;;; We must only return NIL when it is *certain* that a check will not
;;; be done, since if we pass up this chance to do the check, it will
;;; be too late. The penalty for being too conservative is duplicated
;;; We must only return NIL when it is *certain* that a check will not
;;; be done, since if we pass up this chance to do the check, it will
;;; be too late. The penalty for being too conservative is duplicated