PositionalJudgementProblem3/Pro assessment

[Diagram]
Black has the lead  

Bill: This problem comes from the [ext] 28th game of the 29th Meijin League, between Cho U (White) and Yamashita Keigo. The commentary there states:

"White's territory is dazzling to the eye, but Black's thickness is even more wonderful."

Then Ishida Akira says, "While you can't say that Black has won, he is certainly in the lead."

DrStraw: Interesting. I looked at this and thought white has less territory than black (20 pts in LL vs. 14 in UL + a few in the middle, so the use of the word dazzling puzzles me. Obviously black has way more thickness so I think there is no way for white to win.

Slarty: It seems that white has more than komi in cash lead, and sente.

John F. There's an important omission. The Japanese is:

左下の分かれは黒に軍配が上がるという。白の実利に目を奪われそうになるが、それ以上に黒の厚みが素晴らしい。

I think this tells us that the reference to White's profit (rather than territory) "catching the eye" is in relation to the lower-left corner only. (The omitted first bit says "As regards the outcome in the lower left, I'd say the referee's decision would go to Black.")

RobertJasiek: Black's current territory is 13 + 6 = 19. White's is 21 + (13 + 1) / 2 + 6.5 = 34.5. The territory count is -15.5. The influence stone difference is 13 - 5 = 8 but 2 or 3 of the white influence stones are weak. It is White's turn. The aji in the black thickness is relatively small. Black has good moves at C8, C9, E14 affecting the stability of weak white stones. White's next move cannot eliminate all important weaknesses. The black thickness has good development directions. F14 is a representative next move affecting the influence stone difference but not the thickness or territory count. Hence, it should be easy for Black to use his influence, compensate the territory count and win.

John F. Robert: None of the moves C8, C9, E14 or F14 were played in the game, the final territories were rather different from the current territory estimate, and the Black thickness did not develop in any direction. Nevertheles, I'm not disputing the details of your assessment. But I do find the contrast of your approach with the pro assessment (the topic here) quite stark.

The comment in the Asahi web page and also in the Kido yearbook make it clear that Black's thickness after 27 is startling, and is what defines this game. And I infer that is why Bill chose it. The commentaries mention only the thickness vis-a-vis the corner profit by way of evaluation, apparently ignoring other factors. In essence, the comments are just saying, "This is not just thickness, it is THICKNESS."

But I feel confident in saying that the other factors are not really being ignored. They are being taken for granted. They are being taken for granted for two reasons: (1) The usual way of dealing with them is commonly known even by amateurs - I have six books on my desk at the moment which say, essentially, forget about counting when evaluating; and (2) they can be dealt with simply and efficiently, at least to the level required by this stage of the game.

The commonest technique is offseting by making comparisons. Here we can say that Black and White have one stone each in the upper right, and these offset each other, though with a slight edge to Black, being nearer the corner. The upper left and lower right corners can be viewed essentially as two-stone shimaris which offset each other, though with a big edge to Black - White's shimari is thinner and in the upper left White has effectively ended up strengthening Black by adding a pair of stones.

Against this Black has to give komi and White has sente. If we assume these factors cancel out Black's edge to some degree, the evaluation of the position boils down entirely to the lower left corner - which is precisely the approach demonstrated by the commentaries.

If we look at just this lower left corner, even amateurs are familiar with many josekis that can be categorised as a close balance of profit versus thickness, and I imagine everyone here would feel confident in saying that while White may have a (very) few points more than usual in such josekis, Black's thickness is VERY different from the sort of wishy-washy wall he usually gets. Here he's not only got no weaknesses, he has virtually already got two eyes and he has forcing plays in reserve.

We could, if absolutely necessary - but I don't think it is necessary at all - make an estimate of the value of the thickness by counting the wall (7 stones long at a conservative estimate, which makes it worth (7 * 6) / 2 = 21, or more simply 3 pts per stone. However, these counts are normally used for just walls. The thickness here is a whole house, not a wall, so must be worth much more.

Therefore the only decision to make to conclude the evaluation is to compare any possible edge White has from the other factors (i.e. just possibly komi and sente outweigh the White inefficiency in the upper left, etc) with the edge Black has from the "joseki" in the lower left.

It's easy to be wise after the event, i.e. having already read what the pros said, but it seems to me very easy to come to the same conclusion as quoted: "Although we can't say Black has won, he is certainly in the lead."

More to the point, that pro way of looking at the position seems easier to apply than counting, especially in actual play and in the fast games typical of amateurs, and it is appropriate to the level of complexity of the position, i.e it doesn't try to do more than can safely be done. On that basis the pro method seems more reliable, and there is the big ancillary advantage (I think) that being in tune with the pro approach enables us to get more out of their commentaries.

Furthermore, it is my judgement that the pro method enables White to find his next move. I won't mention it here in case it's a spoiler, but it would appear that White's assessment was that he was behind and so had to "broaden" the game in the hope of causing confusion. Amusingly, he ended up losing a group in the very area he tried to stir up. Another commentary described this as a good example of thick play by Yamashita.


PositionalJudgementProblem3/Pro assessment last edited by 109.147.101.213 on October 15, 2015 - 19:30
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