rattac;
inversion H0; clear H0; subst;
inversion H; clear H; subst;
arithNormalize;
arithSimplify.
Qed.

Lemma ratAdd_eqRat_compat_l : forall r1 r2 r3,
eqRat r1 r2 ->
r1 + r3 == r2 + r3.