You are in a room - there are two unmarked exit doors, one leads to certain death and the other to safety. A guard is next to each door. You know that one guard is a total liar and one always tells the truth, but you do NOT know which is which. The guards know which door is which and also know that one of them always tells the truth. You are allowed to ask only one guard a question - to enable you to exit via the 'safe door' (unless you want to die, but that is another posting!). What question would you ask?
