Consider a standard chessboard with 64 squares with a coin on each square, randomly facing heads or tails up. There is a devil in the room with you and he arbitrarily selects some square and tells you that it is the special square. At this point, you are required to flip one and only one coin on a square of your choice. A friend then comes in and looks at the board. His job is to determine the location of the special square correctly solely by looking at the board. You and your friend can discuss the test beforehand to agree on a strategy, but you are not allowed to communicate in any way once your friend enters the room. What coin do you flip, and how does your friend determine the special square?
