2. Anton, Boris, Vasya, and Grisha met. It is known that each of them is either from the tribe of knights (who always tell the truth) or from the tribe of liars (who always lie). Anton said that he and Grisha are from different tribes. Boris and Vasya called each other liars. And Grisha claimed that there are at least two knights among them. How many of them are there really?
Answer: One knight.

Solution. If Borya and Vasya were from the same tribe, they would have called each other knights. This did not happen. Therefore, one of them is a knight and the other is a liar. If Anton were right, there would be exactly two knights. In this case, Grisha would also be telling the truth, which contradicts the fact that he and Anton are from different tribes. Therefore, Anton is a liar, and Grisha turns out to be his fellow tribesman, i.e., also a liar.

Scoring. Full solution: 12 points. If the correct tribal distribution is indicated (Anton and Grisha are liars, and among Borya and Vasya, one is a knight and the other is a liar) and it is noted that in this case each speaks in accordance with their status, but it is not proven that there are no other solutions, 6 points. If only one of the two possible tribal distribution options is provided, 3 points.