Oldest recorded go game with a ko fight

Ko is a Japanese go term adopted into English usage. It describes a situation where two alternating single stone captures would repeat the original board position. The alternating captures could repeat indefinitely, preventing the game from ending. The ko rule resolves the situation.

The term �ko� is also used more generally in reference to other repeating patterns and rules involving them, although �superko� is the general term for repetitions other than the take-and-take-back ko, which is sometimes called �basic ko� to distinguish it from them.

Ko and the ko rule

For the position shown on the left in the diagram, Black can capture the stone by a play at a. The resulting position is shown on the right. Without a ko rule, in this position White could recapture the stone at b, reverting to the position shown on the left, and then Black could also recapture. If neither player gave way, then we would have Black a, White b, Black a, White b, . repeated ad infinitum, stalling the progress of the game. This situation is known as ko.

The ko rule resolves the situation:

If one player captures the ko, the opponent is prohibited from recapturing the ko immediately.

So, if in left position of the diagram above Black captures at a, White may not play at the marked point during his first move after the black capture. Instead White has to play elsewhere [1] . After that Black can choose either to win the ko by playing at b in the right position in the diagram, or to play elsewhere as well. Playing elsewhere however would allow White to take the ko back, since the recapture restriction is only valid for the next turn. [2] .

More ko positions

Kos need not occur only in the center of the board. They can also show up at the sides or corners of the board, as shown in the diagram below.