4. If S and T are finite sets show that |S x T| = [SIT|. 5. If S is a finite set show that |P(S) | = 2151. 6. Prove that: (a) for any set S, ids is a bijection. (b) The composite of onto set maps y and y is onto. (c) The composite of 1-1 set maps is 1-1. (d) If 4 : S - T and v : T -+ W are 1-1 correspondences show that the inverse of y and also wop are 1-1 correspondences