## 28.

In this problem, there are two characters: A and B. Each of them is either a knight or a liar. A makes the following statement: "At least one of us is a liar." Who among the two characters A and B is the knight and who is the liar?
28. Suppose A is a liar. If this were the case, then the statement "At least one of us is a liar" would be false (since liars make false statements). Therefore, in this case, A and B would both be knights. Thus, if A were a liar, he would not be a liar, which is impossible. Hence, we conclude that A is not a liar, he is a knight. But then the statement made by A must be true. Therefore, at least one of the two characters A and B is indeed a liar. Since A is a knight, B must be the liar. Thus, $A-$ is a knight, and B is a liar.