Theory EquivClass (Isabelle2005: October 2005)

# Theory EquivClass

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theory EquivClass
imports Trancl Perm
begin

    (*  Title:      ZF/EquivClass.thy
        ID:         $Id: EquivClass.thy,v 1.8 2005/06/17 14:15:11 haftmann Exp $
        Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
        Copyright   1994  University of Cambridge

    *)

    header{*Equivalence Relations*}

    theory EquivClass imports Trancl Perm begin

    constdefs

      quotient   :: "[i,i]=>i"    (infixl "'/'/" 90)  (*set of equiv classes*)
          "A//r == {r``{x} . x:A}"

      congruent  :: "[i,i=>i]=>o"
          "congruent(r,b) == ALL y z. <y,z>:r --> b(y)=b(z)"

      congruent2 :: "[i,i,[i,i]=>i]=>o"
          "congruent2(r1,r2,b) == ALL y1 z1 y2 z2.
               <y1,z1>:r1 --> <y2,z2>:r2 --> b(y1,y2) = b(z1,z2)"

    syntax
      RESPECTS ::"[i=>i, i] => o"  (infixr "respects" 80)
      RESPECTS2 ::"[i=>i, i] => o"  (infixr "respects2 " 80)
        --{*Abbreviation for the common case where the relations are identical*}

    translations
      "f respects r" == "congruent(r,f)"
      "f respects2 r" => "congruent2(r,r,f)"

    subsection{*Suppes, Theorem 70:
        @{term r} is an equiv relation iff @{term "converse(r) O r = r"}*}

    (** first half: equiv(A,r) ==> converse(r) O r = r **)

    lemma sym_trans_comp_subset:
        "[| sym(r); trans(r) |] ==> converse(r) O r <= r"
    by (unfold trans_def sym_def, blast)

    lemma refl_comp_subset:
        "[| refl(A,r); r <= A*A |] ==> r <= converse(r) O r"
    by (unfold refl_def, blast)

    lemma equiv_comp_eq:
        "equiv(A,r) ==> converse(r) O r = r"
    apply (unfold equiv_def)
    apply (blast del: subsetI intro!: sym_trans_comp_subset refl_comp_subset)
    done

    (*second half*)
    lemma comp_equivI:
        "[| converse(r) O r = r;  domain(r) = A |] ==> equiv(A,r)"
    apply (unfold equiv_def refl_def sym_def trans_def)
    apply (erule equalityE)
    apply (subgoal_tac "ALL x y. <x,y> : r --> <y,x> : r", blast+)
    done

    (** Equivalence classes **)

    (*Lemma for the next result*)
    lemma equiv_class_subset:
        "[| sym(r);  trans(r);  <a,b>: r |] ==> r``{a} <= r``{b}"
    by (unfold trans_def sym_def, blast)

    lemma equiv_class_eq:
        "[| equiv(A,r);  <a,b>: r |] ==> r``{a} = r``{b}"
    apply (unfold equiv_def)
    apply (safe del: subsetI intro!: equalityI equiv_class_subset)
    apply (unfold sym_def, blast)
    done

    lemma equiv_class_self:
        "[| equiv(A,r);  a: A |] ==> a: r``{a}"
    by (unfold equiv_def refl_def, blast)

    (*Lemma for the next result*)
    lemma subset_equiv_class:
        "[| equiv(A,r);  r``{b} <= r``{a};  b: A |] ==> <a,b>: r"
    by (unfold equiv_def refl_def, blast)

    lemma eq_equiv_class: "[| r``{a} = r``{b};  equiv(A,r);  b: A |] ==> <a,b>: r"
    by (assumption | rule equalityD2 subset_equiv_class)+

    (*thus r``{a} = r``{b} as well*)
    lemma equiv_class_nondisjoint:
        "[| equiv(A,r);  x: (r``{a} Int r``{b}) |] ==> <a,b>: r"
    by (unfold equiv_def trans_def sym_def, blast)

    lemma equiv_type: "equiv(A,r) ==> r <= A*A"
    by (unfold equiv_def, blast)

    lemma equiv_class_eq_iff:
         "equiv(A,r) ==> <x,y>: r <-> r``{x} = r``{y} & x:A & y:A"
    by (blast intro: eq_equiv_class equiv_class_eq dest: equiv_type)

    lemma eq_equiv_class_iff:
         "[| equiv(A,r);  x: A;  y: A |] ==> r``{x} = r``{y} <-> <x,y>: r"
    by (blast intro: eq_equiv_class equiv_class_eq dest: equiv_type)

    (*** Quotients ***)

    (** Introduction/elimination rules -- needed? **)

    lemma quotientI [TC]: "x:A ==> r``{x}: A//r"
    apply (unfold quotient_def)
    apply (erule RepFunI)
    done

    lemma quotientE:
        "[| X: A//r;  !!x. [| X = r``{x};  x:A |] ==> P |] ==> P"
    by (unfold quotient_def, blast)

    lemma Union_quotient:
        "equiv(A,r) ==> Union(A//r) = A"
    by (unfold equiv_def refl_def quotient_def, blast)

    lemma quotient_disj:
        "[| equiv(A,r);  X: A//r;  Y: A//r |] ==> X=Y | (X Int Y <= 0)"
    apply (unfold quotient_def)
    apply (safe intro!: equiv_class_eq, assumption)
    apply (unfold equiv_def trans_def sym_def, blast)
    done

    subsection{*Defining Unary Operations upon Equivalence Classes*}

    (** Could have a locale with the premises equiv(A,r)  and  congruent(r,b)
    **)

    (*Conversion rule*)
    lemma UN_equiv_class:
        "[| equiv(A,r);  b respects r;  a: A |] ==> (UN x:r``{a}. b(x)) = b(a)"
    apply (subgoal_tac "∀x ∈ r``{a}. b(x) = b(a)")
     apply simp
     apply (blast intro: equiv_class_self)
    apply (unfold equiv_def sym_def congruent_def, blast)
    done

    (*type checking of  UN x:r``{a}. b(x) *)
    lemma UN_equiv_class_type:
        "[| equiv(A,r);  b respects r;  X: A//r;  !!x.  x : A ==> b(x) : B |]
         ==> (UN x:X. b(x)) : B"
    apply (unfold quotient_def, safe)
    apply (simp (no_asm_simp) add: UN_equiv_class)
    done

    (*Sufficient conditions for injectiveness.  Could weaken premises!
      major premise could be an inclusion; bcong could be !!y. y:A ==> b(y):B
    *)
    lemma UN_equiv_class_inject:
        "[| equiv(A,r);   b respects r;
            (UN x:X. b(x))=(UN y:Y. b(y));  X: A//r;  Y: A//r;
            !!x y. [| x:A; y:A; b(x)=b(y) |] ==> <x,y>:r |]
         ==> X=Y"
    apply (unfold quotient_def, safe)
    apply (rule equiv_class_eq, assumption)
    apply (simp add: UN_equiv_class [of A r b])
    done

    subsection{*Defining Binary Operations upon Equivalence Classes*}

    lemma congruent2_implies_congruent:
        "[| equiv(A,r1);  congruent2(r1,r2,b);  a: A |] ==> congruent(r2,b(a))"
    by (unfold congruent_def congruent2_def equiv_def refl_def, blast)

    lemma congruent2_implies_congruent_UN:
        "[| equiv(A1,r1);  equiv(A2,r2);  congruent2(r1,r2,b);  a: A2 |] ==>
         congruent(r1, %x1. \<Union>x2 ∈ r2``{a}. b(x1,x2))"
    apply (unfold congruent_def, safe)
    apply (frule equiv_type [THEN subsetD], assumption)
    apply clarify
    apply (simp add: UN_equiv_class congruent2_implies_congruent)
    apply (unfold congruent2_def equiv_def refl_def, blast)
    done

    lemma UN_equiv_class2:
        "[| equiv(A1,r1);  equiv(A2,r2);  congruent2(r1,r2,b);  a1: A1;  a2: A2 |]
         ==> (\<Union>x1 ∈ r1``{a1}. \<Union>x2 ∈ r2``{a2}. b(x1,x2)) = b(a1,a2)"
    by (simp add: UN_equiv_class congruent2_implies_congruent
                  congruent2_implies_congruent_UN)

    (*type checking*)
    lemma UN_equiv_class_type2:
        "[| equiv(A,r);  b respects2 r;
            X1: A//r;  X2: A//r;
            !!x1 x2.  [| x1: A; x2: A |] ==> b(x1,x2) : B
         |] ==> (UN x1:X1. UN x2:X2. b(x1,x2)) : B"
    apply (unfold quotient_def, safe)
    apply (blast intro: UN_equiv_class_type congruent2_implies_congruent_UN
                        congruent2_implies_congruent quotientI)
    done

    (*Suggested by John Harrison -- the two subproofs may be MUCH simpler
      than the direct proof*)
    lemma congruent2I:
        "[|  equiv(A1,r1);  equiv(A2,r2);
            !! y z w. [| w ∈ A2;  <y,z> ∈ r1 |] ==> b(y,w) = b(z,w);
            !! y z w. [| w ∈ A1;  <y,z> ∈ r2 |] ==> b(w,y) = b(w,z)
         |] ==> congruent2(r1,r2,b)"
    apply (unfold congruent2_def equiv_def refl_def, safe)
    apply (blast intro: trans)
    done

    lemma congruent2_commuteI:
     assumes equivA: "equiv(A,r)"
         and commute: "!! y z. [| y: A;  z: A |] ==> b(y,z) = b(z,y)"
         and congt:   "!! y z w. [| w: A;  <y,z>: r |] ==> b(w,y) = b(w,z)"
     shows "b respects2 r"
    apply (insert equivA [THEN equiv_type, THEN subsetD])
    apply (rule congruent2I [OF equivA equivA])
    apply (rule commute [THEN trans])
    apply (rule_tac [3] commute [THEN trans, symmetric])
    apply (rule_tac [5] sym)
    apply (blast intro: congt)+
    done

    (*Obsolete?*)
    lemma congruent_commuteI:
        "[| equiv(A,r);  Z: A//r;
            !!w. [| w: A |] ==> congruent(r, %z. b(w,z));
            !!x y. [| x: A;  y: A |] ==> b(y,x) = b(x,y)
         |] ==> congruent(r, %w. UN z: Z. b(w,z))"
    apply (simp (no_asm) add: congruent_def)
    apply (safe elim!: quotientE)
    apply (frule equiv_type [THEN subsetD], assumption)
    apply (simp add: UN_equiv_class [of A r])
    apply (simp add: congruent_def)
    done

    ML
    {*
    val sym_trans_comp_subset = thm "sym_trans_comp_subset";
    val refl_comp_subset = thm "refl_comp_subset";
    val equiv_comp_eq = thm "equiv_comp_eq";
    val comp_equivI = thm "comp_equivI";
    val equiv_class_subset = thm "equiv_class_subset";
    val equiv_class_eq = thm "equiv_class_eq";
    val equiv_class_self = thm "equiv_class_self";
    val subset_equiv_class = thm "subset_equiv_class";
    val eq_equiv_class = thm "eq_equiv_class";
    val equiv_class_nondisjoint = thm "equiv_class_nondisjoint";
    val equiv_type = thm "equiv_type";
    val equiv_class_eq_iff = thm "equiv_class_eq_iff";
    val eq_equiv_class_iff = thm "eq_equiv_class_iff";
    val quotientI = thm "quotientI";
    val quotientE = thm "quotientE";
    val Union_quotient = thm "Union_quotient";
    val quotient_disj = thm "quotient_disj";
    val UN_equiv_class = thm "UN_equiv_class";
    val UN_equiv_class_type = thm "UN_equiv_class_type";
    val UN_equiv_class_inject = thm "UN_equiv_class_inject";
    val congruent2_implies_congruent = thm "congruent2_implies_congruent";
    val congruent2_implies_congruent_UN = thm "congruent2_implies_congruent_UN";
    val congruent_commuteI = thm "congruent_commuteI";
    val UN_equiv_class2 = thm "UN_equiv_class2";
    val UN_equiv_class_type2 = thm "UN_equiv_class_type2";
    val congruent2I = thm "congruent2I";
    val congruent2_commuteI = thm "congruent2_commuteI";
    val congruent_commuteI = thm "congruent_commuteI";
    *}

    end

### Suppes, Theorem 70: @{term r} is an equiv relation iff @{term "converse(r) O r = r"}

lemma sym_trans_comp_subset:

      [| sym(r); trans(r) |] ==> converse(r) O r ⊆ r

lemma refl_comp_subset:

      [| refl(A, r); r ⊆ A × A |] ==> r ⊆ converse(r) O r

lemma equiv_comp_eq:

      equiv(A, r) ==> converse(r) O r = r

lemma comp_equivI:

      [| converse(r) O r = r; domain(r) = A |] ==> equiv(A, r)

lemma equiv_class_subset:

      [| sym(r); trans(r); ⟨a, b⟩ ∈ r |] ==> r `` {a} ⊆ r `` {b}

lemma equiv_class_eq:

      [| equiv(A, r); ⟨a, b⟩ ∈ r |] ==> r `` {a} = r `` {b}

lemma equiv_class_self:

      [| equiv(A, r); a ∈ A |] ==> a ∈ r `` {a}

lemma subset_equiv_class:

      [| equiv(A, r); r `` {b} ⊆ r `` {a}; b ∈ A |] ==> ⟨a, b⟩ ∈ r

lemma eq_equiv_class:

      [| r `` {a} = r `` {b}; equiv(A, r); b ∈ A |] ==> ⟨a, b⟩ ∈ r

lemma equiv_class_nondisjoint:

      [| equiv(A, r); x ∈ r `` {a} ∩ r `` {b} |] ==> ⟨a, b⟩ ∈ r

lemma equiv_type:

      equiv(A, r) ==> r ⊆ A × A

lemma equiv_class_eq_iff:

      equiv(A, r) ==> ⟨x, y⟩ ∈ r <-> r `` {x} = r `` {y} ∧ x ∈ A ∧ y ∈ A

lemma eq_equiv_class_iff:

      [| equiv(A, r); x ∈ A; y ∈ A |] ==> r `` {x} = r `` {y} <-> ⟨x, y⟩ ∈ r

lemma quotientI:

      x ∈ A ==> r `` {x} ∈ A // r

lemma quotientE:

      [| X ∈ A // r; !!x. [| X = r `` {x}; x ∈ A |] ==> P |] ==> P

lemma Union_quotient:

      equiv(A, r) ==> \<Union>A // r = A

lemma quotient_disj:

      [| equiv(A, r); X ∈ A // r; Y ∈ A // r |] ==> X = Y ∨ X ∩ Y ⊆ 0

### Defining Unary Operations upon Equivalence Classes

lemma UN_equiv_class:

      [| equiv(A, r); b respects r; a ∈ A |] ==> (\<Union>x∈r `` {a}. b(x)) = b(a)

lemma UN_equiv_class_type:

      [| equiv(A, r); b respects r; X ∈ A // r; !!x. x ∈ A ==> b(x) ∈ B |]
      ==> (\<Union>x∈X. b(x)) ∈ B

lemma UN_equiv_class_inject:

      [| equiv(A, r); b respects r; (\<Union>x∈X. b(x)) = (\<Union>y∈Y. b(y));
         X ∈ A // r; Y ∈ A // r;
         !!x y. [| x ∈ A; y ∈ A; b(x) = b(y) |] ==> ⟨x, y⟩ ∈ r |]
      ==> X = Y

### Defining Binary Operations upon Equivalence Classes

lemma congruent2_implies_congruent:

      [| equiv(A, r1.0); congruent2(r1.0, r2.0, b); a ∈ A |] ==> b(a) respects r2.0

lemma congruent2_implies_congruent_UN:

      [| equiv(A1.0, r1.0); equiv(A2.0, r2.0); congruent2(r1.0, r2.0, b); a ∈ A2.0 |]
      ==> (%x1. \<Union>x2∈r2.0 `` {a}. b(x1, x2)) respects r1.0

lemma UN_equiv_class2:

      [| equiv(A1.0, r1.0); equiv(A2.0, r2.0); congruent2(r1.0, r2.0, b); a1.0 ∈ A1.0;
         a2.0 ∈ A2.0 |]
      ==> (\<Union>x1∈r1.0 `` {a1.0}. \<Union>x2∈r2.0 `` {a2.0}. b(x1, x2)) =
          b(a1.0, a2.0)

lemma UN_equiv_class_type2:

      [| equiv(A, r); congruent2(r, r, b); X1.0 ∈ A // r; X2.0 ∈ A // r;
         !!x1 x2. [| x1 ∈ A; x2 ∈ A |] ==> b(x1, x2) ∈ B |]
      ==> (\<Union>x1∈X1.0. \<Union>x2∈X2.0. b(x1, x2)) ∈ B

lemma congruent2I:

      [| equiv(A1.0, r1.0); equiv(A2.0, r2.0);
         !!y z w. [| w ∈ A2.0; ⟨y, z⟩ ∈ r1.0 |] ==> b(y, w) = b(z, w);
         !!y z w. [| w ∈ A1.0; ⟨y, z⟩ ∈ r2.0 |] ==> b(w, y) = b(w, z) |]
      ==> congruent2(r1.0, r2.0, b)

lemma congruent2_commuteI:

      [| equiv(A, r); !!y z. [| y ∈ A; z ∈ A |] ==> b(y, z) = b(z, y);
         !!y z w. [| w ∈ A; ⟨y, z⟩ ∈ r |] ==> b(w, y) = b(w, z) |]
      ==> congruent2(r, r, b)

lemma congruent_commuteI:

      [| equiv(A, r); Z ∈ A // r; !!w. w ∈ A ==> (%z. b(w, z)) respects r;
         !!x y. [| x ∈ A; y ∈ A |] ==> b(y, x) = b(x, y) |]
      ==> (%w. \<Union>z∈Z. b(w, z)) respects r