16 secret agents spying each other
Source: Spanish Mathematical Olympiad 1996 P5
July 31, 2018
combinatorics
Problem Statement
At Port Aventura there are secret agents, each of whom is watching one or more other agents. It is known that if agent is watching agent , then is not watching . Moreover, any agents can be ordered so that the first is watching the second, the second is watching the third, etc, the last is watching the first. Show that any agents can also be so ordered.