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From:  Robert Jasiek <jasiek@snafu.de>
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Subject:  Rules FAQ
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Title: Rules FAQ
Author: Robert Jasiek <jasiek@snafu.de>
Frequency: monthly
Last Update: 2009-02-12; First Day: 1999-04-12
Distribution: rec.games.go
Copyright: free non-commercial usage for promotion

0 CONTENTS

1 Purpose of this Paper
2 Information for Beginners
3 Important Concepts
4 Particular Rules
5 Troublesome Details
6 Tournament Rules
7 Links

1 PURPOSE OF THIS PAPER

This paper is a basic reference for important rules terms,
rules, and tournament rules. Beginners should read
especially chapters 2 and 3, players chapters 3 to 5,
tournament players and organizers chapter 6.

2 INFORMATION FOR BEGINNERS
2.1 What Must I Know as a Beginner?

The game is played on a grid board. Typically it has 19x19
intersections, but 9x9 are also fine. Two players compete.
The first player uses black stones, the other white.

The players alternate. A player may play or pass. Playing
is putting one's own stone on an empty intersection and
removing any surrounded opposing stones. To avoid
cycles, a play may not recreate any prior configuration of
all stones on the board.

Two successive passes end the game. Then the player with
more intersections wins. Intersections are his if only his
stones occupy or surround them.

2.2 Which Rules do I Need as a Beginner?

You can play with short rules as in 2.1. Other rules may
be different, but the game is the same, i. e. strategy,
tactics, and the score do not change. Extremely rare
exceptions confirm this rule.

The winner can be determined by area or by territory.
Either includes empty intersections surrounded only by own
stones. While area adds intersections occupied by own
stones, territory adds opposing prisoners instead.

All rules, except short rules, have further phases after
alternation and before scoring. Towards a game end it is
often clear which stones will be removed. The additional
phases allow the players to agree on which stones shall be
removed. Thereby final removals do not require alternation.

Whether you score by area or by territory or whether you
remove by alternation or by agreement should mainly depend
on which rules are used by people you play with.

2.3 Which Rules Should I Teach?

One possibility is to use a board with 9x9 intersections,
short rules as in 2.1, and count each player's score by
using a finger to scan the board for his intersections.

3 IMPORTANT CONCEPTS

While strategy and tactics virtually remain the same,
concepts vary in different rules. However, the following
gives a comprehensive overview on standard terms.

3.1 Stone, String

The physical device that colours one intersection in a
play is a STONE. Two intersections of the board are
ADJACENT if they have a line but no intersection between
them. Two intersections with either black, white, or no
stones on them are CONNECTED if they are adjacent or if
there is a chain of adjacent intersections of their type
between them. A REGION consists of an intersection and
any intersections connected to it. A black or white
region is called a STRING.

3.2 Surrounded

An intersection of one colour is SURROUNDED by another
colour if each leaving path reaches the other colour first
after the one colour. Hereby it can only be surrounded
black by white, white by black, empty by black, or empty
by white. A region can be surrounded. For strings there is
an alternative notion of no liberty (or breath). A LIBERTY
of a string is an empty intersection adjacent to it. Thus
a string is surrounded if and only if it has no liberty.

3.3 Removal, Suicide

A removal empties the intersections of surrounded stones
if there are any. Hereby removal of opposing stones is
executed first, if necessary. Rules may either require or
forbid removal of own stones. This is called suicide or no
suicide. In practice, suicide might be used for so called ko
fights or in capturing races.

3.4 Capture, Prisoner

Rules that score territory call a removal a capture
because all removed stones are seriously kept as prisoners.

3.5 Move, Play, Pass

The players have alternate turns. On each turn a player makes
a move that is either a play or a pass. A play places one's
own stone on an empty intersection. It can then include
removal of surrounded stones, if any. A pass merely continues
alternation by giving the opponent the next turn.

3.6 Compensation

The first move advantage by black can be compensated by
compensation points (komi) that are added to the white score
after the game end. Komi can be adjusted by 0.5 to avoid
ties. Today integer values for komi for 19x19 boards
typically range between 5 and 7. For 13x13 boards one should
use 8, for 9x9 boards 6; however, there is no real consensus
for small board komi values yet. -
A weaker player (black) can get the right to place an agreed
number of compensation stones (handicap) before white's first
play. Rules may allow free or fixed handicap. Free handicap
does not apply any restriction. Fixed handicap requires
traditional placement on set intersections.

3.7 Phases

Normally, a game consists of the phases alternation,
agreement, scoring. A game stop is between alternation and
agreement, the game end is between agreement and scoring,
and after scoring both players accept the counted score as
the result. The main part of the game is the alternation
phase. Special rules are invoked after it. Typically, two
successive passes in alternation are the game stop and start
the agreement phase. In it the players may agree on strings
to be removed. If they agree, then they remove those strings
from the board; this ends the game. Sometimes they might
disagree, then no strings are removed but alternation is
resumed as if the last game stop did not occur.

3.8 Recreation

The position is the pattern of black and white stones on the
board. Without extra rule a position might be repeated
infinitely. The easiest rule to prohibit this says: A play
may not recreate a position. This refers to positions after
completion of plays, i.e. after possible removals. The rule
is called "superko". -
Some rules use concepts different from superko. They combine
a "2-play rule" with a "long cycle rule". The first says:
Two successive plays may not recreate a position. The second
says: If a position is recreated after more than two moves,
then the game ends either immediately or, as a variant, as
soon as the players agree, with the result "without result".
In practice the 2-play rule is sufficient for almost all
cases. It handles the relevant standard pattern of two
adjacent intersections. For superko this is just a special
application.

3.9 Scoring

The score is the result after the game end as defined by
the rules. There are two different scoring methods: area
scoring and territory scoring. Rules use one of them. Both
give the same result in almost all cases and both evaluate
the difference of the black and the white scores. A player's
AREA score is the sum of intersections with own stones and
of empty intersections surrounded only by own stones. Simply
speaking, a player's TERRITORY score is the sum of empty
intersections surrounded only by own stones and of prisoners
of opposing colour. With both scoring methods empty
intersections that are not surrounded by either black or
white are neutral.

3.10 Counting

A score must be determined by some mechanical procedure in
practice; this is called counting. There are various methods.
Some rules prescribe one. A possible method is to use one's
finger to count point by point. Other methods rearrange a lot
of stones on the board.

4 PARTICULAR RULES

Rules vary extremely. However, in practice they often give
the same result.

4.1 Short Rules

Examples of short rules are the Simple Rules or the
Tromp-Taylor rules. They have no game stop and no agreement.
Both are superfluous since necessary removals may already be
performed in the alternation. Two successive passes end the
game that is scored then. Short rules use area scoring,
superko, and suicide. Further settings are left for
tournament rules.

4.2 American Rules

These are used by the American Go Association. They use
situational superko, no suicide, and 7.5 komi. They permit
free or fixed handicap. Their most remarkable feature is to
allow one of area scoring or territory scoring. Herefore
pass stones (one prisoner compensates each pass) and white
moving last always ensure the same result, regardless of the
applied scoring method.

4.3 Chinese Rules

These are used in continental China and sometimes in other
countries. Area scoring and no suicide are used.

4.3.1 Official Chinese Rules

In practice, ko rules roughly amount to a 2-play rule and a
long cycle rule. The mentioned superko is overridden. The
counting is a sophisticated half counting, where empty
intersections and then after rearrangements stones of one
colour are added to be compared with half the non-neutral
intersections. The komi as a half komi is 3.75. In full
counting, counts and komi would be twice as big.

4.3.2 Simplified Chinese Rules

Positional superko is used. A counting method is not
prescribed. The full komi should be 7.5.

4.4 Japanese Rules

The differences mainly affect handling of late game phases
but often do not alter scores. Japanese rules use some
traditional territory scoring that attempts to exclude so
called sekis. No suicide applies. The core of the ko rules
is a 2-play rule and a long cycle rule. Typically, komi is
6.5. Fixed handicap should be used. The counting is a
sophisticated rearrangement of empty intersections and
filling-in of prisoners.

4.4.1 Game Finishing Process

A game finishes with the following process: 1) So called
dame (neutral points) and defensive moves (necessary
connections etc. due to occupied dame) are filled.
2) The hypothetical analysis, which presumes perfect play,
determines so called life or death of each string and the
scoring intersections. 3) Without making any approach moves,
dead stones are removed from scoring intersections and added
to the prisoners. 4) The score is counted. (2) and (3) do not
allow to play out life and death since actually filling
intersections costs points in Japanese rules.

4.4.2 Official Japanese Rules

There are the Japanese 1989 Rules, which are used in Japan
and elsewhere, and the World Amateur Go Championships Rules,
which are used in some particular tournaments. Korean rules
are similar to Japanese rules but have a very different text
and differ in rare positions. Official Japanese rules are
very incomplete and have messy late game phases. E.g., the
Japanese 1989 Rules allow filling of dame during alternation,
after it, or both and have a so called ko-pass-rule for the
hypothetical analysis. Now professional Japanese rules are
explained precisely by a rules expert's interpretation called
"the Japanese 2003 Rules".

4.4.3 Simplified Japanese Rules

As a recent invention, they are not used yet. They are
complete and have clear late game phases. Filling of dame is
done during alternation.

4.4.4 Verbal Japanese Rules

They are used for informal games in many countries and
undefined, except that the game finishing process is used.
In a tournament without any official rules of play, disputes
are not solved due to the rules but with a referee.

4.5 Ing Rules

Ing rules use area scoring, suicide, 8 komi with black
winning ties, and free handicap.

4.5.1 Official Ing Rules

The ko rules are a mess but somehow resemble superko.
Details could fill books. The late game phases are specified
insufficiently. The peculiar counting method requires 180
stones of each colour throughout the game, fills any stones
on the board after the game end, and leaves exactly one
empty intersection, which determines the winner. The
official rules are used in professional Taiwanese and some
sponsored tournaments. Taiwanese amateurs have their own
rules.

4.5.2 Simplified Ing Rules

Positional superko is used. A counting method is not
prescribed. The late game phases are specified clearly. The
simplified rules are used in EGF tournaments that are said
to use Ing rules.

4.6 New Zealand Rules

Area scoring, suicide, situational superko, 7 komi, and free
handicap are used.

4.7 Go Server Rules

Every go server has its own and often complicated rules, if
any, so they cannot be given in detail here. Concerning
"IGS rules", territory scoring, no suicide, a 2-play rule,
fixed handicap, three game stopping passes, and captures in
an agreement phase are used. Details about agreements and
long cycles are not specified and lead to adjourned games in
case of doubt. Komi is suggested but may be altered. Counting
is automatic. "Yahoo" has territory scoring, no suicide, a
2-play rule, two game stopping passes; long cycles and
disagreements are not handled properly. On "email servers"
players must agree on any rules. -
Typically territory scoring on a go server means that neither
points in any sekis are excluded nor pass stones are used.
Thus while the Japanese seki exception is abandoned,
disagreements about removals may lead to games without result
since playing out can cost points.

4.8 International Rules

The international mailing list go-rules has proposed
international rules, however, none are adopted yet. The core
rules of play shall be clear, complete, and correct.
Currently alternative texts are offered for suicide,
recreation, and scoring. Especially unification of scoring
methods is advocated.

4.9 EGF Rules

The EGF uses the Simplified Ing Rules with 8 komi (black
wins ties) in Ing sponsored tournaments and the Nihon Kiin
1989 Rules with 6.5 komi in Japanese/Korean sponsored
tournaments. If significantly the European Go Championship
has both kinds of sponsors, then boards 1-16 use the Nihon
Kiin 1989 Rules and boards 17+ the Simplified Ing Rules.
However, time settings depend on ranks.

5 TROUBLESOME DETAILS

5.1 Colour Choice

In even games typically the colours are randomly chosen. In
handicap games black receives the handicap stones. -
A manual method for randomly choosing colours is called
nigiri. The older player hides a number of white stones
taken from the bowl, the opponent takes one or two black
stones to guess the parity, and the parity of the number of
white stones is revealed. If the opponent guesses right,
then he takes black, else he takes white.

5.2 Pass Stones

Some rules use pass stones. A passing player adds one own
stone to the prisoners. As a consequence, captures before
the game end can be resolved in alternation without any loss
because any not answered approach move is compensated by one
pass stone. With traditional territory scoring that uses no
pass stones definition problems arise due to this missing
option. Modern territory scoring or equivalence scoring use
pass stones.

5.3 Equivalence

Area scoring and territory scoring are close because either
intersections occupied by own stones or opposing prisoners
are used. Essentially, every prisoner is a stone removed
from some intersection. For area it scores one point less
for the stone's player while for territory it scores one
point more for his opponent. This is equal. Exact equality
for the entire game must also consider passes by using pass
stones and an equal number of moves by requiring white to
pass last. This is done by equivalence scoring.

5.4 Meaning of Agreement Removals

Removals in an agreement phase under area scoring are fair
because they may as well occur in alternation. Removing a
stone due to agreement includes its then empty intersection
and all adjacent empty intersections in the score. Removing
a stone by means of alternation includes its then empty
intersection and all adjacent newly occupied intersections
in the score. -
With traditional territory scoring this is not possible
since stones on the board do not score. Thus final captures
must occur after the game end due to attempted definitions
in the rules.

5.5 Practical Scoring Differences

Since area scoring and modern territory scoring using pass
stones are equal, correct play is the same for both. Apart
from Japanese rules exceptions like not scoring empty
intersections especially in asymmetrical coexistences or
like a pass-for-ko-rule, traditional territory scoring can
make a different winner in practically ca. every 10000th
even game. This is so rare because of a parity feature
combined with a scarcely odd number of intersections that
are in coexistences but do not score for area at the game
end. With area scoring a komi change from 1.5, 3.5, 5.5, ...
to 2.5, 4.5, 6.5, ... almost always would not change the
winner. So altough occupying the last empty intersections
that would otherwise not score just before a game stop gains
one point each, alternately doing so leaves a total
advantage of at most one point. Due to the parity feature
the player to get it is predetermined when this occupation
starts. More importantly, one final ko is worth 1 point under
traditional territory scoring but 2 or rarely 4 points under
area scoring. Rare one-sided points in coexistences provide
only area. Other practical differences are even rarer. Cute
players include the stones in their endgame value counts
during the middle of an area scoring game.

5.6 Stone Scoring

In ancient times stone scoring was popular. Only stones on
the board are scored. Thus empty intersections surrounded by
own stones are filled until necessary so called eyes remain.
Disconnected stones require more eyes in total, the so
called group tax.

5.7 Old Ing Scoring

Old Ing rules allowed fractional scores by assigning points
to neutral empty regions due to the percentage of black and
white stones surrounding every region.

5.8 Primitive Rules

They do not have passes. Alternation ends when a player
loses due to no legal play. Games can be extremely long and
include special strategies, so called pass fights. Primitive
rules (also called no pass rules or Conway rules) can be
useful in mathematics.

5.9 Tradition

Historically, exceptions arose, which some like as such
especially together with Japanese style rules. So called
sekis are excluded from the score. Special positions, termed
precedents, have special rules. Modern Japanese rules have
generalized a lot of them by a pass-for-ko-rule. After the
game stop or after the game end and particularly in
hypothetical play a stone captured in a possible 2-play cycle
may not be recaptured unless before a pass is made that
specifies the particular 2-play cycle.

5.10 Positional / Situational Superko

Positional superko prohibits a play that recreates a position.
Situational superko refers to the situation, i.e. to the
position together with the right to move. So a play is
prohibited if it recreates a position while the same player
has the right to move. In practice the differences are
extremely rare.

5.11 Handicap Recompensation

With area scoring handicap stones beyond the first provide
a potential extra area of one point per handicap stone. Komi
for white may consider this. Recompensation, H-1 points for H
handicap stones, is virtually only used together with
American rules.

5.12 Mathematics

Go is a complete information game, i.e. at every move each
player knows the entire game situation. Hence theoretically
an algorithm could determine perfect play. However, due to
the complexity of the game with N intersections, for which
it is provably impossible to devise a polynomial time
solution, perfect play or ideal komi are unknown. What one
does know is that in a game without komi the first player wins
or ties and that perfect play is independent of set komi. Many
other propositions have been discovered, some of which
describe the relation between area and territory scoring, solve
tiny endgame positions or cyclical behaviour. -
Go is a very complex game! L(N) := 2.9757342**N is an upper
bound of the number of legal positions. (The sign ** is a text
file notation for "to the power".) For positional superko, no
passes, and no resignation, the number of possible games is
smaller than N**L(N) because L(N) also restricts the maximal
number of moves per game and there are at most N possible
intersections per move. -
Extremely modest estimates look like 10**N, which is based on
an assumption of 10 reasonable intersections per move. A
popular estimate for 19x19 go is 10**761, which must have
originated from a typo and should be 10**361, if at all...
These types of estimates are so popular because humans cannot
even imagine the suggested number of atoms in the universe,
10**80. For comparison, 3**361 is ca. 10**172.

6 TOURNAMENT RULES

6.1 Special Game Ends

If the score considering the komi is zero, then the game is a
tie and should be treated as 0.5 won games for each. Special
rules or undue behaviour like sincere lateness might result
in a referee declaring a win by forfeit, 0:0, or 1:1,
whichever is most appropriate.

6.2 Tournament Systems

A tournament might consist of several stages, of which each
has a seed and a system. A seed appropriately restricts
participation, e.g. due to qualification. The most important
systems are match, league, knockout, Swiss, McMahon. There
are many others and hybrids. A system must fit the aims of a
tournament. A sufficient number of rounds, a proper seed,
and colour variation ensure a fair determination of the best
player. -
A match takes place between two players that either play a
set number of games to see who wins more or a maximal number
of games to see who wins a predetermined number of games
first. In a league a small, usually even number of players
performs a round-robin tournament, so that in each round all
players play and every two players play against each other,
one game e.g. A knockout preferably starts with a number of
players that is a power of two. Losing players are eliminated,
winning players continue until the winner remains. -
In a Swiss system before each round each player's achieved
number of wins is used to pair players with equal numbers as
far as possible. So all players play all rounds and some time
the best player will emerge. However, with greatly varying
strengths too many rounds would be needed. So Swiss is only
useful for particular events or handicap tournaments.
McMahon is the refinement of Swiss. Before the start of the
tournament all players are classified in rank groups, with
ranks R from 0 to T. This means that one assumes a preceding
Swiss tournament where every player has already won R games.
Then in the McMahon tournament the strongest players, who
deserve the rank T, compete for the top places. In practice,
one uses a bar B, that is 1 or 2 ranks below T, so that all
ranks above B are contracted to B and also players slightly
weaker than the top players get their chance. All players in
a McMahon play roughly equal opponents; if they win or lose,
then the opponents will be stronger or weaker.

6.3 Tie Breakers

Tie breakers can refine pairings or results. Typically the
first criterion is the number of wins (or McMahon points);
all further criteria, if any, are tie breakers. They attempt
a refinement where a low number of rounds and a tournament
system do not guarantee sufficient distinction between
players' achievements. However, they must be applied with
care since they are only marginally better than coin tossing.
Examples of tie breakers are direct comparison, which
acknowledges the winner of a game between two players in
question, and SOS, which is the Sum of Opponents' Scores. -
The possible degree of quality of tie breakers is subject to
discussion. It depends on tournament system, whether only the
top or all players shall be distinguished, and other factors.
An alternative to the usage of tie breakers for the final
results ordering is issuing shared places for all players
with the same number of wins (or McMahon points). - One must
fairly assign tie breaker points for opponents missing in
some round; enforcing participation is preferable especially
for top players.

6.4 Pairing

Pairings must be fair, precise, and consider prior
achievements during a tournament. One should consider colour
balance and no pair twice, one might also aim at avoiding a
pair of players from the same club or country, depending on
a tournament's intentions. Pairings might be done manually
in small tournaments; for most tournaments pairing programs
should be used. These can create fair pairings convincingly,
some even watch global balance.

6.5 Thinking Times

The age of killing each other by greater endurance has gone.
Clocks are used to count each player's remaining thinking
time. Typically, every game has a basic time and overtime
periods. Exceeding a time limit loses a game. Basic time
might be 9 hours for a professional top game, 10 minutes for
a lightning game, or something in between that fits a
tournament's intentions. An overtime period requires a fixed
number of moves within a predetermined period, e.g. 1 move
within 60 seconds. A move is finished by pressing the clock.
- Many variants or other time systems exist, e.g., increasing
numbers of moves in further overtime periods, penalty points
for entering further periods, full usage of every overtime
period, thinking time working like an hour glass, etc.

6.6 Tournament Rules

Every tournament uses an announced set of tournament rules.
They especially specify the used set for the core rules of
play, the tournament system, tie breakers, the pairing
method, the winning criteria, compensation methods,
thinking times, direction, jurisdiction, adjournment
methods, penalities for being late, etc. Tournament rules
often deal with details. Not everything can be predicted, so
a sportsmanlike spirit is mentioned. Finally, it should be
clear which of several rule sets takes precedence.

6.7 Tournament Organization

A regional tournament can be organized by a club. Big events
can be held at the request of an association or federation,
who also supervise. A tournament organization is responsible
for providing a venue and playing material. It must be
distinguished from the tournament director and his assistant
directors, who perform the particular tasks of pairing,
collecting results, and ensuring smooth running. Shared
power furthermore demands independent referees.

6.8 Jurisdiction

Before the start of a tournament valid instances of a
jurisdiction as well as the persons to be referees must be
clear. Typically, for a tournament itself there is one
referee as the first instance and a body of three referees
as the second instance. For very peculiar cases a federation
could have a third and final instance. Some tournament rules
replace the second instance by a single person, called chief
referee; to avoid confusion he ought not to judge as the
first instance. Players should respect the referees' tough
job of mediation or decision; referees should seriously
enforce the rules.

6.9 Prizes

The first places of a tournament invoke major prizes. E.g.
the first, second, third places might get 3/6, 2/6, 1/6 of
the available money. In a tournament with many weaker
players it is a good idea to provide some prizes for all
other players that win most rounds as well. While prizes can
be money, books, trophies, etc., one should remember that
money is most universally accepted and trophies serve the
media better than the winners. -
On a related topic, a side event lottery must give equal
chances to all participants. This is only achieved by using
one lot for each.

7 Links

Most rules information, links, short rules:
http://home.snafu.de/jasiek/rules.html (Who's computer is this?)

General links, bestiary, rules:
http://www.goban.demon.co.uk/go/main.html (Who's computer is this?)



Where you can get the newsgroup rec.games.go