rattac.
inversion H0; clear H0; subst.
rewrite mult_1_r in l.
rewrite mult_1_l in l.
rewrite mult_assoc.
rewrite <- (mult_assoc n2).
rewrite (mult_comm n).
rewrite mult_assoc.
apply mult_le_compat;
auto.
Qed.

Lemma ratDistance_ratMult_le : forall r1 r2 r3 r4 d,
(ratDistance r1 r3) <= d ->
(ratDistance r2 r4) <= d ->
r1 <= 1 ->
r2 <= 1 ->
r3 <= 1 ->
r4 <= 1 ->
(ratDistance (r1 * r2) (r3 * r4)) <= (3 / 1) * d.