We introduce personal time-structures and common time-structures to extensive games. These structures restrict the class of extensive games of Kuhn . We show that if a player has perfect recall, then the game is personally time-structured for him. In the other direction, there are many personally time-structured games that do not satisfy perfect recall. The only known condition on memory that is required by a personally time-structured game is that no player is absent-minded. Common time-structures, on the other hand, are not related to the perfect recall condition at all. An extensive game may have perfect recall and yet no common time-structure, and conversly, a game may have a common time-structure, and no player has perfect recall. Common time-structures are used to extend backward induction results to games with imperfect recall.
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