While trekking through the swamp of Knights and Knaves, you come upon a pair of doorways: One leading out of the swamp, the other leading to your doom. The swamp of Knights and Knaves is a strange place, where everyone either always lies or always tells truth. Before the doorways is a great two-headed thurse, guarding the door. "One of us always tells the truth.." begins one head, "..and one always lies" finishes the other. You may only ask a single question to one of the heads
What question can you ask to determine which door you should go through?
The guards were the ones who informed you of the rules