intuition.
rattac.
rewrite mult_0_l in e.
unfold posnatToNat in *.
simpl in *.
destruct p1.
destruct p0.
rewrite mult_1_r in e.
apply plus_is_O in e.
intuition.
eapply mult_is_O in H0.
intuition.
rattac.
rewrite mult_0_l in e.
unfold posnatToNat in *.
simpl in *.
destruct p1.
destruct p0.
rewrite mult_1_r in e.
apply plus_is_O in e.
intuition.
eapply mult_is_O in H1.
intuition.
rewrite (ratAdd_0_r 0).
eapply ratAdd_eqRat_compat; eauto.
Qed.

Theorem ratAdd_nz : forall r1 r2,
~(r1 + r2 == 0) <->
(~r1 == 0) \/ (~r2 == 0).