rattac.
repeat rewrite mult_assoc.
rewrite <- (mult_assoc n1).
rewrite (mult_comm n).
rewrite mult_assoc.
rewrite <- mult_assoc.
rewrite e.
rewrite e0.
rewrite mult_assoc.
do 3 arithSimplify.
Qed.
Add Parametric Morphism : ratMult
with signature (leRat ==> leRat ==> leRat)
as ratMult_leRat_mor.
intuition.
eapply ratMult_leRat_compat; trivial.
Qed.
Add Parametric Morphism : ratMult
with signature (eqRat ==> eqRat ==> eqRat)
as ratMult_eqRat_mor.
intuition.
eapply ratMult_eqRat_compat; trivial.
Qed.

Theorem ratAdd_0 : forall r1 r2,
r1 + r2 == 0 <->
r1 == 0 /\ r2 == 0.