A prisoner is told “If you tell a lie we will hang you; if you tell the truth we will shoot you.” What can he say to save himself?
You will hang me. If they hang him, then the statement was true and they could only hang him for telling a lie. If they shoot him, then it makes the statement a lie and they were only to shoot him for telling the truth. An alternate solution is to say, “You will not shoot me,” leading to the same quandary for the killers.