I asked a friend the classic question about the two guards and two doors that goes as follows:
The rules are clear: there are two doors. One leads to the castle, the other, to certain death. You may ask one question – to one guard – to help you decipher which door is the correct one. It sounds simple enough, but there’s a catch: one guard always lies, and one always tells the truth.
His answer is to ask any guard, "is the truth telling guard in front of the castle door". And if the guard says yes he goes through that door, and if he says no then go through the other door.
Is this correct? I haven't heard it being answered like this before.