How is your positional judgement? Game 17

Bill Spight · #1

These topics are based upon Elf's commentaries on GoGoD games. As always, assume area scoring with 7½ pts. komi.

After :b37:

Elf estimates one player's winrate as 90½% with 56.6k playouts. Which player is it?

Click Here To Show Diagram Code: [go]$$Bcm37 White to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X . X X . | $$ | . . . O . . . . . , . . . . . O X . X | $$ | . . . . . . . . . . . . . . . O O X . | $$ | . . . . . . . . . . . . . . . . X O . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . O O . . | $$ | . . . O O O . . . . . . . . . O X . . | $$ | . . X O X O . . . , . . . . . , X . . | $$ | . X O X X X O . . . . . . X . X . . . | $$ | . X O . . . X . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Enjoy!

bayu · #2

TelegraphGo · #3

Could this be it? The first one I get right on record? Probably not, since I don't even know the joseki they played :razz:

I have a faint recognition of the bottom left and top right results, but not enough to be able to reproduce how they came onto the board. I'll start by looking at the top right.
It's pretty clear that W had one stone captured here - the R17 stone only ever gets played when B is afraid of capturing immediately and allowing W a ko by playing R17 themselves like in the position below:

Click Here To Show Diagram Code: [go]$$Wcm37 B doesn't want to capture $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X . B X . | $$ | . . . O . . . . . , . . . . . O X O . | $$ | . . . . . . . . . . . . . . . O O X . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . O O . . | $$ | . . . O O O . . . . . . . . . O X . . | $$ | . . X O X O . . . , . . . . . , X . . | $$ | . X O X X X O . . . . . . X . X . . . | $$ | . X O . . . X . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

So that means it's a 7 black stones v. 6 white stones commitment. Since B has committed one more stone, we can compare to a similar result where black has committed one more stone than white.

Click Here To Show Diagram Code: [go]$$Bcm37 A simpler result $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . X . . . . . | $$ | . . . O . . . . . , . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . O O . . | $$ | . . . O O O . . . . . . . . . O X . . | $$ | . . X O X O . . . , . . . . . , X . . | $$ | . X O X X X O . . . . . . X . X . . . | $$ | . X O . . . X . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Compared to this result, in game black has the corner much more solidly, but with a lower position. White in game has a significantly stronger position, but with ladder aji. If the ladder is easy for white to handle, then the game position is much better for white than the simple one above - white is just way harder to attack severely.
So let's look at the bottom left corner to see how the ladder aji is. It's white's turn right now, and W is about to sacrifice the two stone for influence. The first move that comes to my mind is:

Click Here To Show Diagram Code: [go]$$Bcm37 Double hane when B is liberty short $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X . X X . | $$ | . . . O . . . . . , . . . . . O X . X | $$ | . . . . . . . . . . . . . . . O O X . | $$ | . . . . . . . . . . . . . . . . X O . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . O O . . | $$ | . . . O O O . . . . . . . . . O X . . | $$ | . . B O X O . . . , . . . . . , X . . | $$ | . X O X X X O . . . . . . X . X . . . | $$ | . X O . . . X W . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

But to all those who've seen this sort of sequence before it's obvious that W is supposed to take advantage of B's one stone before doing this. The question is whether W should employ a driving tesuji by Atari underneath to prevent the open skirt, or simply Atari from the top to prevent the cutting point. Since W has no help nor development on the left side yet, I would prefer leaving an open skirt to a cutting point, so my suggested variation is:

Click Here To Show Diagram Code: [go]$$Wcm37 White to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X . X X . | $$ | . . . O . . . . . , . . . . . O X . X | $$ | . . . . . . . . . . . . . . . O O X . | $$ | . . . . . . . . . . . . . . . . X O . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . O O . . | $$ | . . 1 O O O . . . . . . . . . O X . . | $$ | . 2 X O X O . . . , . . . . . , X . . | $$ | . X O X X X O 5 . . . . . X . X . . . | $$ | . X O . . 4 X 3 . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

This bottom left position looks absurdly good for W. B is surrounded with only a handful of points (and bad endgame aji on top of that). On top of that, this is the ideal kind position to have on the opposite side of the board of a ladder. If B tries to play a ladder breaker, it will be inefficient, because it will be too close to thickness. All of W's stones work beautifully together - W's bottom right stones aren't really attackable due to W's big lead in influence, so the game looks hideously difficult for B. I've been confident with all the other ones, but this time really - if AI favors black here then I'm gonna start 2-2 invading san-san openings for territory.

jlt · #4

Bill Spight · #5

Just a note about how I choose the games to show. First, OC, is that I look for games with Elf winrates around 90% or higher around move 30. These may be a bit too easy for those who reply, but they are not always so easy. And that's a good place in the game to evaluate the position. Second, I look for games by Takagawa, Go Seigen, Lee Changho, and Fujisawa Hideyuki because they are human masters of the fuseki. Also, Takemiya, because who understands Cosmic Go? (Nobody, according to Elf. :lol:

) Also, Cho Chikun, because if we still had a Meijin, wouldn't he be it?

I have rejected a few games because some of Elf's variations were too far above my head. OC, I do not pretend to understand all of this, but I do want to say something sensible.

Kirby · #6

Tryss · #7

What was the komi of the original game?

Bill Spight · #8

Tryss wrote:

What was the komi of the original game?

5½ komi.

I am avoiding 0 komi games, and even 4½ komi games, because the question of whether the players have made mistakes or not in a 0 komi game is too difficult. In no komi game Elf usually says that White gives up many percentage points in the opening.

xela · #9

Echoing bayu (post #2 above):

And that leads us to an interesting question: evaluation assuming both players are strong, versus evaluation assuming both players are amateurs?

jlt · **#10**

@xela: I looked at positional judgements by early versions of LeelaZero, and by Leela 0.11.

Knotwilg · **#11**

no-LZ analysis

LZ

Bill Spight · **#12**

My discussion of Elf's commentary.

Honinbo final, game 2, 1995-05-24a. Kato Masao (W) vs. Cho Chikun

dhu163 · **#13**

seems easy

All is joseki except for upper right and lower left both of which are better for W. Next move is double hane on lower side.

On lower left, W has F5 misplaced and overconcentrated, but can make up for it with the tight local shape of the double hane.

On the right, W's outside is put to good use saving a move not needing to extend with R6 and instead directly developing.

On the lower left, W has several different aji, probably B6 is best if you have to play something, but W can tenuki and also has several ko threats.

Upper right: B has one extra stone. Just around 10 pts with some 3rd line potential that is limited by a cutting point. The shape is way too confined to a small area. W has some points with the ladder as B has no good ladder breaker. Locally perhaps 2pts with 6 or 7 lines of potential with another move. That is simply more than B.

Lower left: This was W's first corner and W needs to add another sente move to continue. B has 13 pts. W has a wall of height 13 if W adds another move, with one weakness on the left. This is normally estimated at around 26 pts, which seems reasonable. But W is also supporting the life of the Q6 stones.

Basically B expects a centre move as in return for a ladder breaker. If we count the right side as cancelling B's lower right, then W at the moment has 13 more in the lower left and the upper left corner which should be counted as 13 normally also. komi should compensate for B's initiative. Upon discounting the ladder breaker, it seems as though W is leading by around 15 pts. I find that a bit hard to believe. Probably I haven't sufficiently counted the W's weaknesses (perhaps there are 1.5 cutting points, subtracting 3pts?) and the fact that all B's groups are alive. Also W probably has less in the lower left than this estimate because B has potential on both sides. This still doesn't seem consistent to me. If the lead really were that much the winrate should be 99%.

Perhaps B hane on the lower side isn't optimal. It is sometimes better to pull back for better aji on the left as the lower side isn't valuable and even after adding a move, problems remain even on the lower side.

How is your positional judgement? Game 17

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