Seirawan chess (also SHARPER chess or S-Chess), is a chess variant invented by American grandmaster Yasser Seirawan and Bruce Harper in 2007. It is played on the standard 8×8 board and uses two new pieces, the hawk (which moves like a knight or a bishop) and the elephant (which moves like a knight or a rook). Yasser Seirawan has given simultaneous exhibitions for the game. The first ever event was a 12 board simultaneous exhibition held March 31, 2007 in Vancouver, Canada.
The initial position is that of standard chess. Each side has additionally two pieces in hand (a hawk and an elephant):
The elephant and the hawk are introduced to the game in the following way: whenever the player moves a piece (king, queen, knight, bishop or rook) from its starting position (that hasn't already been moved), one of the pieces in hand may be placed immediately on the square just vacated. One cannot use the placing of an elephant or hawk to block check. If the player moves all his pieces from the first rank without placing one or both in hand pieces, he forfeits the right to do so. After castling, the player may put one of the pieces in hand on either the king's or the rook's square, but he may not place both pieces in hand in the same turn. Pawns may promote to a hawk or an elephant in this game (in addition to the normal chess pieces).
When notating games in algebraic notation, the letter E is used for the Elephant and H for the Hawk. If the player places one of the two pieces on the board, it is written after a slash. For example, 1. Nc3/E means that the player moved his knight from b1 to c3 and placed the elephant on b1 (see diagram).
Seirawan has expressed dissatisfaction with the name Seirawan chess, noting that the variant was a joint development with friend Bruce Harper. The name SHARPER chess (a combination of the names Seirawan and Harper) has been suggested. Seirawan has also used the term S-Chess when discussing the game.