I don't know if its a paradox, but Wikipedia had it listed when I checked a year ago. A judge sentenced a prisoner to death, and the prisoner was told that he would be executed at noon on any of the weekdays the following week, when he least expected it. So the prisoner starts thinking about which day he is going to be executed, and realises he cannot be executed on Friday, because he will be expecting it after the Thursday. HE then works out that he cannot be executed on THursday because after Wednesday, he expects it on Thursday. He uses this logic all the way to Monday and relaxes that he cannot be executed without expecting it. The next Wednesday, at noon, the prisoner hears a knock, its the executioner, who took the prisoner completely by suprise. I hope I said it OK...I thought it was pretty clever when I firts heard it.