Looking at LibertÃ©'s question "Are you a liar?" how would you know that the person is telling the truth if he answers NO? I understand that if he answers YES, then he's definitely a liar, because he could be lying about the fact that he's a liar....But if he answers NO, then can't he be lying?

I'm confused...

The question I would ask the first person would be:

"If I asked the second person if they were a liar what would they say?"

If the first person is a liar then the second person is honest so the answer would be YES.

If the first person is honest then the second person is a liar so the answer would be NO.

In this way we can work out the order of the liars and honest people.