http://tromp.github.io/go.html

##### The Logical Rules

1. Go is played on a 19×19 square grid of points, by two players called Black and White.

2. Each point on the grid may be colored black, white or empty.

3. A point P, not colored C, is said to reach C, if there is a path of (vertically or horizontally)

adjacent points of P’s color from P to a point of color C.

4. Clearing a color is the process of emptying all points of that color that don’t reach empty.

5. Starting with an empty grid, the players alternate turns, starting with Black.

6. A turn is either a pass; or a move that doesn’t repeat an earlier grid coloring.

7. A move consists of coloring an empty point one’s own color;

then clearing the opponent color, and then clearing one’s own color.

8. The game ends after two consecutive passes.

9. A player’s score is the number of points of her color, plus the number of empty points that reach only her color.

10. The player with the higher score at the end of the game is the winner. Equal scores result in a tie.

##### Comments

1. The grid of points is usually marked by a set of 19×19 lines on a wooden board.

Each player has an arbitrarily large set of stones of his own color.

By prior agreement a rectangle of different dimensions may be used.

2. Using boards, coloring a point (intersection) black or white means placing a stone of that color on the point.

Coloring a point empty, i.e. emptying a point, means removing the stone from it.

3. Connected stones of the same color, sometimes called strings, all reach the same colors.

Reaching empty means having empty points adjacent to the string, called liberties.

4. Strings without liberties cannot exist on the board at the end of a turn.

5. For handicap games, the weaker player, taking black, may be given an n stone handicap;

these are n consecutive moves played before the first white move.

6. This is the positional superko (PSK) rule, while the situational superko (SSK) rule forbids repeating the same grid coloring with the same player to move. Only in exceedingly rare cases does the difference matter, sufficient reason for the simpler PSK rule to be prefered.

7. For any specific move, at most one of the clearing processes can have effect;

the first is called capture, the second suicide. Allowing suicide means that a play on an empty point can be illegal only due to superko.

8. As a practical shortcut, the following amendment allows dead stone removal:

After only 2 consecutive passes, the players may end the game by agreeing on which points to empty.

After 4 consecutive passes, the game ends as is.

9. This is called area scoring. An almost equivalent result is reached by territory scoring where in addition to empty surrounded space we count opponent stones captured instead of own stones not captured.

10. By prior agreement, for games between equals, a fixed amount can be added to white’s final score.

This is called komi, and can be chosen a non-integer such as 5.5 to avoid ties.