Ko

Ko is a distinctive rule in Go that addresses situations where repeated captures of single stones could endlessly return the board to its previous state. This rule prevents infinite loops and introduces strategic depth, as players must carefully plan their moves to navigate or exploit ko situations.

The Ko Rule

1. When a player captures a stone, the opponent cannot immediately recapture in a way that recreates the same board position. Instead, they must play elsewhere on the board, introducing a delay in the cycle. This prevents the game from entering an infinite loop and resolves potential stalemates.
2. The original player can choose to either reinforce their position to prevent a recapture or respond to the opponent’s intervening move. This dynamic creates opportunities for strategic exchanges.

Ko Fights and Ko Threats

In the earlier example, capturing the ko has a minor impact. However, there are scenarios where winning the ko can be far more crucial. In ko fights players often create unrelated threats elsewhere on the board, forcing the opponent to respond and allowing a recapture in the ko. 

Ko fights can significantly impact the game, as resolving a ko in one’s favor often results in territorial gains or strategic advantages. However, losing a ko can be equally costly.

Double Ko and Triple Ko

Double Ko is a more complex situation where two interconnected kos exist, allowing for advanced tactics and prolonged fights. 

Triple Ko: A triple ko occurs when three separate points on the board form a repeating cycle of captures and recaptures. This cycle can continue indefinitely as players alternate between these moves without either side gaining an advantage. Triple ko situations are significant because they often lead to rule-based resolutions, depending on the governing rule set being used. For example, some rules declare the game a draw if a triple ko occurs, while others might mandate specific adjustments or penalties.

In our 19×19 course we introduce the basics of ko fights. If you’re already familiar with the concept of ko and want to improve your skills, be sure to check out the Ko — Take Control Over the Chaos course by Stanisław Frejlak 1p.