Traveling teams
Source: Poland 2014 - Second Round P4
July 28, 2019
combinatorics
Problem Statement
() teams took part in the football league matches and there were matchweeks. In each matchweek each team played one match. Any two teams met with each other during the matches in exactly one game. Moreover, in each match one team was the host and the second was a guest.
Say a team is traveling, if in any two consecutive matchweeks it was once a host and once a guest. Prove that there are at most two traveling teams.