Theory Sum_Type (Isabelle2005: October 2005)

# Theory Sum_Type

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theory Sum_Type
imports Product_Type
begin

    (*  Title:      HOL/Sum_Type.thy
        ID:         $Id: Sum_Type.thy,v 1.6 2005/08/16 13:36:29 paulson Exp $
        Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
        Copyright   1992  University of Cambridge
    *)

    header{*The Disjoint Sum of Two Types*}

    theory Sum_Type
    imports Product_Type
    begin

    text{*The representations of the two injections*}

    constdefs
      Inl_Rep :: "['a, 'a, 'b, bool] => bool"
      "Inl_Rep == (%a. %x y p. x=a & p)"

      Inr_Rep :: "['b, 'a, 'b, bool] => bool"
      "Inr_Rep == (%b. %x y p. y=b & ~p)"

    global

    typedef (Sum)
      ('a, 'b) "+"          (infixr 10)
        = "{f. (? a. f = Inl_Rep(a::'a)) | (? b. f = Inr_Rep(b::'b))}"
      by auto

    local

    text{*abstract constants and syntax*}

    constdefs
      Inl :: "'a => 'a + 'b"
       "Inl == (%a. Abs_Sum(Inl_Rep(a)))"

      Inr :: "'b => 'a + 'b"
       "Inr == (%b. Abs_Sum(Inr_Rep(b)))"

      Plus :: "['a set, 'b set] => ('a + 'b) set"        (infixr "<+>" 65)
       "A <+> B == (Inl`A) Un (Inr`B)"
        --{*disjoint sum for sets; the operator + is overloaded with wrong type!*}

      Part :: "['a set, 'b => 'a] => 'a set"
       "Part A h == A Int {x. ? z. x = h(z)}"
        --{*for selecting out the components of a mutually recursive definition*}

    (** Inl_Rep and Inr_Rep: Representations of the constructors **)

    (*This counts as a non-emptiness result for admitting 'a+'b as a type*)
    lemma Inl_RepI: "Inl_Rep(a) : Sum"
    by (auto simp add: Sum_def)

    lemma Inr_RepI: "Inr_Rep(b) : Sum"
    by (auto simp add: Sum_def)

    lemma inj_on_Abs_Sum: "inj_on Abs_Sum Sum"
    apply (rule inj_on_inverseI)
    apply (erule Abs_Sum_inverse)
    done

    subsection{*Freeness Properties for @{term Inl} and  @{term Inr}*}

    text{*Distinctness*}

    lemma Inl_Rep_not_Inr_Rep: "Inl_Rep(a) ~= Inr_Rep(b)"
    by (auto simp add: Inl_Rep_def Inr_Rep_def expand_fun_eq)

    lemma Inl_not_Inr [iff]: "Inl(a) ~= Inr(b)"
    apply (simp add: Inl_def Inr_def)
    apply (rule inj_on_Abs_Sum [THEN inj_on_contraD])
    apply (rule Inl_Rep_not_Inr_Rep)
    apply (rule Inl_RepI)
    apply (rule Inr_RepI)
    done

    lemmas Inr_not_Inl = Inl_not_Inr [THEN not_sym, standard]
    declare Inr_not_Inl [iff]

    lemmas Inl_neq_Inr = Inl_not_Inr [THEN notE, standard]
    lemmas Inr_neq_Inl = sym [THEN Inl_neq_Inr, standard]

    text{*Injectiveness*}

    lemma Inl_Rep_inject: "Inl_Rep(a) = Inl_Rep(c) ==> a=c"
    by (auto simp add: Inl_Rep_def expand_fun_eq)

    lemma Inr_Rep_inject: "Inr_Rep(b) = Inr_Rep(d) ==> b=d"
    by (auto simp add: Inr_Rep_def expand_fun_eq)

    lemma inj_Inl: "inj(Inl)"
    apply (simp add: Inl_def)
    apply (rule inj_onI)
    apply (erule inj_on_Abs_Sum [THEN inj_onD, THEN Inl_Rep_inject])
    apply (rule Inl_RepI)
    apply (rule Inl_RepI)
    done
    lemmas Inl_inject = inj_Inl [THEN injD, standard]

    lemma inj_Inr: "inj(Inr)"
    apply (simp add: Inr_def)
    apply (rule inj_onI)
    apply (erule inj_on_Abs_Sum [THEN inj_onD, THEN Inr_Rep_inject])
    apply (rule Inr_RepI)
    apply (rule Inr_RepI)
    done

    lemmas Inr_inject = inj_Inr [THEN injD, standard]

    lemma Inl_eq [iff]: "(Inl(x)=Inl(y)) = (x=y)"
    by (blast dest!: Inl_inject)

    lemma Inr_eq [iff]: "(Inr(x)=Inr(y)) = (x=y)"
    by (blast dest!: Inr_inject)

    subsection{*The Disjoint Sum of Sets*}

    (** Introduction rules for the injections **)

    lemma InlI [intro!]: "a : A ==> Inl(a) : A <+> B"
    by (simp add: Plus_def)

    lemma InrI [intro!]: "b : B ==> Inr(b) : A <+> B"
    by (simp add: Plus_def)

    (** Elimination rules **)

    lemma PlusE [elim!]:
        "[| u: A <+> B;
            !!x. [| x:A;  u=Inl(x) |] ==> P;
            !!y. [| y:B;  u=Inr(y) |] ==> P
         |] ==> P"
    by (auto simp add: Plus_def)

    text{*Exhaustion rule for sums, a degenerate form of induction*}
    lemma sumE:
        "[| !!x::'a. s = Inl(x) ==> P;  !!y::'b. s = Inr(y) ==> P
         |] ==> P"
    apply (rule Abs_Sum_cases [of s])
    apply (auto simp add: Sum_def Inl_def Inr_def)
    done

    lemma sum_induct: "[| !!x. P (Inl x); !!x. P (Inr x) |] ==> P x"
    by (rule sumE [of x], auto)

    lemma UNIV_Plus_UNIV [simp]: "UNIV <+> UNIV = UNIV"
    apply (rule set_ext)
    apply(rename_tac s)
    apply(rule_tac s=s in sumE)
    apply auto
    done

    subsection{*The @{term Part} Primitive*}

    lemma Part_eqI [intro]: "[| a : A;  a=h(b) |] ==> a : Part A h"
    by (auto simp add: Part_def)

    lemmas PartI = Part_eqI [OF _ refl, standard]

    lemma PartE [elim!]: "[| a : Part A h;  !!z. [| a : A;  a=h(z) |] ==> P |] ==> P"
    by (auto simp add: Part_def)

    lemma Part_subset: "Part A h <= A"
    by (auto simp add: Part_def)

    lemma Part_mono: "A<=B ==> Part A h <= Part B h"
    by blast

    lemmas basic_monos = basic_monos Part_mono

    lemma PartD1: "a : Part A h ==> a : A"
    by (simp add: Part_def)

    lemma Part_id: "Part A (%x. x) = A"
    by blast

    lemma Part_Int: "Part (A Int B) h = (Part A h) Int (Part B h)"
    by blast

    lemma Part_Collect: "Part (A Int {x. P x}) h = (Part A h) Int {x. P x}"
    by blast

    ML
    {*
    val Inl_RepI = thm "Inl_RepI";
    val Inr_RepI = thm "Inr_RepI";
    val inj_on_Abs_Sum = thm "inj_on_Abs_Sum";
    val Inl_Rep_not_Inr_Rep = thm "Inl_Rep_not_Inr_Rep";
    val Inl_not_Inr = thm "Inl_not_Inr";
    val Inr_not_Inl = thm "Inr_not_Inl";
    val Inl_neq_Inr = thm "Inl_neq_Inr";
    val Inr_neq_Inl = thm "Inr_neq_Inl";
    val Inl_Rep_inject = thm "Inl_Rep_inject";
    val Inr_Rep_inject = thm "Inr_Rep_inject";
    val inj_Inl = thm "inj_Inl";
    val Inl_inject = thm "Inl_inject";
    val inj_Inr = thm "inj_Inr";
    val Inr_inject = thm "Inr_inject";
    val Inl_eq = thm "Inl_eq";
    val Inr_eq = thm "Inr_eq";
    val InlI = thm "InlI";
    val InrI = thm "InrI";
    val PlusE = thm "PlusE";
    val sumE = thm "sumE";
    val sum_induct = thm "sum_induct";
    val Part_eqI = thm "Part_eqI";
    val PartI = thm "PartI";
    val PartE = thm "PartE";
    val Part_subset = thm "Part_subset";
    val Part_mono = thm "Part_mono";
    val PartD1 = thm "PartD1";
    val Part_id = thm "Part_id";
    val Part_Int = thm "Part_Int";
    val Part_Collect = thm "Part_Collect";

    val basic_monos = thms "basic_monos";
    *}

    end

lemma Inl_RepI:

      Inl_Rep a ∈ Sum

lemma Inr_RepI:

      Inr_Rep b ∈ Sum

lemma inj_on_Abs_Sum:

      inj_on Abs_Sum Sum

### Freeness Properties for @{term Inl} and @{term Inr}

lemma Inl_Rep_not_Inr_Rep:

      Inl_Rep a ≠ Inr_Rep b

lemma Inl_not_Inr:

      Inl a ≠ Inr b

lemmas Inr_not_Inl:

      Inr b ≠ Inl a

lemmas Inr_not_Inl:

      Inr b ≠ Inl a

lemmas Inl_neq_Inr:

      Inl a = Inr b ==> R

lemmas Inl_neq_Inr:

      Inl a = Inr b ==> R

lemmas Inr_neq_Inl:

      Inr b = Inl a ==> R

lemmas Inr_neq_Inl:

      Inr b = Inl a ==> R

lemma Inl_Rep_inject:

      Inl_Rep a = Inl_Rep c ==> a = c

lemma Inr_Rep_inject:

      Inr_Rep b = Inr_Rep d ==> b = d

lemma inj_Inl:

      inj Inl

lemmas Inl_inject:

      Inl x = Inl y ==> x = y

lemmas Inl_inject:

      Inl x = Inl y ==> x = y

lemma inj_Inr:

      inj Inr

lemmas Inr_inject:

      Inr x = Inr y ==> x = y

lemmas Inr_inject:

      Inr x = Inr y ==> x = y

lemma Inl_eq:

      (Inl x = Inl y) = (x = y)

lemma Inr_eq:

      (Inr x = Inr y) = (x = y)

### The Disjoint Sum of Sets

lemma InlI:

      a ∈ A ==> Inl a ∈ A <+> B

lemma InrI:

      b ∈ B ==> Inr b ∈ A <+> B

lemma PlusE:

      [| u ∈ A <+> B; !!x. [| x ∈ A; u = Inl x |] ==> P;
         !!y. [| y ∈ B; u = Inr y |] ==> P |]
      ==> P

lemma sumE:

      [| !!x. s = Inl x ==> P; !!y. s = Inr y ==> P |] ==> P

lemma sum_induct:

      [| !!x. P (Inl x); !!x. P (Inr x) |] ==> P x

lemma UNIV_Plus_UNIV:

      UNIV <+> UNIV = UNIV

### The @{term Part} Primitive

lemma Part_eqI:

      [| a ∈ A; a = h b |] ==> a ∈ Part A h

lemmas PartI:

      h b ∈ A ==> h b ∈ Part A h

lemmas PartI:

      h b ∈ A ==> h b ∈ Part A h

lemma PartE:

      [| a ∈ Part A h; !!z. [| a ∈ A; a = h z |] ==> P |] ==> P

lemma Part_subset:

      Part A h ⊆ A

lemma Part_mono:

      A ⊆ B ==> Part A h ⊆ Part B h

lemmas basic_monos:

      A ⊆ A

      P --> P

      [| P1.0 --> Q1.0; P2.0 --> Q2.0 |] ==> P1.0 ∨ P2.0 --> Q1.0 ∨ Q2.0

      [| P1.0 --> Q1.0; P2.0 --> Q2.0 |] ==> P1.0 ∧ P2.0 --> Q1.0 ∧ Q2.0

      (!!x. P x --> Q x) ==> (∃x. P x) --> (∃x. Q x)

      (!!x. P x --> Q x) ==> Collect P ⊆ Collect Q

      A ⊆ B ==> x ∈ A --> x ∈ B

      A ⊆ B ==> Part A h ⊆ Part B h

lemmas basic_monos:

      A ⊆ A

      P --> P

      [| P1.0 --> Q1.0; P2.0 --> Q2.0 |] ==> P1.0 ∨ P2.0 --> Q1.0 ∨ Q2.0

      [| P1.0 --> Q1.0; P2.0 --> Q2.0 |] ==> P1.0 ∧ P2.0 --> Q1.0 ∧ Q2.0

      (!!x. P x --> Q x) ==> (∃x. P x) --> (∃x. Q x)

      (!!x. P x --> Q x) ==> Collect P ⊆ Collect Q

      A ⊆ B ==> x ∈ A --> x ∈ B

      A ⊆ B ==> Part A h ⊆ Part B h

lemma PartD1:

      a ∈ Part A h ==> a ∈ A

lemma Part_id:

      Part A (%x. x) = A

lemma Part_Int:

      Part (A ∩ B) h = Part A h ∩ Part B h

lemma Part_Collect:

      Part (A ∩ {x. P x}) h = Part A h ∩ {x. P x}