src/HOL/Library/Groups_Big_Fun.thy
author haftmann
Fri Mar 22 19:18:08 2019 +0000 (4 months ago)
changeset 69946 494934c30f38
parent 69164 74f1b0f10b2b
permissions -rw-r--r--
improved code equations taken over from AFP
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(* Author: Florian Haftmann, TU Muenchen *)
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section \<open>Big sum and product over function bodies\<close>
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theory Groups_Big_Fun
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imports
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  Main
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begin
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subsection \<open>Abstract product\<close>
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locale comm_monoid_fun = comm_monoid
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begin
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definition G :: "('b \<Rightarrow> 'a) \<Rightarrow> 'a"
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where
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  expand_set: "G g = comm_monoid_set.F f \<^bold>1 g {a. g a \<noteq> \<^bold>1}"
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interpretation F: comm_monoid_set f "\<^bold>1"
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  ..
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lemma expand_superset:
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  assumes "finite A" and "{a. g a \<noteq> \<^bold>1} \<subseteq> A"
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  shows "G g = F.F g A"
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  apply (simp add: expand_set)
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  apply (rule F.same_carrierI [of A])
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  apply (simp_all add: assms)
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  done
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lemma conditionalize:
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  assumes "finite A"
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  shows "F.F g A = G (\<lambda>a. if a \<in> A then g a else \<^bold>1)"
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  using assms
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  apply (simp add: expand_set)
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  apply (rule F.same_carrierI [of A])
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  apply auto
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  done
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lemma neutral [simp]:
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  "G (\<lambda>a. \<^bold>1) = \<^bold>1"
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  by (simp add: expand_set)
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lemma update [simp]:
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  assumes "finite {a. g a \<noteq> \<^bold>1}"
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  assumes "g a = \<^bold>1"
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  shows "G (g(a := b)) = b \<^bold>* G g"
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proof (cases "b = \<^bold>1")
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  case True with \<open>g a = \<^bold>1\<close> show ?thesis
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    by (simp add: expand_set) (rule F.cong, auto)
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next
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  case False
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  moreover have "{a'. a' \<noteq> a \<longrightarrow> g a' \<noteq> \<^bold>1} = insert a {a. g a \<noteq> \<^bold>1}"
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    by auto
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  moreover from \<open>g a = \<^bold>1\<close> have "a \<notin> {a. g a \<noteq> \<^bold>1}"
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    by simp
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  moreover have "F.F (\<lambda>a'. if a' = a then b else g a') {a. g a \<noteq> \<^bold>1} = F.F g {a. g a \<noteq> \<^bold>1}"
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    by (rule F.cong) (auto simp add: \<open>g a = \<^bold>1\<close>)
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  ultimately show ?thesis using \<open>finite {a. g a \<noteq> \<^bold>1}\<close> by (simp add: expand_set)
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qed
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lemma infinite [simp]:
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  "\<not> finite {a. g a \<noteq> \<^bold>1} \<Longrightarrow> G g = \<^bold>1"
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  by (simp add: expand_set)
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lemma cong [cong]:
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  assumes "\<And>a. g a = h a"
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  shows "G g = G h"
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  using assms by (simp add: expand_set)
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lemma not_neutral_obtains_not_neutral:
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  assumes "G g \<noteq> \<^bold>1"
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  obtains a where "g a \<noteq> \<^bold>1"
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  using assms by (auto elim: F.not_neutral_contains_not_neutral simp add: expand_set)
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lemma reindex_cong:
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  assumes "bij l"
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  assumes "g \<circ> l = h"
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  shows "G g = G h"
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proof -
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  from assms have unfold: "h = g \<circ> l" by simp
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  from \<open>bij l\<close> have "inj l" by (rule bij_is_inj)
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  then have "inj_on l {a. h a \<noteq> \<^bold>1}" by (rule subset_inj_on) simp
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  moreover from \<open>bij l\<close> have "{a. g a \<noteq> \<^bold>1} = l ` {a. h a \<noteq> \<^bold>1}"
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    by (auto simp add: image_Collect unfold elim: bij_pointE)
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  moreover have "\<And>x. x \<in> {a. h a \<noteq> \<^bold>1} \<Longrightarrow> g (l x) = h x"
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    by (simp add: unfold)
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  ultimately have "F.F g {a. g a \<noteq> \<^bold>1} = F.F h {a. h a \<noteq> \<^bold>1}"
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    by (rule F.reindex_cong)
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  then show ?thesis by (simp add: expand_set)
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qed
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lemma distrib:
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  assumes "finite {a. g a \<noteq> \<^bold>1}" and "finite {a. h a \<noteq> \<^bold>1}"
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  shows "G (\<lambda>a. g a \<^bold>* h a) = G g \<^bold>* G h"
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proof -
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  from assms have "finite ({a. g a \<noteq> \<^bold>1} \<union> {a. h a \<noteq> \<^bold>1})" by simp
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  moreover have "{a. g a \<^bold>* h a \<noteq> \<^bold>1} \<subseteq> {a. g a \<noteq> \<^bold>1} \<union> {a. h a \<noteq> \<^bold>1}"
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    by auto (drule sym, simp)
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  ultimately show ?thesis
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    using assms
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    by (simp add: expand_superset [of "{a. g a \<noteq> \<^bold>1} \<union> {a. h a \<noteq> \<^bold>1}"] F.distrib)
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qed
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lemma swap:
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  assumes "finite C"
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  assumes subset: "{a. \<exists>b. g a b \<noteq> \<^bold>1} \<times> {b. \<exists>a. g a b \<noteq> \<^bold>1} \<subseteq> C" (is "?A \<times> ?B \<subseteq> C")
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  shows "G (\<lambda>a. G (g a)) = G (\<lambda>b. G (\<lambda>a. g a b))"
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proof -
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  from \<open>finite C\<close> subset
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    have "finite ({a. \<exists>b. g a b \<noteq> \<^bold>1} \<times> {b. \<exists>a. g a b \<noteq> \<^bold>1})"
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    by (rule rev_finite_subset)
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  then have fins:
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    "finite {b. \<exists>a. g a b \<noteq> \<^bold>1}" "finite {a. \<exists>b. g a b \<noteq> \<^bold>1}"
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    by (auto simp add: finite_cartesian_product_iff)
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  have subsets: "\<And>a. {b. g a b \<noteq> \<^bold>1} \<subseteq> {b. \<exists>a. g a b \<noteq> \<^bold>1}"
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    "\<And>b. {a. g a b \<noteq> \<^bold>1} \<subseteq> {a. \<exists>b. g a b \<noteq> \<^bold>1}"
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    "{a. F.F (g a) {b. \<exists>a. g a b \<noteq> \<^bold>1} \<noteq> \<^bold>1} \<subseteq> {a. \<exists>b. g a b \<noteq> \<^bold>1}"
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    "{a. F.F (\<lambda>aa. g aa a) {a. \<exists>b. g a b \<noteq> \<^bold>1} \<noteq> \<^bold>1} \<subseteq> {b. \<exists>a. g a b \<noteq> \<^bold>1}"
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    by (auto elim: F.not_neutral_contains_not_neutral)
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  from F.swap have
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    "F.F (\<lambda>a. F.F (g a) {b. \<exists>a. g a b \<noteq> \<^bold>1}) {a. \<exists>b. g a b \<noteq> \<^bold>1} =
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      F.F (\<lambda>b. F.F (\<lambda>a. g a b) {a. \<exists>b. g a b \<noteq> \<^bold>1}) {b. \<exists>a. g a b \<noteq> \<^bold>1}" .
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  with subsets fins have "G (\<lambda>a. F.F (g a) {b. \<exists>a. g a b \<noteq> \<^bold>1}) =
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    G (\<lambda>b. F.F (\<lambda>a. g a b) {a. \<exists>b. g a b \<noteq> \<^bold>1})"
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    by (auto simp add: expand_superset [of "{b. \<exists>a. g a b \<noteq> \<^bold>1}"]
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      expand_superset [of "{a. \<exists>b. g a b \<noteq> \<^bold>1}"])
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  with subsets fins show ?thesis
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    by (auto simp add: expand_superset [of "{b. \<exists>a. g a b \<noteq> \<^bold>1}"]
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      expand_superset [of "{a. \<exists>b. g a b \<noteq> \<^bold>1}"])
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qed
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lemma cartesian_product:
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  assumes "finite C"
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  assumes subset: "{a. \<exists>b. g a b \<noteq> \<^bold>1} \<times> {b. \<exists>a. g a b \<noteq> \<^bold>1} \<subseteq> C" (is "?A \<times> ?B \<subseteq> C")
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  shows "G (\<lambda>a. G (g a)) = G (\<lambda>(a, b). g a b)"
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proof -
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  from subset \<open>finite C\<close> have fin_prod: "finite (?A \<times> ?B)"
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    by (rule finite_subset)
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  from fin_prod have "finite ?A" and "finite ?B"
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    by (auto simp add: finite_cartesian_product_iff)
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  have *: "G (\<lambda>a. G (g a)) =
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    (F.F (\<lambda>a. F.F (g a) {b. \<exists>a. g a b \<noteq> \<^bold>1}) {a. \<exists>b. g a b \<noteq> \<^bold>1})"
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    apply (subst expand_superset [of "?B"])
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    apply (rule \<open>finite ?B\<close>)
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    apply auto
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    apply (subst expand_superset [of "?A"])
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    apply (rule \<open>finite ?A\<close>)
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    apply auto
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    apply (erule F.not_neutral_contains_not_neutral)
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    apply auto
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    done
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  have "{p. (case p of (a, b) \<Rightarrow> g a b) \<noteq> \<^bold>1} \<subseteq> ?A \<times> ?B"
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    by auto
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  with subset have **: "{p. (case p of (a, b) \<Rightarrow> g a b) \<noteq> \<^bold>1} \<subseteq> C"
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    by blast
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  show ?thesis
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    apply (simp add: *)
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    apply (simp add: F.cartesian_product)
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    apply (subst expand_superset [of C])
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    apply (rule \<open>finite C\<close>)
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    apply (simp_all add: **)
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    apply (rule F.same_carrierI [of C])
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    apply (rule \<open>finite C\<close>)
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    apply (simp_all add: subset)
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    apply auto
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    done
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qed
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lemma cartesian_product2:
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  assumes fin: "finite D"
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  assumes subset: "{(a, b). \<exists>c. g a b c \<noteq> \<^bold>1} \<times> {c. \<exists>a b. g a b c \<noteq> \<^bold>1} \<subseteq> D" (is "?AB \<times> ?C \<subseteq> D")
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  shows "G (\<lambda>(a, b). G (g a b)) = G (\<lambda>(a, b, c). g a b c)"
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proof -
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  have bij: "bij (\<lambda>(a, b, c). ((a, b), c))"
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    by (auto intro!: bijI injI simp add: image_def)
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  have "{p. \<exists>c. g (fst p) (snd p) c \<noteq> \<^bold>1} \<times> {c. \<exists>p. g (fst p) (snd p) c \<noteq> \<^bold>1} \<subseteq> D"
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    by auto (insert subset, blast)
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  with fin have "G (\<lambda>p. G (g (fst p) (snd p))) = G (\<lambda>(p, c). g (fst p) (snd p) c)"
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    by (rule cartesian_product)
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  then have "G (\<lambda>(a, b). G (g a b)) = G (\<lambda>((a, b), c). g a b c)"
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    by (auto simp add: split_def)
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  also have "G (\<lambda>((a, b), c). g a b c) = G (\<lambda>(a, b, c). g a b c)"
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    using bij by (rule reindex_cong [of "\<lambda>(a, b, c). ((a, b), c)"]) (simp add: fun_eq_iff)
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  finally show ?thesis .
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qed
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lemma delta [simp]:
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  "G (\<lambda>b. if b = a then g b else \<^bold>1) = g a"
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proof -
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  have "{b. (if b = a then g b else \<^bold>1) \<noteq> \<^bold>1} \<subseteq> {a}" by auto
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  then show ?thesis by (simp add: expand_superset [of "{a}"])
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qed
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lemma delta' [simp]:
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  "G (\<lambda>b. if a = b then g b else \<^bold>1) = g a"
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proof -
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  have "(\<lambda>b. if a = b then g b else \<^bold>1) = (\<lambda>b. if b = a then g b else \<^bold>1)"
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    by (simp add: fun_eq_iff)
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  then have "G (\<lambda>b. if a = b then g b else \<^bold>1) = G (\<lambda>b. if b = a then g b else \<^bold>1)"
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    by (simp cong del: cong)
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  then show ?thesis by simp
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qed
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end
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subsection \<open>Concrete sum\<close>
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context comm_monoid_add
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begin
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sublocale Sum_any: comm_monoid_fun plus 0
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  rewrites "comm_monoid_set.F plus 0 = sum"
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  defines Sum_any = Sum_any.G
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proof -
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  show "comm_monoid_fun plus 0" ..
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  then interpret Sum_any: comm_monoid_fun plus 0 .
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  from sum_def show "comm_monoid_set.F plus 0 = sum" by (auto intro: sym)
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qed
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end
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syntax (ASCII)
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  "_Sum_any" :: "pttrn \<Rightarrow> 'a \<Rightarrow> 'a::comm_monoid_add"    ("(3SUM _. _)" [0, 10] 10)
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syntax
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  "_Sum_any" :: "pttrn \<Rightarrow> 'a \<Rightarrow> 'a::comm_monoid_add"    ("(3\<Sum>_. _)" [0, 10] 10)
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translations
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  "\<Sum>a. b" \<rightleftharpoons> "CONST Sum_any (\<lambda>a. b)"
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lemma Sum_any_left_distrib:
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  fixes r :: "'a :: semiring_0"
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  assumes "finite {a. g a \<noteq> 0}"
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  shows "Sum_any g * r = (\<Sum>n. g n * r)"
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proof -
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  note assms
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  moreover have "{a. g a * r \<noteq> 0} \<subseteq> {a. g a \<noteq> 0}" by auto
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  ultimately show ?thesis
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    by (simp add: sum_distrib_right Sum_any.expand_superset [of "{a. g a \<noteq> 0}"])
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qed  
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lemma Sum_any_right_distrib:
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  fixes r :: "'a :: semiring_0"
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  assumes "finite {a. g a \<noteq> 0}"
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  shows "r * Sum_any g = (\<Sum>n. r * g n)"
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proof -
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  note assms
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  moreover have "{a. r * g a \<noteq> 0} \<subseteq> {a. g a \<noteq> 0}" by auto
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  ultimately show ?thesis
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    by (simp add: sum_distrib_left Sum_any.expand_superset [of "{a. g a \<noteq> 0}"])
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qed
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lemma Sum_any_product:
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  fixes f g :: "'b \<Rightarrow> 'a::semiring_0"
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  assumes "finite {a. f a \<noteq> 0}" and "finite {b. g b \<noteq> 0}"
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  shows "Sum_any f * Sum_any g = (\<Sum>a. \<Sum>b. f a * g b)"
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proof -
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  have subset_f: "{a. (\<Sum>b. f a * g b) \<noteq> 0} \<subseteq> {a. f a \<noteq> 0}"
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    by rule (simp, rule, auto)
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  moreover have subset_g: "\<And>a. {b. f a * g b \<noteq> 0} \<subseteq> {b. g b \<noteq> 0}"
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    by rule (simp, rule, auto)
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  ultimately show ?thesis using assms
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    by (auto simp add: Sum_any.expand_set [of f] Sum_any.expand_set [of g]
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      Sum_any.expand_superset [of "{a. f a \<noteq> 0}"] Sum_any.expand_superset [of "{b. g b \<noteq> 0}"]
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      sum_product)
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qed
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lemma Sum_any_eq_zero_iff [simp]: 
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  fixes f :: "'a \<Rightarrow> nat"
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  assumes "finite {a. f a \<noteq> 0}"
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  shows "Sum_any f = 0 \<longleftrightarrow> f = (\<lambda>_. 0)"
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  using assms by (simp add: Sum_any.expand_set fun_eq_iff)
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subsection \<open>Concrete product\<close>
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context comm_monoid_mult
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begin
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sublocale Prod_any: comm_monoid_fun times 1
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  rewrites "comm_monoid_set.F times 1 = prod"
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  defines Prod_any = Prod_any.G
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proof -
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  show "comm_monoid_fun times 1" ..
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  then interpret Prod_any: comm_monoid_fun times 1 .
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  from prod_def show "comm_monoid_set.F times 1 = prod" by (auto intro: sym)
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qed
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end
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syntax (ASCII)
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  "_Prod_any" :: "pttrn \<Rightarrow> 'a \<Rightarrow> 'a::comm_monoid_mult"  ("(3PROD _. _)" [0, 10] 10)
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syntax
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  "_Prod_any" :: "pttrn \<Rightarrow> 'a \<Rightarrow> 'a::comm_monoid_mult"  ("(3\<Prod>_. _)" [0, 10] 10)
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translations
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  "\<Prod>a. b" == "CONST Prod_any (\<lambda>a. b)"
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lemma Prod_any_zero:
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  fixes f :: "'b \<Rightarrow> 'a :: comm_semiring_1"
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  assumes "finite {a. f a \<noteq> 1}"
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  assumes "f a = 0"
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  shows "(\<Prod>a. f a) = 0"
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proof -
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  from \<open>f a = 0\<close> have "f a \<noteq> 1" by simp
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  with \<open>f a = 0\<close> have "\<exists>a. f a \<noteq> 1 \<and> f a = 0" by blast
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  with \<open>finite {a. f a \<noteq> 1}\<close> show ?thesis
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    by (simp add: Prod_any.expand_set prod_zero)
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qed
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lemma Prod_any_not_zero:
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  fixes f :: "'b \<Rightarrow> 'a :: comm_semiring_1"
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  assumes "finite {a. f a \<noteq> 1}"
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  assumes "(\<Prod>a. f a) \<noteq> 0"
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  shows "f a \<noteq> 0"
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  using assms Prod_any_zero [of f] by blast
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lemma power_Sum_any:
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  assumes "finite {a. f a \<noteq> 0}"
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  shows "c ^ (\<Sum>a. f a) = (\<Prod>a. c ^ f a)"
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proof -
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  have "{a. c ^ f a \<noteq> 1} \<subseteq> {a. f a \<noteq> 0}"
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    by (auto intro: ccontr)
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  with assms show ?thesis
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    by (simp add: Sum_any.expand_set Prod_any.expand_superset power_sum)
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qed
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end