(********* we have to define Bounded *********************)
Definition Bounded (P : Ens -> Prop) :=
EXISTS (fun A : Ens => Bounded_By A P).
(********** unions of two sets, then big Unions ************)
Parameter union : forall A B : Ens, Ens.

Axiom union_pr1 : forall A B : Ens, SUB A (union A B).