 However, it has been shown that not all social norms involve sanctions (Diamond 1935; Hoebel 1954). Moreover, sanctioning works generally well in small groups and in the context of repeated interactions, where the identity of participants is known and monitoring is relatively easy. Still, even in such cases there may be a so-called second-order public goods problem. That is, imposing negative sanctions on transgressors is in everybody’s interest, but the individual who observes a transgression faces a dilemma: she is to decide whether or not to punish the transgressor, where punishing typically involves costs; besides, there is no guarantee that other individuals will also impose a penalty on transgressors when faced with the same dilemma. An answer to this problem has been to assume that there exist “meta-norms” that tell people to punish transgressors of lower-level norms (Axelrod 1986). This solution, however, only shifts the problem one level up: upholding the meta-norm itself requires the existence of a higher-level sanctioning system.