Checkers
Alpha-beta pruning can be explained simply as a technique for not exploring those branches of a search tree that analysis indicates not to be of further interest either to the player making the analysis (this is obvious) or to his opponent (and this is frequently overlooked).
– Arthur L. Samuel, from Some Studies in Machine Learning Using the Game of Checkers. II—Recent Progress. IBM Journal, November 1967, pp. 601-617.