Prisoner’s dilemma giving payoffs to interactions, 2b > c > b > 0.

Entries are interaction-payoffs of an individual whose strategy is given by the row when interacting with an individual whose strategy is given by the column. Cooperation provides a benefit of b to both players, but costs c to the cooperating player. This payoff specification corresponds to a public goods setting, in which paying a cost of c provides a public good worth b to each player. An equivalent interpretation is gift giving, in which a cost c* = c − b can be paid to provide a gift worth b to the opposing player.