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Chess is played on a square board, divided into 64 squares of alternating color (32 white, 32 black), upon which move 16 "light" and 16 "dark" pieces. Chess sets are usually either black and white, red and black, or white and green.
Sets used for play are commonly made of wood or plastic, although ornamental sets of stone, glass, or metal are often used to decorate homes. Likewise, the chessboards themselves can be made of wood, cardboard, leather, stone, glass, or any other material that the design can be placed on. Many times the board is also used in the game of checkers. Many travel boards fold into a box and the pieces fit inside.
The board is placed so that a light-colored square is in the right corner; a dark one in the left. Each player controls sixteen pieces: a king, a queen, two rooks, two bishops, two knights, and eight pawns. At the beginning of the game, the pieces are arranged as shown in the diagram to the left: the rooks are the pieces in the corners, next to them are the knights, then the bishops, and queen and king in the center, behind the eight pawns. Note that the White queen starts on a white square, and the Black queen starts on a black square.
The "color" of each player is determined either by mutual agreement; or by random means. The player controlling the white pieces moves first, then the players alternate moves. While this arguably gives White an advantage, the advantage is generally seen as minor; it is not believed that White can force a win, if Black is played properly. Fritz 8, having analyzed the opening position to a depth of "17", estimated that White has a "quarter-pawn" advantage.
Each piece moves in a different fashion, some pieces can move horizontally, some diagonally, others can "jump"; some pieces can move more than one square (in a single turn) -- others cannot; every piece has different rules regarding its movement. Pieces can also "capture" other pieces, thus removing them from the game. Two of the most commonly confused moves are: castling and en passant. In addition, under certain circumstances, a pawn can become a queen; via a process known as "queening".
If a player having the move touches one of his pieces he is under compulsion to move it; if he touches a hostile piece he must capture it, provided that the piece can be properly moved or captured in either case. This rule is of no effect if the piece so touched cannot be moved or captured, as the case may be. Castling is treated as a move of the King rather than a move of two pieces; the King must be touched before the Rook in order to perform Castling. If the Rook is touched first, then the Rook must be moved if possible. So long as the hand has not left the piece to be moved, the latter can be placed on any accessible square. If a player touches a piece with the sole object of adjusting its position, he must apprise his opponent of his intention by saying "J'adoube" beforehand.
If a player has castled illegally, Rook and King must be moved back, and the King must make another move, if there is a legal one. If not, any other move can be played. A player who makes an illegal move with a piece must retract that move, and make another one if possible with the same piece. If the mistake is only noticed later on, the game should be restarted from the position in which the error occurred.
White is checkmated
A player's king is never captured. When a player makes a move that threatens the opposing king with capture, the king is said to be in check, and the player with the move is required to immediately eliminate the threat by one of three means:
Move the king to a square not threatened;
Capture the threatening piece; or
Place a piece between the king and the threatening piece.
A player may never leave his king in check at the end of his move.
In informal games, it is customary to announce "check" when making a move that puts the opponent's king in check. In formal competitions, this is not only unnecessary but may be considered annoying or distracting.
If a player's king is placed in check, and there is no legal move that player can make to escape check, then the king is said to be checkmated, the game ends, and that player loses. The diagram to the right shows a typical checkmate position. The white king is under attack by the black queen; every square to which the king could move is also attacked; and he cannot capture the queen, because he would then be attacked by the rook.
White is stalemated
The game ends in a draw on one of these conditions:
The player to move is not in check but has no legal move (This is called a stalemate, and such a position is shown in the diagram to the left.);
There is no possibility for either player to mate the opponent, because there are insufficient pieces remaining;
By agreement of the players.
Either player may claim a draw by indicating that one of the following conditions exists:
Fifty moves have been played by each player without a piece being captured or a pawn moved.
The same board position has been repeated three times, with the same player to move and all pieces having the same rights to move, including such things as the right to castle or capture en passant. In particular, if a player is able to check the opposing king continually (perpetual check) and he indicates his intention to do so, the game is considered a draw.
Tournament games are played under time constraints. Each player must make all his moves in a specified time, or be in danger of forfeit.
If there is a checkmate on the board, the player delivering checkmate wins, no matter what is subsequently noticed about the time.
If player A calls attention to the fact that player B is out of time, but it is then noted that player A is also out of time, the game is drawn.
If player A calls attention to the fact that player B is out of time, player A is not out of time, and player A has sufficient material to checkmate (either a pawn, a knight and a bishop, two bishops, a rook, or a queen), then player A wins immediately.
If player A calls attention to the fact that player B is out of time, and player A does not have sufficient material to checkmate, the game is drawn.
Various tournament rules have been devised to prevent players from playing on with no practical chances of winning on the board, intending merely to win when their opponent runs out of time. For example, a king and rook versus a king, bishop, and pawn cannot be won by either player 99% of the time, even though both sides theoretically have enough material to checkmate. The player with more time might play quickly in hopes of inducing a blunder or running out the opponent's clock. If a player believes his opponent is attempting to win a drawn position on time, he may appeal to a tournament official, who may impose a result or a penalty in accordance with whatever rules are in effect for that tournament.
In formal competition, each player is obliged to record each move as it is played in order to settle disputes about illegal positions and overstepping time control. Algebraic chess notation is presently used for this, though some older books still use descriptive chess notation.