Editing Alpha–beta pruning (section)

== Core idea ==
A [[game tree]] can represent many two-player [[zero-sum game]]s, such as chess, checkers, and reversi. Each node in the tree represents a possible situation in the game. Each terminal node (outcome) of a branch is assigned a numeric score that determines the value of the outcome to the player with the next move.<ref name="levy198601">{{cite magazine |last=Levy |first=David |date=January 1986 |title=Alpha-Beta Soup |url=https://archive.org/details/MacUser8601January1986/page/n101/mode/2up |magazine=MacUser |pages=98–102 |access-date=2021-10-19}}</ref>

The algorithm maintains two values, alpha and beta, which respectively represent the minimum score that the maximizing player is assured of and the maximum score that the minimizing player is assured of. Initially, alpha is negative infinity and beta is positive infinity, i.e. both players start with their worst possible score. Whenever the maximum score that the minimizing player (i.e. the "beta" player) is assured of becomes less than the minimum score that the maximizing player (i.e., the "alpha" player) is assured of (i.e. beta &lt; alpha), the maximizing player need not consider further descendants of this node, as they will never be reached in the actual play.

To illustrate this with a real-life example, suppose somebody is playing chess, and it is their turn. Move "A" will improve the player's position.  The player continues to look for moves to make sure a better one hasn't been missed.  Move "B" is also a good move, but the player then realizes that it will allow the opponent to force checkmate in two moves. Thus, other outcomes from playing move B no longer need to be considered since the opponent can force a win. The maximum score that the opponent could force after move "B" is negative infinity: a loss for the player. This is less than the minimum position that was previously found; move "A" does not result in a forced loss in two moves.