3.3.6 Practice your proof skills by giving formal proofs of the following results from Theorems 3.8 and 3.9. With practice you should be able to prove all of parts of these theorems (and of Theorem 3.10) these without looking at the arguments in the notes! (a) A = . (b) A (B C) = (A B) C. (c) (A C) C = A. (d) A B B C A C