Multiplayer zero sum games In a course I'm taking, the professor mentioned that a zero sum games are only interesting for 2 players.
Can someone explain me that?

Take any $n$-player game. Add a $n+1$th dummy player who has a single action available and a payoff function $u_{n+1}$ given by $u_{n+1}(a_1,\ldots,a_n,a_{n+1})=-\sum_{i=1}^n u_i(a_1,\ldots,a_n)$. This $n+1$-player game is a zero-sum game that is strategically equivalent to the original $n$-player game.  
