intros X R u v Der_g.
elim Der_g.
intros.
apply Derive1; auto.
intros.
apply Derive2; auto.
Qed.

(* Specifications: *)
Lemma Derivegstar_Derivestar :
forall (X R : Ensf) (u v : Word), Derivegstar X R u v -> Derivestar R u v.