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Omicron Chess is basically the same game as Omega Chess, except the board has two fewer ranks than the Omega Chess board. The Omega Chess board can be seen as a 12x12 board, with most of the sides blacked out. SjaakII cannot implement boards larger than 128 squares, so 12x12 is out. However, 12x10 does work fine. This change in board size makes Omicron Chess to Omega Chess as Capablanca Chess to Freeling's Grand Chess.
In addition to the regular chess pieces, both sides have two extra pieces: the Champion (C) and the Wizard (W). The Champion jumps one or two squares orthogonally, or two squares diagonally (Betza notation: WAD). The Wizard moves one square diagonally or makes a (1,3) (Camel) leap (Betza notation: FC). Under XBoard/WinBoard, the Champion is represented by two crossed swords and the Wizard is represented by a turban.
Pawns move the same as in regular chess: they move one step forward and capture diagonally. On their initial move they may move forward two spaces. If they do, they can be captured en-passant on the next turn. Unlike in Omega chess, pawns can only move two spaces on their initial move, not three.
The board is 12x10 squares in size, but apart from the four corner squares, the edges are removed and play no part in the game, leaving a 10x8 playing area with four extra squares in the corners.
The starting position is shown in the figure left: standard chess pieces are placed as normal, with the two Champions to either side and the Wizards in the corner squares.