 A simple set of eight “reactive” strategies, in which a player acts solely on the basis of the opponent’s previous move, is shown in  Figure 15.  Coded with “1” for cooperate and “0” for defect and three places representing first move i, response to cooperation on the other side c, and response to defection on the other side d, these give us 8 strategies that include all defect, all cooperate, tit for tat as well as several other variations. 