Question 5.

Prove or disprove the following statements. To prove a statement is true, give a formal argument (in cases involving implications among FD's, use Armstrong's Axioms). To disprove falsity, give a counter example. a) {A -> B, C -> AB} ---> {C -> B}. b) {KL -> M, L -> N} ---> {KN -> M}. c) {A -> C, BD -> A, C -> D} ---> {AB -> CD} d) A relation scheme with only three attributes is necessarily at least in 3NF.