algorithms that can produce perfect play from any position, are known for some simple games such as Tic Tac Toe/Noughts and crosses (draw with perfect play) and Connect Four (first player wins). Physical limitations of computer hardware aside, in principle it is possible to solve any game under the condition that the complete state is known and there is no random chance. While endgame tablebases for other board games like checkers, chess variants or nine men's morris exist, when a game is not specified, it is assumed to be chess. Tablebases have enhanced competitive play and facilitated the composition of endgame studies. For this reason, tablebases also called into question the 50-move rule since many positions are now seen to exist that would be a win for one side but are drawn because of the 50-move rule initially, as individual cases were found, exceptions to the rule were introduced, but when more extreme cases were later discovered the exceptions were removed. Some positions which humans had analyzed as draws were proven to be winnable in some cases the tablebase analysis could find a mate in more than five hundred moves, far beyond the horizon of humans, and beyond the capability of a computer during play. The solutions have profoundly advanced the chess community's understanding of endgame theory. As of 2022, work is still underway to solve all eight-piece positions. By August 2012, tablebases had solved chess for every position with up to seven pieces (the positions with a lone king versus a king and five pieces were omitted because they were considered to be "rather obvious"). By 2005, all chess positions with up to six pieces (including the two kings) had been solved. Tablebases are generated by retrograde analysis, working backward from a checkmated position. Typically the database records each possible position with certain pieces remaining on the board, and the best moves with White to move and with Black to move. Thus, the tablebase acts as an oracle, always providing the optimal moves. The tablebase contains the game-theoretical value (win, loss, or draw) in each possible position, and how many moves it would take to achieve that result with perfect play. It is typically used by a computer chess engine during play, or by a human or computer that is retrospectively analysing a game that has already been played. A typical interface for querying a tablebaseĪn endgame tablebase is a computerized database that contains precalculated exhaustive analysis of chess endgame positions.
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