intuition.
unfold ratInverse.
destruct r2.
destruct n.
rewrite H.
rewrite rat_num_0.
rewrite ratMult_0_l.
eapply rat0_le_all.
rewrite H.
rewrite <- ratMult_num_den.
eapply rat_le_1.
unfold posnatMult, natToPosnat, posnatToNat.
destruct p.
rewrite mult_comm.
intuition.
Qed.

Theorem ratFraction_ge_1_inv :
forall r1 r2,
1 <= r1 * (ratInverse r2) ->
r2 <= r1.