Hint Extern 0 (RIntro _ (rel_impl _ _) _ _) =>
eapply rel_impl_rintro : typeclass_instances.

(* Specifications: *)
Lemma rel_impl_relim {A B} (R1 R2: rel A B) x y:
RElim (rel_impl R1 R2) x y (R1 x y) (R2 x y).