(** Compatibility between a compilation environment and an address-taken set. *)
Definition compat_cenv (atk: VSet.t) (cenv: compilenv) : Prop :=
forall id, VSet.In id atk -> VSet.In id cenv -> False.

Lemma compat_cenv_union_r:
forall atk1 atk2 cenv,
compat_cenv (VSet.union atk1 atk2) cenv -> compat_cenv atk2 cenv.