What the report covers

The assignment explains extensive-form games and uses them to think about the credibility of decisions. It is not a prisoner's-dilemma reprint, and it is not a history of Joseon's opening, which belongs to a different paper.

Start with the tree, then ask what a strategy is, then ask which plans survive when every node is taken seriously.

Trees, strategies, and information

Each node belongs to a player. A strategy in the extensive form is a complete plan: an action at every node where that player might have to move, including nodes that will not be reached if earlier choices go another way.

If a player cannot observe a previous move, the tree uses information sets. A paper should say whether the example is a game of perfect or imperfect information, rather than drawing a tree that hides that fact.

Credibility and backward induction

A promise or a threat written at the start of the tree may not be believable at a later node. Backward induction starts at the end and asks what a rational player would actually do there. Subgame-perfect equilibrium, in Selten's line of thought, requires optimality in every subgame, not only on the path that is supposed to be played.

That is the sense in which 'credibility of a decision' is a technical question, not a moral slogan.

A fair assignment example

Take a two- or three-move textbook tree — entry and predation, or a simple bargaining tree — mark the backward-induction path, and state which off-path threat is not credible. If you add a real organisation,

Sources

1. Osborne, M. J. (2004). An introduction to game theory. Oxford University Press.
2. Watson, J. (2013). Strategy: An introduction to game theory(3rd ed.). W. W. Norton.
3. Selten, R. (1965). Spieltheoretische Behandlung eines Oligopolmodells mit Nachfrageträgheit. Zeitschrift für die gesamte Staatswissenschaft(the subgame-perfect idea later named by Selten).

Last updated: November 13, 2026

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