theorem divides_to_congruent: \forall n,m,p:nat. O < p \to m \le n \to
divides p (n - m) \to congruent n m p.
intros.elim H2.
-apply (eq_times_plus_to_congruent n m p n2).
+apply (eq_times_plus_to_congruent n m p n1).
assumption.
rewrite < sym_plus.
apply minus_to_plus.assumption.