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_unop: forall op ty1 ty v1 m v, type_unop op ty1 = OK ty -> sem_unary_operation op v1 ty1 m = Some v -> wt_val v1 ty1 -> wt_val v ty.