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Go (board game)

Go is an ancient strategic board game originating from China at least two thousand years ago. It is highly popular in East Asia, and Internet gaming has served to greatly increase its popularity throughout the rest of the world in recent years.

In China it is called 圍棋 wéiqí (way-chee), in Korea its name is 바둑 baduk, and in Japan 囲碁 igo (ee-go), which gave rise to the English name Go from the Japanese character 碁.

 Table of contents 1 The essential rules of Go 2 Nature of the game 3 The Go world 4 History 5 Mathematical theory of Go endgames 6 See also 7 External links and references

The essential rules of Go

• Turns: Two players, Black and White, each with a limitless number of lens-shaped tokens, called stones, take turns placing stones on the board.
• Stones are placed on the board's points (line intersections).
• Black moves first in an even game. In a handicap game, black (the weaker player) will have a number of stones on the board, and white will start play.
• The Object of the game is to surround and control more points, or territory, than your opponent.
• Tactical rules
• A single stone may be placed on (almost) any empty intersection. Stones are not moved after being placed, though they may be captured and removed from the board.
• A group of stones is a bunch of stones connected via straight lines (not diagonals)
• When you place a stone on an empty board it will usually have 4 empty spaces surrounding it (stones on the edge have 3, and stones at the corners have 2): these are called liberties.
• The number of liberties in group is the total number of empty spaces connected to any stone in it.
• If a stone of the opposite color is placed at the last liberty of a stone or group, that stone or group is captured (removed from board).
• Stones may not be placed on points where there is no liberty, unless placing a stone there would capture one or more stones (thus creating a liberty).
• An eye is a blank space (or group of blank space) inside a group of stones. Thus, an opponent cannot place a stone inside a single-space eye unless it is the final liberty of this group (thereby killing it). A group that has two separate eyes or more is thus impossible to kill.
• Ko rule: If a capture would recreate the previous configuration of the whole board, it is illegal and cannot be played. The rule then is that a move must be played elsewhere before recapture. This situation is called a "ko" and may begin a "ko fight", where challenging moves are made in turn to contest and "take back" the ko.
• End of Game: The game is over when both players pass, having no more profitable moves to make.
• All "dead" stones (stones not part of "living" groups) are removed.
• Scoring: Each player's score is the number of points under that color's control. Captured stones are placed within the territory of the player who lost them, reducing it. "Dame" are neutral points, or points inbetween boundary lines that belong to neither player and are not counted.
• The winner is the player with the greater score, naturally.

There are a small number of slight variations for these rules. These variations are subtle, mainly affecting scoring, and do not much change the character of the game. For a more detailed treatment, see
Go rules.

In a game between players of unequal strength, a handicap is used: the weaker player starts out with a number of stones on the board. See Go handicap for the details.

Nature of the game

3 Japanese professional Go players observe some younger amateurs as they dissect a life and death problem in the corner of the board. From the US Go Congress in Houston, 2003. ()

Although the rules of Go are very simple, the game itself can be extremely complex. Go is a complete-knowledge, deterministic, strategy game like chess, checkers, and reversi, although its depth exceeds even those games. Its large board and lack of restrictions allows great scope in strategy, as decisions in one part of the board are influenced by a seemingly unrelated situation in distant parts of the board, and moves made early in the game can shape the nature of conflict hundreds of moves later.

The game emphasises the importance and tensions of balance on multiple levels. To secure an area of the board, it is good to play moves close together; but to cover the largest area one needs to spread out. To ensure one does not fall behind, aggressive play is required; but playing too aggressively leaves weaknesses undefended that can be exploited. Playing too low (close to the edge) secures insufficient territory; yet playing too high (far from the edge) allows the opponent to invade. Many people find the game attractive for its reflection of the polarities found in life.

See Go strategy and tactics for an introductory explanation of how to play well, and the Go demonstration game.

It is commonly said that no game has ever been played twice. This may be true: On a 19x19 board, there are about 3361*0.012=2.1x10170 possible positions, most of which are the end result of about (120!)2 = 4.5x10397 different (no-capture) games, for a total of about 9.3x10567 games. Allowing captures gives as many as 107.49*1048 possible games, most of which last for over 1.6x1049 moves! (By contrast, the number of legal positions in chess is estimated to be between 1043 and 1050, and physicists estimate that there are not more than 1090 protons in the entire universe.)

Computers and Go

Although attempts have been made to program computers to play Go, success in that area has been moderate at best. Even the strongest programs are no better than an average club player, and would easily be beaten by a strong player even getting a nine stone handicap. This is attributed to many qualities of the game, including the "optimising" nature of the victory condition, the virtually unlimited placement of each stone, the large board size, and the high degree of pattern-recognition involved. For this reason, many in the field of artificial intelligence consider Go to be a better measure of a computer's capacity for thought than chess. See computer Go article for detail.

Use of computer networks to allow humans to meet, discuss games, and play one another, although generally considered inferior to face-to-face play, is becoming much more common. There are servers and software to facilitate this; see Additional Resources below for more information.

Other board games commonly compared with Go

Go appears to stand apart among games in its rules and gameplay; it is difficult to find another board game which could be considered of the same "family" as Go. However, on learning about the game, people will attempt to compare it with other games they may already have experienced. This is a non-exhaustive list of some games that are often compared with Go.

• Variations of chess
• Western chess: This game dominates Western culture as the pinnacle of strategic game play; its history in the culture stretches back many centuries. By comparison, Go has only been known to Western culture as a challenging strategic game since the 1950s. Many consider Go to be more challenging and elegant, though adherents of Chess are in no hurry to convert.
• Shogi: Early Western literature often made the error of referring to Go as "Japanese Chess". The Japanese do have their own variant of Chess, called Shogi; it is far more similar to the other Chess variants than to Go. Shogi schools were founded in Japan about the same time as Go schools, but it never received as much favour as Go.
• Xiangqi: This is the Chinese variant of Chess, most usually called "Chinese Chess" by Westerners. Like most Chess variants, it has great depth of strategy, but bears few similarities to Go in game play.
• Reversi: Marketed by one game company as "Othello", Reversi bears superficial similarity to Go, with black and white circular pieces, an undifferentiated grid for a board, simple rules, and a goal of covering more of the board than the opponent. The game play is quite unlike Go, however, and the depth of strategy in Reversi is not comparable to Go.
• Gomoku, Renju and Pente: Played with the same equipment as Go (a 19x19 grid, black and white stones), in these games the goal is to create five stones in a row. The rules are thus completely unrelated, and the game style is much shorter and less strategic than Go.
• Alak is a Go-like game restricted to a single spatial dimension.
• Hex is a connection game which is often compared to go.

Although one could play Go with a piece of card for a board and a bag of plastic tokens, Go players pride themselves on their game sets. The traditional Go board (called a goban in Japanese) is solid wood, about 15-20cm thick, preferably from the rare golden-coloured Kaya tree, and stands on its own attached legs. Players sit on reed mats (tatami) on the floor to play. The stones (go-ishi) come in matching solid wood pots (go-ke) and are made out of clamshell (white) and slate (black) and are extremely smooth. The natural resources of Japan have been unable to keep up with the enormous demand for the native clams and slow-growing Kaya trees; both must be of sufficient age to grow to the desired size, and they are now extremely rare at the age and quality required, raising the price of such equipment tremendously.

In clubs and at tournaments, where large numbers of sets must be maintained (and usually purchased) by one organisation, the expensive traditional sets are not usually used. For these situations, table boards (of the same design as floor boards, but only about 2-5cm thick and without legs) are used, and the stones are made of glass rather than slate and shell. Bowls will often be plastic if cheap wooden bowls cannot be had. Plastic stones can be had, but are considered inferior to glass as they are generally much lighter, and most players find them too unpleasant to justify the difference in price.

The dimensions of the board (traditionally the grid is 45.45cm long and 42.42cm wide, with space beyond to allow stones to be played on the edges and corners of the grid) often surprise newcomers: it is not a perfect square, but is longer than it is wide, roughly in the proportion 12:11. Two reasons are frequently given for this. One is that when the players sit at the board, the angle at which they view the board gives a foreshortening of the grid; the board is slightly longer between the players to compensate for this. Another reason is that the Japanese aesthetic finds any structure which is perfectly symmetrical to be in bad taste, and the board is not made a perfect square for this reason.

Traditional stones are made so that black stones are slightly larger in diameter than white; this is probably to compensate for the optical illusion created by contrasting colours that makes the white stones appear larger on the board than black stones. The difference is slight, and since its effect is to make the stones appear the same size on the board, it can be surprising to discover they are not.

The bowls for the stones are of a simple shape, like a flattened sphere with a level underside. The lid is loose-fitting and is upturned before play to place opponent's stones captured during the game. The bowls are usually made of turned wood, although small lidded baskets of woven bamboo or reeds make an attractive cheaper alternative.

There is even an art to placing a Go stone, held between the tips of the outstretched index and middle fingers and striking the board firmly to create a sharp click. Many consider the acoustic properties of the wood of the board to be quite important. The traditional goban will usually have its underside carved with a pyramid called a Heso recessed into the board. Tradition holds that this is to give a better resonance to the stone's click, but the more conventional explanation is to allow the board to expand and contract without splitting the wood. A board is seen as more attractive when it is marked with slight dents from decades -- or centuries -- of stones striking the surface.

The Go world

Ranks

In countries where Go is popular, ranks are employed to indicate playing strength. The Japanese formalised the teaching and ranking of Go, and modelled the system after their existing martial arts schools.

Players who are competent are ranked starting at 1 dan, through to 9 dan which is the highest rank (in the Japanese Edo period, only one player held this rank at a time, and was called Meijin). Approaching 1 dan, a player first progresses through kyu ranks, with 1 kyu being the rank below 1 dan, and a greater kyu ranking indicating a greater distance in strength from 1 dan. Since beginners will commonly progress through elementary concepts quickly, it is difficult to set a lower bound to the kyu ranks, but nominal starting points of 20, 25 or 30 are commonly used.

The distinction between each rank is, by definition, one handicap stone. In other words, the difference in rank between two players is theoretically equal to the number of handicap stones required for each player to have an even chance of winning. Beating this handicap consistently is the indicator that a player's strength has improved, and his rank should be adjusted upward by one stone, thus changing the number of handicap stones required.

In China, Japan and Korea, there are two distinct ranking sets, one for professional players (who receive a fee for each game they play, bonuses for winning, and fees for other related activities) and one for amateur players. In Japan, amateur ranks are only recognised up to 8 dan (before the year 2001, only amateur ranks up to 7 dan were recognised).

Player pools that do not regularly mix (such as different countries, or online versus real-life player groups) often result in divergent playing strengths for the same rank level. Players asked to give their rank will therefore often qualify it with "in my country" or "on this Internet server".

Top players

Although for many centuries the strongest players in the world came from Japan, players from China in the 1980s and South Korea in the 1990s have reached the same or even a higher level. Nowadays, top players from these three countries are of comparable strength, although Korean players dominate the major international titles. All three countries have professional competitions where there is sometimes a high amount of prize money.

Players from other countries have traditionally been much weaker, except for some players who have taken up professional courses in one of the Asian countries. This is attributable to the fact that details of the game have been unknown outside of Asia for most of the game's history. A German scientist, Otto Korschelt, is credited with the first systematic description of the game in a Western language in 1880 AD; it was not until the 1950s that Western players would take up the game as more than a passing interest.

History

The origins of the game are unknown, but the oldest surviving references come from China in the 6th century BC. Except for changes in the board size and starting position, has essentially kept the same rules since that time, which quite likely makes it the oldest board game still played today. It had reached Japan by the 7th century, and gained popularity at the imperial court in the 8th. By the beginning of the 13th century, the game was played in the general public in Japan.

Early in the 17th century, the then best player in Japan, Honinbo Sansa, was made head of a newly founded Go academy (the Honinbo school, the first of several competing schools founded about the same time), which developed the level of playing greatly, and introduced the martial-arts style system of ranking players. The government discontinued its support for the Go academies in 1868 as a result of the fall of the Tokugawa shogunate.

In honour of the Honinbo school, whose players consistently dominated the other schools during their history, one of the most prestigious Japanese Go championships is called the "Honinbo" tournament.

Historically, Go has been unequal in terms of gender. However, the opening of new, open tournaments and the rise of strong female players, most notably Rui Naiwei, has in recent years legitimised the strength and competitiveness of emerging female players.

Around 2000, in Japan, the manga (Japanese comic) and anime series Hikaru no Go has popularized Go among the youth and started a Go boom in Japan.

Mathematical theory of Go endgames

Elwyn Berlekamp and David Wolfe have developed a mathematical theory of the late endgame in Go based on the combinatorial game theory of John Horton Conway. Whilst not of general utility in most play, it greatly aids the analysis of certain classes of positions.