Proof
fun (A : Ens) (P : Ens -> Prop) (X : Ens) (h : IN X (Set_Of A P)) =>
the_restriction P A X (Set_Of_pr2 A P X h).

(* Specifications: *)
Theorem Set_Of_th4 : forall (A : Ens) (P : Ens -> Prop), SUB (Set_Of A P) A.
Proof Set_Of_th3.