In Rules of Play, Salen & Zimmerman describe Marc LeBlanc’s 3-to-15 game. Its rules are:

1. Two players alternate turns.
2. A player’s turn consists of picking a number between 1 and 9.
3. No number can be picked more than once.
4. If any three of the numbers picked by a player add up to 15, the player wins the game.

3-to-15 shares the same underlying mechanics as Tic-Tac-Toe (per the image to the right), even though its written rules are entirely different. Try playing a few games of 3-to-15. Is it the same game as Tic-Tac-Toe, or do you think the differing ways the games are presented results in them being truly different games?