I noticed that there is a discussion on rules in Jesper Juul’s blog. More and more, I feel that there would be need to distinguish rules (as something based on agreement,that comes with possibility to cheat) and system in computer games (that regulates play in implemented ways). If one considers sports, there are rules and the laws of nature that both contributes to a sport game, but probably no-one would call gravity as a rule (see also my entries Games and Philosophical Investigations and On Rules, Game Systems, and Practices).
