Life In 19x19

Unclear sequence (to me) from Workshop Lectures Vol. 2
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Author:  Aidoneus [ Thu Jan 31, 2019 3:52 pm ]
Post subject:  Unclear sequence (to me) from Workshop Lectures Vol. 2

This is example 2 from the chapter Choosing the Proper Pincer of Workshop Lectures vol. 2, by Yilun Yang. (I played what seemed a reasonable sequence to produce the example position.) The author states that 15 is the proper move, though LZ disagrees. But my real question concerns move 19 which he gives as Q17, and he states that White is in trouble. I immediately thought that after White Q18, Black R18, White P18 that White is OK and that it is Black that needs to be careful. So, I loaded the position in Lizzie/LZ and its evaluation was that Black's Q17 is about 9% worse than playing Q18. Are we missing something or did the author have something else in mind as a follow up?

Edit: BTW, the example is how to punish move 10.

Proper pincer example 2.sgf [227 Bytes]
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Author:  Uberdude [ Thu Jan 31, 2019 4:19 pm ]
Post subject:  Re: Unclear sequence (to me) from Workshop Lectures Vol. 2

Are you sure you transcribed the sequence correctly? White 10 as big knight move seems pretty odd and easy to punish: p16 attach looks much better and simpler to me then p15 as it easily connects black and cuts white (whereas p15 cuts white but doesn't connect black so there's a fight, which yes could be a nice fight for black but it's a fight so black has chances to mess up). White more sensible move of small knight for 10 at p15 instead could revert to the shown sequence.

Anyway, regarding q17 vs q18, this is indeed a shape that crops up fairly often. Each has pros and cons. The pros of q17 are that:
1) it takes a white liberty
2) if white answers at p18 descent then if black blocks (it's usual) at q18 then black has 2 more points of eyespace (important) / territory (less important) than compared to q18 first and white pushing at q17, black r17, white p18 black r18. This can often make the difference between a carpenter square type of shape being alive (or at least a seki or weird ko) in sente vs an L type group being unsettled. Getting one extra move in the centre fighting if your corner is already alive is huge.
The cons are:
3) it's an empty triangle so there are some possibilities of liberty shortage if white can get the q18 and s16 points.
4) gives white the choice to q18 instead of p18 to create corner shape weaknesses, though this will mean white takes gote not sente locally.
Pros/cons of q18 are basically the opposite of above.

As for why q17 is bad here, that seems to be because white will indeed play q18 hane, and because black pushed white along on the outside white does have severe aims at s16 if black plays on the top side after p18 connect. And if black defends the corner then white can safely jump to m17, which is not possible without a white stone at q18 in addition to p18 as black has the push and cut tesuji. It doesn't surprise me that a pro like Yilun Yang could get something like this wrong (my suspicion is he didn't give enough thought to white q18 because p18 descend is normally better (for sente) to consider the s16 tesuji followup). There are situations in which q17 is better than q18 though (I've seen Ilya Shikshin play it several times -- he often gets into fights) and plenty of weaker players might not even consider it as rejected by the over-simplistic empty triangle is bad mantra. So it's good to add to your vocabulary, even if it's not appropriate in this book example.

Author:  Aidoneus [ Thu Jan 31, 2019 4:38 pm ]
Post subject:  Re: Unclear sequence (to me) from Workshop Lectures Vol. 2

Yeah, after move 9 in my reconstruction we reach the book's example position. Move 10 is said to be bad, and the author shows how to punish the move. As weak as I am, I also thought that P16 looked better than P15, and LZ thinks so too, which I mentioned, but Yilun Yang claimed that P16 (A) was bad because "Attaching at A would leave too many weaknesses in Black."

But thank you for your analysis of the position after White move 18!

Author:  Bill Spight [ Thu Jan 31, 2019 8:25 pm ]
Post subject:  Re: Unclear sequence (to me) from Workshop Lectures Vol. 2

A few thoughts and variations. :)

With the help of Deep Leela. Not as good as LZ. Cum grano salis.

I think that the jump to the second line is vindicated. And maybe Yang's positional judgement. So much needs to be reconsidered these days.

Author:  Aidoneus [ Thu Jan 31, 2019 9:00 pm ]
Post subject:  Re: Unclear sequence (to me) from Workshop Lectures Vol. 2

@Bill: Interesting lines, thanks. I am afraid that I did not make it clear, however, that Yilun Yang said that Q17 was correct. In fact, he just ends the example at that point and says "White is in trouble." Hence my confusion.

Author:  Bill Spight [ Fri Feb 01, 2019 1:57 am ]
Post subject:  Re: Unclear sequence (to me) from Workshop Lectures Vol. 2

Oh, I think I understood you. :)

My first thought was that if Q-17 was correct, it was because White's hane at Q-18 was incorrect, and the only reason for that, it seemed to me, was the sacrifice I showed. Which doesn't turn out so good.

Then I wanted to show the importance of 4 dame vs. 5 dame for White. (Thanks, Bruce Wilcox!)

Then Deep Leela showed me the push in the center, and how sacrificing the corner could be good for Black. :)

Author:  Aidoneus [ Fri Feb 01, 2019 6:36 am ]
Post subject:  Re: Unclear sequence (to me) from Workshop Lectures Vol. 2

I think that the author could (should!) have done more than just said that White is in trouble. But, yeah, giving hime the benefit of the doubt, maybe he meant giving up the corner for influence.

Considering the thiness of the book and explanations, I am glad that I purchased the half-price SmartGo version.

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