(* Title: ZF/Trancl.thy
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1992 University of Cambridge
*)
section\<open>Relations: Their General Properties and Transitive Closure\<close>
theory Trancl imports Fixedpt Perm begin
definition
refl :: "[i,i]=>o" where
"refl(A,r) == (\<forall>x\<in>A. <x,x> \<in> r)"
definition
irrefl :: "[i,i]=>o" where
"irrefl(A,r) == \<forall>x\<in>A. <x,x> \<notin> r"
definition
sym :: "i=>o" where
"sym(r) == \<forall>x y. <x,y>: r \<longrightarrow> <y,x>: r"
definition
asym :: "i=>o" where
"asym(r) == \<forall>x y. <x,y>:r \<longrightarrow> ~ <y,x>:r"
definition
antisym :: "i=>o" where
"antisym(r) == \<forall>x y.<x,y>:r \<longrightarrow> <y,x>:r \<longrightarrow> x=y"
definition
trans :: "i=>o" where
"trans(r) == \<forall>x y z. <x,y>: r \<longrightarrow> <y,z>: r \<longrightarrow> <x,z>: r"
definition
trans_on :: "[i,i]=>o" ("trans[_]'(_')") where
"trans[A](r) == \<forall>x\<in>A. \<forall>y\<in>A. \<forall>z\<in>A.
<x,y>: r \<longrightarrow> <y,z>: r \<longrightarrow> <x,z>: r"
definition
rtrancl :: "i=>i" ("(_^*)" [100] 100) (*refl/transitive closure*) where
"r^* == lfp(field(r)*field(r), %s. id(field(r)) \<union> (r O s))"
definition
trancl :: "i=>i" ("(_^+)" [100] 100) (*transitive closure*) where
"r^+ == r O r^*"
definition
equiv :: "[i,i]=>o" where
"equiv(A,r) == r \<subseteq> A*A & refl(A,r) & sym(r) & trans(r)"
subsection\<open>General properties of relations\<close>
subsubsection\<open>irreflexivity\<close>
lemma irreflI:
"[| !!x. x \<in> A ==> <x,x> \<notin> r |] ==> irrefl(A,r)"
by (simp add: irrefl_def)
lemma irreflE: "[| irrefl(A,r); x \<in> A |] ==> <x,x> \<notin> r"
by (simp add: irrefl_def)
subsubsection\<open>symmetry\<close>
lemma symI:
"[| !!x y.<x,y>: r ==> <y,x>: r |] ==> sym(r)"
by (unfold sym_def, blast)
lemma symE: "[| sym(r); <x,y>: r |] ==> <y,x>: r"
by (unfold sym_def, blast)
subsubsection\<open>antisymmetry\<close>
lemma antisymI:
"[| !!x y.[| <x,y>: r; <y,x>: r |] ==> x=y |] ==> antisym(r)"
by (simp add: antisym_def, blast)
lemma antisymE: "[| antisym(r); <x,y>: r; <y,x>: r |] ==> x=y"
by (simp add: antisym_def, blast)
subsubsection\<open>transitivity\<close>
lemma transD: "[| trans(r); <a,b>:r; <b,c>:r |] ==> <a,c>:r"
by (unfold trans_def, blast)
lemma trans_onD:
"[| trans[A](r); <a,b>:r; <b,c>:r; a \<in> A; b \<in> A; c \<in> A |] ==> <a,c>:r"
by (unfold trans_on_def, blast)
lemma trans_imp_trans_on: "trans(r) ==> trans[A](r)"
by (unfold trans_def trans_on_def, blast)
lemma trans_on_imp_trans: "[|trans[A](r); r \<subseteq> A*A|] ==> trans(r)"
by (simp add: trans_on_def trans_def, blast)
subsection\<open>Transitive closure of a relation\<close>
lemma rtrancl_bnd_mono:
"bnd_mono(field(r)*field(r), %s. id(field(r)) \<union> (r O s))"
by (rule bnd_monoI, blast+)
lemma rtrancl_mono: "r<=s ==> r^* \<subseteq> s^*"
apply (unfold rtrancl_def)
apply (rule lfp_mono)
apply (rule rtrancl_bnd_mono)+
apply blast
done
(* @{term"r^* = id(field(r)) \<union> ( r O r^* )"} *)
lemmas rtrancl_unfold =
rtrancl_bnd_mono [THEN rtrancl_def [THEN def_lfp_unfold]]
(** The relation rtrancl **)
(* @{term"r^* \<subseteq> field(r) * field(r)"} *)
lemmas rtrancl_type = rtrancl_def [THEN def_lfp_subset]
lemma relation_rtrancl: "relation(r^*)"
apply (simp add: relation_def)
apply (blast dest: rtrancl_type [THEN subsetD])
done
(*Reflexivity of rtrancl*)
lemma rtrancl_refl: "[| a \<in> field(r) |] ==> <a,a> \<in> r^*"
apply (rule rtrancl_unfold [THEN ssubst])
apply (erule idI [THEN UnI1])
done
(*Closure under composition with r *)
lemma rtrancl_into_rtrancl: "[| <a,b> \<in> r^*; <b,c> \<in> r |] ==> <a,c> \<in> r^*"
apply (rule rtrancl_unfold [THEN ssubst])
apply (rule compI [THEN UnI2], assumption, assumption)
done
(*rtrancl of r contains all pairs in r *)
lemma r_into_rtrancl: "<a,b> \<in> r ==> <a,b> \<in> r^*"
by (rule rtrancl_refl [THEN rtrancl_into_rtrancl], blast+)
(*The premise ensures that r consists entirely of pairs*)
lemma r_subset_rtrancl: "relation(r) ==> r \<subseteq> r^*"
by (simp add: relation_def, blast intro: r_into_rtrancl)
lemma rtrancl_field: "field(r^*) = field(r)"
by (blast intro: r_into_rtrancl dest!: rtrancl_type [THEN subsetD])
(** standard induction rule **)
lemma rtrancl_full_induct [case_names initial step, consumes 1]:
"[| <a,b> \<in> r^*;
!!x. x \<in> field(r) ==> P(<x,x>);
!!x y z.[| P(<x,y>); <x,y>: r^*; <y,z>: r |] ==> P(<x,z>) |]
==> P(<a,b>)"
by (erule def_induct [OF rtrancl_def rtrancl_bnd_mono], blast)
(*nice induction rule.
Tried adding the typing hypotheses y,z \<in> field(r), but these
caused expensive case splits!*)
lemma rtrancl_induct [case_names initial step, induct set: rtrancl]:
"[| <a,b> \<in> r^*;
P(a);
!!y z.[| <a,y> \<in> r^*; <y,z> \<in> r; P(y) |] ==> P(z)
|] ==> P(b)"
(*by induction on this formula*)
apply (subgoal_tac "\<forall>y. <a,b> = <a,y> \<longrightarrow> P (y) ")
(*now solve first subgoal: this formula is sufficient*)
apply (erule spec [THEN mp], rule refl)
(*now do the induction*)
apply (erule rtrancl_full_induct, blast+)
done
(*transitivity of transitive closure!! -- by induction.*)
lemma trans_rtrancl: "trans(r^*)"
apply (unfold trans_def)
apply (intro allI impI)
apply (erule_tac b = z in rtrancl_induct, assumption)
apply (blast intro: rtrancl_into_rtrancl)
done
lemmas rtrancl_trans = trans_rtrancl [THEN transD]
(*elimination of rtrancl -- by induction on a special formula*)
lemma rtranclE:
"[| <a,b> \<in> r^*; (a=b) ==> P;
!!y.[| <a,y> \<in> r^*; <y,b> \<in> r |] ==> P |]
==> P"
apply (subgoal_tac "a = b | (\<exists>y. <a,y> \<in> r^* & <y,b> \<in> r) ")
(*see HOL/trancl*)
apply blast
apply (erule rtrancl_induct, blast+)
done
(**** The relation trancl ****)
(*Transitivity of r^+ is proved by transitivity of r^* *)
lemma trans_trancl: "trans(r^+)"
apply (unfold trans_def trancl_def)
apply (blast intro: rtrancl_into_rtrancl
trans_rtrancl [THEN transD, THEN compI])
done
lemmas trans_on_trancl = trans_trancl [THEN trans_imp_trans_on]
lemmas trancl_trans = trans_trancl [THEN transD]
(** Conversions between trancl and rtrancl **)
lemma trancl_into_rtrancl: "<a,b> \<in> r^+ ==> <a,b> \<in> r^*"
apply (unfold trancl_def)
apply (blast intro: rtrancl_into_rtrancl)
done
(*r^+ contains all pairs in r *)
lemma r_into_trancl: "<a,b> \<in> r ==> <a,b> \<in> r^+"
apply (unfold trancl_def)
apply (blast intro!: rtrancl_refl)
done
(*The premise ensures that r consists entirely of pairs*)
lemma r_subset_trancl: "relation(r) ==> r \<subseteq> r^+"
by (simp add: relation_def, blast intro: r_into_trancl)
(*intro rule by definition: from r^* and r *)
lemma rtrancl_into_trancl1: "[| <a,b> \<in> r^*; <b,c> \<in> r |] ==> <a,c> \<in> r^+"
by (unfold trancl_def, blast)
(*intro rule from r and r^* *)
lemma rtrancl_into_trancl2:
"[| <a,b> \<in> r; <b,c> \<in> r^* |] ==> <a,c> \<in> r^+"
apply (erule rtrancl_induct)
apply (erule r_into_trancl)
apply (blast intro: r_into_trancl trancl_trans)
done
(*Nice induction rule for trancl*)
lemma trancl_induct [case_names initial step, induct set: trancl]:
"[| <a,b> \<in> r^+;
!!y. [| <a,y> \<in> r |] ==> P(y);
!!y z.[| <a,y> \<in> r^+; <y,z> \<in> r; P(y) |] ==> P(z)
|] ==> P(b)"
apply (rule compEpair)
apply (unfold trancl_def, assumption)
(*by induction on this formula*)
apply (subgoal_tac "\<forall>z. <y,z> \<in> r \<longrightarrow> P (z) ")
(*now solve first subgoal: this formula is sufficient*)
apply blast
apply (erule rtrancl_induct)
apply (blast intro: rtrancl_into_trancl1)+
done
(*elimination of r^+ -- NOT an induction rule*)
lemma tranclE:
"[| <a,b> \<in> r^+;
<a,b> \<in> r ==> P;
!!y.[| <a,y> \<in> r^+; <y,b> \<in> r |] ==> P
|] ==> P"
apply (subgoal_tac "<a,b> \<in> r | (\<exists>y. <a,y> \<in> r^+ & <y,b> \<in> r) ")
apply blast
apply (rule compEpair)
apply (unfold trancl_def, assumption)
apply (erule rtranclE)
apply (blast intro: rtrancl_into_trancl1)+
done
lemma trancl_type: "r^+ \<subseteq> field(r)*field(r)"
apply (unfold trancl_def)
apply (blast elim: rtrancl_type [THEN subsetD, THEN SigmaE2])
done
lemma relation_trancl: "relation(r^+)"
apply (simp add: relation_def)
apply (blast dest: trancl_type [THEN subsetD])
done
lemma trancl_subset_times: "r \<subseteq> A * A ==> r^+ \<subseteq> A * A"
by (insert trancl_type [of r], blast)
lemma trancl_mono: "r<=s ==> r^+ \<subseteq> s^+"
by (unfold trancl_def, intro comp_mono rtrancl_mono)
lemma trancl_eq_r: "[|relation(r); trans(r)|] ==> r^+ = r"
apply (rule equalityI)
prefer 2 apply (erule r_subset_trancl, clarify)
apply (frule trancl_type [THEN subsetD], clarify)
apply (erule trancl_induct, assumption)
apply (blast dest: transD)
done
(** Suggested by Sidi Ould Ehmety **)
lemma rtrancl_idemp [simp]: "(r^*)^* = r^*"
apply (rule equalityI, auto)
prefer 2
apply (frule rtrancl_type [THEN subsetD])
apply (blast intro: r_into_rtrancl )
txt\<open>converse direction\<close>
apply (frule rtrancl_type [THEN subsetD], clarify)
apply (erule rtrancl_induct)
apply (simp add: rtrancl_refl rtrancl_field)
apply (blast intro: rtrancl_trans)
done
lemma rtrancl_subset: "[| R \<subseteq> S; S \<subseteq> R^* |] ==> S^* = R^*"
apply (drule rtrancl_mono)
apply (drule rtrancl_mono, simp_all, blast)
done
lemma rtrancl_Un_rtrancl:
"[| relation(r); relation(s) |] ==> (r^* \<union> s^*)^* = (r \<union> s)^*"
apply (rule rtrancl_subset)
apply (blast dest: r_subset_rtrancl)
apply (blast intro: rtrancl_mono [THEN subsetD])
done
(*** "converse" laws by Sidi Ould Ehmety ***)
(** rtrancl **)
lemma rtrancl_converseD: "<x,y>:converse(r)^* ==> <x,y>:converse(r^*)"
apply (rule converseI)
apply (frule rtrancl_type [THEN subsetD])
apply (erule rtrancl_induct)
apply (blast intro: rtrancl_refl)
apply (blast intro: r_into_rtrancl rtrancl_trans)
done
lemma rtrancl_converseI: "<x,y>:converse(r^*) ==> <x,y>:converse(r)^*"
apply (drule converseD)
apply (frule rtrancl_type [THEN subsetD])
apply (erule rtrancl_induct)
apply (blast intro: rtrancl_refl)
apply (blast intro: r_into_rtrancl rtrancl_trans)
done
lemma rtrancl_converse: "converse(r)^* = converse(r^*)"
apply (safe intro!: equalityI)
apply (frule rtrancl_type [THEN subsetD])
apply (safe dest!: rtrancl_converseD intro!: rtrancl_converseI)
done
(** trancl **)
lemma trancl_converseD: "<a, b>:converse(r)^+ ==> <a, b>:converse(r^+)"
apply (erule trancl_induct)
apply (auto intro: r_into_trancl trancl_trans)
done
lemma trancl_converseI: "<x,y>:converse(r^+) ==> <x,y>:converse(r)^+"
apply (drule converseD)
apply (erule trancl_induct)
apply (auto intro: r_into_trancl trancl_trans)
done
lemma trancl_converse: "converse(r)^+ = converse(r^+)"
apply (safe intro!: equalityI)
apply (frule trancl_type [THEN subsetD])
apply (safe dest!: trancl_converseD intro!: trancl_converseI)
done
lemma converse_trancl_induct [case_names initial step, consumes 1]:
"[| <a, b>:r^+; !!y. <y, b> :r ==> P(y);
!!y z. [| <y, z> \<in> r; <z, b> \<in> r^+; P(z) |] ==> P(y) |]
==> P(a)"
apply (drule converseI)
apply (simp (no_asm_use) add: trancl_converse [symmetric])
apply (erule trancl_induct)
apply (auto simp add: trancl_converse)
done
end