Proposition 1. If the discount parameter, w, is sufficiently high, there is no best strategy independent of the strategy used by the other player. - Robert Axelrod

Proposition 3. Any strategy which may be the first to cooperate can be collectively stable only when w is sufficiently large.

Proposition 5. ALL D is always collectively stable.

A major goal of investigating how cooperative norms in societal settings have been established is a better understanding of how to promote cooperative norms in international settings. This is not as utopian as it might seem because international norms against slavery and colonialism are already strong, while international norms are partly effective against racial discrimination, chemical warfare, and the proliferation of nuclear weapons. Because norms sometimes become established surprisingly quickly, there may be some useful cooperative norms that could be hurried along with relatively modest interventions.