Players alternatingly place stones in empty cells. The goal of the game is to capture the majority of the corners. A corner is captured by creating a Y-structure (examples are shown below), which is a connected group of stones that (1) connects two adjacent edges, and (2) connects to any other edge on the board. Rule 2 ensures that once a corner has been captured by one player, it remains captured by that player. Since a full board has all corners captured and the board has an odd number of corners, no game can end in a draw. As the first player has a strong first-player advantage, there is a swap rule which states that the second player may choose to swap sides in its first move.
This Y-structure captures the top corner.
This Y-structure captures both the top and top-right corner.
This Y-structure also captures both the top and top-right corner.