+nlemma union_is_morph :
+ ∀A. (powerclass_setoid A) ⇒_1 (unary_morphism1_setoid1 (powerclass_setoid A) (powerclass_setoid A)).
+(*XXX ∀A.Ω^A ⇒_1 (Ω^A ⇒_1 Ω^A). avec non-unif-coerc*)
+#X; napply (mk_binary_morphism1 … (λA,B.A ∪ B));
+#A1 A2 B1 B2 EA EB; napply ext_set; #x;
+nchange in match (x ∈ (A1 ∪ B1)) with (?∨?);
+napply (.= (set_ext ??? EA x)‡#);
+napply (.= #‡(set_ext ??? EB x)); //;
+nqed.
+
+nlemma union_is_ext: ∀A. 𝛀^A → 𝛀^A → 𝛀^A.
+ #S A B; @ (A ∪ B); #x y Exy; @; *; #H1;
+##[##1,3: @; ##|##*: @2 ]
+##[##1,3: napply (. (Exy^-1)╪_1#)
+##|##2,4: napply (. Exy╪_1#)]
+nassumption;
+nqed.
+
+alias symbol "hint_decl" = "hint_decl_Type1".
+unification hint 0 ≔
+ A : setoid, B,C : 𝛀^A;
+ R ≟ (mk_ext_powerclass ? (B ∪ C) (ext_prop ? (union_is_ext ? B C)))
+(*-------------------------------------------------------------------------*) ⊢
+ ext_carr A R ≡ union ? (ext_carr ? B) (ext_carr ? C).
+
+unification hint 0 ≔ S:Type[0], A,B:Ω^S;
+ MM ≟ mk_unary_morphism1 ??
+ (λA.mk_unary_morphism1 ?? (λB.A ∪ B) (prop11 ?? (union_is_morph S A)))
+ (prop11 ?? (union_is_morph S))
+(*--------------------------------------------------------------------------*) ⊢
+ fun11 ?? (fun11 ?? MM A) B ≡ A ∪ B.
+
+nlemma union_is_ext_morph:∀A.
+ (ext_powerclass_setoid A) ⇒_1
+ (unary_morphism1_setoid1 (ext_powerclass_setoid A) (ext_powerclass_setoid A)).
+(*XXX ∀A:setoid.𝛀^A ⇒_1 (𝛀^A ⇒_1 𝛀^A). with coercion non uniformi *)
+#A; napply (mk_binary_morphism1 … (union_is_ext …));
+#x1 x2 y1 y2 Ex Ey; napply (prop11 … (union_is_morph A)); nassumption.
+nqed.
+
+unification hint 1 ≔
+ AA : setoid, B,C : 𝛀^AA;
+ A ≟ carr AA,
+ R ≟ (mk_unary_morphism1 ??
+ (λS:𝛀^AA.
+ mk_unary_morphism1 ??
+ (λS':𝛀^AA.
+ mk_ext_powerclass AA (S ∪ S') (ext_prop AA (union_is_ext ? S S')))
+ (prop11 ?? (union_is_ext_morph AA S)))
+ (prop11 ?? (union_is_ext_morph AA))) ,
+ BB ≟ (ext_carr ? B),
+ CC ≟ (ext_carr ? C)
+(*------------------------------------------------------*) ⊢
+ ext_carr AA (R B C) ≡ union A BB CC.
+