1. Anderson, T., Blank, M., Daniels, B., & Lebling, D. (1977). Zork. Cambridge, MA: Massachusetts Institute of Technology.
2. Barham, D., Goodjohn, P., Medhurst, J., Morris, D., Plumb, S., Friday, P., et al. (1987). MIST. Essex: University of Essex.
3. Bartle, R. (2003). Designing virtual worlds. Indianapolis, IN: New Riders.
4. Blandford, M. (1985). AMP: Adventure for multiple players.
5. Cao, C. (2004). EverQuest 2. San Diego, CA: Sony Online Entertainment.