra I M' \<subseteq> Pow (space ?P)"
using prod_algebra_sets_into_space by (simp add: space_PiM)
show "sets ?D = sigma_sets (space ?P) (prod_algebra I M')"
by (simp add: sets_PiM space_PiM)
show "sets ?P' = sigma_sets (space ?P) (prod_algebra I M')"
by (simp add: sets_PiM space_PiM cong: prod_algebra_cong)
let ?A = "\<lambda>i. \<Pi>\<^sub>E i\<in>I. space (M' i)"
show "range ?A \<subseteq> prod_algebra I M'" "(\<Union>i. ?A i) = space (Pi\<^sub>M I M')"
by (auto simp: space_PiM intro!: space_in_prod_algebra cong: prod_algebra_cong)
{ fix i show "emeasure ?D (\<Pi>\<^sub>E i\<in>I. space (M' i)) \<noteq> \<infinity>" by auto }
next
fix E assume E: "E \<in> prod_algebra I M'"
from prod_algebraE[OF E] guess J Y . note J = this
from E have "E \<in> sets ?P" by (auto simp: sets_PiM)
then have "emeasure ?D E = emeasure M (?X -` E \<inter> space M)"
by (simp add: emeasure_distr X)
also have "?X -` E \<inter> space M = (\<Inter>i\<in>J. X i -` Y i \<inter> space M)"
using J `I \<noteq> {}` measurable_space[OF rv] by (auto simp: prod_emb_def PiE_iff split: split_if_asm)
also have "emeasure M (\<Inter>i\<in>J. X i -` Y i \<inter> space M) = (\<Prod> i\<in>J. emeasure M (X i -` Y i \<inter> space M))"
using `indep_vars M' X I` J `I \<noteq> {}` using indep_varsD[of M' X I J]
by (auto simp: emeasure_eq_measure setprod_ereal)
also have "\<dots> = (\<Prod> i\<in>J. emeasure (?D' i) (Y i))"
using rv J by (simp add: emeasure_distr)
also have "\<dots> = emeasure ?P' E"
using P.emeasure_PiM_emb[of J Y] J by (simp add: prod_emb_def)
finally show "emeasure ?D E = emeasure ?P' E" .
qed
next
assume "?D = ?P'"
show "indep_vars M' X I" unfolding indep_vars_def
proof (intro conjI indep_setsI ballI rv)
fix i show "sigma_sets (space M) {X i -` A \<inter> space M |A. A \<in> sets (M' i)} \<subseteq> events"
by (auto intro!: sets.sigma_sets_subset measurable_sets rv)
next
fix J Y' assume J: "J \<noteq> {}" "J \<subseteq> I" "finite J"
assume Y': "\<forall>j\<in>J. Y' j \<in> sigma_sets (space M) {X j -` A \<inter> space M |A. A \<in> sets (M' j)}"
have "\<forall>j\<in>J. \<exists>Y. Y' j = X j -` Y \<inter> space M \<and> Y \<in> sets (M' j)"
proof
fix j assume "j \<in> J"
from Y'[rule_format, OF this] rv[of j]
show "\<exists>Y. Y' j = X j -` Y \<inter> space M \<and> Y \<in> sets (M' j)"
by (subst (asm) sigma_sets_vimage_commute[symmetric, of _ _ "space (M' j)"])
(auto dest: measurable_space simp: sets.sigma_sets_eq)
qed
from bchoice[OF this] obtain Y where
Y: "\<And>j. j \<in> J \<Longrightarrow> Y' j = X j -` Y j \<inter> space M" "\<And>j. j \<in> J \<Longrightarrow> Y j \<in> sets (M' j)" by auto
let ?E = "prod_emb I M' J (Pi\<^sub>E J Y)"
from Y have "(\<Inter>j\<in>J. Y' j) = ?X -` ?E \<inter> space M"
using J `I \<noteq> {}` measurable_space[OF rv] by (auto simp: prod_emb_def PiE_iff split: split_if_asm)
then have "emeasure M (\<Inter>j\<in>J. Y' j) = emeasure M (?X -` ?E \<inter> space M)"
by simp
also have "\<dots> = emeasure ?D ?E"
using Y J by (intro emeasure_distr[symmetric] X sets_PiM_I) auto
also have "\<dots> = emeasure ?P' ?E"
using `?D = ?P'` by simp
also have "\<dots> = (\<Prod> i\<in>J. emeasure (?D' i) (Y i))"
using P.emeasure_PiM_emb[of J Y] J Y by (simp add: prod_emb_def)
also have "\<dots> = (\<Prod> i\<in>J. emeasure M (Y' i))"
using rv J Y by (simp add: emeasure_distr)
finally have "emeasure M (\<Inter>j\<in>J. Y' j) = (\<Prod> i\<in>J. emeasure M (Y' i))" .
then show "prob (\<Inter>j\<in>J. Y' j) = (\<Prod> i\<in>J. prob (Y' i))"
by (auto simp: emeasure_eq_measure setprod_ereal)
qed
qed
qed
lemma (in prob_space) indep_varD:
assumes indep: "indep_var Ma A Mb B"
assumes sets: "Xa \<in> sets Ma" "Xb \<in> sets Mb"
shows "prob ((\<lambda>x. (A x, B x)) -` (Xa \<times> Xb) \<inter> space M) =
prob (A -` Xa \<inter> space M) * prob (B -` Xb \<inter> space M)"
proof -
have "prob ((\<lambda>x. (A x, B x)) -` (Xa \<times> Xb) \<inter> space M) =
prob (\<Inter>i\<in>UNIV. (case_bool A B i -` case_bool Xa Xb i \<inter> space M))"
by (auto intro!: arg_cong[where f=prob] simp: UNIV_bool)
also have "\<dots> = (\<Prod>i\<in>UNIV. prob (case_bool A B i -` case_bool Xa Xb i \<inter> space M))"
using indep unfolding indep_var_def
by (rule indep_varsD) (auto split: bool.split intro: sets)
also have "\<dots> = prob (A -` Xa \<inter> space M) * prob (B -` Xb \<inter> space M)"
unfolding UNIV_bool by simp
finally show ?thesis .
qed
lemma (in prob_space) prob_indep_random_variable:
assumes ind[simp]: "indep_var N X N Y"
assumes [simp]: "A \<in> sets N" "B \<in> sets N"
shows "\<P>(x in M. X x \<in> A \<and> Y x \<in> B) = \<P>(x in M. X x \<in> A) * \<P>(x in M. Y x \<in> B)"
proof-
have " \<P>(x in M. (X x)\<in>A \<and> (Y x)\<in> B ) = prob ((\<lambda>x. (X x, Y x)) -` (A \<times> B) \<inter> space M)"
by (auto intro!: arg_cong[where f= prob])
also have "...= prob (X -` A \<inter> space M) * prob (Y -` B \<inter> space M)"
by (auto intro!: indep_varD[where Ma=N and Mb=N])
also have "... = \<P>(x in M. X x \<in> A) * \<P>(x in M. Y x \<in> B)"
by (auto intro!: arg_cong2[where f= "op *"] arg_cong[where f= prob])
finally show ?thesis .
qed
lemma (in prob_space)
assumes "indep_var S X T Y"
shows indep_var_rv1: "random_variable S X"
and indep_var_rv2: "random_variable T Y"
proof -
have "\<forall>i\<in>UNIV. random_variable (case_bool S T i) (case_bool X Y i)"
using assms unfolding indep_var_def indep_vars_def by auto
then show "random_variable S X" "random_variable T Y"
unfolding UNIV_bool by auto
qed
lemma (in prob_space) indep_var_distribution_eq:
"indep_var S X T Y \<longleftrightarrow> random_variable S X \<and> random_variable T Y \<and>
distr M S X \<Otimes>\<^sub>M distr M T Y = distr M (S \<Otimes>\<^sub>M T) (\<lambda>x. (X x, Y x))" (is "_ \<longleftrightarrow> _ \<and> _ \<and> ?S \<Otimes>\<^sub>M ?T = ?J")
proof safe
assume "indep_var S X T Y"
then show rvs: "random_variable S X" "random_variable T Y"
by (blast dest: indep_var_rv1 indep_var_rv2)+
then have XY: "random_variable (S \<Otimes>\<^sub>M T) (\<lambda>x. (X x, Y x))"
by (rule measurable_Pair)
interpret X: prob_space ?S by (rule prob_space_distr) fact
interpret Y: prob_space ?T by (rule prob_space_distr) fact
interpret XY: pair_prob_space ?S ?T ..
show "?S \<Otimes>\<^sub>M ?T = ?J"
proof (rule pair_measure_eqI)
show "sigma_finite_measure ?S" ..
show "sigma_finite_measure ?T" ..
fix A B assume A: "A \<in> sets ?S" and B: "B \<in> sets ?T"
have "emeasure ?J (A \<times> B) = emeasure M ((\<lambda>x. (X x, Y x)) -` (A \<times> B) \<inter> space M)"
using A B by (intro emeasure_distr[OF XY]) auto
also have "\<dots> = emeasure M (X -` A \<inter> space M) * emeasure M (Y -` B \<inter> space M)"
using indep_varD[OF `indep_var S X T Y`, of A B] A B by (simp add: emeasure_eq_measure)
also have "\<dots> = emeasure ?S A * emeasure ?T B"
using rvs A B by (simp add: emeasure_distr)
finally show "emeasure ?S A * emeasure ?T B = emeasure ?J (A \<times> B)" by simp
qed simp
next
assume rvs: "random_variable S X" "random_variable T Y"
then have XY: "random_variable (S \<Otimes>\<^sub>M T) (\<lambda>x. (X x, Y x))"
by (rule measurable_Pair)
let ?S = "distr M S X" and ?T = "distr M T Y"
interpret X: prob_space ?S by (rule prob_space_distr) fact
interpret Y: prob_space ?T by (rule prob_space_distr) fact
interpret XY: pair_prob_space ?S ?T ..
assume "?S \<Otimes>\<^sub>M ?T = ?J"
{ fix S and X
have "Int_stable {X -` A \<inter> space M |A. A \<in> sets S}"
proof (safe intro!: Int_stableI)
fix A B assume "A \<in> sets S" "B \<in> sets S"
then show "\<exists>C. (X -` A \<inter> space M) \<inter> (X -` B \<inter> space M) = (X -` C \<inter> space M) \<and> C \<in> sets S"
by (intro exI[of _ "A \<inter> B"]) auto
qed }
note Int_stable = this
show "indep_var S X T Y" unfolding indep_var_eq
proof (intro conjI indep_set_sigma_sets Int_stable rvs)
show "indep_set {X -` A \<inter> space M |A. A \<in> sets S} {Y -` A \<inter> space M |A. A \<in> sets T}"
proof (safe intro!: indep_setI)
{ fix A assume "A \<in> sets S" then show "X -` A \<inter> space M \<in> sets M"
using `X \<in> measurable M S` by (auto intro: measurable_sets) }
{ fix A assume "A \<in> sets T" then show "Y -` A \<inter> space M \<in> sets M"
using `Y \<in> measurable M T` by (auto intro: measurable_sets) }
next
fix A B assume ab: "A \<in> sets S" "B \<in> sets T"
then have "ereal (prob ((X -` A \<inter> space M) \<inter> (Y -` B \<inter> space M))) = emeasure ?J (A \<times> B)"
using XY by (auto simp add: emeasure_distr emeasure_eq_measure intro!: arg_cong[where f="prob"])
also have "\<dots> = emeasure (?S \<Otimes>\<^sub>M ?T) (A \<times> B)"
unfolding `?S \<Otimes>\<^sub>M ?T = ?J` ..
also have "\<dots> = emeasure ?S A * emeasure ?T B"
using ab by (simp add: Y.emeasure_pair_measure_Times)
finally show "prob ((X -` A \<inter> space M) \<inter> (Y -` B \<inter> space M)) =
prob (X -` A \<inter> space M) * prob (Y -` B \<inter> space M)"
using rvs ab by (simp add: emeasure_eq_measure emeasure_distr)
qed
qed
qed
lemma (in prob_space) distributed_joint_indep:
assumes S: "sigma_finite_measure S" and T: "sigma_finite_measure T"
assumes X: "distributed M S X Px" and Y: "distributed M T Y Py"
assumes indep: "indep_var S X T Y"
shows "distributed M (S \<Otimes>\<^sub>M T) (\<lambda>x. (X x, Y x)) (\<lambda>(x, y). Px x * Py y)"
using indep_var_distribution_eq[of S X T Y] indep
by (intro distributed_joint_indep'[OF S T X Y]) auto
lemma (in prob_space) indep_vars_nn_integral:
assumes I: "finite I" "indep_vars (\<lambda>_. borel) X I" "\<And>i \<omega>. i \<in> I \<Longrightarrow> 0 \<le> X i \<omega>"
shows "(\<integral>\<^sup>+\<omega>. (\<Prod>i\<in>I. X i \<omega>) \<partial>M) = (\<Prod>i\<in>I. \<integral>\<^sup>+\<omega>. X i \<omega> \<partial>M)"
proof cases
assume "I \<noteq> {}"
def Y \<equiv> "\<lambda>i \<omega>. if i \<in> I then X i \<omega> else 0"
{ fix i have "i \<in> I \<Longrightarrow> random_variable borel (X i)"
using I(2) by (cases "i\<in>I") (auto simp: indep_vars_def) }
note rv_X = this
{ fix i have "random_variable borel (Y i)"
using I(2) by (cases "i\<in>I") (auto simp: Y_def rv_X) }
note rv_Y = this[measurable]
interpret Y: prob_space "distr M borel (Y i)" for i
using I(2) by (cases "i \<in> I") (auto intro!: prob_space_distr simp: Y_def indep_vars_def)
interpret product_sigma_finite "\<lambda>i. distr M borel (Y i)"
..
have indep_Y: "indep_vars (\<lambda>i. borel) Y I"
by (rule indep_vars_cong[THEN iffD1, OF _ _ _ I(2)]) (auto simp: Y_def)
have "(\<integral>\<^sup>+\<omega>. (\<Prod>i\<in>I. X i \<omega>) \<partial>M) = (\<integral>\<^sup>+\<omega>. (\<Prod>i\<in>I. max 0 (Y i \<omega>)) \<partial>M)"
using I(3) by (auto intro!: nn_integral_cong setprod.cong simp add: Y_def max_def)
also have "\<dots> = (\<integral>\<^sup>+\<omega>. (\<Prod>i\<in>I. max 0 (\<omega> i)) \<partial>distr M (Pi\<^sub>M I (\<lambda>i. borel)) (\<lambda>x. \<lambda>i\<in>I. Y i x))"
by (subst nn_integral_distr) auto
also have "\<dots> = (\<integral>\<^sup>+\<omega>. (\<Prod>i\<in>I. max 0 (\<omega> i)) \<partial>Pi\<^sub>M I (\<lambda>i. distr M borel (Y i)))"
unfolding indep_vars_iff_distr_eq_PiM[THEN iffD1, OF `I \<noteq> {}` rv_Y indep_Y] ..
also have "\<dots> = (\<Prod>i\<in>I. (\<integral>\<^sup>+\<omega>. max 0 \<omega> \<partial>distr M borel (Y i)))"
by (rule product_nn_integral_setprod) (auto intro: `finite I`)
also have "\<dots> = (\<Prod>i\<in>I. \<integral>\<^sup>+\<omega>. X i \<omega> \<partial>M)"
by (intro setprod.cong nn_integral_cong)
(auto simp: nn_integral_distr nn_integral_max_0 Y_def rv_X)
finally show ?thesis .
qed (simp add: emeasure_space_1)
lemma (in prob_space)
fixes X :: "'i \<Rightarrow> 'a \<Rightarrow> 'b::{real_normed_field, banach, second_countable_topology}"
assumes I: "finite I" "indep_vars (\<lambda>_. borel) X I" "\<And>i. i \<in> I \<Longrightarrow> integrable M (X i)"
shows indep_vars_lebesgue_integral: "(\<integral>\<omega>. (\<Prod>i\<in>I. X i \<omega>) \<partial>M) = (\<Prod>i\<in>I. \<integral>\<omega>. X i \<omega> \<partial>M)" (is ?eq)
and indep_vars_integrable: "integrable M (\<lambda>\<omega>. (\<Prod>i\<in>I. X i \<omega>))" (is ?int)
proof (induct rule: case_split)
assume "I \<noteq> {}"
def Y \<equiv> "\<lambda>i \<omega>. if i \<in> I then X i \<omega> else 0"
{ fix i have "i \<in> I \<Longrightarrow> random_variable borel (X i)"
using I(2) by (cases "i\<in>I") (auto simp: indep_vars_def) }
note rv_X = this[measurable]
{ fix i have "random_variable borel (Y i)"
using I(2) by (cases "i\<in>I") (auto simp: Y_def rv_X) }
note rv_Y = this[measurable]
{ fix i have "integrable M (Y i)"
using I(3) by (cases "i\<in>I") (auto simp: Y_def) }
note int_Y = this
interpret Y: prob_space "distr M borel (Y i)" for i
using I(2) by (cases "i \<in> I") (auto intro!: prob_space_distr simp: Y_def indep_vars_def)
interpret product_sigma_finite "\<lambda>i. distr M borel (Y i)"
..
have indep_Y: "indep_vars (\<lambda>i. borel) Y I"
by (rule indep_vars_cong[THEN iffD1, OF _ _ _ I(2)]) (auto simp: Y_def)
have "(\<integral>\<omega>. (\<Prod>i\<in>I. X i \<omega>) \<partial>M) = (\<integral>\<omega>. (\<Prod>i\<in>I. Y i \<omega>) \<partial>M)"
using I(3) by (simp add: Y_def)
also have "\<dots> = (\<integral>\<omega>. (\<Prod>i\<in>I. \<omega> i) \<partial>distr M (Pi\<^sub>M I (\<lambda>i. borel)) (\<lambda>x. \<lambda>i\<in>I. Y i x))"
by (subst integral_distr) auto
also have "\<dots> = (\<integral>\<omega>. (\<Prod>i\<in>I. \<omega> i) \<partial>Pi\<^sub>M I (\<lambda>i. distr M borel (Y i)))"
unfolding indep_vars_iff_distr_eq_PiM[THEN iffD1, OF `I \<noteq> {}` rv_Y indep_Y] ..
also have "\<dots> = (\<Prod>i\<in>I. (\<integral>\<omega>. \<omega> \<partial>distr M borel (Y i)))"
by (rule product_integral_setprod) (auto intro: `finite I` simp: integrable_distr_eq int_Y)
also have "\<dots> = (\<Prod>i\<in>I. \<integral>\<omega>. X i \<omega> \<partial>M)"
by (intro setprod.cong integral_cong)
(auto simp: integral_distr Y_def rv_X)
finally show ?eq .
have "integrable (distr M (Pi\<^sub>M I (\<lambda>i. borel)) (\<lambda>x. \<lambda>i\<in>I. Y i x)) (\<lambda>\<omega>. (\<Prod>i\<in>I. \<omega> i))"
unfolding indep_vars_iff_distr_eq_PiM[THEN iffD1, OF `I \<noteq> {}` rv_Y indep_Y]
by (intro product_integrable_setprod[OF `finite I`])
(simp add: integrable_distr_eq int_Y)
then show ?int
by (simp add: integrable_distr_eq Y_def)
qed (simp_all add: prob_space)
lemma (in prob_space)
fixes X1 X2 :: "'a \<Rightarrow> 'b::{real_normed_field, banach, second_countable_topology}"
assumes "indep_var borel X1 borel X2" "integrable M X1" "integrable M X2"
shows indep_var_lebesgue_integral: "(\<integral>\<omega>. X1 \<omega> * X2 \<omega> \<partial>M) = (\<integral>\<omega>. X1 \<omega> \<partial>M) * (\<integral>\<omega>. X2 \<omega> \<partial>M)" (is ?eq)
and indep_var_integrable: "integrable M (\<lambda>\<omega>. X1 \<omega> * X2 \<omega>)" (is ?int)
unfolding indep_var_def
proof -
have *: "(\<lambda>\<omega>. X1 \<omega> * X2 \<omega>) = (\<lambda>\<omega>. \<Prod>i\<in>UNIV. (case_bool X1 X2 i \<omega>))"
by (simp add: UNIV_bool mult_commute)
have **: "(\<lambda> _. borel) = case_bool borel borel"
by (rule ext, metis (full_types) bool.simps(3) bool.simps(4))
show ?eq
apply (subst *)
apply (subst indep_vars_lebesgue_integral)
apply (auto)
apply (subst **, subst indep_var_def [symmetric], rule assms)
apply (simp split: bool.split add: assms)
by (simp add: UNIV_bool mult_commute)
show ?int
apply (subst *)
apply (rule indep_vars_integrable)
apply auto
apply (subst **, subst indep_var_def [symmetric], rule assms)
by (simp split: bool.split add: assms)
qed
end