 A common view is that a multi-player PD structure is reflected in what Garret Hardin popularized as “the tragedy of the commons.” Each member of a group of neighboring farmers prefers to allow his cow to graze on the commons, rather than keeping it on his own inadequate land, but the commons will be rendered unsuitable for grazing if more than some threshold number use it. More generally, there is some social benefit \(B\) that each member can achieve if sufficiently many pay a cost \(C\). We might represent the payoff matrix as follows: