There are 2021 people at a meeting. It is known that one person at the meeting doesn't have any friends there and another person has only one friend there. In addition, it is true that, given any 4 people, at least 2 of them are friends. Show that there are 2018 people at the meeting that are all friends with each other.
Note. If A is friend of B then B is a friend of A. combinatoricsgraph theorycliqueClique number