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Aliases (info)
LosingKoThreat
LossMakingThreat

Paths
Mistake
SecondCourseOnKo
ForcingAndInitiative

Referenced by
Oiotoshi
LocalKoThreat
SenteGainsNothing
RemoveDoubleThrea...
ValueOfAKoThreat
DoubleKoThreats
BasicKofightExample
KoThreatPlayingOrder
TemporarySeki
AlmostAlmostFill
TemperatureAndTer...
TheAjiMachine
3354Enclosure
SowDiscordInTheEn...
SimpleOrComplicated
LosingSente

 

Loss-Making Threats
Path: ForcingAndInitiative   · Prev: KoThreat   · Next: KikashiSenteDiscussion
Path: Mistake   · Prev: KyuDisease   · Next: Low
Path: SecondCourseOnKo   · Prev: LocalKoThreat   · Next: ThereAreNoKoThreatsInTheOpening

    Keywords: Ko

Generally playing a threat just because it is sente, and for no other reason, is a typical novice mistake.

When it comes to ko fights, this becomes a more difficult discussion. Ko threats that are loss-making have a special name, sonko, in Japanese; and to become a ko expert one has to pay great attention to the idea. You do need ko threats in a ko fight. Playing loss-making threats is clumsy, and assumes that the ko fight is all that matters. That need not be the case.


[Diagram]
Choice of threat

Should Black prefer a, b or c here? We assume Black is looking for a ko threat in this part of the board.


[Diagram]
Like a failed invasion

Usually playing c is the worst idea. After White plays at 2, Black's stone looks like mochikomi. Black can probably make further threats here such as d, but after White e Black has lost some further points.


[Diagram]
Best taste

From the point of view of avoiding possible loss, Black's best choice is this threat. When White answers at 2, Black 1 looks like a kikashi, that is, has some positive effect in addition to being sente. Of course Black 1 has aspects of aji keshi - just about any ko threat does (see the aji machine).


[Diagram]
Not clear

It isn't clear without more information whether Black 1 is a loss. After White 2 Black has the play at d, and one should know before coming to a judgement whether White could play e or f. If White can play f and capture everything that would constitute a big loss for Black, but the fight might be big enough to distract attention from the ko. White might play 2 at e, in which case Black will probably be satisfied.

Summary: Threats that come in deeper risk loss; threats from outside risk little.

Charles Matthews



Some examples of a local ko threat that may make a loss.

Example 1:

[Diagram]
Local threat



Suppose White plays the marked stone as a threat during the ko fight in the corner.

[Diagram]
A change in the position



If Black answers it as shown, and White later wins the fight, it is a bit disappointing.

[Diagram]
Poor exchange for White



In this position the exchange of the marked stones looks better for Black.

[Diagram]
Better prospects for White



Here White would want to jump at least as far as a.

Example 2:

[Diagram]
Local threat 2

If Black wins the ko, White will regret the exchange of W1 for B2, since it loses 2/3 point, on average, by comparison with the position when Black wins the ko without that exchange.


[Diagram]
Black wins ko

(We assume that B1 is sente, threatening to invade White's surrounding territory.)

Therefore, even though White has a local ko threat, she should play it only if it is crucial; for instance, if it is necessary to win the ko or if it forces Black to make a losing ko threat of his own.



Path: ForcingAndInitiative   · Prev: KoThreat   · Next: KikashiSenteDiscussion
Path: Mistake   · Prev: KyuDisease   · Next: Low
Path: SecondCourseOnKo   · Prev: LocalKoThreat   · Next: ThereAreNoKoThreatsInTheOpening

This is a copy of the living page "Loss-Making Threats" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.