Before revision: Cooperation among individuals has been one of the most puzzling phonemena in economics and other social sciences. In this paper, I introduce a novel solution concept, dubbed the optimin criterion, which (to the best of my knowledge) is the first parameter-free concept that can selectively explain the direction of well-established non-Nash deviations towards cooperation in games, including the repeated prisoner's dilemma, the traveler's dilemma, the centipede game, and the repeated public goods game.
After revision: Applications of the maximin criterion extend beyond economics to statistics, computer science, politics, and operations research. However, the maximin criterion---be it von Neumann's, Wald's, or Rawls'---draws fierce criticism due to its extremely pessimistic stance. I propose a novel concept, dubbed the optimin criterion, which (to the best of my knowledge) is the first parameter-free concept that can selectively explain the direction of well-established non-Nash deviations towards cooperation in games, including the repeated prisoner's dilemma, the traveler's dilemma, the centipede game, and the repeated public goods game.