this stuff was originally on basics on kos; I decided to move that material here and remove that page; we can decide to integrate some stuff into the main page up above, but I see currently no point in doing so - Dieter
Ko fights can sometimes be a bit confusing, and the 'optimal' way of playing can be highly complex. Most ko situations involve some sort of a trade: one player gets to "win" the ko (either by connecting, or by capturing some stones), while the other player is compensated by having two moves in a row in another part of the board. You can see examples of these things, with diagrams, on the other pages in the Ko Pages - Beginner path.
The following principles may be useful:
- When your opponent starts a ko, you are not allowed to retake immediately, and you have to play somewhere else. If your opponent plays his next stone resolving the ko (by connecting or capturing), he has won the ko.
- The winner of the ko should gain something from it. This may be the life of his group, or the death of his opponent's group, or the reduction of his opponent's territory, etc.
- In order to stop him from winning the ko, you play what is known as a ko threat. A ko threat is a play which, if left unanswered, will lead to a certain gain to you. Because, if the ko threat is not answered, you get to play two stones there, while your opponent uses a move to resolve the ko.
- When deciding whether to answer the ko threat or to resolve the ko, your opponent should consider the value of the ko threat and the value of the ko. In general, he should connect the ko if the threat is worth less than the ko, or answer the threat if the ko is worth less than the threat.
- The "winner" of the ko may or may not be better off overall, depending on the value of the ko threat elsewhere. It is possible to lose the game by trying too hard to win one ko.
- It may be tempting to play moves that lose points in order to win a ko, but this is often a mistake.
- Sometimes a ko is too small, compared to situations elsewhere on the board, to be worth fighting right away. It's OK to leave a ko unresolved, if something else looks more important.