Riddle: There is somewhere far away, a room. In this room there are two robots, seemingly identical in appearance. There is absolutely no way to tell them apart. The only difference is that one robot will always tell you the truth and the other will always tell the opposite of the truth. You are sent to this room. The room is completely empty except fr the two robots and two doors at either side of the room. One room will lead you to paradise and the other to death. You are allowed to ask either robot one, only one, question. What can you ask that will lead you to paradise regardless of the robot you ask.
Answer: What would the other robot tell me is paradise? The one who tells the truth would say a lie because the other rogbot would lie to you and the dishonest robot would tell you the way to death because he lies about what the truthful robot would tell you. Either way, go through the door they don't tell you to go through.