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 Post subject: SHAPE PROBLEM n 3
Post #1 Posted: Sun May 02, 2021 12:59 pm 
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Hi all!

I ask another shape problem that I cannot understand. Actually it's not the last one, in the next post I'll show you the other one.

Suppose this sequence happens



If you ask KataGo, for example, it says the position is perfectly 50%-50% and it "sees" this exchange perfectly playable for both players. And that's ok. As a human player I cannot understand why.

I see this position like this:

W has big safe corner (about 18 points)
W has sente (ok sente here is intended as "having the move" or whatever you prefer like "has the initiative")

B has some sort of connection and thickness, but I feel it as a little overconcentrate
B has locally maybe 8-10 points and gote (ok intended as "non having the move")
B has some (potential) bad aji because of the c8 stone

Many thanks in advance!

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 Post subject: Re: SHAPE PROBLEM n 3
Post #2 Posted: Sun May 02, 2021 1:20 pm 
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C8 has no aji because of D8.

Black's group C7 is super-strong and exerts nice influence.

Black has an L-shaped formation, whereas all white stones are on the lower side, so Black has developed better.

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 Post subject: Re: SHAPE PROBLEM n 3
Post #3 Posted: Sun May 02, 2021 3:52 pm 
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Quote:
W has big safe corner (about 18 points)
W has sente (ok sente here is intended as "having the move" or whatever you prefer like "has the initiative")

B has some sort of connection and thickness, but I feel it as a little overconcentrate
B has locally maybe 8-10 points and gote (ok intended as "non having the move")
B has some (potential) bad aji because of the c8 stone



My two cents:

1. I don't see that shape has anything to do with this.
2. I don't see that White has a big safe corner. He certainly has something, but not big either in relation to spending so many stones on it but also in terms of gaps. At some point Black can make free moves against this corner. These will offset anything White keeps in the corner.
3. White may have sente but does not clearly have the initiative. When it comes to deciding where to play next (which is what the initiative is about) White is burdened by having to protect his investments on the lower side. He will be constrained to play there at some early point. If he plays at the top instead, he will be outnumbered by there Black and so even more clearly he will not have the initiative.
4. Any overconcentration for Black is matched by White's in the corner. Instead, this Black group is a Go Seigen group which means the rest of that quadrant will be a no man's land. White will thus be hard pressed to get further profit there from his lower-left group. Black probably cannot get profit in this area either, but he can expand his influence with forcing moves against the corner - White can't.
5. Because the group on the left side is a Go Seigen group, there is no significant aji there. And worrying about aji this early in the game is like wondering about the fish in the water when you're supposed to be rowing the boat.
6. On the large assumption that I'm right in pointing out wrong descriptions of the situation, that still doesn't amount to saying any of the actual moves have been bad. It is therefore too early to say who may have lead. They are still sparring.


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 Post subject: Re: SHAPE PROBLEM n 3
Post #4 Posted: Sun May 02, 2021 5:26 pm 
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One thing you can observe is that White's stones are all on one side. That's not unusual for White in a parallel opening but it may indicate Black's development is more balanced, which compensates for the clearly overconcentrated shape in the lower left.

Black's connection, which is allegedly the last move, loses 10% and 1,5 point says Katago. In the opening that's enough to call it a mistake. Locally Katago likes the second line stretch better, as we know by know, and globally it prefers switching to reinforce the upper left with a knight's move.

White did not make a single mistake of that size, but her two moves, 10-12 presumably, the invasion 10 and the hane 12, are not in KataGo's repertoire and lose some. There's just too much focus by White on that lower left. As John points out, Black has free moves on the lower side, threatening a 3-3 later.


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 Post subject: Re: SHAPE PROBLEM n 3
Post #5 Posted: Sun May 02, 2021 8:22 pm 
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Fllecha wrote:
Hi all!

...
If you ask KataGo, for example, it says the position is perfectly 50%-50% and it "sees" this exchange perfectly playable for both players. And that's ok. As a human player I cannot understand why.
...


Katago on my machine finds White ~57% with a 0.8 point lead with komi = 6.5 and Japanese rules. I set it up and left it running for about 2 million playouts. The evaluation began at 56-something % and increased to slightly over 57% over time. Blue for White's next is to play the hane at D9 as a forcing move and then turn elsewhere. However, directly enclosing the bottom right with Q6, approaching the upper right at P17, or invading the upper left at C17 are all reasonable alternatives that favor White.

Why does this come out this way? The main point is that during the sequence given, both Black and White make sub-optimal moves more or less continuously. Indeed, katago calculates that Black could have been slightly ahead by playing in any of the upper left, upper right, or lower right rather than connecting at C7! Beginning with the approach in the lower left, both sides stay fixated on the lower left corner while the rest of the board remains unexplored. The reason it is (sort of) balanced at the end of the sequence is that there is still a lot of opportunity spread across the rest of the board rather than anything specific about the lower left, IMHO.

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 Post subject: Re: SHAPE PROBLEM n 3
Post #6 Posted: Mon May 03, 2021 12:36 am 
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John Fairbairn wrote:
4. Any overconcentration for Black is matched by White's in the corner. Instead, this Black group is a Go Seigen group which means the rest of that quadrant will be a no man's land. White will thus be hard pressed to get further profit there from his lower-left group. Black probably cannot get profit in this area either, but he can expand his influence with forcing moves against the corner - White can't.


Thanks All for the replyes.

I just want to ask you if there are some articles on Go Seigen Groups. Of course I tried to google it but all the links lead to Go Seigen life and stuff like that. Thanks!

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 Post subject: Re: SHAPE PROBLEM n 3
Post #7 Posted: Mon May 03, 2021 12:41 am 
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Knotwilg wrote:

Black's connection, which is allegedly the last move, loses 10% and 1,5 point says Katago. In the opening that's enough to call it a mistake. Locally Katago likes the second line stretch better, as we know by know, and globally it prefers switching to reinforce the upper left with a knight's move.



Yes, second line stretch is now preferred by AI as in the famous joseki, but I put that move (which I agree that is suboptimal) because it is the one that my opponents plays the most.

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 Post subject: Re: SHAPE PROBLEM n 3
Post #8 Posted: Mon May 03, 2021 5:00 am 
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Quote:
I just want to ask you if there are some articles on Go Seigen Groups. Of course I tried to google it but all the links lead to Go Seigen life and stuff like that


The original source was New in Go in the GoGoD Encyclopaedia and this is still available on http://www.gogodonline.co.uk. In printed form it appeared in The Go Companion (Slate & Shell).

A brief digest appeared on this forum in: https://lifein19x19.com/viewtopic.php?f ... &view=next in the thread More insight on AlphaGo?


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