The Two Guards Riddle: A Couple of Insights
Remember that riddle with the two doors and the two guards, where one always lies and one always tells the truth? I was reminded of it when it came up in a podcast recently. After some thought, I had a couple of insights. Just to recap, the riddle goes like this. You are trapped in a room with two exits. One leads out to freedom, while the other leads to certain death. You can't tell the difference without taking the risk and stepping through a door. There are two guards in the room with you. These guards will happily let you step through a door. They have a peculiar quirk: one guard always lies, while the other always tells the truth, but again you don't know which is which. They know which door leads out and which leads to death. You can ask ONE of the guards ONE yes-or-no question. Your goal, of course, is to use that one question to determine which door you should pass through and avoid certain death. An example question that would not work: "Does the left door lead