(********* 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_pr2 : forall A B : Ens, SUB B (union A B).
Axiom
union_pr3 :
forall (A B C : Ens) (h : SUB A C) (k : SUB B C), SUB (union A B) C.