unfold ratAdd_rel in *.
intuition.
destruct H.
destruct H0.
exists (x + x0).
intuition.
eapply ratAdd_eqRat_compat; eauto.
Qed.

Lemma expRat_eqRat_compat : forall n r1 r2,
r1 == r2 ->
expRat r1 n == expRat r2 n.