Ordo X
An abstract board game for 2 players by Dieter Stein.

Material

Terminology

“Group”

Orthogonally or diagonally connected group of all pieces of a player.

Figure 1Pieces of the same color must be always connected.

“Singleton”

A single piece (in contrast to an → ordo).

“Ordo”

Orthogonally (in a straight horizontal or vertical line) connected group of two or more pieces of a player.

Figure 2Ordos are always orthogonally connected.

“Home row”

Nearest row on the board seen from a player’s perspective.

Figure 3Home rows

Setup

Pieces are setup as shown in figure 3.

Figure 4Initial setup

Objective

Players move their pieces trying to reach the opponent’s home row.

Play

Players choose their colors and take a seat on their side of the board. White starts, then players take turns making a move. They may not pass.

Connection

Throughout the game, after a player’s move, all pieces of said player must be connected in one sole group.

Moves and Captures

In general, pieces move (orthogonally or diagonally) forward or sideways, never backwards.

Figure 5Move directions: forward and sideways.

A sideways move must be instantly followed by any other move (including the same or other pieces, but now forward only) in the same turn. Apart from that, a sideways move is a regular move in every respect (see below).

There are two possible ways to move the pieces: singleton moves and ordo moves.

Singleton Moves

A singleton can move forward or sideways, orthogonally or diagonally in a straight line any number of empty squares. It may end the move in an empty square or a square occupied by an opponent’s piece, which is then captured and removed from the board.

Figure 6The marked piece has 5 possible moves. Moving one space ahead and further moves to the left are not allowed as they would split the group. If the piece is moved to the left or the right, the player must make another (forward) move.

Ordo Moves

A group of more than one piece, which is connected in a straight horizontal or vertical (never diagonal!) line (a so called “ordo”), can move side by side or go in single file any number of empty squares. It may move orthogonally forward, diagonally forward, or sideways. It must move in parallel and it may not capture.

Figure 7Orthogonal ordo moves. Note: Sideways ordo moves must be instantly followed by another forward move.

Figure 8Diagonal ordo moves.

Figure 9Forward ordo moves in single file.

Figure 10Sideways ordo moves in single file. Note: a sideways move must be followed by a forward move in the same turn.

Disconnection

If a player disconnects the opponent’s group by capturing a piece, then said player must also remove all opponent pieces, which are not part of the largest subgroup. If there are subgroups with the same number of pieces, the attacking player may choose the pieces to remove.

Figure 11White captures a piece and removes it together with the smaller subgroup made of 2 other pieces.

End of the Game

The main goal of the game is to place (at least) one piece on the opponent’s home row.

Figure 12White wins the game.

Also, a player wins the game if he manages to capture all pieces of the opponent.

Remark

If a player has only one piece left, said piece is still considered a group!