riddle

[neach]

This was in the film the Labrynth and has been driving me mad. There are two doors, one good and one bad, and two gargoyles guarding them. One always lies, and the other always tells the truth. What question(s) can you ask to find out the right door.

[Quizmonster]

Approach Gargoyle A and ask: "If I asked Gargoyle B which door is good, what would he say?" When he answers, choose the other door!

If Gargoyle A is the liar, he will lie about the truth-teller's answer. But the truth-teller's answer would be the right door. If Gargoyle A is the truth-teller, he will 'truthfully' tell you the lie that the liar would tell you...ie the wrong door. So, once again, you take the other door. Whichever is which - you can work out which is the right door.

[incitatus]

this is a combination of logic gates. by combining them in any order you get a not gate (if i remember rightly) which always lies.