Oust
Overview
Oust is a two player abstract game played on a Go board that was invented by Mark Steere in 2007.

Board

Oust can be played on a rectangular grid of any size, odd or even.

Object of the Game

The goal of Oust is to capture all opponent's stones on the board.

Play

The game begins with an empty board.

Each player has an allocated color: Black or White.

Starting with Black, players take turns placing stones of their own color on empty intersections of the board.  There are two kinds of legal moves a player can make:

  • Non-capturing move. A player can put his stone on any empty intersection that does not have any horizontally or vertically adjacent stones of that player's color.  Some examples of non-capturing moves are shown with transparent stones in the following picture:

Transparent white stones show some possible non-capturing moves for White.

  • Capturing move.  A player can put his stone on an empty intersection that is horizontally or vertically adjacent to another stone (or stones) of his color if by doing so the player creates a group of horizontally or vertically connected stones of his color (including the placed one) that meets the following conditions:
          - the player's new group of stones touches at least one opponent's stone;
          - all groups of opponent's stones that touch the player's group must be smaller than the player's group.
    When making such a move all opponent's groups touching the player's group are removed from the board and the player gets an extra turn. Below are some examples:

 

 
The transparent black stone shows one of the possible capturing moves.  By placing this black stone the Black player creates a group of three black stones that touches one white group containing two stones and another white group containing a single stone. Both white groups are smaller than the formed black group so this is a legal capturing move.   After the move all touching white groups are removed from the board.
     
 
The transparent white stone shows one of the possible capturing moves. By placing this white stone, the White player creates a group of two white stones that touches one black group containing a single stone.  This black group is smaller than the formed white group so this is a legal capturing move.   After the move all touching black groups are removed from the board.
     
   
The transparent white stones show some of the illegal moves. The top transparent stone cannot be placed because it forms a group of white stones that touches a black group that is not smaller.  The bottom transparent stone cannot be placed because it forms a group of white stones that doesn't touch any black stones.    

If a player doesn't have any legal moves then he passes his turn, but a player must move if possible.  A player wins the game by capturing all the opponent's stones.

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