(* Author: Tobias Nipkow, Alex Krauss *)header "Regular sets"theory Regular_Setimports Mainbegintype_synonym 'a lang = "'a list set"definition conc :: "'a lang \<Rightarrow> 'a lang \<Rightarrow> 'a lang" (infixr "@@" 75) where"A @@ B = {xs@ys | xs ys. xs:A & ys:B}"overloading lang_pow == "compow :: nat \<Rightarrow> 'a lang \<Rightarrow> 'a lang"begin primrec lang_pow :: "nat \<Rightarrow> 'a lang \<Rightarrow> 'a lang" where "lang_pow 0 A = {[]}" | "lang_pow (Suc n) A = A @@ (lang_pow n A)"enddefinition star :: "'a lang \<Rightarrow> 'a lang" where"star A = (\<Union>n. A ^^ n)"subsection{* @{term "op @@"} *}lemma concI[simp,intro]: "u : A \<Longrightarrow> v : B \<Longrightarrow> u@v : A @@ B"by (auto simp add: conc_def)lemma concE[elim]: assumes "w \<in> A @@ B"obtains u v where "u \<in> A" "v \<in> B" "w = u@v"using assms by (auto simp: conc_def)lemma conc_mono: "A \<subseteq> C \<Longrightarrow> B \<subseteq> D \<Longrightarrow> A @@ B \<subseteq> C @@ D"by (auto simp: conc_def) lemma conc_empty[simp]: shows "{} @@ A = {}" and "A @@ {} = {}"by autolemma conc_epsilon[simp]: shows "{[]} @@ A = A" and "A @@ {[]} = A"by (simp_all add:conc_def)lemma conc_assoc: "(A @@ B) @@ C = A @@ (B @@ C)"by (auto elim!: concE) (simp only: append_assoc[symmetric] concI)lemma conc_Un_distrib:shows "A @@ (B \<union> C) = A @@ B \<union> A @@ C"and "(A \<union> B) @@ C = A @@ C \<union> B @@ C"by autolemma conc_UNION_distrib:shows "A @@ UNION I M = UNION I (%i. A @@ M i)"and "UNION I M @@ A = UNION I (%i. M i @@ A)"by autosubsection{* @{term "A ^^ n"} *}lemma lang_pow_add: "A ^^ (n + m) = A ^^ n @@ A ^^ m"by (induct n) (auto simp: conc_assoc)lemma lang_pow_empty: "{} ^^ n = (if n = 0 then {[]} else {})"by (induct n) autolemma lang_pow_empty_Suc[simp]: "({}::'a lang) ^^ Suc n = {}"by (simp add: lang_pow_empty)lemma conc_pow_comm: shows "A @@ (A ^^ n) = (A ^^ n) @@ A"by (induct n) (simp_all add: conc_assoc[symmetric])lemma length_lang_pow_ub: "ALL w : A. length w \<le> k \<Longrightarrow> w : A^^n \<Longrightarrow> length w \<le> k*n"by(induct n arbitrary: w) (fastsimp simp: conc_def)+lemma length_lang_pow_lb: "ALL w : A. length w \<ge> k \<Longrightarrow> w : A^^n \<Longrightarrow> length w \<ge> k*n"by(induct n arbitrary: w) (fastsimp simp: conc_def)+subsection{* @{const star} *}lemma star_if_lang_pow[simp]: "w : A ^^ n \<Longrightarrow> w : star A"by (auto simp: star_def)lemma Nil_in_star[iff]: "[] : star A"proof (rule star_if_lang_pow) show "[] : A ^^ 0" by simpqedlemma star_if_lang[simp]: assumes "w : A" shows "w : star A"proof (rule star_if_lang_pow) show "w : A ^^ 1" using `w : A` by simpqedlemma append_in_starI[simp]:assumes "u : star A" and "v : star A" shows "u@v : star A"proof - from `u : star A` obtain m where "u : A ^^ m" by (auto simp: star_def) moreover from `v : star A` obtain n where "v : A ^^ n" by (auto simp: star_def) ultimately have "u@v : A ^^ (m+n)" by (simp add: lang_pow_add) thus ?thesis by simpqedlemma conc_star_star: "star A @@ star A = star A"by (auto simp: conc_def)lemma conc_star_comm: shows "A @@ star A = star A @@ A"unfolding star_def conc_pow_comm conc_UNION_distribby simplemma star_induct[consumes 1, case_names Nil append, induct set: star]:assumes "w : star A" and "P []" and step: "!!u v. u : A \<Longrightarrow> v : star A \<Longrightarrow> P v \<Longrightarrow> P (u@v)"shows "P w"proof - { fix n have "w : A ^^ n \<Longrightarrow> P w" by (induct n arbitrary: w) (auto intro: `P []` step star_if_lang_pow) } with `w : star A` show "P w" by (auto simp: star_def)qedlemma star_empty[simp]: "star {} = {[]}"by (auto elim: star_induct)lemma star_epsilon[simp]: "star {[]} = {[]}"by (auto elim: star_induct)lemma star_idemp[simp]: "star (star A) = star A"by (auto elim: star_induct)lemma star_unfold_left: "star A = A @@ star A \<union> {[]}" (is "?L = ?R")proof show "?L \<subseteq> ?R" by (rule, erule star_induct) autoqed autolemma concat_in_star: "set ws \<subseteq> A \<Longrightarrow> concat ws : star A"by (induct ws) simp_alllemma in_star_iff_concat: "w : star A = (EX ws. set ws \<subseteq> A & w = concat ws)" (is "_ = (EX ws. ?R w ws)")proof assume "w : star A" thus "EX ws. ?R w ws" proof induct case Nil have "?R [] []" by simp thus ?case .. next case (append u v) moreover then obtain ws where "set ws \<subseteq> A \<and> v = concat ws" by blast ultimately have "?R (u@v) (u#ws)" by auto thus ?case .. qednext assume "EX us. ?R w us" thus "w : star A" by (auto simp: concat_in_star)qedlemma star_conv_concat: "star A = {concat ws|ws. set ws \<subseteq> A}"by (fastsimp simp: in_star_iff_concat)lemma star_insert_eps[simp]: "star (insert [] A) = star(A)"proof- { fix us have "set us \<subseteq> insert [] A \<Longrightarrow> EX vs. concat us = concat vs \<and> set vs \<subseteq> A" (is "?P \<Longrightarrow> EX vs. ?Q vs") proof let ?vs = "filter (%u. u \<noteq> []) us" show "?P \<Longrightarrow> ?Q ?vs" by (induct us) auto qed } thus ?thesis by (auto simp: star_conv_concat)qedlemma star_decom: assumes a: "x \<in> star A" "x \<noteq> []" shows "\<exists>a b. x = a @ b \<and> a \<noteq> [] \<and> a \<in> A \<and> b \<in> star A"using a by (induct rule: star_induct) (blast)+subsection {* Arden's Lemma *}lemma arden_helper: assumes eq: "X = A @@ X \<union> B" shows "X = (A ^^ Suc n) @@ X \<union> (\<Union>m\<le>n. (A ^^ m) @@ B)"proof (induct n) case 0 show "X = (A ^^ Suc 0) @@ X \<union> (\<Union>m\<le>0. (A ^^ m) @@ B)" using eq by simpnext case (Suc n) have ih: "X = (A ^^ Suc n) @@ X \<union> (\<Union>m\<le>n. (A ^^ m) @@ B)" by fact also have "\<dots> = (A ^^ Suc n) @@ (A @@ X \<union> B) \<union> (\<Union>m\<le>n. (A ^^ m) @@ B)" using eq by simp also have "\<dots> = (A ^^ Suc (Suc n)) @@ X \<union> ((A ^^ Suc n) @@ B) \<union> (\<Union>m\<le>n. (A ^^ m) @@ B)" by (simp add: conc_Un_distrib conc_assoc[symmetric] conc_pow_comm) also have "\<dots> = (A ^^ Suc (Suc n)) @@ X \<union> (\<Union>m\<le>Suc n. (A ^^ m) @@ B)" by (auto simp add: le_Suc_eq) finally show "X = (A ^^ Suc (Suc n)) @@ X \<union> (\<Union>m\<le>Suc n. (A ^^ m) @@ B)" .qedlemma Arden: assumes "[] \<notin> A" shows "X = A @@ X \<union> B \<longleftrightarrow> X = star A @@ B"proof assume eq: "X = A @@ X \<union> B" { fix w assume "w : X" let ?n = "size w" from `[] \<notin> A` have "ALL u : A. length u \<ge> 1" by (metis Suc_eq_plus1 add_leD2 le_0_eq length_0_conv not_less_eq_eq) hence "ALL u : A^^(?n+1). length u \<ge> ?n+1" by (metis length_lang_pow_lb nat_mult_1) hence "ALL u : A^^(?n+1)@@X. length u \<ge> ?n+1" by(auto simp only: conc_def length_append) hence "w \<notin> A^^(?n+1)@@X" by auto hence "w : star A @@ B" using `w : X` using arden_helper[OF eq, where n="?n"] by (auto simp add: star_def conc_UNION_distrib) } moreover { fix w assume "w : star A @@ B" hence "EX n. w : A^^n @@ B" by(auto simp: conc_def star_def) hence "w : X" using arden_helper[OF eq] by blast } ultimately show "X = star A @@ B" by blast next assume eq: "X = star A @@ B" have "star A = A @@ star A \<union> {[]}" by (rule star_unfold_left) then have "star A @@ B = (A @@ star A \<union> {[]}) @@ B" by metis also have "\<dots> = (A @@ star A) @@ B \<union> B" unfolding conc_Un_distrib by simp also have "\<dots> = A @@ (star A @@ B) \<union> B" by (simp only: conc_assoc) finally show "X = A @@ X \<union> B" using eq by blast qedlemma reversed_arden_helper: assumes eq: "X = X @@ A \<union> B" shows "X = X @@ (A ^^ Suc n) \<union> (\<Union>m\<le>n. B @@ (A ^^ m))"proof (induct n) case 0 show "X = X @@ (A ^^ Suc 0) \<union> (\<Union>m\<le>0. B @@ (A ^^ m))" using eq by simpnext case (Suc n) have ih: "X = X @@ (A ^^ Suc n) \<union> (\<Union>m\<le>n. B @@ (A ^^ m))" by fact also have "\<dots> = (X @@ A \<union> B) @@ (A ^^ Suc n) \<union> (\<Union>m\<le>n. B @@ (A ^^ m))" using eq by simp also have "\<dots> = X @@ (A ^^ Suc (Suc n)) \<union> (B @@ (A ^^ Suc n)) \<union> (\<Union>m\<le>n. B @@ (A ^^ m))" by (simp add: conc_Un_distrib conc_assoc) also have "\<dots> = X @@ (A ^^ Suc (Suc n)) \<union> (\<Union>m\<le>Suc n. B @@ (A ^^ m))" by (auto simp add: le_Suc_eq) finally show "X = X @@ (A ^^ Suc (Suc n)) \<union> (\<Union>m\<le>Suc n. B @@ (A ^^ m))" .qedtheorem reversed_Arden: assumes nemp: "[] \<notin> A" shows "X = X @@ A \<union> B \<longleftrightarrow> X = B @@ star A"proof assume eq: "X = X @@ A \<union> B" { fix w assume "w : X" let ?n = "size w" from `[] \<notin> A` have "ALL u : A. length u \<ge> 1" by (metis Suc_eq_plus1 add_leD2 le_0_eq length_0_conv not_less_eq_eq) hence "ALL u : A^^(?n+1). length u \<ge> ?n+1" by (metis length_lang_pow_lb nat_mult_1) hence "ALL u : X @@ A^^(?n+1). length u \<ge> ?n+1" by(auto simp only: conc_def length_append) hence "w \<notin> X @@ A^^(?n+1)" by auto hence "w : B @@ star A" using `w : X` using reversed_arden_helper[OF eq, where n="?n"] by (auto simp add: star_def conc_UNION_distrib) } moreover { fix w assume "w : B @@ star A" hence "EX n. w : B @@ A^^n" by (auto simp: conc_def star_def) hence "w : X" using reversed_arden_helper[OF eq] by blast } ultimately show "X = B @@ star A" by blast next assume eq: "X = B @@ star A" have "star A = {[]} \<union> star A @@ A" unfolding conc_star_comm[symmetric] by(metis Un_commute star_unfold_left) then have "B @@ star A = B @@ ({[]} \<union> star A @@ A)" by metis also have "\<dots> = B \<union> B @@ (star A @@ A)" unfolding conc_Un_distrib by simp also have "\<dots> = B \<union> (B @@ star A) @@ A" by (simp only: conc_assoc) finally show "X = X @@ A \<union> B" using eq by blast qedend