1. Alfrink, K. (2011, May). New games for new cities, presentation, future everything std.
2. Anderson, A. (2011). Long after the thrill: Sustaining passionate users. Retrieved from http://www.slideshare.net/stephenpa/long-after-the-thrill-sustaining-passionate-users
3. Aparicio, A. F., Vela, F. L. G., Sánchez, J. L. G., & Montes, J. L. I. (2012). Analysis and application of gamification. In Proceedings of the 13th International Conference on Interacción Persona-Ordenador (p. 17). ACM. https://doi.org/10.1145/2379636.2379653.
4. Ariely, D. (2008). Predictably irrational: The hidden forces that shape our decisions. Harper Perennial.
5. Avedon, E. M., & Sutton-Smith, B. (1971). The study of games. New York: Wiley.