Extensive form
A game written down as a tree showing who moves when, what they may do, and what they know at the time they do it.
Often misread asAssuming that putting moves in sequence automatically means later players observe the earlier ones, so that order of moves and knowledge of moves become the same thing.
How to see it
The game drawn as it is lived, one decision at a time
The extensive form is the game as a tree: who moves, in what order, knowing what, with payoffs at the ends. It carries information the table does not, namely the sequence of events and what each player has seen by the time they choose.
The checkSequence and observation are separate; information sets are what say whether the later mover actually saw the earlier move.
Try itDraw the prisoner's dilemma as a tree with one player moving first. Then say what you must add to the picture to stop the second player from seeing that move. If you cannot answer, you do not yet have information sets.
Games that show it
Know these first
Leads on to
Easily confused with
Sources
- Kuhn, H. (1953). In Kuhn, H. & Tucker, A. (eds), Contributions to the Theory of Games, Volume II, Annals of Mathematics Studies 28, Princeton University Press, 193-216.
- Osborne, M. & Rubinstein, A. (1994). MIT Press.