src/HOL/Codatatype/BNF_Def.thy

moved theorems closer to where they are used

(*  Title:      HOL/Codatatype/BNF_Def.thy
    Author:     Dmitriy Traytel, TU Muenchen
    Copyright   2012

Definition of bounded natural functors.
*)

header {* Definition of Bounded Natural Functors *}

theory BNF_Def
imports BNF_Util
keywords
  "print_bnfs" :: diag and
  "bnf_def" :: thy_goal
begin

lemma collect_o: "collect F o g = collect ((\<lambda>f. f o g) ` F)"
by (rule ext) (auto simp only: o_apply collect_def)

lemma converse_mono:
"R1 ^-1 \<subseteq> R2 ^-1 \<longleftrightarrow> R1 \<subseteq> R2"
unfolding converse_def by auto

lemma converse_shift:
"R1 \<subseteq> R2 ^-1 \<Longrightarrow> R1 ^-1 \<subseteq> R2"
unfolding converse_def by auto

definition csquare where
"csquare A f1 f2 p1 p2 \<longleftrightarrow> (\<forall> a \<in> A. f1 (p1 a) = f2 (p2 a))"

(* The pullback of sets *)
definition thePull where
"thePull B1 B2 f1 f2 = {(b1,b2). b1 \<in> B1 \<and> b2 \<in> B2 \<and> f1 b1 = f2 b2}"

lemma wpull_thePull:
"wpull (thePull B1 B2 f1 f2) B1 B2 f1 f2 fst snd"
unfolding wpull_def thePull_def by auto

lemma wppull_thePull:
assumes "wppull A B1 B2 f1 f2 e1 e2 p1 p2"
shows
"\<exists> j. \<forall> a' \<in> thePull B1 B2 f1 f2.
   j a' \<in> A \<and>
   e1 (p1 (j a')) = e1 (fst a') \<and> e2 (p2 (j a')) = e2 (snd a')"
(is "\<exists> j. \<forall> a' \<in> ?A'. ?phi a' (j a')")
proof(rule bchoice[of ?A' ?phi], default)
  fix a' assume a': "a' \<in> ?A'"
  hence "fst a' \<in> B1" unfolding thePull_def by auto
  moreover
  from a' have "snd a' \<in> B2" unfolding thePull_def by auto
  moreover have "f1 (fst a') = f2 (snd a')"
  using a' unfolding csquare_def thePull_def by auto
  ultimately show "\<exists> ja'. ?phi a' ja'"
  using assms unfolding wppull_def by auto
qed

lemma wpull_wppull:
assumes wp: "wpull A' B1 B2 f1 f2 p1' p2'" and
1: "\<forall> a' \<in> A'. j a' \<in> A \<and> e1 (p1 (j a')) = e1 (p1' a') \<and> e2 (p2 (j a')) = e2 (p2' a')"
shows "wppull A B1 B2 f1 f2 e1 e2 p1 p2"
unfolding wppull_def proof safe
  fix b1 b2
  assume b1: "b1 \<in> B1" and b2: "b2 \<in> B2" and f: "f1 b1 = f2 b2"
  then obtain a' where a': "a' \<in> A'" and b1: "b1 = p1' a'" and b2: "b2 = p2' a'"
  using wp unfolding wpull_def by blast
  show "\<exists>a\<in>A. e1 (p1 a) = e1 b1 \<and> e2 (p2 a) = e2 b2"
  apply(rule bexI[of _ "j a'"]) unfolding b1 b2 using a' 1 by auto
qed

lemma wppull_id: "\<lbrakk>wpull UNIV UNIV UNIV f1 f2 p1 p2; e1 = id; e2 = id\<rbrakk> \<Longrightarrow>
   wppull UNIV UNIV UNIV f1 f2 e1 e2 p1 p2"
by (erule wpull_wppull) auto

lemma Id_alt: "Id = Gr UNIV id"
unfolding Gr_def by auto

lemma Gr_UNIV_id: "f = id \<Longrightarrow> (Gr UNIV f)^-1 O Gr UNIV f = Gr UNIV f"
unfolding Gr_def by auto

lemma Gr_mono: "A \<subseteq> B \<Longrightarrow> Gr A f \<subseteq> Gr B f"
unfolding Gr_def by auto

lemma wpull_Gr:
"wpull (Gr A f) A (f ` A) f id fst snd"
unfolding wpull_def Gr_def by auto

definition "pick_middle P Q a c = (SOME b. (a,b) \<in> P \<and> (b,c) \<in> Q)"

lemma pick_middle:
assumes "(a,c) \<in> P O Q"
shows "(a, pick_middle P Q a c) \<in> P \<and> (pick_middle P Q a c, c) \<in> Q"
unfolding pick_middle_def apply(rule someI_ex)
using assms unfolding relcomp_def by auto

definition fstO where "fstO P Q ac = (fst ac, pick_middle P Q (fst ac) (snd ac))"
definition sndO where "sndO P Q ac = (pick_middle P Q (fst ac) (snd ac), snd ac)"

lemma fstO_in: "ac \<in> P O Q \<Longrightarrow> fstO P Q ac \<in> P"
by (metis assms fstO_def pick_middle surjective_pairing)

lemma fst_fstO: "fst bc = (fst \<circ> fstO P Q) bc"
unfolding comp_def fstO_def by simp

lemma snd_sndO: "snd bc = (snd \<circ> sndO P Q) bc"
unfolding comp_def sndO_def by simp

lemma sndO_in: "ac \<in> P O Q \<Longrightarrow> sndO P Q ac \<in> Q"
by (metis assms sndO_def pick_middle surjective_pairing)

lemma csquare_fstO_sndO:
"csquare (P O Q) snd fst (fstO P Q) (sndO P Q)"
unfolding csquare_def fstO_def sndO_def using pick_middle by auto

lemma wppull_fstO_sndO:
shows "wppull (P O Q) P Q snd fst fst snd (fstO P Q) (sndO P Q)"
using pick_middle unfolding wppull_def fstO_def sndO_def relcomp_def by auto

lemma snd_fst_flip: "snd xy = (fst o (%(x, y). (y, x))) xy"
by (simp split: prod.split)

lemma fst_snd_flip: "fst xy = (snd o (%(x, y). (y, x))) xy"
by (simp split: prod.split)

lemma flip_rel: "A \<subseteq> (R ^-1) \<Longrightarrow> (%(x, y). (y, x)) ` A \<subseteq> R"
by auto

lemma pointfreeE: "f o g = f' o g' \<Longrightarrow> f (g x) = f' (g' x)"
unfolding o_def fun_eq_iff by simp

ML_file "Tools/bnf_def_tactics.ML"
ML_file"Tools/bnf_def.ML"

end