(* Definition stackframe_of (f: Clight.function) : assert := fun rho => sepcon_list (map (fun idt => var_block Share.top idt rho) (Clight.fn_vars f)). *)

Lemma  subst_derives:
forall a v P Q, (forall rho, P rho |-- Q rho) -> forall rho, subst a v P rho |-- subst a v Q rho.