(* Lemma fashionable_extends : forall P, %(box fashionM P) = box fashionM P. *)

(* Specifications: *)
Lemma with_val_extends : forall v P,
%(with_val v P) = with_val v (%P).
Lemma expr_type_extends : forall e tau,
%expr_type e tau = expr_type e tau.
Lemma etype_valid_extends : forall G env,
%etype_valid env G = etype_valid env G.
Lemma ty_lam_extends : forall sigma tau,
%ty_lam sigma tau = ty_lam sigma tau.