Hint Extern 60 (RStep _ (subrel _ (flip _))) =>
eapply subrel_sym_flip : typeclass_instances.
(** ** Implication *)
Definition rel_impl {A B} (R1 R2: rel A B): rel A B :=
fun x y => R1 x y -> R2 x y.
Global Instance rel_impl_subrel {A B}:
Monotonic (@rel_impl A B) (subrel --> subrel ++> subrel).
Global Instance rel_impl_subrel_params:
Params (@rel_impl) 4.

(* Specifications: *)
Lemma rel_impl_rintro {A B} (R1 R2: rel A B) x y:
RIntro (R1 x y -> R2 x y) (rel_impl R1 R2) x y.