 For any strategy \(\bi\) in the IPD (or indeed in any iterated finite game), however, there are strategies \(\bj\) different from \(\bi\) such that \(\bj\) mimics the way \(\bi\) plays when it plays against \(\bi\) or \(\bj\). The existence of these “neutral mutants” implies that MS cannot be satisfied and so no EPD has usn-stability. This argument, of course, uses the assumption that any strategy in the iterated game is a possible invader. There may be good reason to restrict the available strategies. For example, if the players are assumed to have no knowledge of previous interactions, then it may be appropriate to restrict available strategies to the unconditional ones. Since a pair of players then get the same payoffs in every round of an iterated game, we may as well take each round of the evolutionary game to be one-shot games between every pair of players rather than iterated games. Indeed, this is the kind of evolutionary game that Maynard Smith himself considered. In this framework, any strategy \(\bS\) such that \((\bS,\bS)\) is a strict nash equilibrium in the underlying one-shot game (including unconditional defection in the PD) meets the MS condition. Thus MS and usn-stability are non-trivial conditions in some contexts.