1. Axhausen, K.: Social networks and travel: some hypotheses. http://e-collection.ethbib.ethz.ch/ecol-pool/incoll/incoll_964.pdf - accessed July 2005 (2003)
2. Bhat, C.R, Guo, J., Srinivasan, S., Sivakumar, A.: Activity-based Travel Demand Modeling for Metropolitan Areas in Texas: Software-related Processes and Mechanisms for the Activity-travel Pattern Generation Microsimulator. Research Report 4080-5, Center for Transportation Research, Austin, Texas (2003)
3. Cory, G.A.: The Reciprocal Modular Brain in Economics and Politics. Kluwer (1999)
4. Gill, C., Postlethwaite, N., Seaford, R.: Reciprocity in Ancient Greece, Clarendon Press (1998)
5. Gintis, H., Bowles, S., Boyd, R., Fehr E.: Explaining altruistic behavior in humans. Evol. Human Behav. 24, 153–172 (2003)