There used to be 26 football teams in the National Football League (NFL) with 13 teams in each of two conferences (each conference was divided into divisions, but that is irrelevant here). An NFL guideline said that each team’s 14-game schedule should include exactly 11 games against teams in its own conference and three games against teams in the other conference. By considering the right part of a graph model of this scheduling problem, show that this guideline could not be satisfied!