"For example I was trying to prove this problem: (A-B)-C = (A-C)-(B-C) I thought I would just need to look at the definition of - and work my way to (x is an element of A and x is not an element of C)and ~(x is an element of B and x is not an element of C) I got part way through this proof and got stuck, but when I looked at my teachers solutions he used a theorem that brought in absolute complemen" . . . .