eapply Or_left_id.
Qed.

(* Specifications: *)
Corollary Or_right_id_s : forall s r, (r || Empty) ~= s = r ~= s.
(** [Or] is idempotent. *)
Lemma Or_idem_s : forall s r, (r || r) ~= s = r ~= s.
Theorem Or_idem : forall r, r || r =R= r.