The game models introduced in Section 2 have been used to describe the uncertainty that the players have about what their opponents are going to do and are thinking in a game situation. In the analyses provided thus far, the structure of the game (i.e., who is playing, what are the preferences of the different players, and which actions are available) is assumed to be common knowledge among the players. However, there are many situations where the players do not have such complete information about the game. There is no inherent difficulty in using the models from Section 2 to describe situations where players are not perfectly informed about the structure of the game (for example, where there is some uncertainty about available actions).