intros n m p H'; red in H'.
elim H'; intros q E.
red in |- *.
exists q.
rewrite E.
auto with zarith.
Qed.

(* Specifications: *)
Theorem Zeq_mult_simpl :
forall a b c : Z, c <> 0%Z -> (a * c)%Z = (b * c)%Z -> a = b.