case n; case m; simpl in |- *; auto; unfold Pos.compare.
intros p p0; rewrite (ZC4 p p0).
generalize (Pcompare_Eq_eq p0 p).
case (Pcompare p0 p Datatypes.Eq); simpl in |- *; auto.
intros H'; rewrite H'; auto.
intros p p0; rewrite (ZC4 p p0).
generalize (Pcompare_Eq_eq p0 p).
case (Pcompare p0 p Datatypes.Eq); simpl in |- *; auto.
intros H'; rewrite H'; auto.
Qed.

Theorem Zpower_nat_O : forall z : Z, Zpower_nat z 0 = Z_of_nat 1.
intros z; unfold Zpower_nat in |- *; simpl in |- *; auto.