1.4 Some Fundamental Notions of Game Theory 17 form with perfect or imperfect information (in Chapter 3 the history of a game is defined mathematically for repeated games). Also, the prisoner's dilemma is a static game with imperfect information. Second, the terminology used in game theory dif- fers from that used in communications. In the latter, "imperfect" usually refers to the situation where a quantity is not known perfectly (e.g., because of intrinsic estimation errors), whereas in game theory the underlying notion is the knowledge of the history of the game. In fact, scenarios where some quantities are estimated correspond to the framework of games with incomplete information. (f ) Zero-sum games are those where the sum of utilities is zero (or a constant). The idea is that if someone wins something, someone else necessarily has to lose. Zero-sum games have been studied extensively in the game theory literature (e.g., see Sorin (2002)). In this book, no specific section is dedicated to this class of games. The main reason for this is that this special structure does not seem to appear very often in wireless games, as indicated by the wireless literature (Special issue, 2008). 1.4 SOME FUNDAMENTAL NOTIONS OF GAME THEORY In this section, several fundamental game-theory notions are defined. Understanding