Local Ko Threat

    Keywords: Ko, Go term

Chinese: 本身劫 (ben3 shen1 jie2)
Japanese: ソバコウ (soba-kō)
Korean: 자체팻감

A local ko threat is a ko threat which cannot be ignored, because the follow-up would make winning the ko irrelevant--by killing (Example 1) or saving (Example 2) the stones over which the ko is being fought. This kind of threat should therefore be played before any other kind, the exception being when it is a loss-making threat. If your opponent has such a threat, it will be to your advantage to remove it, if possible, before the ko fight begins; see an example of removing a local threat.

Local ko threats are sometimes also called internal ko threats.

[Diagram]

Example 1

In this diagram, Black is playing ko for the life of his group in the corner. Black has just captured the ko with black+square. The point a is now a local ko threat for White. If Black ignores this and connects the ko, White will play b, killing the black group. So Black must play at b himself to avoid this. White can now retake the ko.

[Diagram]

Example 2

In this example, Black is fighting a ko for the life of the group. When white+circle takes the ko, we can see that Black has a local ko threat at a (atari two White stones).

The Japanese for local ko threat, soba ko, literally means "ko (threat) nearby/at the side".


Example 3

Zhang Li - Huang Yizhong 08.10.2005

[Diagram]

[Diagram]

[Diagram]

[Diagram]

moves 33-42

[Diagram]

moves 43-52

[Diagram]

moves 52- ; start of ko

tderz here does the ko start

[Diagram]

internal ko threats

tderz: 8 at C19

[Diagram]

internal ko threats (2)

tderz: 4 at C19, 7 at 1

[Diagram]

internal ko threats (3)

tderz: W6 at D19; W8 resolves the ko
W4 is a very nice internal ko threat,
it's worth an own problem!

/W4 problem

[Diagram]

tderz the ko is resolved now, rest of game is exciting too.


This is a copy of the living page "Local Ko Threat" at Sensei's Library.
(OC) 2011 the Authors, published under the OpenContent License V1.0.
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