Corollary check_rval_wt:
  forall a x, wt_expr ce e a -> check_rval a = OK x -> wt_rvalue ce e a.Corollary check_lval_wt:
  forall a x, wt_expr ce e a -> check_lval a = OK x -> wt_lvalue ce e a.

Lemma pres_sem_cmp: forall ty1 ty2 msg ty c v1 v2 m v, comparison_type ty1 ty2 msg = OK ty -> sem_cmp c v1 ty1 v2 ty2 m = Some v -> wt_val v ty.