I've come to a problem while doing the Mathematical thinking Course on Coursera.
The problem statement is:
There are two football teams in a town. Each of the citizens is supporting one of the teams. If among someone's friends there are more fans of another team, than of his own, this person tend to switch to supporting the other team. Each day one of such persons switch. Is it possible that this switching process goes forever (assume that friendship is always mutual and that the population of the city and friendship do not change)?
And here's the instructor's explanation: https://www.coursera.org/learn/what-is-a-proof/lecture/9kr3d/termination
He makes an assumption that if a friend of a friend switches sides, they will not affect the number of one's friends team preference and make one go back and forth indefinitely.