intros; unfold Dge in |- *; unfold Dcompare in |- *; simpl in |- *.
rewrite (Zmin_n_n d).
rewrite <- (Zminus_diag_reverse d).
unfold two_p in |- *.
rewrite (Zcompare_mult_compat 1 n1 n2).
apply Zcompare.Zge_compare; assumption.
Qed.

Lemma Dgt_Zgt :
forall n1 n2 d : Z, (n1 > n2)%Z -> Dgt (Diadic n1 d) (Diadic n2 d).