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  • Go (game)

  • Go is an abstract strategy board game for two players, in which the aim is

  • to surround more territory than the opponent. The game was invented in ancient China more

  • than 2,500 years ago, and is therefore believed

  • to be the oldest board game continuously played today.

  • It was considered one of the four essential arts of the cultured aristocratic Chinese scholars in

  • antiquity. The earliest written reference

  • to the game is generally recognized as the historical annal Zuo Zhuan.

  • Despite its relatively simple rules, Go is very complex, even more so than chess. Compared to chess,

  • Go has both a larger board with more scope for play and longer games, and, on average,

  • many more alternatives to consider per move. The playing pieces are called "stones".

  • One player uses the white stones and the other, black.

  • The players take turns placing the stones on the vacant intersections of a board

  • with a 19×19 grid of lines. Beginners often play on smaller 9×9 and 13×13 boards,

  • and archaeological evidence shows that the game was played in earlier centuries on a board

  • with a 17×17 grid. However, boards with a 19×19 grid had become standard

  • by the time the game had reached Korea in the 5th century CE

  • and later Japan in the 7th century CE. Once placed on the board, stones may not be moved,

  • but stones are removed from the board when "captured". Capture happens when a stone

  • or group of stones is surrounded by opposing stones on all orthogonally-adjacent points.

  • The game proceeds until neither player wishes to make another move;

  • the game has no set ending conditions beyond this. When a game concludes,

  • the territory is counted along with captured stones and komi to determine the winner.

  • Games may also be terminated by resignation. As of mid-2008, there were well

  • over 40 million Go players worldwide, the overwhelming majority of them living in East Asia.

  • the International Go Federation has a total of 75 member countries

  • and four Association Membership organizations in multiple countries.

  • Overview

  • [^] Go is an adversarial game with the objective of surrounding a larger total area of the board

  • with one's stones than the opponent. As the game progresses,

  • the players position stones on the board to map out formations and potential territories.

  • Contests between opposing formations are often extremely complex and may result in the expansion,

  • reduction, or wholesale capture and loss of formation stones.

  • [^] A basic principle of Go is that a group of stones must have at least one "liberty"

  • to remain on the board. A "liberty" is an open "point" bordering the group.

  • An enclosed liberty is called an "eye", and a group of stones with two or more eyes is said

  • to be unconditionally "alive". Such groups cannot be captured, even if surrounded. A group

  • with one eye or no eyes is "dead" and cannot resist eventual capture. The general strategy is

  • to expand one's territory, attack the opponent's weak groups, and always stay mindful of the

  • "life status" of one's own groups. The liberties of groups are countable. Situations

  • where mutually opposing groups must capture each other or die are called capturing races,

  • or semeai. In a capturing race, the group with more liberties will ultimately be able

  • to capture the opponent's stones. Capturing races and the elements of life

  • or death are the primary challenges of Go.

  • A player may pass on determining that the game offers no further opportunities

  • for profitable play. The game ends when both players pass, and is then scored. For each player,

  • the number of captured stones is subtracted from the number of controlled points in "liberties"

  • or "eyes", and the player with the greater score wins the game. Games may also be won

  • by resignation of the opponent.

  • Finer points

  • In the opening stages of the game, players typically establish positions in the corners

  • and around the sides of the board. These bases help

  • to quickly develop strong shapes which have many options for life and establish formations

  • for potential territory. Players usually start in the corners,

  • because establishing territory is easier with the aid of two edges of the board.

  • Established corner opening sequences are called "joseki" and are often studied independently.

  • "Dame" are points that lie in-between the boundary walls of black and white,

  • and as such are considered to be of no value to either side. "Seki"

  • are mutually alive pairs of white and black groups where neither has two eyes. A "ko"

  • is a repeated-position shape that may be contested by making forcing moves elsewhere.

  • After the forcing move is played, the ko may be "taken back" and returned to its original position.

  • Some "ko fights" may be important and decide the life of a large group,

  • while others may be worth just one or two points. Some ko fights are referred to as "picnic kos"

  • when only one side has a lot to lose. The Japanese call it a hanami ko. Playing

  • with others usually requires a knowledge of each player's strength, indicated by the player's rank.

  • A difference in rank may be compensated by a handicapBlack is allowed to place two

  • or more stones on the board to compensate for White's greater strength.

  • There are different rule-sets, which are almost entirely equivalent, except

  • for certain special-case positions. Aside from the order of play and scoring rules,

  • there are essentially only two rules in Go: Almost all other information about how the game is

  • played is a heuristic, meaning it is learned information about how the game is played, rather

  • than a rule. Other rules are specialized, as they come about through different rule-sets,

  • but the above two rules cover almost all of any played game.

  • Although there are some minor differences between rule sets used in different countries,

  • most notably in Chinese and Japanese scoring rules,

  • these differences do not greatly affect the tactics and strategy of the game. Except where noted,

  • the basic rules presented here are valid independent of the scoring rules used.

  • The scoring rules are explained separately. Go terms

  • for which there are no ready English equivalent are commonly called by their Japanese names.

  • Basic rules

  • [^] Two players, Black and White,

  • take turns placing a stone of their own color on a vacant point of the grid on a Go board.

  • Black plays first. If there is a large difference in skill between the players,

  • the weaker player typically uses Black and is allowed to place two or more stones on the board

  • to compensate for the difference. The official grid comprises 19×19 lines,

  • though the rules can be applied to any grid size. 13×13 and 9×9 boards are popular choices

  • to teach beginners, or for playing quick games. Once placed, a stone may not be moved

  • to a different point. Vertically

  • and horizontally adjacent stones of the same color form a chain that cannot subsequently be

  • subdivided and, in effect, becomes a single larger stone. Only stones immediately connected

  • to one another by the lines on the board create a chain;

  • stones that are diagonally adjacent are not connected. Chains may be expanded

  • by placing additional stones on adjacent intersections, and can be connected together

  • by placing a stone on an intersection that is adjacent to two or more chains of the same color.

  • [^] A vacant point adjacent to a stone is called a liberty for that stone.

  • Stones in a chain share their liberties. A chain of stones must have at least one liberty

  • to remain on the board. When a chain is surrounded by opposing stones so that it has no liberties,

  • it is captured and removed from the board.

  • Ko rule

  • An example of a situation in which the ko rule applies Players are not allowed

  • to make a move that returns the game to the previous position. This rule, called the ko rule,

  • prevents unending repetition.

  • As shown in the example pictured: Black has just played the stone marked 1, capturing a white stone

  • at the intersection marked with the red circle. If White were allowed

  • to play on the marked intersection, that move would capture the black stone marked 1

  • and recreate the situation before Black made the move marked 1.

  • Allowing this could result in an unending cycle of captures by both players.

  • The ko rule therefore prohibits White from playing at the marked intersection immediately.

  • Instead White must play elsewhere, or pass; Black can then end the ko by filling

  • at the marked intersection, creating a five-stone black chain. If White wants to continue the ko,

  • White tries to find a play elsewhere on the board that Black must answer; if Black answers,

  • then White can retake the ko. A repetition of such exchanges is called a ko fight.

  • While the various rule-sets agree on the ko rule prohibiting returning the board

  • to an immediately previous position, they deal in different ways

  • with the relatively uncommon situation in which a player might recreate a past position that is

  • further removed. See Rules of Go: Repetition for further information.

  • Suicide

  • [^] A player may not place a stone such that it or its group immediately has no liberties,

  • unless doing so immediately deprives an enemy group of its final liberty. In the latter case,

  • the enemy group is captured, leaving the new stone with at least one liberty.

  • This rule is responsible for the all-important difference between one and two eyes: if a group

  • with only one eye is fully surrounded on the outside, it can be killed

  • with a stone placed in its single eye. The Ing and New Zealand rules do not have this rule,

  • and there a player might destroy one of its own groups—"commit suicide".

  • This play would only be useful in a limited set of situations involving a small interior space.

  • In the example at right, it may be useful as a ko threat.

  • Komi

  • Because Black has the advantage of playing the first move,

  • the idea of awarding White some compensation came into being during the 20th century.

  • This is called komi, which gives white a 6.5-point compensation under Japanese rules.

  • Under handicap play, White receives only a 0.5-point komi, to break a possible tie.

  • Scoring rules

  • [^] Two general types of scoring system are used, and players determine which to use before play.

  • Both systems almost always give the same result.

  • Territory scoring counts the number of empty points a player's stones surround, together

  • with the number of stones the player captured.

  • Area scoring counts the number of points a player's stones occupy and surround. It is associated

  • with contemporary Chinese play and was probably established there

  • during the Ming Dynasty in the 15th or 16th century. After both players have passed consecutively,

  • the stones that are still on the board, but unable to avoid capture, called dead stones, are removed.

  • Area scoring : A player's score is the number of stones that the player has on the board,

  • plus the number of empty intersections surrounded by that player's stones.

  • Territory scoring : In the course of the game, each player retains the stones they capture,

  • termed prisoners. Any dead stones removed at the end of the game become prisoners.

  • The score is the number of empty points enclosed by a player's stones,

  • plus the number of prisoners captured by that player.

  • If there is disagreement about which stones are dead, then under area scoring rules,

  • the players simply resume play to resolve the matter.

  • The score is computed using the position after the next time the players pass consecutively.

  • Under territory scoring, the rules are considerably more complex; however, in practice,

  • players generally play on, and, once the status of each stone has been determined, return

  • to the position at the time the first two consecutive passes occurred and remove the dead stones.

  • For further information, see Rules of Go.

  • Given that the number of stones a player has on the board is directly related

  • to the number of prisoners their opponent has taken, the resulting net score,

  • that is the difference between Black's and White's scores, is identical under both rulesets. Thus,

  • the net result given by the two scoring systems rarely differs by more than a point.

  • Life and death

  • While not actually mentioned in the rules of Go,

  • the concept of a living group of stones is necessary for a practical understanding of the game.

  • Examples of eyes. The black groups at the top of the board are alive, as they have

  • at least two eyes. The black groups at the bottom are dead as they only have one eye.

  • The point marked a is a false eye. When a group of stones is mostly surrounded

  • and has no options to connect with friendly stones elsewhere,

  • the status of the group is either alive, dead or unsettled. A group of stones is said

  • to be alive if it cannot be captured, even if the opponent is allowed to move first. Conversely,

  • a group of stones is said to be dead if it cannot avoid capture,

  • even if the owner of the group is allowed the first move. Otherwise, the group is said

  • to be unsettled: the defending player can make it alive or the opponent can kill it,

  • depending on who gets to play first. An "eye" is an empty point or group of points surrounded

  • by one player's stones. If the eye is surrounded by Black stones, the "suicide rule" forbids White

  • to place a stone in a single-point eye surround

  • by Black unless the placement results in a capture of Black stones that creates a liberty

  • for White's new stone. Effectively, the capture rule is applied before the suicide rule,

  • and both are applied before White's play is completed. By the interplay of the capture

  • and suicide rules, survival for a group can be guaranteed only by having two or more eyes.

  • If two such eyes exist, the opponent can never capture a group of stones,

  • because one liberty is always remaining. One eye is not enough for life,

  • because a point that would normally be suicide may be filled by the opponent,

  • thereby capturing the group. In the "Examples of eyes" diagram, all the circled points are eyes.

  • The two black groups in the upper corners are alive, as both have at least two eyes.

  • The groups in the lower corners are dead, as both have only one eye.

  • The group in the lower left may seem to have two eyes,

  • but the surrounded empty point marked a is not actually an eye. White can play there

  • and take a black stone. Such a point is often called a false eye.

  • Seki (mutual life)

  • [^] Example of seki.

  • Neither Black nor White can play on the marked points without reducing their own liberties

  • for those groups to one. – Above deprecated. --> There is an exception

  • to the requirement that a group must have two eyes to be alive, a situation called seki.

  • Where different colored groups are adjacent and share liberties, the situation may reach a position

  • when neither player wants to move first, because doing so would allow the opponent to capture;

  • in such situations therefore both players' stones remain on the board in mutual life or "seki".

  • Neither player receives any points for those groups, but

  • at least those groups themselves remain living, as opposed to being captured.

  • Seki can occur in many ways. The simplest are: In the "Example of seki " diagram,

  • the circled points are liberties shared by both a black and a white group. Neither player wants

  • to play on a circled point, because doing so would allow the opponent to capture.

  • All the other groups in this example, both black and white, are alive with at least two eyes.

  • Seki can result from an attempt by one player to invade

  • and kill a nearly settled group of the other player.

  • Tactics

  • In Go, tactics deal with immediate fighting between stones, capturing and saving stones, life,

  • death and other issues localized to a specific part of the board. Larger issues, not limited

  • to only part of the board, are referred to as strategy, and are covered in their own section.

  • Capturing tactics

  • There are several tactical constructs aimed at capturing stones.

  • These are among the first things a player learns after understanding the rules.

  • Recognizing the possibility that stones can be captured using these techniques is an important step

  • forward. A ladder. Black cannot escape unless the ladder connects

  • to black stones further down the board that will intercept with the ladder.

  • The most basic technique is the ladder. To capture stones in a ladder,

  • a player uses a constant series of capture threatscalled atarito force the opponent into a zigzag

  • pattern as shown in the adjacent diagram.

  • Unless the pattern runs into friendly stones along the way,

  • the stones in the ladder cannot avoid capture.

  • Experienced players recognize the futility of continuing the pattern and play elsewhere.

  • The presence of a ladder on the board does give a player the option

  • to play a stone in the path of the ladder, thereby threatening to rescue their stones,

  • forcing a response. Such a move is called a ladder breaker and may be a powerful strategic move.