Alice: Let's take turns flipping a coin. The first person who gets heads wins. I'll go first. Bob: But you might win on the very first throw. Let's compensate by giving me one extra throw on my first turn. Alice: Fine. Bob:
And let's use my coin, which comes up heads with probability π. Alice:
Well, then I better know π before I agree. What value of π makes the game fair to each player?