1. The problem statement, all variables and given/known data For what conditions on sets A and B does A-B = B-A hold? 2. Relevant equations A - B = A n B^c B - A = B n A^c 3. The attempt at a solution I know that A = B is the answer, but I just don't know where to start...please don't give me the whole proof, I want to figure it out myself. I just need a hint or an idea of where to start.