Given what that player has observed, an information set shows the decision vertices available to the player which are undistinguishable to them at the current point in the game.
In a perfect information game, every information set only contains one member.
You can circle, or box, or circle. https://www.youtube.com/watch?v=8qDKhulJ-9k&ab_channel=KatherineSilz-Carson
- Each node can only be part of one information set.
- Each node in an information set must have the same branches.
In a game of Perfect Information, players always know what node they are at. Each information set contains exactly one node.
In a game of Imperfect Information, at least one information set contains more than one node.