Ltac StepL REC C' a :=
  let b := fresh "b" in let ofs := fresh "ofs" in
  let E := fresh "E" in let S := fresh "SAFE" in
  exploit (REC LV C'); eauto; intros [b [ofs E]];
  assert (S: safe (ExprState f (C' (Eloc b ofs (typeof a))) k e m)) by
    (eapply (eval_simple_lvalue_safe C'); eauto);
  simpl in S.Ltac StepR REC C' a :=
  let v := fresh "v" in let E := fresh "E" in let S := fresh "SAFE" in
  exploit (REC RV C'); eauto; intros [v E];
  assert (S: safe (ExprState f (C' (Eval v (typeof a))) k e m)) by
    (eapply (eval_simple_rvalue_safe C'); eauto);
  simpl in S.

Lemma simple_can_eval_rval: forall r C, simple r = true -> context RV RV C -> safe (ExprState f (C r) k e m) -> exists v, eval_simple_rvalue e m r v /\ safe (ExprState f (C (Eval v (typeof r))) k e m).