Some researchers have proposed the concept of marked nulls. A marked null ⊥i is equal to itself, but if i ≠ j, then ⊥i ≠ ⊥j . One application of marked nulls is to allow certain updates through views. Consider the view instructor info (Section 4.2). Show how you can use marked nulls to allow the insertion of the tuple (99999, "Johnson", "Music") through instructor info.