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_binop: forall ce op ty1 ty2 ty v1 v2 v m, type_binop op ty1 ty2 = OK ty -> sem_binary_operation ce op v1 ty1 v2 ty2 m = Some v -> wt_val v1 ty1 -> wt_val v2 ty2 -> wt_val v ty.