Local Notation predOfType T := (sort_of_simpl_pred (@pred_of_argType T)).

(* Specifications: *)
Lemma oextractE (T : Type) (x : T) (xP : Some x) : oextract xP = x.
Lemma Some_oextract T (x : option T) (x_ex : x) : Some (oextract x_ex) = x.