Go

How to play Go

The rules

• Two players, Black and White, play on a grid of lines — 19 by 19 on a full board. Stones go on the points where the lines cross, 361 in all, not in the squares. The nine marked points are for handicap stones.
• The board starts empty. Black plays first, and then the players take turns, placing one stone at a time. A stone never moves once it is placed. Instead of placing a stone, you may pass.
• The empty points right next to a stone along the lines are its liberties: four in the middle of the board, three on the edge, two in a corner. Diagonals do not count in Go.
• Stones of one colour that touch along the lines form a chain. A chain shares its liberties, and it lives or dies as one.
• Take away the last liberty of a stone or a chain, and it is captured: it comes off the board at once and is kept as a prisoner.
• You may not place a stone where it would have no liberties — unless that stone takes the last liberty of an enemy stone or chain. Then the enemy is captured, and your stone stays.
• Ko: when a single stone has just captured a single stone, and could be captured straight back, the other player must first play somewhere else. Otherwise the same two captures could go back and forth for ever.
• A group with two separate empty points inside it — two eyes — can never be captured, because the opponent cannot place a stone in either of them.
• Seki: sometimes stones of both colours are locked together so that neither side can attack without putting itself in danger. Then they all stay on the board, and the empty points between them belong to nobody.
• The game is over when both players pass, one after the other. Stones that cannot escape capture are dead: they come off and count as prisoners.
• Each player scores one point for every empty point they have surrounded — their territory — and one point for every prisoner. The higher score wins.
• Handicap: a weaker player can take Black and start with 2 to 9 stones on the marked points. On the full board, two go on d4 and q16, a third on q4, a fourth on d16, and so on up to nine. White then plays first.

In this version

• You can play on 9×9 or 13×13 as well as 19×19. The smaller boards give shorter games.
• When both have passed, press the groups you think are dead to mark them (the machine makes a suggestion). «Count up» then adds up territory and prisoners. If you do not agree, press «Play on».
• There is no komi unless you choose it: White can be given 6.5 points to make up for moving second.
• The machine plays on random playouts (Monte Carlo). It is a beginner on 9×9 and weaker the larger the board; on 19×19 it is mostly for trying out the rules.
• «Strong — GNU Go» hands the machine's moves to GNU Go 3.8, a separate program that runs in your browser and is free software under the GNU General Public License (its source code is at gnu.org/software/gnugo). It is a real club player; the first move takes a few seconds while it loads.
• On a crowded board the first press places a transparent stone, and a second press on the same point places it.

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