 When Kendall et al began organizing their IPD tournaments to mark the 20th anniversary of the publication of Axelrod's influential book, they received an innocent-seeming inquiry: could one entrant make multiple submissions? If they did not immediately realize the significance of this question, they must surely have done so when a group from the Technical University of Graz attempted to enter more than 10,000 individually named strategies to the first tournament. Most of these aspiring entries were disallowed. As it turned out, however, the winning strategy came from a group from the University of Southhampton who themselves submitted over half of the 223 strategies that were allowed. As the groups from Graz and Southhampton realized (and participants in Axelrod's earlier tournament apparently did not), a good way to win a round-robin IPD is to accompany one's entrant with an army of “enablers” that boost its score relative to others. In extreme form, the master strategy and its enablers begin by playing a short code sequence of \(\bC\) and \(\bD\) moves by which each can be identified by either. Thereafter the enablers always cooperate against the master (allowing themselves to be exploited) and defect against all others (thereby lowering scores of the master's competitors). The master defects against the enablers and plays a reasonable strategy (like TFT) against all others. Under these circumstances the score of the master depends on only two factors: the size of its enabling army, and the accuracy and cost of the identifying code sequence. Accuracy is less than perfect if an outside strategy “accidentally” begins a game with the code sequence. Cost is the payoff value lost by using early moves to signal one's identity rather than to follow a more productive strategy. Longer codes produce greater accuracy at greater cost. Coming to a better appreciation of these ideas, Kendall et al organized additional tournaments in 2005, one restricting each author to a single entry and another restricting each author to a team of twenty entries (though, as Slany and Klienrich observe, such restrictions are difficult or impossible to enforce.)