A gruesome logic puzzle goes thus: A man has been condemned to death. His jailer knocks on his jail cell and says: you will be executed sometime this March, but whenever it happens, it’s going to come as a surprise. The prisoner goes back to his bench while the other prisoners in his cell mutter their sympathies. Five minutes later, the condemned man is jumping up for joy. The other prisoners are aghast: why are you so happy you idiot? Don’t you know you’re going to be hanged next month?