SECOND ANSWERS Say to a friend: “Will the next word you speak be ‘no’? Please answer by saying ‘yes’ or ‘no.’” POSTSCRIPT
I do not know who first thought of the red-and-green-light version of the computer prediction paradox. It was the basis for a variation I introduced as a betting game in a Scientific American column that became chapter 11 of my New M athematical Diversions. For two other prediction paradoxes, each more difficult to resolve than this one, see puzzles 20 and 31 of this book. Charles Blabbage is an obvious play on Charles Bab bage, the British pioneer of computers that can be pro grammed. Babbage’s good friend and disciple, Ada Au gusta, the beautiful young countess of Lovelace, was wealthy, witty, intelligent, a good mathematician, and the only legitimate child of the poet Lord Byron. She was the first to say that computers do only what they are told to do. The character of Ada, in Nabokov’s novel A da, is partly based on Lady Lovelace. If you want to know more about this remarkable pair, see Charles Babbage and His Calculating Engines by Philip and Emily Morrison; A da, Countess o f Lovelace by Doris Langley Moore; and “Byron’s Daughter” by B. H. Neumann in the Mathematical Gazette, Vol. 57, June 1973, pp. 94-7.
Place the 26 black cards of a deck in one pile. Next to it place, say, 13 red cards. Turn your back and ask someone to take as many cards as he likes from the black pile and shuf fle them into the red pile. Then take the same number of cards from the former all-red pile and shuffle them into the black pile. You turn around, massage your temples, and announce that your clairvoyant powers tell you that the number of red
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