1. The problem statement, all variables and given/known data GIve a formal proof or derivation of: (a iff (b iff c)) iff ((a iff b) iff c)) 3. The attempt at a solution I've tried it for a long time. Idea is to assume (a iff (b iff c)) then get ((a iff b) iff c)) and then vice versa. BUt no matter how I try, I always get some if conditions istead of the iff.