Hint Extern 0 (RIntro _ (_ ++> _) _ _) =>
eapply arrow_rintro : typeclass_instances.

Lemma arrow_relim {A1 A2 B1 B2} RA RB f g m n P Q:
@RElim B1 B2 RB (f m) (g n) P Q ->
@RElim (A1 -> B1) (A2 -> B2) (RA ++> RB) f g (RA m n /\ P) Q.