Definition Naturals := REPLACEMENT Element_of_NN.

(* Specifications: *)
Theorem Naturals_pr1 : forall X : Ens, Element_of_NN X -> IN X Naturals.
Proof REPLACEMENT_pr1 Element_of_NN Bounded_NN.
Theorem Naturals_pr2 : forall X : Ens, IN X Naturals -> Element_of_NN X.
Proof REPLACEMENT_pr2 Element_of_NN Bounded_NN.