Lambda-Search in Game Trees — with Application to Go

  • Thomas Thomsen
Conference paper

DOI: 10.1007/3-540-45579-5_2

Part of the Lecture Notes in Computer Science book series (LNCS, volume 2063)
Cite this paper as:
Thomsen T. (2001) Lambda-Search in Game Trees — with Application to Go. In: Marsland T., Frank I. (eds) Computers and Games. CG 2000. Lecture Notes in Computer Science, vol 2063. Springer, Berlin, Heidelberg


This paper proposes a new method for searching two-valued (binary) game trees in games like chess or Go. Lambda-search uses null-moves together with different orders of threat-sequences (so-called lambda-trees), focusing the search on threats and threat-aversions, but still guaranteeing to find the minimax value (provided that the game-rules allow passing or zugzwang is not a motive). Using negligible working memory in itself, the method seems able to offer a large relative reduction in search space over standard alpha-beta comparable to the relative reduction in search space of alpha-beta over minimax, among other things depending upon how non-uniform the search tree is. Lambda-search is compared to other resembling approaches, such as null-move pruning and proof-number search, and it is explained how the concept and context of different orders of lambda-trees may ease and inspire the implementation of abstract game-specific knowledge. This is illustrated on open-space Go block tactics, distinguishing between different orders of ladders, and offering some possible grounding work regarding an abstract formalization of the concept of relevancy-zones (zones outside of which added stones of any colour cannot change the status of the given problem).


binary tree search threat-sequences null-moves proof-number search abstract game-knowledge Go block tactics 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2001

Authors and Affiliations

  • Thomas Thomsen
    • 1
  1. 1.Stockholmsgade 11, 4th.CopenhagenDenmark

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