Kriegspiel (chess) follows. The game is played with three boards, one for each player; the third is for the umpire (and spectators). Each opponent knows the exact position of just their pieces, and does not know where the opponent's pieces are (but can keep track of how many there are). Only the umpire knows the position of the game. The game proceeds in the following way: The umpire announces: Pawn promotions are not announced. Kriegspiel is sometimes used in chess problems. In these, usual variations introduced by different black moves are replaced by variations introduced by different announcements. An example of a
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