(** * The [option_le] relator *)
Inductive option_le {A1 A2} (RA: rel A1 A2): rel (option A1) (option A2) :=
| Some_le_def x y: RA x y -> option_le RA (Some x) (Some y)
| None_le_def y: option_le RA None y.
Global Instance Some_le:
Monotonic (@Some) (forallr R @ A1 A2 : rel, R ++> option_le R).

Lemma None_le {A B} R y:
RIntro True (@option_le A B R) None y.