Oiotoshi / Discussion

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Sub-page of Oiotoshi

unkx80: I moved this lengthy discussion from the parent page. However, the contents are useful as an example of how not to set up an oiotoshi, probably on a new page.

Example 4

(modified from The Second Book of Go)


B1 starts the oiotoshi. If White tries to run away at W2, B3 is atari again, and this time running away at W4 doesn't help White at all since now the whole group is captured.

So White shouldn't have run away at W2, but instead connected with W5.

Oiotoshi tesuji  

Using the previous example as reference, it is easy to see that if White saves the white+circle stones here, Black can capture white+square, blocking off White's progress along the top side. B1 can also be called oiotoshi. (I'm not sure whether this example is relevant enough (and correct)! Comments, please. -- Jan)

BillSpight: B1 is premature. It requires the atari play black+circle below.

Oiotoshi tesuji (not premature)  

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

Oi-Otoshi dissent  

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 B1 hadn't been played, but on the other hand, one ko threat has been lost.)

White should of course connect at a instead of W4 and Black can capture only one stone which can be captured without sacrificing at B1 anyway.

-- Alain Wettach

White connects  


Normal play  

After B1, W2 is White's correct response. If White does not play there, Black can throw in at B6.

After W2, B5 and W6 are miai. Black can count 1/3 point in the ko (1/3 of white+circle).

Black error  

W6 fills at B1.

In this case Black has lost 1 point for the throw-in stone at B1, and does not have 1/3 point in ko. B1 gives away 1 1/3 points.

Cruncher: Well, after playing W2, the position is identical to Jan's original "Second Oiotoshi" diagram, and the idea of that example was to show that playing W2 in the "Second Oiotoshi" diagram is the wrong move.

...so does that mean that all of you are right? ;-)

Bill: It looks to me that W2 in that diagram is B5 in this one. So I'm not sure what you are referring to.

Cruncher: I actually meant "...is identical to the starting situation in Jan's diagram...", that is, before B1 is played there. But I guess the keyword here that I missed is tesuji: playing the premature B1 doesn't really change anything and just recreates an equivalent of the original example - where white can still escape from.

Bill: The throw-in of B1 is worse than zokusuji. Compare the results with and without it.

Yet, this "worse than zokusuji" is absolute sente through to its conclusion. White can only either completely obey black or accept at least the loss of all 4 stones.

dnerra: This claim misses that B1 as suggested by black also threatens to capture 4 stones. I agree with all of Bill's comments.

Bill: We don't know the rest of the board, so we cannot say that the play is sente. In the position as shown, I would think that B1, next, or B1 - B3 where B1 is the throw-in, would both be gote, since securing Black's stones would be quite large by comparison to taking or saving a few stones.
White keeps his options open.  
Black takes in gote  

Bill: Taking one stone with B3, above, would be bad play by Black until late in the game.

In fact, B1 and W2 are miai. Either Black plays B1 as a prelude to taking the ko with B3, or the play goes W2 - B1, W3.

White later improves the situation while threatening to save all of his stones without ko.  
White threatens to start a ko that would save all his stones and break into black's territory  

Nobody said this was a koyose sequence, Bill. Both moves have merit, and the rest of the board matters. Closing the side is huge, and finishing the job cleanly might be bigger than 1 1/3 points.

Bob Myers: Umm, this is no ko; Black simply ataris to the right of 1.

Bill: Well,, I do not believe that there is a case where a Black throw in is better than the simple atari, except perhaps as a losing ko threat, which is very unlikely. In all normal cases the simple atari is as good or better.

See Throw in or Not.

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Oiotoshi / Discussion last edited by BillSpight on May 30, 2004 - 17:06
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