Proof restriction_bounded_Out.
Definition Set_Of (A : Ens) (P : Ens -> Prop) :=
REPLACEMENT (Restriction P A).

(* Specifications: *)
Theorem Set_Of_pr1 :
forall (A : Ens) (P : Ens -> Prop) (X : Ens),
Restriction P A X -> IN X (Set_Of A P).