Riddle: You come to a fork in the road. You see an old man sitting there. You know that one road leads to danger and the other road leads you safely to the city. You can only ask the man one question to determine whether he is the truthsayer or the liar. What do you ask him?
Answer: Tell me when you find out. I think it's something like: "If this is the correct road, then you will accompany on it, will you not?"