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Oiotoshi
Path: Tesuji   · Prev: ThrowIn   · Next: EyeStealingTesuji
  Difficulty: Beginner   Keywords: Tesuji, Tactics, Go term

Oiotoshi describes a situation where a stone or group of stones is put into atari in such a way that there is no escape. This occurs usually when the only way to save such a group is to connect, and that the resulting group is still in atari.

The term oiotoshi also describes the process of setting up such a situation.


Here's an example (modified from The Second Book of Go):

[Diagram]
Diag.: Oiotoshi

Black 1 starts the oiotoshi. If White tries to run away at 2, Black 3 is atari again, and this time running away at 4 doesn't help White at all since now the whole group is in atari at a.

So White shouldn't have run away at 2, but instead connected at a or 4.



[Diagram]
Diag.: Oiotoshi tesuji

Using the previous example as reference, it is easy to see that if White saves her two circled stones here, Black can capture the White stone with a square; blocking off White's progress along the top side. Black 1 is also called oiotoshi. (I'm not sure whether this example is relevant enough (and correct)! Comments, please. -- Jan)



BillSpight: Black 1 is premature. It requires the atari (circled) below.

[Diagram]
Diag.: Oiotoshi tesuji


I don't think this is premature. Doesn't this work? (Thomas Nordhaus)

[Diagram]
Diag.:


Bill is right, in the starting position the tesuji is premature and brings almost nothing. (Capturing one stone will be a bigger sente than if 1 hadn't been played, but on the other hand, one ko threat has been lost.)

White should of course connect at 4 and Black can capture only one stone which he can capture without sacrificing at 1 anyway.

-- AlainWettach

[Diagram]
Diag.:


Bill:

[Diagram]
Diag.: Normal play

After Black 1, White 2 is White's correct response. If White does not play there, Black can throw in at 6. After White 2, Black 5 and White 6 are miai. Black can count 1/3 point in the ko (1/3 of the marked stone).


[Diagram]
Diag.: Black error

White 6 fills at 1.
In this case Black has lost 1 point for the throw-in stone at 1, and does not have 1/3 point in ko. Black 1 gives away 1 1/3 points.



Oiotoshi is also known under the terms 'connect and die' and 'serial atari'.

See also: Damezumari and Throw In. The Crane's Nest is a classic example of oiotoshi.

-- Jan de Wit



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This is a copy of the living page "Oiotoshi" at Sensei's Library.
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