1. Let R be the universal set. Let A = {1}, B = (0,1) = {x : 0 < x < 1} and C = [0,1] = {x : 0 x 1]. Write down the following sets. AB; AB; BC; AC; AC Are any of the pairs of sets A, B and C disjoint?

2. Let A,B,C,D be nonempty sets. Prove thatA B C D if and only if A C and B D.