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AGA Rules Committee
April 1, 1991


1) The Board and Stones: Go is a game of strategy between two sides
usually played on a 19x19 grid (the board). The game may also be played
on smaller boards, 13x13 and 9x9 being the two most common variants. The board is initially vacant, unless a handicap is given (see Rule 4). The
two sides, known as Black and White, are each provided with an adequate
supply of playing tokens, known as stones, of the appropriate color.

2) Play: The players alternate in moving, with Black playing first. In
handicap games, White moves first after Black has placed his or her
handicap stones. A move consists in playing a stone of one's color on an
empty intersection (including edges and corners), or in passing. Certain
moves are illegal (Rules 5 and 6), but a pass is always legal (Rule 7).
Points are awarded for controlling space in a manner described below
(Rule 12). The object of the game is to end with the greater total
number of points.

3) Compensation: In an even (non-handicap) game, Black gives White a
compensation of 5 1/2 points for the advantage of the first move. This
compensation is added to White's score at the end of the game. In
handicap games, Black gives White 1/2 point compensation. This avoids
draws.

4) Handicaps: The game may be played with a handicap to compensate for
differences in player strengths. The weaker player takes Black, and
either moves first, giving only 1/2 point compensation to White, as in
Rule 3 (this is known as a "one stone handicap"), or places from 2 to 9
stones on the board before the first White move.

If the players have agreed to use area counting to score the game (Rule
12), White receives an additional point of compensation for each Black
handicap stone after the first.

5) Capture: A liberty of a stone is a vacant, horizontally or vertically
adjacent intersection. A single stone in the middle of an empty board
has four liberties: the vacant intersections above, below, left and
right of the stone. The intersections diagonal to the stone are not
adjacent and are not counted as liberties of  the stone. A single stone
on a side intersection has a maximum of three liberties; a single stone
in the corner has a maximum of two liberties.

Stones of the same color are said to be connected if they are adjacent
along horizontal or vertical lines on the board (each occupies a liberty
of the other). Two stones are part of the same string if they are linked
by a chain of connected stones of the same color. The liberties of a
string of stones are the liberties of all the individual stones in that
string.

After a player moves, any stone or string of stones belonging to the
opponent which is completely surrounded by the player's own stones,
leaving no liberties, is captured, and removed from the board. Such
stones become prisoners of the capturing player. It is illegal for a
player to move so as to create a string of his or her own stones which
is completely surrounded (without liberties) after any surrounded
opposing stones are captured.

6) Repeated Board Position (Ko): It is illegal to play in such a way as
to exactly recreate a previous full board position from the game, with
the same player to move. The most typical example is a situation where
the players can each alternately capture and recapture a single stone.
This is known as ko. ("Ko" is the Japanese Buddhist word for eternity.)
After the first capture, the player moving next may not recapture
immediately, as this would repeat the board position; instead, that
player must play elsewhere on the board (or pass).

7) Passing: On his or her turn, a player may pass by handing the
opponent a stone, referred to as a pass stone, rather than playing a
stone on the board.

8) Illegal Moves: An illegal move is one violating the rules. If a
player makes an illegal move, it shall be taken back, treated as a pass,
and a pass stone exchanged.

9) Ending the Game: Two consecutive passes normally signal the end of
the game.  After two passes, the players must attempt to agree on the
status of all groups of stones remaining on the board. Any stones which
the players agree could not escape capture if the game continued, but
which have not yet been captured and removed, are termed dead stones. If
the players agree on the status of all such groups, they are removed
from the board as prisoners of the player who could capture, and the
game is scored as in Rule 12. If there is a disagreement over the status
of some group or groups, play is resumed as specified in Rule 10.

10) Disputes: If the players disagree about the status of a group of
stones left on the board after both have passed, play is resumed, with
the opponent of the last player to pass having the move. The game is
over when the players agree on the status of all groups on the board,
or, failing such agreement, if both players pass twice in succession.
In this case any stones remaining on the board are deemed  alive.

11) The Last Move: White must make the last move--if necessary, an
additional pass, with a stone passed to the opponent as usual. The total
number of stones played or passed by the two players during the entire
game must be equal.

12) Counting: There are two methods for counting the score at the end of
the game.  One is based on territory, the other on area. Although
players' scores may differ under the two methods, the difference in
their scores, and the game result, will be the same.

Territory: Those empty points on the board which are entirely surrounded
by live stones of a single color are considered the territory of the
player of that color.  An empty point is surrounded by stones of a
single color if one can't reach any stone of the opposing color from
that point by moving only to adjacent empty points.  There are rare
situations (Japanese seki) in which empty points are left at the end of
the game which are not entirely surrounded by stones of a single color,
and which neither player dares to fill.

Area: All live stones of a player's color left on the board together
with any points of territory surrounded by a player constitute that
player's  area.

Neutral Points: Any empty points left on the board at the end of the
game which are not completely surrounded by either player's stones are
known as neutral points, and are not counted toward either player's
territory or area.

Counting by Territory: When counting by territory, players add up their
total territory less any prisoners held by the opponent (including dead
stones removed at the end of the game). The player with the greater
total (after adjusting for any compensation offered according to Rule 3)
is the winner.

(It is customary for the players to fill in their opponent's territory
with their prisoners, and to then rearrange their territories to
facilitate counting. These are merely mechanical conventions to simplify
counting.)

Counting by Area: When counting by area, the players add up their total
area. Prisoners are ignored. The player with the greater total area
(after adjusting for any compensation offered according to Rules 3 and
4) is the winner.