We study an economy in which exchange occurs pairwise, there is no commitment, and anonymous agents choose between random monetary trade or deterministic credit trade. To accomplish the latter, agents can exploit a costly technology that allows limited recordkeeping and enforcement. An equilibrium with money and credit is shown to exist if the cost of using the technology is sufficiently small. Anonymity, record-keeping and enforcement limitations also permit some incidence of default, in equilibrium.
Camera, G., & Li, Y. (2008). Another example of a credit system that coexists with money. Journal of Money, Credit, and Banking, 40(6): 1295-1308. http://doi.org/10.1111/j.1538-4616.2008.00158.x