4. On the island, there live knights who always tell the truth and liars who always lie. In the island's football team, there are 11 people. Player number 1 said: "In our team, there are as many knights as there are liars." Player number 2 said: "In our team, the number of knights and the number of liars differ by one," and so on. Player number 11 said: "In our team, the number of knights and the number of liars differ by ten." How many knights are in the team, and if there are any, what are their numbers? Find all possible answers to this question.
4. Answer: There are either no knights at all, or there is only one and he plays under number 10. The two answers cannot both be true, as they contradict each other. This means there can be no more than one true answer. If there is no true answer, then the team consists entirely of liars, in which case indeed none of the answers are true. If there is 1 knight and 10 liars in the team, then the answer of the player under number 10 is true, and the rest of the answers are false.

Criteria: correct solution - 7 points. Stated but not explained why there cannot be two correct answers, no other errors - 5 points. The case of no knights in the team is lost - 2 points. Only noted that there may be no knights - 1 point. Only the answer - 0 points.