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There are many variations on the basic game of Go. Some are ancient digressions, while other are modern deviations. They are often to be found as side events at tournaments, for instance the U.S. Go Congress, has a "Crazy Go" evening scheduled each year.
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The difficulty in defining the rules of Go has led to a situation where there are many subtly different rulesets in existence. They are distinct over such areas as scoring method, ko, suicide, handicap placement and what to do about neutral points at the end of the game. In the main these differences are small enough to avoid changing the character and strategy of the game, so we do not consider them here. For more information, see Rules of Go.
There are some versions that are so distinct as to be considered variants. In other cases the effect of rule differences on actual play is minor, but for these the tactical consequences are substantive.
Tibetan Go is played on a 17×17 board, and starts with six stones (called Bo) from each colour placed on the third line as shown. White makes the first move.[1] It has a unique ko rule: one may not play a stone at an intersection where the opponent has just removed a stone. This ko rule is so different from the other major rulesets that it alone significantly changes the character of the game. For instance, snapbacks must be delayed by at least one move, allowing an opponent a chance to create life. Finally, a player who controls all four corner points (the 1-1 points) gets a bonus of 40 points, and if he also controls the centre point he gets a further bonus of 10 points. (Control means occupies or surrounds.)
A different form of Go (baduk) evolved in Korea called sunjang baduk. It has been played from at least the 7th century. Its most distinctive feature is the prescribed opening. The starting position dictates the placement of 16 stones (8 black, 8 white) as shown, and the first move is prescribed for Black at the center of the board. However, the counting system for determining territory at the end of the game also has some important differences. Namely, stones internal to territory and irrelevant to boundary definition, are removed before counting territory.
In another Korean variant, bangneki, the players wager on the outcome of the game. A fixed stake ("bang") is paid for every ten points on the board by which the loser is beaten. [2][3]
Batoo is a modern Korean variant. The name stems from a combination of the Korean words baduk and juntoo (“battle”). It is played entirely in cyberspace, and differs from standard Go in a number of ways, most noticeably in the way in which certain areas of the board are worth different points values. The other principle difference is that both players place three stones before the game begins, and may also place a special “hidden stone”, which affects the board as a regular stone but is invisible to the opponent. Batoo has become very popular among young people in Korea.
The first player to capture a stone wins. It was invented by Japanese professional Yasutoshi Yasuda who describes it in his book Go As Communication. Yasuda was first inspired by the need for a medium to address the problem of bullying in Japan, but soon found that "First Capture" also works as an activity with senior citizens and even developmentally delayed individuals. He sees it as a game in its own right, not just as a prelude to Go, but also as a way to introduce simple concepts that lead to Go. For the latter purpose, he recommends progressing to "Most Capture", in which the player capturing the most stones wins; then it is natural to introduce the idea of capturing territory, not just the opponent's stones. This variation is often called Atari Go in the West, where it is becoming increasingly popular as a preliminary means of introducing Go itself to beginners.
Environmental Go, invented by Elwyn Berlekamp, adds an element of mathematical precision to the game.[4] In lieu of playing a stone, a player may take the highest remaining card from a pack of cards valued in steps of ½ from ½ to 20: the player's score will be the territory captured, plus the total value of cards taken. In effect, the players participate in a downward auction for the number of points they think sente is worth at each stage in the game. The professional players Jiang Zhujiu and Rui Naiwei played the first Environmental Go game in April 1998. Since then the variant has seen little activity on the international scene.
In Cards Go players draw from a pack of cards contain instructions to play one of a fixed set of commonly occurring shapes.[5] If the said shape cannot be placed on the board, then an illegal move is deemed to have been played: this necessitates resignation.
In Multi-player Go, stones of different colors are used so that four players or more can play on one board.
Paper and Pencil Go is a Go variant that can be played just with paper and pencil.[6] Unlike in standard Go, games played under these rules are guaranteed to end in a finite number of moves, and no ko rules are needed. It differs from standard Go in the following aspects:
This involves two teams of players taking either the Black or the White stones. Each player in the team must play in turn, playing out of sequence will normally result in a small penalty (usually three prisoners). Partners may not consult on how to play, or engage in any form of signaling. Communication between partners may only take the following forms listed below.
Pair Go is a gender specific form of Rengo, calling for teams composed of one male and one female member.[7] It was popularised by the Japan Pair Go Association as a means of increasing female participation in the game. They hoped that this increase in itself would add a new appeal to the game. The Ricoh Cup, the annual professional Pair Go world championship debuted in 1994.[8] The International Pair Go Association sponsors an annual amateur world championship in Tokyo in November, which has been running uninterrupted since 1989.[9] They first introduced the variant to Europe at the 1992 European Congress in Canterbury, England. Amateur Pair Go tournaments have been held in the United States at U.S. Go Congresses since 2005 at least [10] and in Denver, CO.
One (as a handicap) or both of the players cannot see the board in this variant. Therefore they have to remember the whole position. This is considered much more difficult than playing blind chess. Indeed, most club standard players can play blind chess, but only professional players are able to complete a game of blind 19×19 Go.
Both players use stones of the same color. This variation is regarded as a useful tool for developing one's reading skills.
These variants are not purely strategic games, as the element of luck is quite important.
This game requires two players, a referee and three playing sets. Each player sees only his own board, while the referee can see them both and also have his own set. Players place stones on their boards, with no knowledge of what other players are doing. A referee keeps track of the game on the central board. If any player makes an illegal move, the referee informs him about it (some play that the referee says only that the move is illegal, while some, that the player is told whether the intersection is occupied or there is illegal ko capture). The player is allowed to make another move.
This is a crossover between rengo and shadow Go. There are two teams with two players each, a referee and five Go sets. The players move alternatingly as in rengo. Each player keeps track of their own moves on their own board; they are not informed about teammates' or opponents' moves. The referee keeps track of the complete game and informs a player if their move was illegal, in which case they can try again. The referee removes captured stones from all affected boards.[11] Because of the asymmetry in information, this may be an undecidable game; which would mean that there is in principle no computer or algorithm that can tell from a given position who will win.[12]
Although Go is most commonly played on a board with 19×19 lines, 9×9 and 13×13 boards are also available. They are used by beginners and by players who want a game that finishes more quickly. Due to flexibility of configuration, the two smaller sizes are more often played on the online Go servers such as KGS Go Server, which allows board sizes from 2×2 to 38×38.
The annual Milton Keynes Go Tournament has a popular side-event that is played on a stylised map of Milton Keynes.[13] Its non-conventional lattice presents some interesting possibilities.
Harald Schwarz invented a Go variant that is played on a circular lattice.[14]
A toroidal board is two dimensional surface with an implied third dimension because it is as if a standard board has been rolled and two opposite edges joined to form a tube and then the ends of the tube joined. It can be simulated on a standard 19×19 board, but requires imagination on the part of the players to perform an abstract join at the edges. It is noteworthy that the toroidal board has no corners, so standard joseki do not apply. This kind of variant can also be performed with three other identifications, see Surface construction from polygons.
TriGo is a go variant that uses a triangular-grid goban, where each stone has up to six liberties. To compensate for this, there are several rule changes: ko and superko are limited in scope, komi is not used, and after the first stone is placed, every turn consists of placing two stones. After both players have passed a turn, the score is counted (the sum of captured stones and territory), and in the case of a draw the player passing first wins.
Alak is a Go-like game restricted to a single spatial dimension. Go can be extended to three dimensions. An example is Diamond Go, which uses the structure of a carbon diamond crystal lattice.[15] With many Go variants, the nature of the game changes dramatically if they do not keep the standard 4-connectivity of the points, which Diamond Go maintains.
A program called Freed Go can be used to play with boards with generic topology. It has embedded 11 different boards, either three-dimensional shapes (including cube, sphere, cylinder, diamond, torus and Mobius strip) or flat fields with points connected to three, five or six neighboring points, but it's also possible to create custom boards.[16]