Proof Domain_th1_Out.
(***** same thing for Range *********)
Definition Range (R : Ens) := REPLACEMENT (Range_prop R).

Theorem Range_pr1 : forall (R X : Ens) (p : Range_prop R X), IN X (Range R).
Proof fun R : Ens => REPLACEMENT_pr1 (Range_prop R) (Range_prop_bounded R).