intuition.
unfold ratInverse.
destruct r.
destruct n.
exfalso.
eapply H.
eapply rat_num_0.
destruct p.
unfold posnatToNat, natToPosnat.
destruct x.
omega.
eapply eqRat_terms; intuition.
Qed.

Lemma ratInverse_ratMult : forall r1 r2,
~ r1 == 0 ->
~ r2 == 0 ->
ratInverse (r1 * r2) == ratInverse r1 * ratInverse r2.