Introduction

Sligo is a territory game for two players: Black and White. It's played on the intersections (points) of an initially empty square board. Each player must have access to a sufficient number of stones of their own color.

This game is a mix of all the placement and movement rules of Corey Clark's Slither and the capture rule and winning condition of the ancient game of Go. Captures are performed after placements. Area scoring is used, and suicide is not allowed. The ko rule isn't needed.

Definitions

A player's group is a set of one or more orthogonally contiguous stones of that player's color. A portion of a larger group is not a group.

A liberty of a group is an empty point orthogonally adjacent to that group. A group without liberties is said to be surrounded.

A player's territory is a set of orthogonally contiguous empty points such that all points orthogonally adjacent to it are occupied by stones of that player's color.

A weak pair is a set of two like-colored, diagonally adjacent stones such that there is no like-colored stone orthogonally adjacent to both.

Play

Black plays first, then turns alternate. On your turn, you must either pass or place a stone of your color on an empty point. Before placing a stone, you may also move a stone of your color to an orthogonally or diagonally adjacent empty point.

After placing a stone, remove all surrounded enemy groups. In the resulting position, there must be no weak pairs and no surrounded groups of any color on the board.

Play stops when both players pass consecutively. At this point, the players may agree which groups, if any, can be removed from the board without changing the scores that would result from continuing the game. If there is such an agreement, the agreed groups are removed, the game ends and the resulting position is used for scoring. If the players don't agree which groups should be removed, play is resumed. In this case, when both players pass consecutively again, the game ends and the current position, without further removals, is used for scoring.

A player's score is the number of stones of their color on the board, plus the number of empty points in territories of their color, plus the value of komi (see below) in the case of White.

The player with the higher score wins the game.

Komi

The komi is the number of points which is added to White's score at the end of the game as a compensation for playing second. Before the game starts, the first player chooses the value of komi, and then the second player chooses sides.