A and B are each either a knight or a liar. A says, "At least one of us is a liar." What are A and B?
Assume that A is a liar. Then his falsely made statement implies that none of A and B is a liar. Hence, both A and B are knights. This is a contradiction.
Accordingly, it follows that A must be a knight, and his true statement implies that B must be a liar.
Consequently, (A, B) = (knight, liar)
Puzzle Solution
