\begin{thebibliography}{1}

\bibitem{zimmerman}
K.~Salen and E.~Zimmerman.
\newblock {\em Rules of Play}.
\newblock The MIT Press, 2004.

\bibitem{bartle}
Richard Bartle.
\newblock Hearts, clubs, diamonds, spades: Players who suit {MUDs}.
\newblock http://aigamedev.com/open/interviews/mario-ai/, 1996.
\newblock [Online; accessed 18-March-2012].

\end{thebibliography}