One of the things you think about as a designer is how opaque is the model going to be? Is the model something that we never want somebody to see under the hood, or is it something where we give them the exact rules? You know, Chess, I know exactly how all the pieces move; there's nothing opaque about the rules or the behavior whatsoever. Most of the... the landscape that I'm studying in Chess really comes from emergence. And so that's a big part of it. In some games, you're expecting the person to slowly reverse-engineer the way the system works underneath; SimCity is kind of like that. Other games like Tetris, right from the very beginning they understand the way the world works and now they're trying to apply the knowledge of those rules to solve a problem. So I think, you know, the level of detail can vary wildly in these games and it just kind of puts the player's focus in a different area.