.25 Consider the following proposed rule for functional dependencies: If and , then . Prove that this rule is not sound by showing a relation r that satisfies and , but does not satisfy . 29 Consider the following set F of functional dependencies on the relation schema r(A,B,C,D,E,F) : ABCDBCDEBDDA a. Compute B+. b. Prove (using Armstrong's axioms) that AF is a superkey