src/HOL/Library/Quotient_Sum.thy

Quotient_Info stores only relation maps

(*  Title:      HOL/Library/Quotient_Sum.thy
    Author:     Cezary Kaliszyk and Christian Urban
*)

header {* Quotient infrastructure for the sum type *}

theory Quotient_Sum
imports Main Quotient_Syntax
begin

fun
  sum_rel :: "('a \<Rightarrow> 'c \<Rightarrow> bool) \<Rightarrow> ('b \<Rightarrow> 'd \<Rightarrow> bool) \<Rightarrow> 'a + 'b \<Rightarrow> 'c + 'd \<Rightarrow> bool"
where
  "sum_rel R1 R2 (Inl a1) (Inl b1) = R1 a1 b1"
| "sum_rel R1 R2 (Inl a1) (Inr b2) = False"
| "sum_rel R1 R2 (Inr a2) (Inl b1) = False"
| "sum_rel R1 R2 (Inr a2) (Inr b2) = R2 a2 b2"

declare [[map sum = sum_rel]]

lemma sum_rel_unfold:
  "sum_rel R1 R2 x y = (case (x, y) of (Inl x, Inl y) \<Rightarrow> R1 x y
    | (Inr x, Inr y) \<Rightarrow> R2 x y
    | _ \<Rightarrow> False)"
  by (cases x) (cases y, simp_all)+

lemma sum_rel_map1:
  "sum_rel R1 R2 (sum_map f1 f2 x) y \<longleftrightarrow> sum_rel (\<lambda>x. R1 (f1 x)) (\<lambda>x. R2 (f2 x)) x y"
  by (simp add: sum_rel_unfold split: sum.split)

lemma sum_rel_map2:
  "sum_rel R1 R2 x (sum_map f1 f2 y) \<longleftrightarrow> sum_rel (\<lambda>x y. R1 x (f1 y)) (\<lambda>x y. R2 x (f2 y)) x y"
  by (simp add: sum_rel_unfold split: sum.split)

lemma sum_map_id [id_simps]:
  "sum_map id id = id"
  by (simp add: id_def sum_map.identity fun_eq_iff)

lemma sum_rel_eq [id_simps]:
  "sum_rel (op =) (op =) = (op =)"
  by (simp add: sum_rel_unfold fun_eq_iff split: sum.split)

lemma sum_reflp:
  "reflp R1 \<Longrightarrow> reflp R2 \<Longrightarrow> reflp (sum_rel R1 R2)"
  by (auto simp add: sum_rel_unfold split: sum.splits intro!: reflpI elim: reflpE)

lemma sum_symp:
  "symp R1 \<Longrightarrow> symp R2 \<Longrightarrow> symp (sum_rel R1 R2)"
  by (auto simp add: sum_rel_unfold split: sum.splits intro!: sympI elim: sympE)

lemma sum_transp:
  "transp R1 \<Longrightarrow> transp R2 \<Longrightarrow> transp (sum_rel R1 R2)"
  by (auto simp add: sum_rel_unfold split: sum.splits intro!: transpI elim: transpE)

lemma sum_equivp [quot_equiv]:
  "equivp R1 \<Longrightarrow> equivp R2 \<Longrightarrow> equivp (sum_rel R1 R2)"
  by (blast intro: equivpI sum_reflp sum_symp sum_transp elim: equivpE)
  
lemma sum_quotient [quot_thm]:
  assumes q1: "Quotient R1 Abs1 Rep1"
  assumes q2: "Quotient R2 Abs2 Rep2"
  shows "Quotient (sum_rel R1 R2) (sum_map Abs1 Abs2) (sum_map Rep1 Rep2)"
  apply (rule QuotientI)
  apply (simp_all add: sum_map.compositionality comp_def sum_map.identity sum_rel_eq sum_rel_map1 sum_rel_map2
    Quotient_abs_rep [OF q1] Quotient_rel_rep [OF q1] Quotient_abs_rep [OF q2] Quotient_rel_rep [OF q2])
  using Quotient_rel [OF q1] Quotient_rel [OF q2]
  apply (simp add: sum_rel_unfold comp_def split: sum.split)
  done

lemma sum_Inl_rsp [quot_respect]:
  assumes q1: "Quotient R1 Abs1 Rep1"
  assumes q2: "Quotient R2 Abs2 Rep2"
  shows "(R1 ===> sum_rel R1 R2) Inl Inl"
  by auto

lemma sum_Inr_rsp [quot_respect]:
  assumes q1: "Quotient R1 Abs1 Rep1"
  assumes q2: "Quotient R2 Abs2 Rep2"
  shows "(R2 ===> sum_rel R1 R2) Inr Inr"
  by auto

lemma sum_Inl_prs [quot_preserve]:
  assumes q1: "Quotient R1 Abs1 Rep1"
  assumes q2: "Quotient R2 Abs2 Rep2"
  shows "(Rep1 ---> sum_map Abs1 Abs2) Inl = Inl"
  apply(simp add: fun_eq_iff)
  apply(simp add: Quotient_abs_rep[OF q1])
  done

lemma sum_Inr_prs [quot_preserve]:
  assumes q1: "Quotient R1 Abs1 Rep1"
  assumes q2: "Quotient R2 Abs2 Rep2"
  shows "(Rep2 ---> sum_map Abs1 Abs2) Inr = Inr"
  apply(simp add: fun_eq_iff)
  apply(simp add: Quotient_abs_rep[OF q2])
  done

end