You might be interested in this 1 page paper by John Nash, which proves the existence of equilibria for finite N-player games (an extremely powerful result). In essence it uses a set theory result (Kakutani's fixed point theorem), and simply notes that his description of a N-player game meets the required conditions for that result to hold. http://www.sscnet.ucla.edu/polisci/faculty/chwe/austen/nash1...