intuition.
eapply leRat_trans.
2:{
eapply eqRat_impl_leRat.
eapply eqRat_symm.
eapply H.
}
apply ratAdd_any_leRat_l.
apply leRat_refl.
Qed.

Lemma ratAdd_eq_impl_leRat_r : forall r1 r2 r3,
r1 == r2 + r3 ->
r3 <= r1.