(** Safe expressions are well-formed with respect to l-values and r-values. *)

Definition expr_kind (a: expr) : kind :=
  match a with
  | Eloc _ _ _ => LV
  | Evar _ _ => LV
  | Ederef _ _ => LV
  | Efield _ _ _ => LV
  | _ => RV
  end.

(* Specifications: *)
Lemma lred_kind: forall e a m a' m', lred ge e a m a' m' -> expr_kind a = LV.
Lemma rred_kind: forall a m t a' m', rred ge a m t a' m' -> expr_kind a = RV.
Lemma callred_kind: forall a m fd args ty, callred ge a m fd args ty -> expr_kind a = RV.
Lemma context_kind: forall a from to C, context from to C -> expr_kind a = from -> expr_kind (C a) = to.
Lemma imm_safe_kind: forall e k a m, imm_safe ge e k a m -> expr_kind a = k.
Lemma safe_expr_kind: forall from C f a k e m, context from RV C -> safe (ExprState f (C a) k e m) -> expr_kind a = from.