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Basic Ko Threats
  Difficulty: Beginner   Keywords: Ko

A basic prerequisite when playing a ko is to be able to find ko threats.

A Ko-threat is a play which threatens a follow-up which will give you a certain gain. A good ko-threat should also have a value of its own.

Here are some hints as to how to find them and how to evaluate how large they are.

Basically, threats can fall into any of these categories:

  • Threats to make dead groups alive or threats to connect two groups so that a previously dead group connects with a living group.
  • Threats to kill living groups or threats to disconnect two groups with the aim of killing one of them.
  • Threats to reduce your opponents territory/expand your own

Without a doubt, the first two are normally the largest, as the change of status of a group often means a difference of 20 points or more.

Here are some examples of ko-threats (The position is obviously constructed :-)


[Diagram]
Diag.: Ko threats

Black playing at either 'A' threatens to make his dead group alive. White must respond at the other 'A'. Value of this threat is around 30 points.

Black playing at 'B' threatens to do a monkey jump to 'x' (and to be certain to finish in sente). White must answer one point below 'B'. Value of this threat: around ten points.

Black playing at 'C' threatens to connect his dead group with his live corner by playing 'y'. White must respond at 'y'. (Ofcourse, black can also play 'y' as his ko-threat, but then, when white responds with 'C', black has only added another dead stone to to his dead group. It is always best to play ko-threats which have a value in themselves as well.) Value of this threat is almost 40 points.

(MFM: Looks to me like 'y' could be a better ko threat, because after White 'C', Black has another ko threat, no??) (Dieter 2k: Black 'y', answered by white 'c', and succesively black 'v' answered by white 'w', are ko-threats that lose two points each. Suppose the ko you're fighting is worth 10 points. You play five of those threats, and lose 10 points in the process. Then you're opponent plays what seems to be a small threat, you resolve the ko, and believe you have won big by playing it. But in reality you have lost the net value of white's threat. That's why black 'c' is a better ko-threat in many cases. But if the ko you are playing is very large, then increasing the number of threats, even losing a few points more, certainly is feasible)

Black playing at 'D' threatens to kill the white group. White must answer at 'z' (or the other way around). Value of this threat is 24 points.

White playing at either 'E' threatens to cut the two black groups apart. Each of them only has one eye, so they will die. Black must respond at the other 'E'. Value of this threat is more than 40 points.



This is a copy of the living page "Basic Ko Threats" at Sensei's Library.
(C) the Authors, published under the OpenContent License V1.0.