Information Sets

Game Theory · Axiom Academy

Unit 1: Introduction to Game Theory A game has perfect information if every player knows exactly where they are in the game tree when they make a decision. Each node represents a distinct, observable state of the game. Classic examples include chess, checkers, and tic-tac-toe. Watch how each player observes the complete history before making their choice: 2. Imperfect Information & Information Sets In many games, players don't know the complete history. An information set is a collection of decision nodes that a player cannot distinguish between when making their choice. When nodes are in the same information set, the player must choose the same action at all of them (because they can't tell them apart): 3. Simultaneous Moves as Imperfect Information Simultaneous moves are a special case of imperfect information. When two players move simultaneously, neither knows the other's choice when deciding their own action. In extensive form, we model this by having one player move first, but the second player doesn't observe that move. The second player's decision nodes form an information set: 4. Comparing Perfect and Imperfect Information Understanding the difference between perfect and imperfect information helps us analyze strategic behavior and solve games appropriately:

This is the written version of the interactive lesson above. See the full Game Theory course.