Definitions

Two stones, or a stone and an empty square, see each other if they lie on the same straight line of orthogonally or diagonally adjacent squares and there are no other stones between them along that line.

You control a square in any of the following situations:

• The square sees stones of your color in three orthogonal directions.
• The square sees stones of your color in two adjacent orthogonal directions and two opposite diagonal directions, provided that each one of the latter directions is adjacent to exactly one of the former.
• The square is on the perimeter of the board and sees stones of your color in two orthogonal directions.

To flip a stone is to replace it with a stone of the opposite color.

Play

Black plays first, then turns alternate. On your turn, place a stone of your color on an empty square not controlled by your opponent or flip an enemy stone on a square you control. If you have no moves available on your turn, you must pass. Passing is otherwise not allowed.

You win if, at the start of your turn, there is a chain of orthogonally adjacent stones of your color touching the two opposite board edges of your color.

Pie rule

The pie rule is used in order to make the game fair. This means White will have the option, on their first turn only, to swap sides with their opponent instead of making a regular move.