Four-player chess written c. 1500. The "Tithitattva" of Raghunandana describes such a version, which continued to be played into the 20th century. The first documented example of a modern four-player chess system was written by Captain George Hope Verney in England in 1881. The most common form of play is two vs. two in which allied pieces cannot eliminate each other, but help the others in defense and offense. The allied players sit across from each other and help checkmate the people to the left and right of them. The game is over when both opposing kings are checkmated. If only one
Chess and is provably less than 10, with a game-tree complexity of approximately 10. The game-tree complexity of chess was first calculated by Claude Shannon as 10, a number known as the Shannon number. Typically an average position has thirty to forty possible moves, but there may be as few as zero (in the case of checkmate or stalemate) or (in a constructed position) as many as 218. Chess has inspired many combinatorial puzzles, such as the knight's tour and the eight queens puzzle. The idea of creating a chess-playing machine dates to the 18th century; around 1769, the chess-playing automaton