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The American Go Association Rules of Go

This document contains the official rules of go for the AGA and several
other documents that comment on them.

Fred Hansen


---------------------------------
Transmittal letter
---------------------------------

    AMERICAN GO ASSOCIATION
    P.O. Box 397, Old Chelsea Station, New York, NY 10113


To:      IGF Rules Committee
From:    AGA Rules Committee
Date:    April 1, 1991
Re:      Rules Proposals

The 1990 Intemational Go Federation Rules Committee  meeting took a
significant step in agreeing in principle, at the initiative of the
Japanese representative, to sanction multiple sets of rules for use in
international amateur play.

As the Committee knows from our previous presentations, the American Go
Association has for several years been working toward a "simplified" set
of rules for use among amateurs--a set of rules at once simple enough to
be understood by beginners, clear and comprehensive enough to guide
tournament play among amateurs--when the  tournament director (and the
strongest players present) may not even be of dan level--and acceptable
to players from all cultural backgrounds.

Our Rules Committee has now adopted a proposed set of AGA Official Rules
of Go which we believe meets these criteria. These rules are similar to
those we presented at the 1990 IGF Rules Committee meeting, but have
benefitted greatly from the discussions we took part in there, both in
committee and with individual participants, and from further discussions
with interested parties in the Canadian Go Association, the New Zealand
Go Association, and various European Go Associations.

The Significance of "Simplified" Rules

We refer to these proposed rules as "simplified" not because they define
a game which is any less subtle or challenging than the traditional
rules.  Rather, they are simplified in that they avoid the need for
amateurs to be familiar with "special cases", or to master complex
confirmation procedures or precedents about the status of certain
positions. We recognize that the rules in effect in Japan, Korea, and
China have matured in cultures with millions of amateur players and
strong, experienced professional associations; they are undoubtedly
appropriate for play among professionals, or among strong amateurs where
expert advice is easily accessible.  For amateur players in the West,
where professionals are few and far between, and entire cities and
regions may lack even dan-level amateur players, however, such rules
present difficulties.  We believe that our "simplified" rules are more
appropriate for use with amateurs, especially where no very strong
players are available as arbiters or  referees.

The Key Issues

On the key issues under discussion internationally, our rules take the
following positions:

Super-Ko: A super-ko rule prohibiting full board repetitions is adopted.
This covers all potential repetitive situations in one stroke, and
guarantees that every game must have a definite outcome. Situations
involving multiple kos and/or other potentially infinite repititions are
rare. When they do arise, the care required to avoid a full-board
repetition is not so much greater than that required in handling
ordinary multi-step or multi-stage kos, and seems to form a natural
strategic component to the game. Most importantly, it is clear in
principle even to beginners how every such situation is handled. We
believe this approach is preferable to handling such potential
repetitions on a case-by-case basis, or causing a game to be annulled.

Use of Pass Stones: Our rules provide that the players must make an
equal number of moves during the game, and that when a player passes, he
or she must pass the opponent a "pass" stone (previously referred to as
a "bookkeeping" stone), which is treated like any other prisoner. The
requirement that the players make an equal number of moves (i.e., that
in an even game White must make the last move) serves to guarantee that
passing is never beneficial before the end of the game. (Without this
proviso, one can  have situations where the players get into rather
strange "pass fights" over who gets the very last move, as James Davies
has pointed out.) The use of pass stones keeps the actual number of
stones played (or exchanged) equal, and thus guarantees that area and
territory counting give the same result. Finally, offering a pass stone
to the opponent provides a neat "language free" method for proposing an
end to the game!

Settling Disputed Status of Groups: The status of disputed groups is to
be settled by playing out the full-board situation.

Playing out the situation allows players of varying levels to resolve
complex life-and-death situations according to their abilities, without
depending on outside authorities or exhaustive analysis, and hence is
most suitable for amateur play. While the new Nihon Ki-in rules are
carefully crafted to resolve most of the difficult cases which used to
require exccptional handling, and are probably very appropriate for
professional play, they depend on a high level of sophistication in
analyzing each position based on rules which are slightly different from
normal play (due to the special handling of kos). In principle,
resolving such end-of-game disputes requires the players--or some
competent authority in attendance--to have the capacity to resolve
life-and-death problems of arbitrary complexity!  Rather than attempt to
resolve each local situation "in principle" in the ideal fashion through
extensive analysis, playing the position out achieves a fair result (it
is based on the relative reading strengths of the players themselves) in
potentially bounded time without the need to appeal to outside
authorities or make use of special rules.

The following features of the confirmation process are intended to
insure that it is unambiguous, and that neither player can use the
opportunity to restart play to gain an artificial advantage:

* After two consecutive passes, the players attempt to agree on which
remaining groups on the board are dead. A mechanism is suggested for
this process which should work even if the players share no common
language. Note that no stones are actually removed until it is clear
that the players agree on the status of all groups on the board.

* Effectively, it is always the opponent of the player disputing a
purportedly dead group's status who moves first when the game is
restarted (although that player may choose to pass).

{{This is no longer true.  The opponent of the last person to pass
moves. -wjh}}

* If play is restarted, the two players must still make the same total
number of moves.  White always makes the very last move (or pass) of the
game.

* The game ends at any point when the players agree on the status of all
groups remaining on the board, or when both players pass twice in
succession, in which case any stones remaining on the board are deemed
alive. If necessary, White will make an additional pass at this point,
passing the obligatory stone to Black, to maintain parity in the number
of moves by the players. (The provision that the game must end after
both players pass twice in succession is designed to prevent one player
from maliciously refusing ever to agree on the status of some group,
prolonging the game indefinitely.)

Points in Seki: The rules count surrounded points in seki, but not the
"neutral" points (points adjacent to stones of both colors). (This
allows one to score a game which is ended before all dame are filled--in
fact, in principle it allows one to score any game position.)

Scoring the Game: The rules allows the use of either "area" or
"territory" counting, by prior agreement. The use of pass stones and the
requirement that the two players each make the same number of moves
insures that the two methods will give the same result in all even
games. The requirement that Black compensate White for any handicap
stones given insures the same result in handicap games as well. (This
could equally well have been achieved by treating White's first n-1
moves in an n-stone handicap game as passes, requiring White to pass
Black n-1 pass stones. The results would then be the same, but the value
of a handicap stone would then change from what we are used to; New
Zealand effectively uses this system (they only count by area), but most
other Chinese-style (area counting) rules seem to compensate White as we
do.)

Self-Capture: Our rules make self-capture illegal. We are aware that
this is more than a matter of additional ko threats, and that there are
some (highly artificial) situations where the unconditional
life-and-death status of a group depends on the rule on self-capture.
The New Zealand Go Association allows self-capture, and some leading
European players, including Matthew MacFadyen, have also suggested that
allowing it might slightly enrich the game. We have chosen to stay with
the traditional prohibition.

Placement of Handicap Stones: Our rules allow free placement of handicap
stones, but tacitly favor the Japanese placement of handicap stones by
describing it as "traditional". Clubs and tournament directors wishing
to make traditional Japanese placement a requirement can easily do so.

Compensation: Our rules maintain the traditional 5 1/ 2 points of compensation.

Handling of Illegal Moves: Our rules provide that an illegal move should
not automatically and immediately result in a loss.  Instead, an illegal
move is "punished" by being treated as a "pass"--i.e., the offending
player is forced to retract the illegal move, giving the opponent a pass
stone and the move.  (In most serious games,  this is quite severe
enough!)

It is also provided that an illegal move must be noted by the opposing
player before their next move. An illegal move not so noted must stand,
unless the players agree to restore the game position prior to the
illegal move. (These rules should be viewed in the context of AGA
Tournament Regulations governing the handling of "disturbed  boards",
repeated or deliberate violations of the rules, etc.)

The AGA Rules Committee has asked the AGA Executive Committee to
recommend, these rules to our next National Board meeting this summer,
where we expect they win be ratified.   {{They were.  --wjh}}

Standards for Sanction

The issue of criteria for IGF sanction of rules for use in international
amateur play is on the agenda for the 1991 IGF Rules Committee meeting.
While we have not had extensive discussion of this question, we propose
that the following might constitute minimal standards for IGF sanction
of a set of rules:

* The statement of the rules must be clear, consistent, and complete.
That is, they must specify unambiguously what constitutes a legal move
at each stage of the game; how the end of the game is determined; how
disputes over the status of  groups are to be resolved; and how the game
is to be scored.

* The rules must have been adopted as the official rules of at least one
IGF member country or territory for some span of time to be determined
by the committee. This will discourage frivolous rules proposals.

We are aware that our own "simplified" rules have not yet met the second
criterion proposed here; we are not asking IGF sanction for these rules
at this time.  We propose to keep the IGF Rules Committee and other
interested parties informed of our experiences promoting these rules in
the United States, with the aim of laying the groundwork for their
eventual sanction for use in international amateur play.

Tournament Regulations

We understand that the issue of tournament regulations is also on the
agenda for the 1991 IGF Rules Committee meeting. The AGA would like to
submit its official Tournament Regulations (drafted by AGA Tournaments
Coordinator Ken Koester), as adopted at our 1990 National Board meeting
in Colorado, for consideration by the committee.


Thank you for your kind consideration of our proposals.



The AGA Rulcs Committee



---------------------------------
The Rules
---------------------------------


AGA Rules Committee
April 1, 1991



                   Official AGA Rules of Go


{The following are the American Go Association Rules of Go for amateur
play. Unless specifically stated otherwise, these rules are in effect at
all AGA sanctioned events. The rules themselves are given in plain text;
commentary is surrounded with curly braces. Illustrative figures are
given at the end.}

{A concise statement of the rules, suitable for distribution to
beginners, posting at tournaments and clubs, etc., is also given.}  Any
paraphrase of these rules which is identical in content is acceptable as
a statement of the AGA Rules of Go so long as it makes reference to the
more complete Official Rules given below.  {By "identical in content" we
mean that the result of applying these paraphrased rules should give the
 same result as would the Official Rules in every situation.}

{These rules are supplemented by the AGA Tournament Regulations
governing time control, player conduct, the role of monitors, etc.}

1) The Board and Stones: Go is a game of strategy between two sides
usually played on a 19xl9 grid (the board). The game may also be played
on smaller boards, 13xl3 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 a nd White, are each provided with an adequate
supply of playing tokens, known as stones , of the appropriate color.

{For recording purposes, the horizontal lines on the  board are
designated 1,2,3,...,19, starting from the bottom as seen by Black. The
vertical lines are designated A,B,C,...,T (skipping 'I'), starting from
the left as seen by Black. Points on the board are identified by their
coordinates, c.g. A-1, C-3, T-19, etc.}

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.

{The nine intersections corresponding to the horizontal lines 4, 10, and
16 and the vertical lines D, K, and Q are called star points, and are
ordered as follows: (See Figure 1.)

        1st star point       Q-16    5th star point   Q-10
        2nd star point    D-4        6th star point   D-10
        3rd star point    Q-4        7th star point   K-16
        4th star point    D-16    8th star point   K-4
            9th star point    K-10 (center point)

{The handicap stones are traditionally played as follows:

        2  stones    on the  1st and 2nd star  points
        3  stones    on the  1st through 3rd star points
        4  stones    on the  1st through 4th star points
        5  stones    on the  1st through 4th star points and the center point
        6  stones    on the  1st through 6th star points
        7  stones    on the  1st through 6th star points and the center point
        8  stones    on the  1st through 8th star points
        9  stones    on the  1st through 9th star points

Handicaps greater than nine stones and handicaps on boards with fewer
than 19 lines are not standardized.}

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.  {Black would otherwise gain an
additional point of area for each handicap stone.}

5) Capture: Stones of the same color are said to be connected if they
are adjacent along horizontal or vertical--not diagonal--lines on the
board. A string of connected stones consists of those stones which can
be reached from a given stone by moving only to adjacent stones of the
same color. A string of connected stones is surrounded by stones of the
opposite color if it has no empty points horizontally or vertically--not
diagonally--adjacent to any of its member stones. (Such adjacent empty
points are known as liberties of the 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 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.

{This means that it is possible to fill an empty space within an
opponent's group and capture even if the player's own stone or stones
would momentarily be surrounded by the group being captured. See Figure
2. But self-capture is illegal.}

6) Repeated Board Position (Ko): It is illegal to play in such a way as
to recreate a previous board position from the game, with the same
player to play.

{The most typical example is a situation where the players can each
alternatcly capture and recapture a single stone. This is known as "ko"
(See  Figure 3). After the first capture, the player moving next may not
capture immediately, as this would repeat the board position;  instead,
that player must play elsewhere on the board (or pass). The player who
first captured may then "fill" the ko (or otherwise resolve it), or play
elsewhere as well (often in response to the other player's previous
move.) If the board position  has changed, and the ko has not yet been
resolved, the opponent is then free to capture, and it is the original
player who may not then immediately recapture. This process is known as
a ko fight, and the moves played away from the ko itself are known as ko
threats.

{Rarely, multiple kos or other repetitive situations will arise; the
principle for handling them is always the same: the players must avoid
repeating the full-board position, so they are periodically, and
alternately, forced to play away from the repetitive situation before
responding.}

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.

{Normally neither player would choose to pass if there were any
worthwhile moves to be made on the board (even if they did not have to
give up a pass stone). Thus, the exchange of a pass stone with the
opponent also serves as a signal that the player passing believes that
the game is over. Of course, the opponent is free to continue to play if
he or she believes that there are worthwhile moves left to make, and the
player who passed is free to respond.}

8) Illegal Moves: An illegal move is one violating the rules. If a
player makes an illegal move--such as moving twice in a row (i.e.,
before the opponent has made a response), attempting to play on an
occupied intersection,  self-capture, or retaking a ko so as to repeat
the full board position, the player must take back his or her move (both
moves, if he or she moved twice in succession), it shall be treated as a
pass, and a pass stone exchanged.

An illegal move must be noted as such by the opponent before he or she
makes his or her move. When a player moves, he or she is tacitly
accepting the opponent's previous move as valid. In particular, if it is
discovered that an earlier move by one of the players was illegal, the
game must nevertheless be continued as it stands unless both players
agree to restore the earlier board position and proceed from that point.

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. Any
stone or group of stones surrounded and captured during this process is
added to the capturing player's prisoners as usual.

{It is recommended, particularly if the players do not share a common
language, that the following procedure be used to determine agreement on
the status of groups. After two consecutive passes, the next player
touches each connected string of opposing stones on the board which he
or she believes to be dead. If the opponent disagrees, he or she also
touches the same string. When a player is done indicating groups he or
she believes are dead, he or she passes, passing a stone to the opponent
as usual, and the opponent follows the same procedure.  At any point, a
player may resume play rather than continuing to indicate dead groups or
passing.  If both players pass and there was no disagreement indicated,
the game is over, and all groups which the players have indicated as
dead are removed from the board. If they both pass while a disagreement
still exists, all stones remaining on the board are alive, and the board
is counted as it stands. (The burden is thus effectively on the player
who would be disadvantaged by such a result to resume play in the event
of a disagreement.)}

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. The players
should agree in advance of play which method they will use. If there is
no agreement, territory counting shall be used.

{Although players' scores may differ under the two methods, the
difference in their scores, and hence 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.

{At the end of the game, the empty points remaining on the board fall
into regions. A region is the smallest set of empty points containing a
given empty point and any empty points adjacent to any empty point in
the set. That is, a region consists of those empty points which can be
reached from a given empty point by moving only to adjacent empty
points. A region is entirely surrounded by stones of a single color if
the only stones adjacent to empty points in the region are of that
color. There are situations (Japanese seki) in which a region of empty
points is left at the end of the game which is not entirely surrounded
by stones of a single color, and which neither player would fill because
to do so would bring dire consequences.  See Figure 4.  When counting by
territory, it is also possible that there will be some neutral points
left between live groups belonging to the two players which have not
been filled, although it is customary to fill all such points before
scoring the game.}

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.  (There will rarely be any such points.)

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.

{In fact, since the total of the two players' areas  will sum to 361,
less any neutral points left on the board in seki, it is generally only
necessary  for one of the two players to count their area; if it exceeds
180, (or 180 adjusted for half of any neutral points in seki), they are
the winner. It is customary for the player doing the counting  according
to this method to fill in their territory and then rearrange the stones
into convenient heaps. Again, these are merely mechanical conventions to
simplify the counting process.}


---------------------------------
A shorter version of the rules
---------------------------------


AGA Rules Committee
April 1, 1991



              Appendix: Concise Rules of Go


1) The Board and Stones: Go is a game of strategy between two sides
usually played on a 19xl9 grid (the board). The game may also be played
on smaller boards, 13xl3 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.


---------------------------------------
An appendix
---------------------------------------

AGA Rules Committee
April 1, 1991


Appendix: Demonstration of the Relationship of Area and Territory Scoring


This appendix shows that with normal play, under the given rules the
"area" and "territory" scores of a game will always be the same.

For the sake of simplicity, start by assuming an even game, that both
players play exactly the same number of stones, only passing at the end,
and that at the end of the game there are no neutral points (all dame
filled and no seki).  Make the following definitions:

    Sw =   number of stones played by white
    Sb  =   number of stones played by black
    Pw =   number of white prisoners
    Pb  =   number of black ppjsoners
    Aw =   number of white stones on the board
    Ab  =   number of black stones on the board
    Tw =   number of points of territory surrounded by white
    Tb  =   number of points of territory surrounded by black

Now, we have the following relationships. Since we are assuming that
both players have played exactly the same number of stones, we have:

        Ab + Pb  =   Sb  =  Sw =  Aw + Pw

This means that:

        Ab  -  Aw = Pw  -   Pb

So, adding Tb - Tw to both sides,

        (Ab + Tb) - (Aw + Tw) = (Tb -  Pb) - (Tw - Pw)        [1]

But the left-hand side of this expression is precisely the score
according to area counting, while the right-hand side is the score
according to territorial  counting!

If a player passes prior to the end of the game, it will reduce that
player's area score by one point per pass relative to the corresponding
territorial score. The convention of handing a "pass" stone to the
opponent when passing keeps the two scores equal. (In general, it can
only hurt a player to pass prior to the end of the game.)

There are also certain rare situations where a game ends with "one-sided
dame" (see Figure 5) which one side can fill but the other cannot. Each
additional stone played represents the gain of a point under area
counting. But since the opponent will be forced to hand over a "pass"
stone on his or her move, each additional stone played also represents
the gain of a point under territory counting--the two remain equivalent!

Finally, in a handicap game, the additional points of compensation paid
by Black to White can be thought of as "reverse pass stones" ensuring
that both players have, in effect, still played exactly the same number
of stones.

If we assume that the two players have played the same number of stones,
with no neutral points left on the board, and that the score in equation
[1] is equal to k, we have:

        (Ab + Tb) - (Aw + Tw)  =  k

But

        (Ab + Tb) + (Aw + Tw) = 361                                 [2]

So k must be odd!

This implies that if such a game is even on the board by traditional
territorial counting (without pass stones), Black must have made the
last move ! At one time, the Chinese rules compensated White with an
extra point when Black got the last move. If Black's last move was to
fill a ko he or she had won, however, it was deemed unfair to penalize
him or her, so eventually the Chinese removed this proviso.  Requiring
that White always have the last move and using pass stones removes the
possibility of a "pass fight" over who gets the very last move.

If there are neutral points on the board at the end  of the game
(presumably in seki, since the players would naturally fill all dame
under the area system), the same argument still shows that the two
systems give the same result if the players have played the same number
of stones, but the parity of k will depend on the number of neutral
points; if there are an odd number of neutral points, k will be even,
and vice versa.  This may explain why some rule systems go to great
lengths to award all points in seki.

Finally, note that in the confirmation phase, by our rules, the final
result remains the same (that is, the "same" as would be calculated
before playing out the confirmation phase if the status of all groups
were taken to be whatever it proves to be through the confirmation
process!) Since the game is over, we can assume that all empty points
belong to the territory of one or the other of the players. Under area
counting, stones of either color played into one's own territory or into
the opponent's territory will not change the score--nor will the "pass"
stones. Under territorial counting, every stone played into one's own or
the opponent's territory will cost a point--but by requiring that the
players make the same number of moves, and by insuring that even passes
cost a point (the "pass" stones), we insure that the end result is still
the same.