Droched

Introduction:Droched (from Irish: Droichead, meaning "bridge") is a board game for two players: Black and White. It is played on the hexes (cells) of an initially empty hexagonal board. The default board size is 9 points per side, but it can be played on a 11–sized board for longer games or on a 7–sized board for shorter games. There is also a location outside the board called the prison. Each player has access to a sufficient supply of stones of their own color.



Definitions:– A group is a set of stones of the same color connected to each other. A single stone is also a group.
– It is said that a group is on a bridge if any of its stones have paths through empty cells connecting it to at least two board edges, two corners, or one board edge and one corner. If none of the stones in a group have those paths, the group is on a broken bridge. The corners are not part of the edges.



Turns:Black plays first, then turns alternate. On your turn, perform one of the following actions:

– Place a stone of your color on an empty cell. Then, in the following order, move to the prison (i) all enemy groups on broken bridges and (ii) all friendly groups on broken bridges.
– Remove an enemy stone from the prison.

At the end of your turn, the stone you placed must not be the only dead stone, and the board position must be different from the board positions at the end of all your previous turns.



End of game:The game ends when a player takes the last action, in which case they are declared the winner.

To make the game fair, before it begins, the first player places several black stones in the prison and then the second player chooses a side. This method of balance is called the komi pie. For handicap games, the weaker player takes black and starts by placing on the board a number of black stones proportional to the difference in skills between the players.



Notes:The prison mechanism was introduced by David Wolfe and Elwyn Berlekamp in their book Mathematical Go: Chilling Gets the Last Point.

—description from the designer