Hint Resolve closed_wrt_Econst_int : closed.

(* Specifications: *)
Lemma closed_wrt_PROPx:
forall S P Q, closed_wrt_vars S Q -> closed_wrt_vars S (PROPx P Q).
Lemma closed_wrtl_PROPx:
forall S P Q, closed_wrt_lvars S Q -> closed_wrt_lvars S (PROPx P Q).