+unification hint 1 ≔
+ A:setoid, B,C : 𝛀^A;
+ R ≟ (mk_unary_morphism1 …
+ (λS:ext_powerclass_setoid A.
+ mk_unary_morphism1 ??
+ (λS':ext_powerclass_setoid A.
+ mk_ext_powerclass A (S∩S') (ext_prop A (intersect_is_ext ? S S')))
+ (prop11 … (intersect_is_ext_morph A S)))
+ (prop11 … (intersect_is_ext_morph A))) ,
+ BB ≟ (ext_carr ? B),
+ CC ≟ (ext_carr ? C)
+ (* ------------------------------------------------------*) ⊢
+ ext_carr A (R B C) ≡ intersect (carr A) BB CC.
+
+(*
+alias symbol "hint_decl" = "hint_decl_Type2".
+unification hint 0 ≔
+ A : setoid, B,C : 𝛀^A ;
+ CC ≟ (ext_carr ? C),
+ BB ≟ (ext_carr ? B),
+ C1 ≟ (carr1 (powerclass_setoid (carr A))),
+ C2 ≟ (carr1 (ext_powerclass_setoid A))
+ ⊢
+ eq_rel1 C1 (eq1 (powerclass_setoid (carr A))) BB CC ≡
+ eq_rel1 C2 (eq1 (ext_powerclass_setoid A)) B C.
+
+unification hint 0 ≔
+ A, B : CPROP ⊢ iff A B ≡ eq_rel1 ? (eq1 CPROP) A B.
+
+nlemma test: ∀U.∀A,B:𝛀^U. A ∩ B = A →
+ ∀x,y. x=y → x ∈ A → y ∈ A ∩ B.
+ #U; #A; #B; #H; #x; #y; #K; #K2;
+ alias symbol "prop2" = "prop21 mem".
+ alias symbol "invert" = "setoid1 symmetry".
+ napply (. K^-1‡H);
+ nassumption;
+nqed.
+
+
+nlemma intersect_ok: ∀A. binary_morphism1 (ext_powerclass_setoid A) (ext_powerclass_setoid A) (ext_powerclass_setoid A).