Theory Relative

(*  Title:      ZF/Constructible/Relative.thy
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
                With modifications by E. Gunther, M. Pagano, 
                and P. Sánchez Terraf
*)

section ‹Relativization and Absoluteness›

theory Relative imports ZF begin

subsection‹Relativized versions of standard set-theoretic concepts›

definition
  empty :: "[i⇒o,i] ⇒ o" where
    "empty(M,z) ≡ ∀x[M]. x ∉ z"

definition
  subset :: "[i⇒o,i,i] ⇒ o" where
    "subset(M,A,B) ≡ ∀x[M]. x∈A ⟶ x ∈ B"

definition
  upair :: "[i⇒o,i,i,i] ⇒ o" where
    "upair(M,a,b,z) ≡ a ∈ z ∧ b ∈ z ∧ (∀x[M]. x∈z ⟶ x = a ∨ x = b)"

definition
  pair :: "[i⇒o,i,i,i] ⇒ o" where
    "pair(M,a,b,z) ≡ ∃x[M]. upair(M,a,a,x) ∧
                     (∃y[M]. upair(M,a,b,y) ∧ upair(M,x,y,z))"


definition
  union :: "[i⇒o,i,i,i] ⇒ o" where
    "union(M,a,b,z) ≡ ∀x[M]. x ∈ z ⟷ x ∈ a ∨ x ∈ b"

definition
  is_cons :: "[i⇒o,i,i,i] ⇒ o" where
    "is_cons(M,a,b,z) ≡ ∃x[M]. upair(M,a,a,x) ∧ union(M,x,b,z)"

definition
  successor :: "[i⇒o,i,i] ⇒ o" where
    "successor(M,a,z) ≡ is_cons(M,a,a,z)"

definition
  number1 :: "[i⇒o,i] ⇒ o" where
    "number1(M,a) ≡ ∃x[M]. empty(M,x) ∧ successor(M,x,a)"

definition
  number2 :: "[i⇒o,i] ⇒ o" where
    "number2(M,a) ≡ ∃x[M]. number1(M,x) ∧ successor(M,x,a)"

definition
  number3 :: "[i⇒o,i] ⇒ o" where
    "number3(M,a) ≡ ∃x[M]. number2(M,x) ∧ successor(M,x,a)"

definition
  powerset :: "[i⇒o,i,i] ⇒ o" where
    "powerset(M,A,z) ≡ ∀x[M]. x ∈ z ⟷ subset(M,x,A)"

definition
  is_Collect :: "[i⇒o,i,i⇒o,i] ⇒ o" where
    "is_Collect(M,A,P,z) ≡ ∀x[M]. x ∈ z ⟷ x ∈ A ∧ P(x)"

definition
  is_Replace :: "[i⇒o,i,[i,i]⇒o,i] ⇒ o" where
    "is_Replace(M,A,P,z) ≡ ∀u[M]. u ∈ z ⟷ (∃x[M]. x∈A ∧ P(x,u))"

definition
  inter :: "[i⇒o,i,i,i] ⇒ o" where
    "inter(M,a,b,z) ≡ ∀x[M]. x ∈ z ⟷ x ∈ a ∧ x ∈ b"

definition
  setdiff :: "[i⇒o,i,i,i] ⇒ o" where
    "setdiff(M,a,b,z) ≡ ∀x[M]. x ∈ z ⟷ x ∈ a ∧ x ∉ b"

definition
  big_union :: "[i⇒o,i,i] ⇒ o" where
    "big_union(M,A,z) ≡ ∀x[M]. x ∈ z ⟷ (∃y[M]. y∈A ∧ x ∈ y)"

definition
  big_inter :: "[i⇒o,i,i] ⇒ o" where
    "big_inter(M,A,z) ≡
             (A=0 ⟶ z=0) ∧
             (A≠0 ⟶ (∀x[M]. x ∈ z ⟷ (∀y[M]. y∈A ⟶ x ∈ y)))"

definition
  cartprod :: "[i⇒o,i,i,i] ⇒ o" where
    "cartprod(M,A,B,z) ≡
        ∀u[M]. u ∈ z ⟷ (∃x[M]. x∈A ∧ (∃y[M]. y∈B ∧ pair(M,x,y,u)))"

definition
  is_sum :: "[i⇒o,i,i,i] ⇒ o" where
    "is_sum(M,A,B,Z) ≡
       ∃A0[M]. ∃n1[M]. ∃s1[M]. ∃B1[M].
       number1(M,n1) ∧ cartprod(M,n1,A,A0) ∧ upair(M,n1,n1,s1) ∧
       cartprod(M,s1,B,B1) ∧ union(M,A0,B1,Z)"

definition
  is_Inl :: "[i⇒o,i,i] ⇒ o" where
    "is_Inl(M,a,z) ≡ ∃zero[M]. empty(M,zero) ∧ pair(M,zero,a,z)"

definition
  is_Inr :: "[i⇒o,i,i] ⇒ o" where
    "is_Inr(M,a,z) ≡ ∃n1[M]. number1(M,n1) ∧ pair(M,n1,a,z)"

definition
  is_converse :: "[i⇒o,i,i] ⇒ o" where
    "is_converse(M,r,z) ≡
        ∀x[M]. x ∈ z ⟷
             (∃w[M]. w∈r ∧ (∃u[M]. ∃v[M]. pair(M,u,v,w) ∧ pair(M,v,u,x)))"

definition
  pre_image :: "[i⇒o,i,i,i] ⇒ o" where
    "pre_image(M,r,A,z) ≡
        ∀x[M]. x ∈ z ⟷ (∃w[M]. w∈r ∧ (∃y[M]. y∈A ∧ pair(M,x,y,w)))"

definition
  is_domain :: "[i⇒o,i,i] ⇒ o" where
    "is_domain(M,r,z) ≡
        ∀x[M]. x ∈ z ⟷ (∃w[M]. w∈r ∧ (∃y[M]. pair(M,x,y,w)))"

definition
  image :: "[i⇒o,i,i,i] ⇒ o" where
    "image(M,r,A,z) ≡
        ∀y[M]. y ∈ z ⟷ (∃w[M]. w∈r ∧ (∃x[M]. x∈A ∧ pair(M,x,y,w)))"

definition
  is_range :: "[i⇒o,i,i] ⇒ o" where
    ― ‹the cleaner
      \<^term>‹∃r'[M]. is_converse(M,r,r') ∧ is_domain(M,r',z)›
      unfortunately needs an instance of separation in order to prove
        \<^term>‹M(converse(r))›.›
    "is_range(M,r,z) ≡
        ∀y[M]. y ∈ z ⟷ (∃w[M]. w∈r ∧ (∃x[M]. pair(M,x,y,w)))"

definition
  is_field :: "[i⇒o,i,i] ⇒ o" where
    "is_field(M,r,z) ≡
        ∃dr[M]. ∃rr[M]. is_domain(M,r,dr) ∧ is_range(M,r,rr) ∧
                        union(M,dr,rr,z)"

definition
  is_relation :: "[i⇒o,i] ⇒ o" where
    "is_relation(M,r) ≡
        (∀z[M]. z∈r ⟶ (∃x[M]. ∃y[M]. pair(M,x,y,z)))"

definition
  is_function :: "[i⇒o,i] ⇒ o" where
    "is_function(M,r) ≡
        ∀x[M]. ∀y[M]. ∀y'[M]. ∀p[M]. ∀p'[M].
           pair(M,x,y,p) ⟶ pair(M,x,y',p') ⟶ p∈r ⟶ p'∈r ⟶ y=y'"

definition
  fun_apply :: "[i⇒o,i,i,i] ⇒ o" where
    "fun_apply(M,f,x,y) ≡
        (∃xs[M]. ∃fxs[M].
         upair(M,x,x,xs) ∧ image(M,f,xs,fxs) ∧ big_union(M,fxs,y))"

definition
  typed_function :: "[i⇒o,i,i,i] ⇒ o" where
    "typed_function(M,A,B,r) ≡
        is_function(M,r) ∧ is_relation(M,r) ∧ is_domain(M,r,A) ∧
        (∀u[M]. u∈r ⟶ (∀x[M]. ∀y[M]. pair(M,x,y,u) ⟶ y∈B))"

definition
  is_funspace :: "[i⇒o,i,i,i] ⇒ o" where
    "is_funspace(M,A,B,F) ≡
        ∀f[M]. f ∈ F ⟷ typed_function(M,A,B,f)"

definition
  composition :: "[i⇒o,i,i,i] ⇒ o" where
    "composition(M,r,s,t) ≡
        ∀p[M]. p ∈ t ⟷
               (∃x[M]. ∃y[M]. ∃z[M]. ∃xy[M]. ∃yz[M].
                pair(M,x,z,p) ∧ pair(M,x,y,xy) ∧ pair(M,y,z,yz) ∧
                xy ∈ s ∧ yz ∈ r)"

definition
  injection :: "[i⇒o,i,i,i] ⇒ o" where
    "injection(M,A,B,f) ≡
        typed_function(M,A,B,f) ∧
        (∀x[M]. ∀x'[M]. ∀y[M]. ∀p[M]. ∀p'[M].
          pair(M,x,y,p) ⟶ pair(M,x',y,p') ⟶ p∈f ⟶ p'∈f ⟶ x=x')"

definition
  surjection :: "[i⇒o,i,i,i] ⇒ o" where
    "surjection(M,A,B,f) ≡
        typed_function(M,A,B,f) ∧
        (∀y[M]. y∈B ⟶ (∃x[M]. x∈A ∧ fun_apply(M,f,x,y)))"

definition
  bijection :: "[i⇒o,i,i,i] ⇒ o" where
    "bijection(M,A,B,f) ≡ injection(M,A,B,f) ∧ surjection(M,A,B,f)"

definition
  restriction :: "[i⇒o,i,i,i] ⇒ o" where
    "restriction(M,r,A,z) ≡
        ∀x[M]. x ∈ z ⟷ (x ∈ r ∧ (∃u[M]. u∈A ∧ (∃v[M]. pair(M,u,v,x))))"

definition
  transitive_set :: "[i⇒o,i] ⇒ o" where
    "transitive_set(M,a) ≡ ∀x[M]. x∈a ⟶ subset(M,x,a)"

definition
  ordinal :: "[i⇒o,i] ⇒ o" where
     ― ‹an ordinal is a transitive set of transitive sets›
    "ordinal(M,a) ≡ transitive_set(M,a) ∧ (∀x[M]. x∈a ⟶ transitive_set(M,x))"

definition
  limit_ordinal :: "[i⇒o,i] ⇒ o" where
    ― ‹a limit ordinal is a non-empty, successor-closed ordinal›
    "limit_ordinal(M,a) ≡
        ordinal(M,a) ∧ ¬ empty(M,a) ∧
        (∀x[M]. x∈a ⟶ (∃y[M]. y∈a ∧ successor(M,x,y)))"

definition
  successor_ordinal :: "[i⇒o,i] ⇒ o" where
    ― ‹a successor ordinal is any ordinal that is neither empty nor limit›
    "successor_ordinal(M,a) ≡
        ordinal(M,a) ∧ ¬ empty(M,a) ∧ ¬ limit_ordinal(M,a)"

definition
  finite_ordinal :: "[i⇒o,i] ⇒ o" where
    ― ‹an ordinal is finite if neither it nor any of its elements are limit›
    "finite_ordinal(M,a) ≡
        ordinal(M,a) ∧ ¬ limit_ordinal(M,a) ∧
        (∀x[M]. x∈a ⟶ ¬ limit_ordinal(M,x))"

definition
  omega :: "[i⇒o,i] ⇒ o" where
    ― ‹omega is a limit ordinal none of whose elements are limit›
    "omega(M,a) ≡ limit_ordinal(M,a) ∧ (∀x[M]. x∈a ⟶ ¬ limit_ordinal(M,x))"

definition
  is_quasinat :: "[i⇒o,i] ⇒ o" where
    "is_quasinat(M,z) ≡ empty(M,z) ∨ (∃m[M]. successor(M,m,z))"

definition
  is_nat_case :: "[i⇒o, i, [i,i]⇒o, i, i] ⇒ o" where
    "is_nat_case(M, a, is_b, k, z) ≡
       (empty(M,k) ⟶ z=a) ∧
       (∀m[M]. successor(M,m,k) ⟶ is_b(m,z)) ∧
       (is_quasinat(M,k) ∨ empty(M,z))"

definition
  relation1 :: "[i⇒o, [i,i]⇒o, i⇒i] ⇒ o" where
    "relation1(M,is_f,f) ≡ ∀x[M]. ∀y[M]. is_f(x,y) ⟷ y = f(x)"

definition
  Relation1 :: "[i⇒o, i, [i,i]⇒o, i⇒i] ⇒ o" where
    ― ‹as above, but typed›
    "Relation1(M,A,is_f,f) ≡
        ∀x[M]. ∀y[M]. x∈A ⟶ is_f(x,y) ⟷ y = f(x)"

definition
  relation2 :: "[i⇒o, [i,i,i]⇒o, [i,i]⇒i] ⇒ o" where
    "relation2(M,is_f,f) ≡ ∀x[M]. ∀y[M]. ∀z[M]. is_f(x,y,z) ⟷ z = f(x,y)"

definition
  Relation2 :: "[i⇒o, i, i, [i,i,i]⇒o, [i,i]⇒i] ⇒ o" where
    "Relation2(M,A,B,is_f,f) ≡
        ∀x[M]. ∀y[M]. ∀z[M]. x∈A ⟶ y∈B ⟶ is_f(x,y,z) ⟷ z = f(x,y)"

definition
  relation3 :: "[i⇒o, [i,i,i,i]⇒o, [i,i,i]⇒i] ⇒ o" where
    "relation3(M,is_f,f) ≡
       ∀x[M]. ∀y[M]. ∀z[M]. ∀u[M]. is_f(x,y,z,u) ⟷ u = f(x,y,z)"

definition
  Relation3 :: "[i⇒o, i, i, i, [i,i,i,i]⇒o, [i,i,i]⇒i] ⇒ o" where
    "Relation3(M,A,B,C,is_f,f) ≡
       ∀x[M]. ∀y[M]. ∀z[M]. ∀u[M].
         x∈A ⟶ y∈B ⟶ z∈C ⟶ is_f(x,y,z,u) ⟷ u = f(x,y,z)"

definition
  relation4 :: "[i⇒o, [i,i,i,i,i]⇒o, [i,i,i,i]⇒i] ⇒ o" where
    "relation4(M,is_f,f) ≡
       ∀u[M]. ∀x[M]. ∀y[M]. ∀z[M]. ∀a[M]. is_f(u,x,y,z,a) ⟷ a = f(u,x,y,z)"


text‹Useful when absoluteness reasoning has replaced the predicates by terms›
lemma triv_Relation1:
     "Relation1(M, A, λx y. y = f(x), f)"
by (simp add: Relation1_def)

lemma triv_Relation2:
     "Relation2(M, A, B, λx y a. a = f(x,y), f)"
by (simp add: Relation2_def)


subsection ‹The relativized ZF axioms›

definition
  extensionality :: "(i⇒o) ⇒ o" where
    "extensionality(M) ≡
        ∀x[M]. ∀y[M]. (∀z[M]. z ∈ x ⟷ z ∈ y) ⟶ x=y"

definition
  separation :: "[i⇒o, i⇒o] ⇒ o" where
    ― ‹The formula ‹P› should only involve parameters
        belonging to ‹M› and all its quantifiers must be relativized
        to ‹M›.  We do not have separation as a scheme; every instance
        that we need must be assumed (and later proved) separately.›
    "separation(M,P) ≡
        ∀z[M]. ∃y[M]. ∀x[M]. x ∈ y ⟷ x ∈ z ∧ P(x)"

definition
  upair_ax :: "(i⇒o) ⇒ o" where
    "upair_ax(M) ≡ ∀x[M]. ∀y[M]. ∃z[M]. upair(M,x,y,z)"

definition
  Union_ax :: "(i⇒o) ⇒ o" where
    "Union_ax(M) ≡ ∀x[M]. ∃z[M]. big_union(M,x,z)"

definition
  power_ax :: "(i⇒o) ⇒ o" where
    "power_ax(M) ≡ ∀x[M]. ∃z[M]. powerset(M,x,z)"

definition
  univalent :: "[i⇒o, i, [i,i]⇒o] ⇒ o" where
    "univalent(M,A,P) ≡
        ∀x[M]. x∈A ⟶ (∀y[M]. ∀z[M]. P(x,y) ∧ P(x,z) ⟶ y=z)"

definition
  replacement :: "[i⇒o, [i,i]⇒o] ⇒ o" where
    "replacement(M,P) ≡
      ∀A[M]. univalent(M,A,P) ⟶
      (∃Y[M]. ∀b[M]. (∃x[M]. x∈A ∧ P(x,b)) ⟶ b ∈ Y)"

definition
  strong_replacement :: "[i⇒o, [i,i]⇒o] ⇒ o" where
    "strong_replacement(M,P) ≡
      ∀A[M]. univalent(M,A,P) ⟶
      (∃Y[M]. ∀b[M]. b ∈ Y ⟷ (∃x[M]. x∈A ∧ P(x,b)))"

definition
  foundation_ax :: "(i⇒o) ⇒ o" where
    "foundation_ax(M) ≡
        ∀x[M]. (∃y[M]. y∈x) ⟶ (∃y[M]. y∈x ∧ ¬(∃z[M]. z∈x ∧ z ∈ y))"


subsection‹A trivial consistency proof for $V_\omega$›

text‹We prove that $V_\omega$
      (or ‹univ› in Isabelle) satisfies some ZF axioms.
     Kunen, Theorem IV 3.13, page 123.›

lemma univ0_downwards_mem: "⟦y ∈ x; x ∈ univ(0)⟧ ⟹ y ∈ univ(0)"
apply (insert Transset_univ [OF Transset_0])
apply (simp add: Transset_def, blast)
done

lemma univ0_Ball_abs [simp]:
     "A ∈ univ(0) ⟹ (∀x∈A. x ∈ univ(0) ⟶ P(x)) ⟷ (∀x∈A. P(x))"
by (blast intro: univ0_downwards_mem)

lemma univ0_Bex_abs [simp]:
     "A ∈ univ(0) ⟹ (∃x∈A. x ∈ univ(0) ∧ P(x)) ⟷ (∃x∈A. P(x))"
by (blast intro: univ0_downwards_mem)

text‹Congruence rule for separation: can assume the variable is in ‹M››
lemma separation_cong [cong]:
     "(⋀x. M(x) ⟹ P(x) ⟷ P'(x))
      ⟹ separation(M, λx. P(x)) ⟷ separation(M, λx. P'(x))"
by (simp add: separation_def)

lemma univalent_cong [cong]:
     "⟦A=A'; ⋀x y. ⟦x∈A; M(x); M(y)⟧ ⟹ P(x,y) ⟷ P'(x,y)⟧
      ⟹ univalent(M, A, λx y. P(x,y)) ⟷ univalent(M, A', λx y. P'(x,y))"
by (simp add: univalent_def)

lemma univalent_triv [intro,simp]:
     "univalent(M, A, λx y. y = f(x))"
by (simp add: univalent_def)

lemma univalent_conjI2 [intro,simp]:
     "univalent(M,A,Q) ⟹ univalent(M, A, λx y. P(x,y) ∧ Q(x,y))"
by (simp add: univalent_def, blast)

text‹Congruence rule for replacement›
lemma strong_replacement_cong [cong]:
     "⟦⋀x y. ⟦M(x); M(y)⟧ ⟹ P(x,y) ⟷ P'(x,y)⟧
      ⟹ strong_replacement(M, λx y. P(x,y)) ⟷
          strong_replacement(M, λx y. P'(x,y))"
by (simp add: strong_replacement_def)

text‹The extensionality axiom›
lemma "extensionality(λx. x ∈ univ(0))"
apply (simp add: extensionality_def)
apply (blast intro: univ0_downwards_mem)
done

text‹The separation axiom requires some lemmas›
lemma Collect_in_Vfrom:
     "⟦X ∈ Vfrom(A,j);  Transset(A)⟧ ⟹ Collect(X,P) ∈ Vfrom(A, succ(j))"
apply (drule Transset_Vfrom)
apply (rule subset_mem_Vfrom)
apply (unfold Transset_def, blast)
done

lemma Collect_in_VLimit:
     "⟦X ∈ Vfrom(A,i);  Limit(i);  Transset(A)⟧
      ⟹ Collect(X,P) ∈ Vfrom(A,i)"
apply (rule Limit_VfromE, assumption+)
apply (blast intro: Limit_has_succ VfromI Collect_in_Vfrom)
done

lemma Collect_in_univ:
     "⟦X ∈ univ(A);  Transset(A)⟧ ⟹ Collect(X,P) ∈ univ(A)"
by (simp add: univ_def Collect_in_VLimit)

lemma "separation(λx. x ∈ univ(0), P)"
apply (simp add: separation_def, clarify)
apply (rule_tac x = "Collect(z,P)" in bexI)
apply (blast intro: Collect_in_univ Transset_0)+
done

text‹Unordered pairing axiom›
lemma "upair_ax(λx. x ∈ univ(0))"
apply (simp add: upair_ax_def upair_def)
apply (blast intro: doubleton_in_univ)
done

text‹Union axiom›
lemma "Union_ax(λx. x ∈ univ(0))"
apply (simp add: Union_ax_def big_union_def, clarify)
apply (rule_tac x="⋃x" in bexI)
 apply (blast intro: univ0_downwards_mem)
apply (blast intro: Union_in_univ Transset_0)
done

text‹Powerset axiom›

lemma Pow_in_univ:
     "⟦X ∈ univ(A);  Transset(A)⟧ ⟹ Pow(X) ∈ univ(A)"
apply (simp add: univ_def Pow_in_VLimit)
done

lemma "power_ax(λx. x ∈ univ(0))"
apply (simp add: power_ax_def powerset_def subset_def, clarify)
apply (rule_tac x="Pow(x)" in bexI)
 apply (blast intro: univ0_downwards_mem)
apply (blast intro: Pow_in_univ Transset_0)
done

text‹Foundation axiom›
lemma "foundation_ax(λx. x ∈ univ(0))"
apply (simp add: foundation_ax_def, clarify)
apply (cut_tac A=x in foundation)
apply (blast intro: univ0_downwards_mem)
done

lemma "replacement(λx. x ∈ univ(0), P)"
apply (simp add: replacement_def, clarify)
oops
text‹no idea: maybe prove by induction on the rank of A?›

text‹Still missing: Replacement, Choice›

subsection‹Lemmas Needed to Reduce Some Set Constructions to Instances
      of Separation›

lemma image_iff_Collect: "r `` A = {y ∈ ⋃(⋃(r)). ∃p∈r. ∃x∈A. p=⟨x,y⟩}"
apply (rule equalityI, auto)
apply (simp add: Pair_def, blast)
done

lemma vimage_iff_Collect:
     "r -`` A = {x ∈ ⋃(⋃(r)). ∃p∈r. ∃y∈A. p=⟨x,y⟩}"
apply (rule equalityI, auto)
apply (simp add: Pair_def, blast)
done

text‹These two lemmas lets us prove ‹domain_closed› and
      ‹range_closed› without new instances of separation›

lemma domain_eq_vimage: "domain(r) = r -`` Union(Union(r))"
apply (rule equalityI, auto)
apply (rule vimageI, assumption)
apply (simp add: Pair_def, blast)
done

lemma range_eq_image: "range(r) = r `` Union(Union(r))"
apply (rule equalityI, auto)
apply (rule imageI, assumption)
apply (simp add: Pair_def, blast)
done

lemma replacementD:
    "⟦replacement(M,P); M(A);  univalent(M,A,P)⟧
     ⟹ ∃Y[M]. (∀b[M]. ((∃x[M]. x∈A ∧ P(x,b)) ⟶ b ∈ Y))"
by (simp add: replacement_def)

lemma strong_replacementD:
    "⟦strong_replacement(M,P); M(A);  univalent(M,A,P)⟧
     ⟹ ∃Y[M]. (∀b[M]. (b ∈ Y ⟷ (∃x[M]. x∈A ∧ P(x,b))))"
by (simp add: strong_replacement_def)

lemma separationD:
    "⟦separation(M,P); M(z)⟧ ⟹ ∃y[M]. ∀x[M]. x ∈ y ⟷ x ∈ z ∧ P(x)"
by (simp add: separation_def)


text‹More constants, for order types›

definition
  order_isomorphism :: "[i⇒o,i,i,i,i,i] ⇒ o" where
    "order_isomorphism(M,A,r,B,s,f) ≡
        bijection(M,A,B,f) ∧
        (∀x[M]. x∈A ⟶ (∀y[M]. y∈A ⟶
          (∀p[M]. ∀fx[M]. ∀fy[M]. ∀q[M].
            pair(M,x,y,p) ⟶ fun_apply(M,f,x,fx) ⟶ fun_apply(M,f,y,fy) ⟶
            pair(M,fx,fy,q) ⟶ (p∈r ⟷ q∈s))))"

definition
  pred_set :: "[i⇒o,i,i,i,i] ⇒ o" where
    "pred_set(M,A,x,r,B) ≡
        ∀y[M]. y ∈ B ⟷ (∃p[M]. p∈r ∧ y ∈ A ∧ pair(M,y,x,p))"

definition
  membership :: "[i⇒o,i,i] ⇒ o" where ― ‹membership relation›
    "membership(M,A,r) ≡
        ∀p[M]. p ∈ r ⟷ (∃x[M]. x∈A ∧ (∃y[M]. y∈A ∧ x∈y ∧ pair(M,x,y,p)))"


subsection‹Introducing a Transitive Class Model›

text‹The class M is assumed to be transitive and inhabited›
locale M_trans =
  fixes M
  assumes transM:   "⟦y∈x; M(x)⟧ ⟹ M(y)"
    and M_inhabited: "∃x . M(x)"

lemma (in M_trans) nonempty [simp]:  "M(0)"
proof -
  have "M(x) ⟶ M(0)" for x
  proof (rule_tac P="λw. M(w) ⟶ M(0)" in eps_induct)
    {
    fix x
    assume "∀y∈x. M(y) ⟶ M(0)" "M(x)"
    consider (a) "∃y. y∈x" | (b) "x=0" by auto
    then 
    have "M(x) ⟶ M(0)" 
    proof cases
      case a
      then show ?thesis using ‹∀y∈x._› ‹M(x)› transM by auto
    next
      case b
      then show ?thesis by simp
    qed
  }
  then show "M(x) ⟶ M(0)" if "∀y∈x. M(y) ⟶ M(0)" for x
    using that by auto
  qed
  with M_inhabited
  show "M(0)" using M_inhabited by blast
qed

text‹The class M is assumed to be transitive and to satisfy some
      relativized ZF axioms›
locale M_trivial = M_trans +
  assumes upair_ax:         "upair_ax(M)"
      and Union_ax:         "Union_ax(M)"

lemma (in M_trans) rall_abs [simp]:
     "M(A) ⟹ (∀x[M]. x∈A ⟶ P(x)) ⟷ (∀x∈A. P(x))"
by (blast intro: transM)

lemma (in M_trans) rex_abs [simp]:
     "M(A) ⟹ (∃x[M]. x∈A ∧ P(x)) ⟷ (∃x∈A. P(x))"
by (blast intro: transM)

lemma (in M_trans) ball_iff_equiv:
     "M(A) ⟹ (∀x[M]. (x∈A ⟷ P(x))) ⟷
               (∀x∈A. P(x)) ∧ (∀x. P(x) ⟶ M(x) ⟶ x∈A)"
by (blast intro: transM)

text‹Simplifies proofs of equalities when there's an iff-equality
      available for rewriting, universally quantified over M.
      But it's not the only way to prove such equalities: its
      premises \<^term>‹M(A)› and  \<^term>‹M(B)› can be too strong.›
lemma (in M_trans) M_equalityI:
     "⟦⋀x. M(x) ⟹ x∈A ⟷ x∈B; M(A); M(B)⟧ ⟹ A=B"
by (blast dest: transM)


subsubsection‹Trivial Absoluteness Proofs: Empty Set, Pairs, etc.›

lemma (in M_trans) empty_abs [simp]:
     "M(z) ⟹ empty(M,z) ⟷ z=0"
apply (simp add: empty_def)
apply (blast intro: transM)
done

lemma (in M_trans) subset_abs [simp]:
     "M(A) ⟹ subset(M,A,B) ⟷ A ⊆ B"
apply (simp add: subset_def)
apply (blast intro: transM)
done

lemma (in M_trans) upair_abs [simp]:
     "M(z) ⟹ upair(M,a,b,z) ⟷ z={a,b}"
apply (simp add: upair_def)
apply (blast intro: transM)
done

lemma (in M_trivial) upair_in_MI [intro!]:
     " M(a) ∧ M(b) ⟹ M({a,b})"
by (insert upair_ax, simp add: upair_ax_def)

lemma (in M_trans) upair_in_MD [dest!]:
     "M({a,b}) ⟹ M(a) ∧ M(b)"
  by (blast intro: transM)

lemma (in M_trivial) upair_in_M_iff [simp]:
  "M({a,b}) ⟷ M(a) ∧ M(b)"
  by blast

lemma (in M_trivial) singleton_in_MI [intro!]:
     "M(a) ⟹ M({a})"
  by (insert upair_in_M_iff [of a a], simp)

lemma (in M_trans) singleton_in_MD [dest!]:
     "M({a}) ⟹ M(a)"
  by (insert upair_in_MD [of a a], simp)

lemma (in M_trivial) singleton_in_M_iff [simp]:
     "M({a}) ⟷ M(a)"
  by blast

lemma (in M_trans) pair_abs [simp]:
     "M(z) ⟹ pair(M,a,b,z) ⟷ z=⟨a,b⟩"
apply (simp add: pair_def Pair_def)
apply (blast intro: transM)
done

lemma (in M_trans) pair_in_MD [dest!]:
     "M(⟨a,b⟩) ⟹ M(a) ∧ M(b)"
  by (simp add: Pair_def, blast intro: transM)

lemma (in M_trivial) pair_in_MI [intro!]:
     "M(a) ∧ M(b) ⟹ M(⟨a,b⟩)"
  by (simp add: Pair_def)

lemma (in M_trivial) pair_in_M_iff [simp]:
     "M(⟨a,b⟩) ⟷ M(a) ∧ M(b)"
  by blast

lemma (in M_trans) pair_components_in_M:
     "⟦⟨x,y⟩ ∈ A; M(A)⟧ ⟹ M(x) ∧ M(y)"
  by (blast dest: transM)

lemma (in M_trivial) cartprod_abs [simp]:
     "⟦M(A); M(B); M(z)⟧ ⟹ cartprod(M,A,B,z) ⟷ z = A*B"
apply (simp add: cartprod_def)
apply (rule iffI)
 apply (blast intro!: equalityI intro: transM dest!: rspec)
apply (blast dest: transM)
done

subsubsection‹Absoluteness for Unions and Intersections›

lemma (in M_trans) union_abs [simp]:
     "⟦M(a); M(b); M(z)⟧ ⟹ union(M,a,b,z) ⟷ z = a ∪ b"
  unfolding union_def
  by (blast intro: transM )

lemma (in M_trans) inter_abs [simp]:
     "⟦M(a); M(b); M(z)⟧ ⟹ inter(M,a,b,z) ⟷ z = a ∩ b"
  unfolding inter_def
  by (blast intro: transM)

lemma (in M_trans) setdiff_abs [simp]:
     "⟦M(a); M(b); M(z)⟧ ⟹ setdiff(M,a,b,z) ⟷ z = a-b"
  unfolding setdiff_def
  by (blast intro: transM)

lemma (in M_trans) Union_abs [simp]:
     "⟦M(A); M(z)⟧ ⟹ big_union(M,A,z) ⟷ z = ⋃(A)"
  unfolding big_union_def
  by (blast  dest: transM)

lemma (in M_trivial) Union_closed [intro,simp]:
     "M(A) ⟹ M(⋃(A))"
by (insert Union_ax, simp add: Union_ax_def)

lemma (in M_trivial) Un_closed [intro,simp]:
     "⟦M(A); M(B)⟧ ⟹ M(A ∪ B)"
by (simp only: Un_eq_Union, blast)

lemma (in M_trivial) cons_closed [intro,simp]:
     "⟦M(a); M(A)⟧ ⟹ M(cons(a,A))"
by (subst cons_eq [symmetric], blast)

lemma (in M_trivial) cons_abs [simp]:
     "⟦M(b); M(z)⟧ ⟹ is_cons(M,a,b,z) ⟷ z = cons(a,b)"
by (simp add: is_cons_def, blast intro: transM)

lemma (in M_trivial) successor_abs [simp]:
     "⟦M(a); M(z)⟧ ⟹ successor(M,a,z) ⟷ z = succ(a)"
by (simp add: successor_def, blast)

lemma (in M_trans) succ_in_MD [dest!]:
     "M(succ(a)) ⟹ M(a)"
  unfolding succ_def
  by (blast intro: transM)

lemma (in M_trivial) succ_in_MI [intro!]:
     "M(a) ⟹ M(succ(a))"
  unfolding succ_def
  by (blast intro: transM)

lemma (in M_trivial) succ_in_M_iff [simp]:
     "M(succ(a)) ⟷ M(a)"
  by blast

subsubsection‹Absoluteness for Separation and Replacement›

lemma (in M_trans) separation_closed [intro,simp]:
     "⟦separation(M,P); M(A)⟧ ⟹ M(Collect(A,P))"
apply (insert separation, simp add: separation_def)
apply (drule rspec, assumption, clarify)
apply (subgoal_tac "y = Collect(A,P)", blast)
apply (blast dest: transM)
done

lemma separation_iff:
     "separation(M,P) ⟷ (∀z[M]. ∃y[M]. is_Collect(M,z,P,y))"
by (simp add: separation_def is_Collect_def)

lemma (in M_trans) Collect_abs [simp]:
     "⟦M(A); M(z)⟧ ⟹ is_Collect(M,A,P,z) ⟷ z = Collect(A,P)"
  unfolding is_Collect_def
  by (blast dest: transM)

subsubsection‹The Operator \<^term>‹is_Replace››


lemma is_Replace_cong [cong]:
     "⟦A=A';
         ⋀x y. ⟦M(x); M(y)⟧ ⟹ P(x,y) ⟷ P'(x,y);
         z=z'⟧
      ⟹ is_Replace(M, A, λx y. P(x,y), z) ⟷
          is_Replace(M, A', λx y. P'(x,y), z')"
by (simp add: is_Replace_def)

lemma (in M_trans) univalent_Replace_iff:
     "⟦M(A); univalent(M,A,P);
         ⋀x y. ⟦x∈A; P(x,y)⟧ ⟹ M(y)⟧
      ⟹ u ∈ Replace(A,P) ⟷ (∃x. x∈A ∧ P(x,u))"
  unfolding Replace_iff univalent_def
  by (blast dest: transM)

(*The last premise expresses that P takes M to M*)
lemma (in M_trans) strong_replacement_closed [intro,simp]:
     "⟦strong_replacement(M,P); M(A); univalent(M,A,P);
         ⋀x y. ⟦x∈A; P(x,y)⟧ ⟹ M(y)⟧ ⟹ M(Replace(A,P))"
apply (simp add: strong_replacement_def)
apply (drule_tac x=A in rspec, safe)
apply (subgoal_tac "Replace(A,P) = Y")
 apply simp
apply (rule equality_iffI)
apply (simp add: univalent_Replace_iff)
apply (blast dest: transM)
done

lemma (in M_trans) Replace_abs:
     "⟦M(A); M(z); univalent(M,A,P);
         ⋀x y. ⟦x∈A; P(x,y)⟧ ⟹ M(y)⟧
      ⟹ is_Replace(M,A,P,z) ⟷ z = Replace(A,P)"
apply (simp add: is_Replace_def)
apply (rule iffI)
 apply (rule equality_iffI)
 apply (simp_all add: univalent_Replace_iff)
 apply (blast dest: transM)+
done


(*The first premise can't simply be assumed as a schema.
  It is essential to take care when asserting instances of Replacement.
  Let K be a nonconstructible subset of nat and define
  f(x) = x if x ∈ K and f(x)=0 otherwise.  Then RepFun(nat,f) = cons(0,K), a
  nonconstructible set.  So we cannot assume that M(X) implies M(RepFun(X,f))
  even for f ∈ M -> M.
*)
lemma (in M_trans) RepFun_closed:
     "⟦strong_replacement(M, λx y. y = f(x)); M(A); ∀x∈A. M(f(x))⟧
      ⟹ M(RepFun(A,f))"
apply (simp add: RepFun_def)
done

lemma Replace_conj_eq: "{y . x ∈ A, x∈A ∧ y=f(x)} = {y . x∈A, y=f(x)}"
by simp

text‹Better than ‹RepFun_closed› when having the formula \<^term>‹x∈A›
      makes relativization easier.›
lemma (in M_trans) RepFun_closed2:
     "⟦strong_replacement(M, λx y. x∈A ∧ y = f(x)); M(A); ∀x∈A. M(f(x))⟧
      ⟹ M(RepFun(A, λx. f(x)))"
apply (simp add: RepFun_def)
apply (frule strong_replacement_closed, assumption)
apply (auto dest: transM  simp add: Replace_conj_eq univalent_def)
done

subsubsection ‹Absoluteness for \<^term>‹Lambda››

definition
 is_lambda :: "[i⇒o, i, [i,i]⇒o, i] ⇒ o" where
    "is_lambda(M, A, is_b, z) ≡
       ∀p[M]. p ∈ z ⟷
        (∃u[M]. ∃v[M]. u∈A ∧ pair(M,u,v,p) ∧ is_b(u,v))"

lemma (in M_trivial) lam_closed:
     "⟦strong_replacement(M, λx y. y = <x,b(x)>); M(A); ∀x∈A. M(b(x))⟧
      ⟹ M(λx∈A. b(x))"
by (simp add: lam_def, blast intro: RepFun_closed dest: transM)

text‹Better than ‹lam_closed›: has the formula \<^term>‹x∈A››
lemma (in M_trivial) lam_closed2:
  "⟦strong_replacement(M, λx y. x∈A ∧ y = ⟨x, b(x)⟩);
     M(A); ∀m[M]. m∈A ⟶ M(b(m))⟧ ⟹ M(Lambda(A,b))"
apply (simp add: lam_def)
apply (blast intro: RepFun_closed2 dest: transM)
done

lemma (in M_trivial) lambda_abs2:
     "⟦Relation1(M,A,is_b,b); M(A); ∀m[M]. m∈A ⟶ M(b(m)); M(z)⟧
      ⟹ is_lambda(M,A,is_b,z) ⟷ z = Lambda(A,b)"
apply (simp add: Relation1_def is_lambda_def)
apply (rule iffI)
 prefer 2 apply (simp add: lam_def)
apply (rule equality_iffI)
apply (simp add: lam_def)
apply (rule iffI)
 apply (blast dest: transM)
apply (auto simp add: transM [of _ A])
done

lemma is_lambda_cong [cong]:
     "⟦A=A';  z=z';
         ⋀x y. ⟦x∈A; M(x); M(y)⟧ ⟹ is_b(x,y) ⟷ is_b'(x,y)⟧
      ⟹ is_lambda(M, A, λx y. is_b(x,y), z) ⟷
          is_lambda(M, A', λx y. is_b'(x,y), z')"
by (simp add: is_lambda_def)

lemma (in M_trans) image_abs [simp]:
     "⟦M(r); M(A); M(z)⟧ ⟹ image(M,r,A,z) ⟷ z = r``A"
apply (simp add: image_def)
apply (rule iffI)
 apply (blast intro!: equalityI dest: transM, blast)
done

subsubsection‹Relativization of Powerset›

text‹What about ‹Pow_abs›?  Powerset is NOT absolute!
      This result is one direction of absoluteness.›

lemma (in M_trans) powerset_Pow:
     "powerset(M, x, Pow(x))"
by (simp add: powerset_def)

text‹But we can't prove that the powerset in ‹M› includes the
      real powerset.›

lemma (in M_trans) powerset_imp_subset_Pow:
     "⟦powerset(M,x,y); M(y)⟧ ⟹ y ⊆ Pow(x)"
apply (simp add: powerset_def)
apply (blast dest: transM)
done

lemma (in M_trans) powerset_abs:
  assumes
     "M(y)"
  shows
    "powerset(M,x,y) ⟷ y = {a∈Pow(x) . M(a)}"
proof (intro iffI equalityI)
  (* First show the converse implication by double inclusion *)
  assume "powerset(M,x,y)"
  with ‹M(y)›  
  show "y ⊆ {a∈Pow(x) . M(a)}"
    using powerset_imp_subset_Pow transM by blast
  from ‹powerset(M,x,y)›
  show "{a∈Pow(x) . M(a)} ⊆ y"
    using transM unfolding powerset_def by auto
next (* we show the direct implication *)
  assume
    "y = {a ∈ Pow(x) . M(a)}"
  then
  show "powerset(M, x, y)"
    unfolding powerset_def subset_def using transM by blast
qed

subsubsection‹Absoluteness for the Natural Numbers›

lemma (in M_trivial) nat_into_M [intro]:
     "n ∈ nat ⟹ M(n)"
by (induct n rule: nat_induct, simp_all)

lemma (in M_trans) nat_case_closed [intro,simp]:
  "⟦M(k); M(a); ∀m[M]. M(b(m))⟧ ⟹ M(nat_case(a,b,k))"
apply (case_tac "k=0", simp)
apply (case_tac "∃m. k = succ(m)", force)
apply (simp add: nat_case_def)
done

lemma (in M_trivial) quasinat_abs [simp]:
     "M(z) ⟹ is_quasinat(M,z) ⟷ quasinat(z)"
by (auto simp add: is_quasinat_def quasinat_def)

lemma (in M_trivial) nat_case_abs [simp]:
     "⟦relation1(M,is_b,b); M(k); M(z)⟧
      ⟹ is_nat_case(M,a,is_b,k,z) ⟷ z = nat_case(a,b,k)"
apply (case_tac "quasinat(k)")
 prefer 2
 apply (simp add: is_nat_case_def non_nat_case)
 apply (force simp add: quasinat_def)
apply (simp add: quasinat_def is_nat_case_def)
apply (elim disjE exE)
 apply (simp_all add: relation1_def)
done

(*NOT for the simplifier.  The assumption M(z') is apparently necessary, but
  causes the error "Failed congruence proof!"  It may be better to replace
  is_nat_case by nat_case before attempting congruence reasoning.*)
lemma is_nat_case_cong:
     "⟦a = a'; k = k';  z = z';  M(z');
       ⋀x y. ⟦M(x); M(y)⟧ ⟹ is_b(x,y) ⟷ is_b'(x,y)⟧
      ⟹ is_nat_case(M, a, is_b, k, z) ⟷ is_nat_case(M, a', is_b', k', z')"
by (simp add: is_nat_case_def)


subsection‹Absoluteness for Ordinals›
text‹These results constitute Theorem IV 5.1 of Kunen (page 126).›

lemma (in M_trans) lt_closed:
     "⟦j<i; M(i)⟧ ⟹ M(j)"
by (blast dest: ltD intro: transM)

lemma (in M_trans) transitive_set_abs [simp]:
     "M(a) ⟹ transitive_set(M,a) ⟷ Transset(a)"
by (simp add: transitive_set_def Transset_def)

lemma (in M_trans) ordinal_abs [simp]:
     "M(a) ⟹ ordinal(M,a) ⟷ Ord(a)"
by (simp add: ordinal_def Ord_def)

lemma (in M_trivial) limit_ordinal_abs [simp]:
     "M(a) ⟹ limit_ordinal(M,a) ⟷ Limit(a)"
  unfolding Limit_def limit_ordinal_def
apply (simp add: Ord_0_lt_iff)
apply (simp add: lt_def, blast)
done

lemma (in M_trivial) successor_ordinal_abs [simp]:
     "M(a) ⟹ successor_ordinal(M,a) ⟷ Ord(a) ∧ (∃b[M]. a = succ(b))"
apply (simp add: successor_ordinal_def, safe)
apply (drule Ord_cases_disj, auto)
done

lemma finite_Ord_is_nat:
      "⟦Ord(a); ¬ Limit(a); ∀x∈a. ¬ Limit(x)⟧ ⟹ a ∈ nat"
by (induct a rule: trans_induct3, simp_all)

lemma (in M_trivial) finite_ordinal_abs [simp]:
     "M(a) ⟹ finite_ordinal(M,a) ⟷ a ∈ nat"
apply (simp add: finite_ordinal_def)
apply (blast intro: finite_Ord_is_nat intro: nat_into_Ord
             dest: Ord_trans naturals_not_limit)
done

lemma Limit_non_Limit_implies_nat:
     "⟦Limit(a); ∀x∈a. ¬ Limit(x)⟧ ⟹ a = nat"
apply (rule le_anti_sym)
apply (rule all_lt_imp_le, blast, blast intro: Limit_is_Ord)
 apply (simp add: lt_def)
 apply (blast intro: Ord_in_Ord Ord_trans finite_Ord_is_nat)
apply (erule nat_le_Limit)
done

lemma (in M_trivial) omega_abs [simp]:
     "M(a) ⟹ omega(M,a) ⟷ a = nat"
apply (simp add: omega_def)
apply (blast intro: Limit_non_Limit_implies_nat dest: naturals_not_limit)
done

lemma (in M_trivial) number1_abs [simp]:
     "M(a) ⟹ number1(M,a) ⟷ a = 1"
by (simp add: number1_def)

lemma (in M_trivial) number2_abs [simp]:
     "M(a) ⟹ number2(M,a) ⟷ a = succ(1)"
by (simp add: number2_def)

lemma (in M_trivial) number3_abs [simp]:
     "M(a) ⟹ number3(M,a) ⟷ a = succ(succ(1))"
by (simp add: number3_def)

text‹Kunen continued to 20...›

(*Could not get this to work.  The λx∈nat is essential because everything
  but the recursion variable must stay unchanged.  But then the recursion
  equations only hold for x∈nat (or in some other set) and not for the
  whole of the class M.
  consts
    natnumber_aux :: "[i⇒o,i] ⇒ i"

  primrec
      "natnumber_aux(M,0) = (λx∈nat. if empty(M,x) then 1 else 0)"
      "natnumber_aux(M,succ(n)) =
           (λx∈nat. if (∃y[M]. natnumber_aux(M,n)`y=1 ∧ successor(M,y,x))
                     then 1 else 0)"

  definition
    natnumber :: "[i⇒o,i,i] ⇒ o"
      "natnumber(M,n,x) ≡ natnumber_aux(M,n)`x = 1"

  lemma (in M_trivial) [simp]:
       "natnumber(M,0,x) ≡ x=0"
*)

subsection‹Some instances of separation and strong replacement›

locale M_basic = M_trivial +
assumes Inter_separation:
     "M(A) ⟹ separation(M, λx. ∀y[M]. y∈A ⟶ x∈y)"
  and Diff_separation:
     "M(B) ⟹ separation(M, λx. x ∉ B)"
  and cartprod_separation:
     "⟦M(A); M(B)⟧
      ⟹ separation(M, λz. ∃x[M]. x∈A ∧ (∃y[M]. y∈B ∧ pair(M,x,y,z)))"
  and image_separation:
     "⟦M(A); M(r)⟧
      ⟹ separation(M, λy. ∃p[M]. p∈r ∧ (∃x[M]. x∈A ∧ pair(M,x,y,p)))"
  and converse_separation:
     "M(r) ⟹ separation(M,
         λz. ∃p[M]. p∈r ∧ (∃x[M]. ∃y[M]. pair(M,x,y,p) ∧ pair(M,y,x,z)))"
  and restrict_separation:
     "M(A) ⟹ separation(M, λz. ∃x[M]. x∈A ∧ (∃y[M]. pair(M,x,y,z)))"
  and comp_separation:
     "⟦M(r); M(s)⟧
      ⟹ separation(M, λxz. ∃x[M]. ∃y[M]. ∃z[M]. ∃xy[M]. ∃yz[M].
                  pair(M,x,z,xz) ∧ pair(M,x,y,xy) ∧ pair(M,y,z,yz) ∧
                  xy∈s ∧ yz∈r)"
  and pred_separation:
     "⟦M(r); M(x)⟧ ⟹ separation(M, λy. ∃p[M]. p∈r ∧ pair(M,y,x,p))"
  and Memrel_separation:
     "separation(M, λz. ∃x[M]. ∃y[M]. pair(M,x,y,z) ∧ x ∈ y)"
  and funspace_succ_replacement:
     "M(n) ⟹
      strong_replacement(M, λp z. ∃f[M]. ∃b[M]. ∃nb[M]. ∃cnbf[M].
                pair(M,f,b,p) ∧ pair(M,n,b,nb) ∧ is_cons(M,nb,f,cnbf) ∧
                upair(M,cnbf,cnbf,z))"
  and is_recfun_separation:
     ― ‹for well-founded recursion: used to prove ‹is_recfun_equal››
     "⟦M(r); M(f); M(g); M(a); M(b)⟧
     ⟹ separation(M,
            λx. ∃xa[M]. ∃xb[M].
                pair(M,x,a,xa) ∧ xa ∈ r ∧ pair(M,x,b,xb) ∧ xb ∈ r ∧
                (∃fx[M]. ∃gx[M]. fun_apply(M,f,x,fx) ∧ fun_apply(M,g,x,gx) ∧
                                   fx ≠ gx))"
     and power_ax:         "power_ax(M)"

lemma (in M_trivial) cartprod_iff_lemma:
     "⟦M(C);  ∀u[M]. u ∈ C ⟷ (∃x∈A. ∃y∈B. u = {{x}, {x,y}});
         powerset(M, A ∪ B, p1); powerset(M, p1, p2);  M(p2)⟧
       ⟹ C = {u ∈ p2 . ∃x∈A. ∃y∈B. u = {{x}, {x,y}}}"
apply (simp add: powerset_def)
apply (rule equalityI, clarify, simp)
 apply (frule transM, assumption)
 apply (frule transM, assumption, simp (no_asm_simp))
 apply blast
apply clarify
apply (frule transM, assumption, force)
done

lemma (in M_basic) cartprod_iff:
     "⟦M(A); M(B); M(C)⟧
      ⟹ cartprod(M,A,B,C) ⟷
          (∃p1[M]. ∃p2[M]. powerset(M,A ∪ B,p1) ∧ powerset(M,p1,p2) ∧
                   C = {z ∈ p2. ∃x∈A. ∃y∈B. z = ⟨x,y⟩})"
apply (simp add: Pair_def cartprod_def, safe)
defer 1
  apply (simp add: powerset_def)
 apply blast
txt‹Final, difficult case: the left-to-right direction of the theorem.›
apply (insert power_ax, simp add: power_ax_def)
apply (frule_tac x="A ∪ B" and P="λx. rex(M,Q(x))" for Q in rspec)
apply (blast, clarify)
apply (drule_tac x=z and P="λx. rex(M,Q(x))" for Q in rspec)
apply assumption
apply (blast intro: cartprod_iff_lemma)
done

lemma (in M_basic) cartprod_closed_lemma:
     "⟦M(A); M(B)⟧ ⟹ ∃C[M]. cartprod(M,A,B,C)"
apply (simp del: cartprod_abs add: cartprod_iff)
apply (insert power_ax, simp add: power_ax_def)
apply (frule_tac x="A ∪ B" and P="λx. rex(M,Q(x))" for Q in rspec)
apply (blast, clarify)
apply (drule_tac x=z and P="λx. rex(M,Q(x))" for Q in rspec, auto)
apply (intro rexI conjI, simp+)
apply (insert cartprod_separation [of A B], simp)
done

text‹All the lemmas above are necessary because Powerset is not absolute.
      I should have used Replacement instead!›
lemma (in M_basic) cartprod_closed [intro,simp]:
     "⟦M(A); M(B)⟧ ⟹ M(A*B)"
by (frule cartprod_closed_lemma, assumption, force)

lemma (in M_basic) sum_closed [intro,simp]:
     "⟦M(A); M(B)⟧ ⟹ M(A+B)"
by (simp add: sum_def)

lemma (in M_basic) sum_abs [simp]:
     "⟦M(A); M(B); M(Z)⟧ ⟹ is_sum(M,A,B,Z) ⟷ (Z = A+B)"
by (simp add: is_sum_def sum_def singleton_0 nat_into_M)

lemma (in M_trivial) Inl_in_M_iff [iff]:
     "M(Inl(a)) ⟷ M(a)"
by (simp add: Inl_def)

lemma (in M_trivial) Inl_abs [simp]:
     "M(Z) ⟹ is_Inl(M,a,Z) ⟷ (Z = Inl(a))"
by (simp add: is_Inl_def Inl_def)

lemma (in M_trivial) Inr_in_M_iff [iff]:
     "M(Inr(a)) ⟷ M(a)"
by (simp add: Inr_def)

lemma (in M_trivial) Inr_abs [simp]:
     "M(Z) ⟹ is_Inr(M,a,Z) ⟷ (Z = Inr(a))"
by (simp add: is_Inr_def Inr_def)


subsubsection ‹converse of a relation›

lemma (in M_basic) M_converse_iff:
     "M(r) ⟹
      converse(r) =
      {z ∈ ⋃(⋃(r)) * ⋃(⋃(r)).
       ∃p∈r. ∃x[M]. ∃y[M]. p = ⟨x,y⟩ ∧ z = ⟨y,x⟩}"
apply (rule equalityI)
 prefer 2 apply (blast dest: transM, clarify, simp)
apply (simp add: Pair_def)
apply (blast dest: transM)
done

lemma (in M_basic) converse_closed [intro,simp]:
     "M(r) ⟹ M(converse(r))"
apply (simp add: M_converse_iff)
apply (insert converse_separation [of r], simp)
done

lemma (in M_basic) converse_abs [simp]:
     "⟦M(r); M(z)⟧ ⟹ is_converse(M,r,z) ⟷ z = converse(r)"
apply (simp add: is_converse_def)
apply (rule iffI)
 prefer 2 apply blast
apply (rule M_equalityI)
  apply simp
  apply (blast dest: transM)+
done


subsubsection ‹image, preimage, domain, range›

lemma (in M_basic) image_closed [intro,simp]:
     "⟦M(A); M(r)⟧ ⟹ M(r``A)"
apply (simp add: image_iff_Collect)
apply (insert image_separation [of A r], simp)
done

lemma (in M_basic) vimage_abs [simp]:
     "⟦M(r); M(A); M(z)⟧ ⟹ pre_image(M,r,A,z) ⟷ z = r-``A"
apply (simp add: pre_image_def)
apply (rule iffI)
 apply (blast intro!: equalityI dest: transM, blast)
done

lemma (in M_basic) vimage_closed [intro,simp]:
     "⟦M(A); M(r)⟧ ⟹ M(r-``A)"
by (simp add: vimage_def)


subsubsection‹Domain, range and field›

lemma (in M_trans) domain_abs [simp]:
     "⟦M(r); M(z)⟧ ⟹ is_domain(M,r,z) ⟷ z = domain(r)"
apply (simp add: is_domain_def)
apply (blast intro!: equalityI dest: transM)
done

lemma (in M_basic) domain_closed [intro,simp]:
     "M(r) ⟹ M(domain(r))"
apply (simp add: domain_eq_vimage)
done

lemma (in M_trans) range_abs [simp]:
     "⟦M(r); M(z)⟧ ⟹ is_range(M,r,z) ⟷ z = range(r)"
apply (simp add: is_range_def)
apply (blast intro!: equalityI dest: transM)
done

lemma (in M_basic) range_closed [intro,simp]:
     "M(r) ⟹ M(range(r))"
apply (simp add: range_eq_image)
done

lemma (in M_basic) field_abs [simp]:
     "⟦M(r); M(z)⟧ ⟹ is_field(M,r,z) ⟷ z = field(r)"
by (simp add: is_field_def field_def)

lemma (in M_basic) field_closed [intro,simp]:
     "M(r) ⟹ M(field(r))"
by (simp add: field_def)


subsubsection‹Relations, functions and application›

lemma (in M_trans) relation_abs [simp]:
     "M(r) ⟹ is_relation(M,r) ⟷ relation(r)"
apply (simp add: is_relation_def relation_def)
apply (blast dest!: bspec dest: pair_components_in_M)+
done

lemma (in M_trivial) function_abs [simp]:
     "M(r) ⟹ is_function(M,r) ⟷ function(r)"
apply (simp add: is_function_def function_def, safe)
   apply (frule transM, assumption)
  apply (blast dest: pair_components_in_M)+
done

lemma (in M_basic) apply_closed [intro,simp]:
     "⟦M(f); M(a)⟧ ⟹ M(f`a)"
by (simp add: apply_def)

lemma (in M_basic) apply_abs [simp]:
     "⟦M(f); M(x); M(y)⟧ ⟹ fun_apply(M,f,x,y) ⟷ f`x = y"
apply (simp add: fun_apply_def apply_def, blast)
done

lemma (in M_trivial) typed_function_abs [simp]:
     "⟦M(A); M(f)⟧ ⟹ typed_function(M,A,B,f) ⟷ f ∈ A -> B"
apply (auto simp add: typed_function_def relation_def Pi_iff)
apply (blast dest: pair_components_in_M)+
done

lemma (in M_basic) injection_abs [simp]:
     "⟦M(A); M(f)⟧ ⟹ injection(M,A,B,f) ⟷ f ∈ inj(A,B)"
apply (simp add: injection_def apply_iff inj_def)
apply (blast dest: transM [of _ A])
done

lemma (in M_basic) surjection_abs [simp]:
     "⟦M(A); M(B); M(f)⟧ ⟹ surjection(M,A,B,f) ⟷ f ∈ surj(A,B)"
by (simp add: surjection_def surj_def)

lemma (in M_basic) bijection_abs [simp]:
     "⟦M(A); M(B); M(f)⟧ ⟹ bijection(M,A,B,f) ⟷ f ∈ bij(A,B)"
by (simp add: bijection_def bij_def)


subsubsection‹Composition of relations›

lemma (in M_basic) M_comp_iff:
     "⟦M(r); M(s)⟧
      ⟹ r O s =
          {xz ∈ domain(s) * range(r).
            ∃x[M]. ∃y[M]. ∃z[M]. xz = ⟨x,z⟩ ∧ ⟨x,y⟩ ∈ s ∧ ⟨y,z⟩ ∈ r}"
apply (simp add: comp_def)
apply (rule equalityI)
 apply clarify
 apply simp
 apply  (blast dest:  transM)+
done

lemma (in M_basic) comp_closed [intro,simp]:
     "⟦M(r); M(s)⟧ ⟹ M(r O s)"
apply (simp add: M_comp_iff)
apply (insert comp_separation [of r s], simp)
done

lemma (in M_basic) composition_abs [simp]:
     "⟦M(r); M(s); M(t)⟧ ⟹ composition(M,r,s,t) ⟷ t = r O s"
apply safe
 txt‹Proving \<^term>‹composition(M, r, s, r O s)››
 prefer 2
 apply (simp add: composition_def comp_def)
 apply (blast dest: transM)
txt‹Opposite implication›
apply (rule M_equalityI)
  apply (simp add: composition_def comp_def)
  apply (blast del: allE dest: transM)+
done

text‹no longer needed›
lemma (in M_basic) restriction_is_function:
     "⟦restriction(M,f,A,z); function(f); M(f); M(A); M(z)⟧
      ⟹ function(z)"
apply (simp add: restriction_def ball_iff_equiv)
apply (unfold function_def, blast)
done

lemma (in M_trans) restriction_abs [simp]:
     "⟦M(f); M(A); M(z)⟧
      ⟹ restriction(M,f,A,z) ⟷ z = restrict(f,A)"
apply (simp add: ball_iff_equiv restriction_def restrict_def)
apply (blast intro!: equalityI dest: transM)
done


lemma (in M_trans) M_restrict_iff:
     "M(r) ⟹ restrict(r,A) = {z ∈ r . ∃x∈A. ∃y[M]. z = ⟨x, y⟩}"
by (simp add: restrict_def, blast dest: transM)

lemma (in M_basic) restrict_closed [intro,simp]:
     "⟦M(A); M(r)⟧ ⟹ M(restrict(r,A))"
apply (simp add: M_restrict_iff)
apply (insert restrict_separation [of A], simp)
done

lemma (in M_trans) Inter_abs [simp]:
     "⟦M(A); M(z)⟧ ⟹ big_inter(M,A,z) ⟷ z = ⋂(A)"
apply (simp add: big_inter_def Inter_def)
apply (blast intro!: equalityI dest: transM)
done

lemma (in M_basic) Inter_closed [intro,simp]:
     "M(A) ⟹ M(⋂(A))"
by (insert Inter_separation, simp add: Inter_def)

lemma (in M_basic) Int_closed [intro,simp]:
     "⟦M(A); M(B)⟧ ⟹ M(A ∩ B)"
apply (subgoal_tac "M({A,B})")
apply (frule Inter_closed, force+)
done

lemma (in M_basic) Diff_closed [intro,simp]:
     "⟦M(A); M(B)⟧ ⟹ M(A-B)"
by (insert Diff_separation, simp add: Diff_def)

subsubsection‹Some Facts About Separation Axioms›

lemma (in M_basic) separation_conj:
     "⟦separation(M,P); separation(M,Q)⟧ ⟹ separation(M, λz. P(z) ∧ Q(z))"
by (simp del: separation_closed
         add: separation_iff Collect_Int_Collect_eq [symmetric])

(*???equalities*)
lemma Collect_Un_Collect_eq:
     "Collect(A,P) ∪ Collect(A,Q) = Collect(A, λx. P(x) ∨ Q(x))"
by blast

lemma Diff_Collect_eq:
     "A - Collect(A,P) = Collect(A, λx. ¬ P(x))"
by blast

lemma (in M_trans) Collect_rall_eq:
     "M(Y) ⟹ Collect(A, λx. ∀y[M]. y∈Y ⟶ P(x,y)) =
               (if Y=0 then A else (⋂y ∈ Y. {x ∈ A. P(x,y)}))"
  by (simp,blast dest: transM)


lemma (in M_basic) separation_disj:
     "⟦separation(M,P); separation(M,Q)⟧ ⟹ separation(M, λz. P(z) ∨ Q(z))"
by (simp del: separation_closed
         add: separation_iff Collect_Un_Collect_eq [symmetric])

lemma (in M_basic) separation_neg:
     "separation(M,P) ⟹ separation(M, λz. ¬P(z))"
by (simp del: separation_closed
         add: separation_iff Diff_Collect_eq [symmetric])

lemma (in M_basic) separation_imp:
     "⟦separation(M,P); separation(M,Q)⟧
      ⟹ separation(M, λz. P(z) ⟶ Q(z))"
by (simp add: separation_neg separation_disj not_disj_iff_imp [symmetric])

text‹This result is a hint of how little can be done without the Reflection
  Theorem.  The quantifier has to be bounded by a set.  We also need another
  instance of Separation!›
lemma (in M_basic) separation_rall:
     "⟦M(Y); ∀y[M]. separation(M, λx. P(x,y));
        ∀z[M]. strong_replacement(M, λx y. y = {u ∈ z . P(u,x)})⟧
      ⟹ separation(M, λx. ∀y[M]. y∈Y ⟶ P(x,y))"
apply (simp del: separation_closed rall_abs
         add: separation_iff Collect_rall_eq)
apply (blast intro!:  RepFun_closed dest: transM)
done


subsubsection‹Functions and function space›

text‹The assumption \<^term>‹M(A->B)› is unusual, but essential: in
all but trivial cases, A->B cannot be expected to belong to \<^term>‹M›.›
lemma (in M_trivial) is_funspace_abs [simp]:
     "⟦M(A); M(B); M(F); M(A->B)⟧ ⟹ is_funspace(M,A,B,F) ⟷ F = A->B"
apply (simp add: is_funspace_def)
apply (rule iffI)
 prefer 2 apply blast
apply (rule M_equalityI)
  apply simp_all
done

lemma (in M_basic) succ_fun_eq2:
     "⟦M(B); M(n->B)⟧ ⟹
      succ(n) -> B =
      ⋃{z. p ∈ (n->B)*B, ∃f[M]. ∃b[M]. p = ⟨f,b⟩ ∧ z = {cons(⟨n,b⟩, f)}}"
apply (simp add: succ_fun_eq)
apply (blast dest: transM)
done

lemma (in M_basic) funspace_succ:
     "⟦M(n); M(B); M(n->B)⟧ ⟹ M(succ(n) -> B)"
apply (insert funspace_succ_replacement [of n], simp)
apply (force simp add: succ_fun_eq2 univalent_def)
done

text‹\<^term>‹M› contains all finite function spaces.  Needed to prove the
absoluteness of transitive closure.  See the definition of
‹rtrancl_alt› in in ‹WF_absolute.thy›.›
lemma (in M_basic) finite_funspace_closed [intro,simp]:
     "⟦n∈nat; M(B)⟧ ⟹ M(n->B)"
apply (induct_tac n, simp)
apply (simp add: funspace_succ nat_into_M)
done


subsection‹Relativization and Absoluteness for Boolean Operators›

definition
  is_bool_of_o :: "[i⇒o, o, i] ⇒ o" where
   "is_bool_of_o(M,P,z) ≡ (P ∧ number1(M,z)) ∨ (¬P ∧ empty(M,z))"

definition
  is_not :: "[i⇒o, i, i] ⇒ o" where
   "is_not(M,a,z) ≡ (number1(M,a)  ∧ empty(M,z)) |
                     (¬number1(M,a) ∧ number1(M,z))"

definition
  is_and :: "[i⇒o, i, i, i] ⇒ o" where
   "is_and(M,a,b,z) ≡ (number1(M,a)  ∧ z=b) |
                       (¬number1(M,a) ∧ empty(M,z))"

definition
  is_or :: "[i⇒o, i, i, i] ⇒ o" where
   "is_or(M,a,b,z) ≡ (number1(M,a)  ∧ number1(M,z)) |
                      (¬number1(M,a) ∧ z=b)"

lemma (in M_trivial) bool_of_o_abs [simp]:
     "M(z) ⟹ is_bool_of_o(M,P,z) ⟷ z = bool_of_o(P)"
by (simp add: is_bool_of_o_def bool_of_o_def)


lemma (in M_trivial) not_abs [simp]:
     "⟦M(a); M(z)⟧ ⟹ is_not(M,a,z) ⟷ z = not(a)"
by (simp add: Bool.not_def cond_def is_not_def)

lemma (in M_trivial) and_abs [simp]:
     "⟦M(a); M(b); M(z)⟧ ⟹ is_and(M,a,b,z) ⟷ z = a and b"
by (simp add: Bool.and_def cond_def is_and_def)

lemma (in M_trivial) or_abs [simp]:
     "⟦M(a); M(b); M(z)⟧ ⟹ is_or(M,a,b,z) ⟷ z = a or b"
by (simp add: Bool.or_def cond_def is_or_def)


lemma (in M_trivial) bool_of_o_closed [intro,simp]:
     "M(bool_of_o(P))"
by (simp add: bool_of_o_def)

lemma (in M_trivial) and_closed [intro,simp]:
     "⟦M(p); M(q)⟧ ⟹ M(p and q)"
by (simp add: and_def cond_def)

lemma (in M_trivial) or_closed [intro,simp]:
     "⟦M(p); M(q)⟧ ⟹ M(p or q)"
by (simp add: or_def cond_def)

lemma (in M_trivial) not_closed [intro,simp]:
     "M(p) ⟹ M(not(p))"
by (simp add: Bool.not_def cond_def)


subsection‹Relativization and Absoluteness for List Operators›

definition
  is_Nil :: "[i⇒o, i] ⇒ o" where
     ― ‹because \<^prop>‹[] ≡ Inl(0)››
    "is_Nil(M,xs) ≡ ∃zero[M]. empty(M,zero) ∧ is_Inl(M,zero,xs)"

definition
  is_Cons :: "[i⇒o,i,i,i] ⇒ o" where
     ― ‹because \<^prop>‹Cons(a, l) ≡ Inr(⟨a,l⟩)››
    "is_Cons(M,a,l,Z) ≡ ∃p[M]. pair(M,a,l,p) ∧ is_Inr(M,p,Z)"


lemma (in M_trivial) Nil_in_M [intro,simp]: "M(Nil)"
by (simp add: Nil_def)

lemma (in M_trivial) Nil_abs [simp]: "M(Z) ⟹ is_Nil(M,Z) ⟷ (Z = Nil)"
by (simp add: is_Nil_def Nil_def)

lemma (in M_trivial) Cons_in_M_iff [iff]: "M(Cons(a,l)) ⟷ M(a) ∧ M(l)"
by (simp add: Cons_def)

lemma (in M_trivial) Cons_abs [simp]:
     "⟦M(a); M(l); M(Z)⟧ ⟹ is_Cons(M,a,l,Z) ⟷ (Z = Cons(a,l))"
by (simp add: is_Cons_def Cons_def)


definition
  quasilist :: "i ⇒ o" where
    "quasilist(xs) ≡ xs=Nil ∨ (∃x l. xs = Cons(x,l))"

definition
  is_quasilist :: "[i⇒o,i] ⇒ o" where
    "is_quasilist(M,z) ≡ is_Nil(M,z) ∨ (∃x[M]. ∃l[M]. is_Cons(M,x,l,z))"

definition
  list_case' :: "[i, [i,i]⇒i, i] ⇒ i" where
    ― ‹A version of \<^term>‹list_case› that's always defined.›
    "list_case'(a,b,xs) ≡
       if quasilist(xs) then list_case(a,b,xs) else 0"

definition
  is_list_case :: "[i⇒o, i, [i,i,i]⇒o, i, i] ⇒ o" where
    ― ‹Returns 0 for non-lists›
    "is_list_case(M, a, is_b, xs, z) ≡
       (is_Nil(M,xs) ⟶ z=a) ∧
       (∀x[M]. ∀l[M]. is_Cons(M,x,l,xs) ⟶ is_b(x,l,z)) ∧
       (is_quasilist(M,xs) ∨ empty(M,z))"

definition
  hd' :: "i ⇒ i" where
    ― ‹A version of \<^term>‹hd› that's always defined.›
    "hd'(xs) ≡ if quasilist(xs) then hd(xs) else 0"

definition
  tl' :: "i ⇒ i" where
    ― ‹A version of \<^term>‹tl› that's always defined.›
    "tl'(xs) ≡ if quasilist(xs) then tl(xs) else 0"

definition
  is_hd :: "[i⇒o,i,i] ⇒ o" where
     ― ‹\<^term>‹hd([]) = 0› no constraints if not a list.
          Avoiding implication prevents the simplifier's looping.›
    "is_hd(M,xs,H) ≡
       (is_Nil(M,xs) ⟶ empty(M,H)) ∧
       (∀x[M]. ∀l[M]. ¬ is_Cons(M,x,l,xs) ∨ H=x) ∧
       (is_quasilist(M,xs) ∨ empty(M,H))"

definition
  is_tl :: "[i⇒o,i,i] ⇒ o" where
     ― ‹\<^term>‹tl([]) = []›; see comments about \<^term>‹is_hd››
    "is_tl(M,xs,T) ≡
       (is_Nil(M,xs) ⟶ T=xs) ∧
       (∀x[M]. ∀l[M]. ¬ is_Cons(M,x,l,xs) ∨ T=l) ∧
       (is_quasilist(M,xs) ∨ empty(M,T))"

subsubsection‹\<^term>‹quasilist›: For Case-Splitting with \<^term>‹list_case'››

lemma [iff]: "quasilist(Nil)"
by (simp add: quasilist_def)

lemma [iff]: "quasilist(Cons(x,l))"
by (simp add: quasilist_def)

lemma list_imp_quasilist: "l ∈ list(A) ⟹ quasilist(l)"
by (erule list.cases, simp_all)

subsubsection‹\<^term>‹list_case'›, the Modified Version of \<^term>‹list_case››

lemma list_case'_Nil [simp]: "list_case'(a,b,Nil) = a"
by (simp add: list_case'_def quasilist_def)

lemma list_case'_Cons [simp]: "list_case'(a,b,Cons(x,l)) = b(x,l)"
by (simp add: list_case'_def quasilist_def)

lemma non_list_case: "¬ quasilist(x) ⟹ list_case'(a,b,x) = 0"
by (simp add: quasilist_def list_case'_def)

lemma list_case'_eq_list_case [simp]:
     "xs ∈ list(A) ⟹list_case'(a,b,xs) = list_case(a,b,xs)"
by (erule list.cases, simp_all)

lemma (in M_basic) list_case'_closed [intro,simp]:
  "⟦M(k); M(a); ∀x[M]. ∀y[M]. M(b(x,y))⟧ ⟹ M(list_case'(a,b,k))"
apply (case_tac "quasilist(k)")
 apply (simp add: quasilist_def, force)
apply (simp add: non_list_case)
done

lemma (in M_trivial) quasilist_abs [simp]:
     "M(z) ⟹ is_quasilist(M,z) ⟷ quasilist(z)"
by (auto simp add: is_quasilist_def quasilist_def)

lemma (in M_trivial) list_case_abs [simp]:
     "⟦relation2(M,is_b,b); M(k); M(z)⟧
      ⟹ is_list_case(M,a,is_b,k,z) ⟷ z = list_case'(a,b,k)"
apply (case_tac "quasilist(k)")
 prefer 2
 apply (simp add: is_list_case_def non_list_case)
 apply (force simp add: quasilist_def)
apply (simp add: quasilist_def is_list_case_def)
apply (elim disjE exE)
 apply (simp_all add: relation2_def)
done


subsubsection‹The Modified Operators \<^term>‹hd'› and \<^term>‹tl'››

lemma (in M_trivial) is_hd_Nil: "is_hd(M,[],Z) ⟷ empty(M,Z)"
by (simp add: is_hd_def)

lemma (in M_trivial) is_hd_Cons:
     "⟦M(a); M(l)⟧ ⟹ is_hd(M,Cons(a,l),Z) ⟷ Z = a"
by (force simp add: is_hd_def)

lemma (in M_trivial) hd_abs [simp]:
     "⟦M(x); M(y)⟧ ⟹ is_hd(M,x,y) ⟷ y = hd'(x)"
apply (simp add: hd'_def)
apply (intro impI conjI)
 prefer 2 apply (force simp add: is_hd_def)
apply (simp add: quasilist_def is_hd_def)
apply (elim disjE exE, auto)
done

lemma (in M_trivial) is_tl_Nil: "is_tl(M,[],Z) ⟷ Z = []"
by (simp add: is_tl_def)

lemma (in M_trivial) is_tl_Cons:
     "⟦M(a); M(l)⟧ ⟹ is_tl(M,Cons(a,l),Z) ⟷ Z = l"
by (force simp add: is_tl_def)

lemma (in M_trivial) tl_abs [simp]:
     "⟦M(x); M(y)⟧ ⟹ is_tl(M,x,y) ⟷ y = tl'(x)"
apply (simp add: tl'_def)
apply (intro impI conjI)
 prefer 2 apply (force simp add: is_tl_def)
apply (simp add: quasilist_def is_tl_def)
apply (elim disjE exE, auto)
done

lemma (in M_trivial) relation1_tl: "relation1(M, is_tl(M), tl')"
by (simp add: relation1_def)

lemma hd'_Nil: "hd'([]) = 0"
by (simp add: hd'_def)

lemma hd'_Cons: "hd'(Cons(a,l)) = a"
by (simp add: hd'_def)

lemma tl'_Nil: "tl'([]) = []"
by (simp add: tl'_def)

lemma tl'_Cons: "tl'(Cons(a,l)) = l"
by (simp add: tl'_def)

lemma iterates_tl_Nil: "n ∈ nat ⟹ tl'^n ([]) = []"
apply (induct_tac n)
apply (simp_all add: tl'_Nil)
done

lemma (in M_basic) tl'_closed: "M(x) ⟹ M(tl'(x))"
apply (simp add: tl'_def)
apply (force simp add: quasilist_def)
done


end