Talk:Go (game)/Rewrite

Placing stones
The two players, Black and White, take turns placing stones of their colour on the intersections of the board, one stone at a time. The usual board size is a 19x19 grid, but for beginners 13x13 and 9x9 are also popular. The board is empty to begin with. Black plays first, unless black is given a handicap of two stones or more (in which case, white plays first). The players may choose any unoccupied intersection to play on, except for those forbidden by the ko and suicide rules (see below). Once played, a stone can never be moved and can be taken off the board only if it is captured. A player may also pass, declining to place a stone, though this is usually only done at the end of the game when both players believe nothing more can be accomplished with further play. When both players pass consecutively, the game ends and is then scored.

Liberties and capture
Vertically and horizontally adjacent stones of the same color form a chain (also called a string or group). Only stones 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, along one of the grid lines of the board, 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.

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. Then, the enemy group is captured. The Ing and New Zealand rules do not have this rule, and there a player might destroy one of its own groups—"commit suicide".

The ko rule
The ko rule states that a player may not play a move that recreates the board from a previous position. The rule prevents an infinite game. An often occuerence is when a player plays a stone in such a way that captures a stone and also only have one liberty. Players have to play somewhere else before capturing the stone. This is called a "ko fight".

Scoring
The aim of the game is to surround more territory than the opponent. 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 captured by that player. Area scoring counts the points of territory surrounded by a player, plus the number of that player's stones on the board.

Territory scoring
Territory is areas of vacant intersections surrounded by stones belonging to one player, such that the opponent cannot place stones within it without these being captured. At the end of the game, the player with more territory is the winner. Stones captured during the game by one side are used to fill in the opponent's territory during the game, thus reducing their score by one point for each captured stone.

Stones inside opposing territory that cannot survive are considered prisoners at the end of the game and need not be captured by explicitly filling all of their liberties.

Komi
In most games, White receives a bonus of 5.5 to 8.5 points as compensation for the advantage Black gains from having the first move. In a tournament, the tournamend directors decides the Komi points. The half point in the Komi prevents draws.

Handicap
Handicaps are extra stones a player may play at the beginning of a game. It is given to the weaker player if a difference in ranks occur and the handicap is equal to the difference in kyu or dan ranks. Handicaps are usually played on the 9 star points but can be played anywhere.

Opening
In the opening of the game, players usually play and gain territory in the corners of the board first, as the presence of two edges make it easier for them to surround territory and establish their stones. From a secure position in a corner, it is possible to lay claim to more territory by extending along the side of the board. The opening is the most theoretically difficult part of the game, and takes a large proportion of professional players' thinking time. The first stone played at a corner of the board is generally placed on the third or fourth lines from the edge. Playing nearer to the edge does not produce enough territory to be efficient, and playing further from the edge does not safely secure the territory.

Middle game
In the middle game, players expand and invade each others territories. The players must think big and fight for the major territories. It is usually more intense and lasts over 100 moves which takes up most of the game. The middle game ends when the major territories are settled and the players must fight for the minor points.

Endgame
Near the end of a game, play becomes divided into localized fights that do not affect each other. One can choose to pass and when there are 2 consecutive passes, the game is ended and it is scored.

History

 * In ancient times the rules of go were passed on verbally, rather than being written down.

Equipment
A typical go board is made of wood, usually 4-5 in thick. The lines forming the playing surface are drawn parallel to the edges. The board is not perfectly square, but is slightly rectangular and is placed so that the narrow sides face the two players. A traditional board would be made out of the wood Katsura and would also have attached legs made from the wood of Kaya.

Go stones are available from a variety of materials including: clam shell, slate, glass, plastic, pottery and bamboo. The standard black stones are 2.18cm in diameter while the white stones are 2.12cm in diameter.

Mathematics and computers
In the endgame, it can often happen that the state of the board consists of several subpositions that do not interact with the others. The whole board position can then be considered as a mathematical sum, or composition, of the individual subpositions. It is this property of go endgames that led John Horton Conway to the discovery of surreal numbers.