intuition.
unfold ratInverse.
destruct r1.
destruct n.
exfalso.
eapply H.
eapply rat_num_0.
destruct r2.
destruct n0.
exfalso.
eapply H0.
eapply rat_num_0.
case_eq (RatIntro (S n) p * RatIntro (S n0) p0); intuition.
inversion H1; clear H1; subst.
unfold ratMult.
unfold natToPosnat, posnatToNat, posnatMult.
simpl.
eapply eqRat_terms.
destruct p.
destruct p0.
trivial.
simpl.
trivial.
Qed.

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