There was a crime, and it was known that either Al, Beth, Dell, or Phil (each a knight or a liar) was guilty. At the trial, the men spoke first, and said:

Phil: Dell did it.
Al: No, Beth is guilty.

Then it was the ladies' turn, who said:

Beth: Al is lying.
Dell: Phil never lies.

Then a lady accused someone, and that let me know she herself was innocent.

And next the other lady accused someone, and that let me know who was guilty.

Who's guilty?

Dell speaks first and accuses Phil.

If she is a knight, then first statement would be true - "Phil never lies" and so "Dell did it", which would mean that Phil didn't do it, and therefore Dell is a liar. That means that Phil does lie, he's also liar, so his statement is a lie and I know that Dell didn't do it.

Dell spoke first, so the other lady to speak must be Beth. She accuses Dell. I already know that Dell didn't do it, so Beth must be a liar, therefore "Al is lying" is a lie. Al is telling the truth, so "No, Beth is guilty" is true.

Beth is guilty!

Posted by Basil on 2005-09-04 02:05:40