Ko threats - basic

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  Difficulty: Introductory   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 might also have a value of its own (be a play you wanted to make anyway), but that is a bonus.

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 opponent's 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).

t:1141 t:1141
[Diagram]

Ko threats

Black playing at either point a threatens to make his dead group alive. White must respond at the other a. The value of this threat is around 30 points.

Black playing at b threatens to make a monkey jump to 'x' (and certainly 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. (Of course, Black can also play y as his kothreat, but then, when White responds with c, Black has only added another dead stone to to his dead group. It is always better to play ko threats which have a value in themselves as well.) The 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 your 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). The value of this threat is at least 30 points.

White playing at either point 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 point e. The value of this threat is more than 40 points.


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This is a copy of the living page "Ko threats - basic" at Sensei's Library.
(OC) 2009 the Authors, published under the OpenContent License V1.0.
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