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[[File:Paul_Klee_Ueberschach.jpg|left|thumb|200px|Paul Klee, Überschach, 1937 <ref>[[Arts#Klee|Paul Klee]], Ueberschach, 1937, [https://commons.wikimedia.org/wiki/File:Paul_Klee_Ueberschach.jpg] [https://en.wikipedia.org/wiki/Wikimedia_Commons|Wikimedia Commons], [https://en.wikipedia.org/wiki/Kunsthaus_Z%C3%BCrich|Kunsthaus Zürich]</ref>]] A chess program needs an internal '''board representation''' to maintain [[Chess Position|chess positions]] for its [[Search|search]], [[Evaluation|evaluation]] and [[Chess Game|game-play]]. Beside modelizing the [[Chessboard|chessboard]] with its [[Pieces|piece]]-placement, some additional information is required to fully specify a chess position, such as [[Side to move|side to move]], [[Castling rights|castling rights]], possible [[En passant|en passant]] target square and the number of [[Reversible moves|reversible moves]] to keep track on the [[Fifty-move rule|fifty-move rule]].