Definition:Chess

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Chess is a game for two players. It is played using pieces placed on a chessboard, where players take turns to move a piece.

A piece is captured if an opposing piece moves onto the same space. The opposing piece is attacking. The captured piece is then removed from the board, unless it is a King. It is forbidden to capture your own piece.

If a piece could be captured in one move by any piece, it is threatened.

A piece cannot move over another piece, unless it is a Knight, or it is castling.

If a King is captured, the player who captured it wins immediately.

A King is put in check if it is threatened by any piece.

This is checkmate if the player who owns the King cannot prevent the King from being captured using one move.

The only other way to win is if a player indicates that he resigns, traditionally by knocking over his own King.

Chessboard

A chessboard is a grid containing alternating black and white squares, as shown.

Chessboard

This may be referred to as an $n\times n$ chessboard, where $n$ is the number of squares along each edge.

Pieces

Each kind of piece can be moved in a different way.

King

The King can move one space in any direction, including diagonally. It cannot be moved into a position where it is in check.

Queen

The Queen can move any number of spaces, but only in 8 different directions: forwards, backwards, left, right, and the four diagonals.

Bishop

Can move any number of spaces, but only in the four diagonals.

Rook

Can move any number of spaces, but not in the diagonals; only in the cardinal directions forwards, backwards, left and right.

Knight

Can move two spaces in any cardinal direction, and then one space at right angles to that direction. As noted above, it may pass over other pieces and cannot stop until reaching the end of its move.

Pawn

A pawn has a number of different moves available to it.

It can move one space towards the opposing player, but only if to do so would not result in capturing a piece. If the pawn has not yet moved, it may move two spaces forwards instead of one.

It may move diagonally towards the opponent and to the left or right, but only if this would result in capturing a piece.

If an opposing pawn moved two spaces on the previous turn, the pawn may capture it en passant by attacking the space it moved over. The pawn attacks as if the opposing pawn only moved one space.

If a pawn moves onto the space on the final row of the board, it may be changed into any other type of piece. If it is changed to a queen, this is called queening.

Castling

Castling is a special move where, in one move, the King moves two spaces towards a Castle and the Castle jumps over the King and lands on the next space.

This can only be done if:

  • The King and Castle are both in their initial positions.
  • The spaces in between the King and Castle are empty.
  • The King is not in check and neither of the two spaces it moves into put it in check.

Drawing

A draw may occur in several possible ways.

Agreement

This requires that both players agree that neither can win.

Stalemate

Stalemate occurs when neither player is in check, but there are no valid moves the next player can perform.

Repetition

If the same position for all pieces occurs multiple times throughout a game, this is a draw. The exact number is dependent on the specific rules used.

Fifty move rule

If during fifty moves, no piece is moved and no capture is made, either player can claim a draw. This rule is sometimes not used.

Insufficient pieces

In some cases neither player has enough pieces to win, for example one player might have a King and the other a King and a Knight. Thus a checkmate is impossible.