Opening study with KataGo

hakuseki · Post by **hakuseki** » Thu Dec 03, 2020 11:14 am

I have a more recent game to discuss, so I'm setting game 9 aside for now. This is another online game. I was playing black.

Game 10, position 1

Click Here To Show Diagram Code: [go]$$Bc No mistakes yet $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . 6 . . . . | $$ | . . 4 , 5 . . . . , . . . . . , 1 . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 2 . . . . . , . . . . . 3 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

In the past I've usually preferred the stability of an early enclosure, but I'm getting the sense that an approach like

is slightly more urgent.

Game 10, position 2

Click Here To Show Diagram Code: [go]$$Bc Shusaku Kosumi is questionable $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . 2 1 3 . . . . 5 . . a . . O b . . . | $$ | . . O , X . . . . , . . . . . , X . . | $$ | . 4 . . . . . . . . . . . . . 7 . . . | $$ | . . . 6 . . . . . . . . . . . c . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . d . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . O . . . . . , . . . . . X . . . | $$ | . . f . . . . . . . . . . e . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

is fine, but a is also a good choice. As far as pincers go, this two-space low pincer seems to be pretty common.

seems a bit dubious, losing about 0.4 points. Locally, b is a good move, and c is not quite as bad as

. d-f are preferred, globally speaking. My thought is that

was played to prevent white's keima press, but because of

the value of white's resulting wall would be reduced, so avoiding the press is less urgent than would otherwise be the case. I think this is a satisfying enough explanation for why tenuki is preferred, but I'm not so sure about the relative values of b and c.

Game 10, position 3

Click Here To Show Diagram Code: [go]$$Wc :w3: is a slight mistake. How should black respond? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . 3 . . . . . . | $$ | . O X X . . . . X . 1 . 2 . O . . . . | $$ | . . O , X . . . . , . . . . . , X . . | $$ | . O . . . . . . . . . . . . . X . . . | $$ | . . . O . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . |[/go]

Click Here To Show Diagram Code: [go]$$Wc A hallucination $$ --------------------------------------- $$ | . . . . . . . . . . . . B . . . . . . | $$ | . . . . . . . . . . . B . B . . . . . | $$ | . O X X . . . . X . O W X W O a . . . | $$ | . . O , X . . . . , . . W . . , X . . | $$ | . O . . . . . . . . . . . . . X . . . | $$ | . . . O . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . |[/go]

I recall that, without reading any actual sequences, I simply visualized the following result and concluded that it was bad, so I simply abandoned my splitting move and played a instead, thus throwing away about 2.5 points.

Click Here To Show Diagram Code: [go]$$Bc Good result for black $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . 7 3 O 1 . . . . . | $$ | . O X X . . . . X . O 5 X 2 O . . . . | $$ | . . O , X . . . . , . 6 4 . . , X . . | $$ | . O . . . . . . . . . . . . . X . . . | $$ | . . . O . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . |[/go]

This sequence should have been very easy for me to read, and the result seems happy for black; white has no territory and two cutting points.

Game 10, position 4

Click Here To Show Diagram Code: [go]$$Bc How to respond to :w4:? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . O . . . . . . | $$ | . O X X . . a . X . O . X 2 O 1 . . . | $$ | . . O , X c b . . , . . . . . , X . . | $$ | . O . . d 4 . . . 3 . . . . . X . . . | $$ | . . . O . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . |[/go]

,

are all mistakes, but I won't focus on those since the fundamental issue was addressed in the previous diagram.
a-d are some options given in policy order (which, it occurs to me, could be a nice convention for enumerating alternative moves). I played b, thinking about the knight's triangle shape. But based on the policy ordering I guess a might be the more intuitive "shape" move. Actually a-c are about equal in value. However, an even stronger option would be to cut and fight at d.

hakuseki · Post by **hakuseki** » Wed Dec 09, 2020 9:42 pm

Diagram 0

Click Here To Show Diagram Code: [go]$$Bc BadukPop has only one star point, but KaTrain has nine. $$ ------------------- $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ | . . , . , . , . . | $$ | . . . . . . . . . | $$ | . . , . , . , . . | $$ | . . . . . . . . . | $$ | . . , . , . , . . | $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ -------------------[/go]

I decided to aim for a high rank on BadukPop, so I'm reviewing my 9x9 games with KataGo.
By the way, I played white in this game, and made mistakes totaling about 17 points. My opponent's mistakes totaled about 16 points, so I lost.

Diagram 1 - The opening

Click Here To Show Diagram Code: [go]$$Bc :b3: and :b5: were suboptimal. White to play. $$ ------------------- $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ | . . , . , b a . . | $$ | . . . 9 . 2 5 . . | $$ | . . d . , 4 3 . . | $$ | . . . 1 . 6 7 . . | $$ | . . e . , 8 c . . | $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ -------------------[/go]

a-e are some possibilities for white's next move. This is in policy order (so, e.g. a is not necessarily the best move, but it is the most intuitive according to KataGo).

Diagram 2 - First mistake

Click Here To Show Diagram Code: [go]$$Wc :w1: is creating a weak group $$ ------------------- $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ | . . , . , . , . . | $$ | . . . X . O X . . | $$ | . . . . , O X . . | $$ | . . . X . O X . . | $$ | . . 1 . , O . . . | $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ -------------------[/go]

This was my move in the game, but a mistake of approximately 1 point. I think creating a separate group here is a poor choice. Actually, move a from diagram 1 would have been the correct answer. I did consider a, but was worried about black cutting. So my actual mistake was not reading that black's cut would fail.

Click Here To Show Diagram Code: [go]$$Wc What I should have read $$ ------------------- $$ | . . . . . . . . . | $$ | . . . . 6 4 . b . | $$ | . . , a 3 2 1 5 . | $$ | . . . X . O X . . | $$ | . . . . , O X . . | $$ | . . . X . O X . . | $$ | . . , . , O 7 . . | $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ -------------------[/go]

This is a sequence I should be able to read. Actually, it is not best play for either player, but it convinces me that black's cut fails. Caveats:

is not necessary. White could play somewhere else, like a, and still win the capturing race, although the complexity would be higher.
Black could interpose a corner reduction at b before retreating to
could instead be played at b, to prevent the aforementioned corner reduction. This seems like a tesuji; is anyone familiar with it?

Actually, this cut did end up getting played later in a somewhat altered situation, which resulted in more mistakes during the game. But I believe those are redundant from a review perspective.

Diagram 3 - Endgame problem 1

Click Here To Show Diagram Code: [go]$$Wc What is white's best endgame move? $$ ------------------- $$ | . . . . . . . X . | $$ | . . . . . X X O . | $$ | . a X . O X O O X | $$ | . . e X X O X X . | $$ | . O b d , O X f . | $$ | . . c X . O X O . | $$ | . . O X X O O . . | $$ | . . O O X O . O . | $$ | . . . X . . . . . | $$ -------------------[/go]

Endgame move suggestions for white are a-f, in policy order.

Diagram 4 - Second mistake

Click Here To Show Diagram Code: [go]$$Wc White cedes the corner $$ ------------------- $$ | . . . . . . . X . | $$ | . . . . . X X O . | $$ | . 2 X . O X O O X | $$ | . . . X X O X X . | $$ | . O , . , O X . . | $$ | . . 1 X . O X O . | $$ | . . O X X O O . . | $$ | . . O O X O . O . | $$ | . . . X . . . . . | $$ -------------------[/go]

I played

at c as listed in diagram 3. I did consider playing a in diagram 3, but I worried that white's stones would be too thin and black could exploit this somehow. Actually, a was the correct answer, and there's no weakness. So my second mistake was failing to read that black has no good attack on white.

Click Here To Show Diagram Code: [go]$$Wc The wedge fails $$ ------------------- $$ | . . . . . . . X . | $$ | . . . . . X X O . | $$ | . 1 X . O X O O X | $$ | . 2 a X X O X X . | $$ | . O 3 b , O X . . | $$ | . . . X . O X O . | $$ | . . O X X O O . . | $$ | . . O O X O . O . | $$ | . . . X . . . . . | $$ -------------------[/go]

Although there are several possibilities to check, perhaps the most obvious idea for black is this wedge at

. But after

, a and b become miai to ruin black's day. So

is successful.

Diagram 5 - Endgame Problem 2

Click Here To Show Diagram Code: [go]$$Wc What is white's best endgame move? $$ ------------------- $$ | . . . . . . . X . | $$ | . . . . . X X O . | $$ | . X X . O X O O X | $$ | a c . X X O X X . | $$ | . O e b , O X d . | $$ | . . O X . O X O . | $$ | . . O X X O O . . | $$ | . . O O X O . O . | $$ | . . . X . . . . . | $$ -------------------[/go]

Diagram 6 - Third mistake

Click Here To Show Diagram Code: [go]$$Wc White wedges and connects $$ ------------------- $$ | . . . . . . . X . | $$ | . . . . . X X O . | $$ | . X X . O X O O X | $$ | . . b X X O X X . | $$ | . O 3 1 2 O X . . | $$ | . a O X 4 O X O . | $$ | . . O X X O O . . | $$ | . . O O X O . O . | $$ | . . . X . . . . . | $$ -------------------[/go]

This is what I played in the game. It achieves two goals -- it connects the white stones, so that white will not need to play a future move at a, and it also reduces black's liberties, so that b may later be played in sente.
However, this is not the best sequence for white. Actually, the solution to diagram 5 was c, a brilliant tesuji.

Diagram 7 - Shining tesuji

Click Here To Show Diagram Code: [go]$$Wc Black has two weak points $$ ------------------- $$ | . . . . . . . X . | $$ | . . . . . X X O . | $$ | a X X . O X O O X | $$ | . 1 . X X O X X . | $$ | . O . b , O X . . | $$ | . . O X . O X O . | $$ | . . O X X O O . . | $$ | . . O O X O . O . | $$ | . . . X . . . . . | $$ -------------------[/go]

If white is allowed to follow up at b, the presence of

coupled with black's shortage of liberties will allow white to start a ko fight to capture the black stones. Therefore black is likely to defend this cutting point. But then white will be able to play the sente corner reduction at a, which is quite big.

Diagram 8 - Endgame problem 3

Click Here To Show Diagram Code: [go]$$Wc What is white's best endgame move? $$ ------------------- $$ | . . . . . . . X . | $$ | . . . . . X X . X | $$ | X X X X O X , . X | $$ | O a O X X O X X . | $$ | . O O O X O X O c | $$ | . . O X X O X O . | $$ | . . O X X O O . . | $$ | . . O O X O . O . | $$ | . . O X X b . . . | $$ -------------------[/go]

Move suggestions a-c are in policy order.

Diagram 9 - Fourth Mistake

Click Here To Show Diagram Code: [go]$$Wc White can't connect now $$ ------------------- $$ | . . . . . . . X . | $$ | . . . . . X X . X | $$ | X X X X O X , . X | $$ | O 4 O X X O X X . | $$ | a O O O X O X O 1 | $$ | . . O X X O X O . | $$ | . . O X X O O . . | $$ | . . O O X O . O . | $$ | . . O X X 2 3 . . | $$ -------------------[/go]

This is the game sequence. At this point I realized that connecting at a would allow black to invade the corner and create a seki. Evidently, I know this corner shape well enough to recognize the weakness once it appears, but not quite well enough to prevent it in advance. Naturally, the correct answer in diagram 8 would have been a.

hakuseki · Post by **hakuseki** » Thu Dec 17, 2020 4:18 am

This is a 9x9 game played on BadukPop. I played black.
Game 12, position 1

Click Here To Show Diagram Code: [go]$$Bc Black should reinforce the top $$ ------------------- $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ | . . , b c . , . . | $$ | . . 5 . . . . . . | $$ | . . d . 1 . 3 . . | $$ | . . 6 . . . . e . | $$ | . . , a 4 . 2 . . | $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ -------------------[/go]

In this position my move was e, but I think that was an overplay. KataGo's policy suggests moves like a-d. Interestingly, the score evaluation for these moves fluctuated a lot as I let it run for about 100k playouts, but generally a seems to be the best, and at the end of the evaluation it was favored by >1 point over any other move.

Click Here To Show Diagram Code: [go]$$Bc Sacrificing the cutting stone $$ ------------------- $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ | . . , . , . , . . | $$ | . . X . . . . . . | $$ | . . , 5 X . X 7 . | $$ | . 6 O 2 3 . . . . | $$ | . . , 1 O . O . . | $$ | . . . . 4 . . . . | $$ | . . . . . . . . . | $$ -------------------[/go]

Black sacrifices

and is able to play

and

in sente, finally securing territory with

.
This isn't the first time I've seen KataGo suggest something like this, yet I virtually never play this way. I did consider playing

, but only long enough to verify that it doesn't lead to me capturing any white stones. It seems like there's a gap in my intuition. Let's try investigating a bit.
Since my hypothesis is that

is needed to make

and

sente, what if I just play

and

directly?

Click Here To Show Diagram Code: [go]$$Bc Black loses sente $$ ------------------- $$ | . . . . . . . . . | $$ | . . . . 4 . . . . | $$ | . . , . , . , . . | $$ | . . X . . . . . . | $$ | . . , 3 X . X . . | $$ | . . O . 1 . . . . | $$ | . . , 2 O . O . . | $$ | . . . . . . . . . | $$ | . . . . . . . . . | $$ -------------------[/go]

Here we see that

answers the threat of

, and simultaneously makes

nonthreatening, allowing white to take sente and reduce black's top. This is complete nonsense for black.

I guess this seems to verify the purpose of the suggested move a in position 1. Maybe I can try to keep an eye out for this kind of move.

hakuseki · Post by **hakuseki** » Sun Jan 03, 2021 11:47 pm

A new 19x19 opening after a couple weeks of 9x9. I'm black. I lost about 40 points by move 80.

Click Here To Show Diagram Code: [go]$$Bc Game 13, position 1 $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 5 . . . . . . . . . . 7 . . . . | $$ | . . . , . . . . . , . . . 6 . , 1 . . | $$ | . . 2 . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . a . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . 3 . . . . . . . . . . . . 4 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

I don't see the two-space high approach much.

should be at a. The difference is about 0.15 points.

Click Here To Show Diagram Code: [go]$$Wc Game 13, position 2 $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . . . . . . X . . . . | $$ | . . . , a 4 . . . , . . . O . , X . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . 3 . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . 1 . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . 2 . . . , . . . . . , . . . | $$ | . . X . . . . . . . . . . . . O . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

should have been at a, although the difference is only about 0.1 point. It occurs to me that I really don't know any principle for deciding between the kosumi and keima responses to a 5-3 approach. Later I might try some kind of general comparison of positions as lightvector previously did for side extensions from an enclosure. For now I'm including this position to remind myself.

Click Here To Show Diagram Code: [go]$$Bc Game 13, position 3 $$ , . . . . . , . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . 2 . . . | $$ . . . . . . . . . . | $$ . . . . 3 . 1 . . . | $$ , . . . . . , . . . | $$ . . . . . . O a . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

When white pincered at

, I jumped out at

, but I should have played the inside contact move at a. The difference is nearly one point. I am guessing this will generalize to most instances of this pincer, so I'll plan to default to a in the future.

Click Here To Show Diagram Code: [go]$$Wc Game 13, position 4 $$ -------------------- $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . a X 2 . . . | $$ , . . . O 1 , X . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ , . . . . . , . . . |[/go]

I answered

with

, but a is about 1.7 points better.
I think this is makes sense to me in retrospect. The 2-space approach is unusual, so it's reasonable to assume it's worse than the typical 1-space approach. But

is allowing white to bend at a and revert to the usual one-space approach joseki. If we reason that the opponent's move is our move, we will think to play at a.
This is likely to lead to the large avalance joseki.

hakuseki · Post by **hakuseki** » Mon Jan 04, 2021 12:07 am

I played white in this 4-stone handicap game. By move 80 I lost about 25.5 points.

Game 14, position 1

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

The game started with this pincer joseki in the upper right. This is pretty common, yet I still hadn't learned the continuation.

Continuation

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

In the game I played elsewhere instead of playing this sequence. This is especially sad because I recently watched a video where this was mentioned, but I wasn't really paying attention. I think I'll remember it next time, though. Missing this sequence cost me about 1.4 points in KataGo's estimation; it also accounts for about 3.3 points of the 25.5 point total mentioned above, as I missed multiple opportunities to start the sequence.

hakuseki · Post by **hakuseki** » Mon Jan 04, 2021 1:54 am

I played another 4H game as white. This time I lost 81.1 points (oops!) by move 80.

Game 15, position 1

Click Here To Show Diagram Code: [go]$$Wc Compare to game 9 $$ -------------------- $$ . . . . . . . . . . | $$ . . . . . . . a . . | $$ . . . . . . 4 3 . . | $$ , . . . . . X 5 . . | $$ . . . . . . 6 . . . | $$ . . . . . . b 1 . . | $$ . . . . . . . . . . | $$ . . . . . . . 2 . . | $$ . . . . . . . . . . | $$ , . . . . . , . . . |[/go]

One nice thing about 4H games is that KataGo plays a lot of pincers as black. I think this will provide valuable practice, as KataGo rarely pincers in even games, but my human opponents pincer often.
Here's a pincer joseki that also appeared in game 9. In that game, KataGo suggested that a and b were nearly equally-good continuations. Today I played a. However, in this 4H game position, KataGo really disliked a. I have yet to see a position where b is considered bad, so I will make it my new default choice.

Game 15, position 2

Click Here To Show Diagram Code: [go]$$Wc :w7: should be played elsewhere $$ -------------------- $$ . . . . . . . . . . | $$ . . . . . . . 1 . . | $$ . . . . . . X O . . | $$ , . . . . . X O . . | $$ . . . . . . X . . . | $$ . . . . . . 2 O . . | $$ . . . . . . 4 3 9 . | $$ . . . . . . 8 X 5 . | $$ . . . . . . . 7 6 . | $$ , . . . . . , . . . |[/go]

This is the game continuation. After

white should tenuki the local position. However, I played

instead, which was a two-point loss. I guess this is aji keshi.

Game 15, position 3

Click Here To Show Diagram Code: [go]$$Wc Where should white play next? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . 1 . 2 . . . . . . . X O . . | $$ | . . . X . . . e h , . . . . . X O . . | $$ | . . . . . 3 . a b . . . . . . X . . . | $$ | . . . . 4 f . c d . . . . . . X O . . | $$ | . . . . . . . . . . . . . . . X O O . | $$ | . . . . . . . . . . . . . . . X X O . | $$ | . . . . . . . . . . . . . . . . O X . | $$ | . . . , . . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . , g . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

In the game I played f, which was not so good. KaTrain on my machine ranks the moves in order e, a, c, b, g, f, h, d.
I think I should have played either a or e, but didn't. So let's look at how I read these two moves.

Variation a

Click Here To Show Diagram Code: [go]$$Wc White's fear $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . O . X . . . . . . . X O . . | $$ | . . . X . . 2 . . , . . . . . X O . . | $$ | . . . . . O . 1 . . . . . . . X . . . | $$ | . . . . X . . . . . . . . . . X O . . | $$ | . . . . . . . . . . . . . . . X O O . | $$ | . . . . . . . . . . . . . . . X X O . | $$ | . . . . . . . . . . . . . . . . O X . | $$ | . . . , . . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . , . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

I didn't play

because I was worried about the weakness at

. I don't think I actually read any sequences following this position, but subconsciously I may have been imagining something like the following:

Click Here To Show Diagram Code: [go]$$Wc White's fear, continued $$ -------------------- $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . . . . O . X . . $$ | . . . X . 1 X . . , $$ | . . . . . O 2 O . . $$ | . . . . X 4 3 . . . $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . . , . . . . . ,[/go]

Fortunately, white can do much better than this, as both of these white responses are mistakes. Starting with

:

Click Here To Show Diagram Code: [go]$$Wc White's fear -- slight improvement $$ -------------------- $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . . . . O . X . . $$ | . . . X . 1 X . . , $$ | . . . . . O 2 O . . $$ | . . . . X 3 4 . . . $$ | . . . . . 5 6 . . . $$ | . . . . . . 7 . . . $$ | . . . . . . . . . . $$ | . . . , . . . . . ,[/go]

White can just keep extending, and now black's corner becomes very weak. Or, even better:

Click Here To Show Diagram Code: [go]$$Wc White's fear -- best response $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . 4 3 O . X . . . . . . . X O . . | $$ | . . . X . . X . . 7 . . . . . X O . . | $$ | . . . 2 1 O . O . . . . . . . X . . . | $$ | . . . . X 5 . . . . . . . . . X O . . | $$ | . . . . 6 . . . . . . . . . . X O O . | $$ | . . . . . . . . . . . . . . . X X O . | $$ | . . . . . . . . . . . . . . . . O X . | $$ | . . . , . . . . . , . . . . . , X . . |[/go]

White can enclose the top. Black's stones are not dead yet, but black will now be thinking about the best way to sacrifice them, rather than chase white into the center.

(hopefully to be continued)

hakuseki · Post by **hakuseki** » Tue Jan 05, 2021 10:03 pm

I played black in this game, and made 24.5 points of mistakes by move 80.

My AI opponent in this game played by stone-scoring rules. However, I'm not currently currently trying to learn strategies under group tax (if I do so, I will start a separate thread for that); I'm still using Japanese rules for analysis, just against a different style of opponent play.

Game 16, position 1

Click Here To Show Diagram Code: [go]$$Wc No mistakes yet $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . X 6 4 3 . . | $$ | . . . O . . . . . , . . . . 5 1 X . . | $$ | . . . . . . . . . . . . . . . 2 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . a . . . . . , . . . . . O . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

This position was discussed in a variation on game 5. At this point, white should play the ladder breaker at a...

Game 16, position 2

Click Here To Show Diagram Code: [go]$$Wc Bad for white $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . X X X O . . | $$ | . . . O . . . . . , . . . . O O X 2 . | $$ | . . . . . . . . . . . . . . . X 1 . . | $$ | . . . . . . . . . . . . . . . . a . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . b 3 . . . . . , . . . . . O . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Instead, white ataris first, and then plays the ladder breaker. This is a mistake, because the

exchange increases the local temperature, so that white no longer has time to tenuki. Black should then ignore the shoulder hit at

and play at a. However, I answered at b instead, which was a 0.6 point mistake.

Game 16, position 3

Click Here To Show Diagram Code: [go]$$Wc Black has two good options $$ -------------------- $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . X X X O . . | $$ , . . . 3 O O X X . | $$ . . . . 5 2 X O b . | $$ . . . . . a 1 4 . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ , . . . . . , . . . |[/go]

In this position I played a, which is a perfectly good move, and in fact KataGo's preferred policy move. However, I want to note that b is also perfectly good, and seems to remove more weakness than a.

Game 16, position 4

Click Here To Show Diagram Code: [go]$$Bc Black to move -- [b]a[/b], [b]b[/b], or [b]c[/b]? $$ -------------------- $$ . . . . . . . . . . | $$ . . 4 3 c . . . . . | $$ . . b 2 X X X O . . | $$ , . . . O O O X X . | $$ . . . . O X X O . . | $$ . . . . a 1 O X . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ , . . . . . , . . . |[/go]

My move here was c, but this is losing one point. The correct move is a:

Click Here To Show Diagram Code: [go]$$Bc Correct sequence $$ -------------------- $$ . . . . . . . . . . | $$ . . O X . . . 3 . . | $$ . . 2 O X X X O . . | $$ , . . . O O O X X . | $$ . . . . O X X O . . | $$ . . . . 1 X O X . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ , . . . . . , . . . |[/go]

threatens a double atari, so white must defend at

. Then black may either finish at

or tenuki.

Game 16, position 5

Click Here To Show Diagram Code: [go]$$Wc Double approach joseki $$ , . . . . . , . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . X . . | $$ . . . . 3 . . . . . | $$ , . . 2 1 c O . . . | $$ . . b 5 X a 4 . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

This seems to be a modern joseki, although

was a mistake given the whole board context. How does black continue?
I wasn't familiar with the joseki and played c, but this mistake cost me 1.5 points. The correct answer is a:

Click Here To Show Diagram Code: [go]$$Bc Correct sequence $$ , . . . . . , . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . X . . | $$ . . . 4 O . . . . . | $$ , . 2 X O . O 3 . . | $$ . . . O X 1 X . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

Game 16, position 6

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

Finally, here's a whole-board puzzle. Black would like to reduce the upper left. After 100k visits on my machine, KataGo chose a move with a policy value below 1%, yet preferred by more than a full point over any other move.

RobertJasiek · Post by **RobertJasiek** » Tue Jan 05, 2021 10:27 pm

hakuseki wrote: This seems to be a modern joseki

$$Bc Correct sequence
$$ , . . . . . , . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . X . . |
$$ . . . 4 O . . . . . |
$$ , . 2 X O . O 3 . . |
$$ . . . O X 1 X . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ --------------------
Click Here To Show Diagram Code
[go]$$Bc Correct sequence $$ , . . . . . , . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . X . . | $$ . . . 4 O . . . . . | $$ , . 2 X O . O 3 . . | $$ . . . O X 1 X . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

This is an old joseki but not known / taught by everybody.

hakuseki · Post by **hakuseki** » Wed Jan 06, 2021 9:28 pm

Another game as white against the stone-scoring AI. I'll try focusing more on 4-4 against this AI. As before, I'm still doing the review without group tax. In this game I lost 32.2 points by move 80.

Game 17, position 1

Click Here To Show Diagram Code: [go]$$Bc Defend or approach? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . 5 . b . . . . | $$ | . . . 1 . . . . . , . . . . . 2 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . a . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . c . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 4 . . . . . , . . . . . 3 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

is a large knight's approach, which is uncommon in modern Go. I assumed this move, being less favored than the knight's move approach, is also less worth responding to, so I played my own approach at c. However, upon review it seems like a or b would be slightly better.

Game 17, position 2

Click Here To Show Diagram Code: [go]$$Wc Defend or approach? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . X . . . . . . | $$ | . . . X . . . . . , . . . . . O . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . c . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . 2 . . . . . . . . . . . . . 1 . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . O . . . . . , . . . . . X . . . | $$ | . . . . . a . . . . . . . b . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Since

is a knight's move approach, I figured it is worth responding to and played a. However, in this case it is slightly better to either double approach at b or defend at c. Well, so far I know very little about this kind of question, but for now I'll guess that answering a large knight's approach is actually bigger than answering a small knight's approach. Maybe because it's harder for black to do something useful in the corner after white defends?

Game 17, position 3

Click Here To Show Diagram Code: [go]$$Bc White [b]a[/b], [b]b[/b], [b]c[/b, or [b]d[/b]? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . b . . . . . . a . . X . O . . . . | $$ | . . . X . . . . . , . . . . . O O . . | $$ | . . . . . . . . . . . . . . . . X . . | $$ | . . . . . . . . . . . . . . O O X . . | $$ | . . . . . . . . . . . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . d O . . | $$ | . . . . . . . . . . . . . . . . 1 . . | $$ | . . . O . . . . . , . . . . . X . . . | $$ | . . . . . O . . . . . . . c . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

The pincer at a is really good, but more importantly extending at d, which was my move, is really bad. I guess a typical joseki move might make a weak stone strong, while this move merely makes a very weak stone into a somewhat weak group. Locally, c would be about 0.6 points better, while a would be a further 0.2 point improvement.

Game 17, position 4

Click Here To Show Diagram Code: [go]$$Bc White to help the C8 stone $$ -------------------- $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . . . . . . . . X $$ | . . . X . . . . . , $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . X . . . . . . . $$ | . . . . . . . . . . $$ | . . c . . . . . . . $$ | . . . , . . . . . , $$ | . . . . . . . . . . $$ | . . O . b . . . . . $$ | . . . . . . . . . . $$ | . . X X . . . . . . $$ | . . O . . . . . . . $$ | . . . O . . X a . , $$ | . . . . . O O . . . $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ --------------------[/go]

Here I played c. I was probably thinking about getting a few points of territory and simultaneously robbing black of a few points of territory. At the same time I would be helping my isolated stone at C8. Aside from the fact that a is quite big, if I want to help the C8 stone I should actually play at b, as this simultaneously attacks black's weak group. This would be an improvement of about 0.6 points.

Game 17, position 5

Click Here To Show Diagram Code: [go]$$Bc White [b]a[/b], [b]b[/b], [b]c[/b], or [b]d[/b]? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . X . . X . O . . . . | $$ | . . . X . . . . . , . . . . . O O . . | $$ | . . . . . . . . . . . . . . . . X . . | $$ | . . b . . . . . . . . . . . O O X . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . . . . . . . . . . . . . c . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . O . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X X . . . . . . . . O . . O O . . | $$ | . . O . . . . . . . . X . . . . X . . | $$ | . . . O . a X d 1 , . . . X . X . . . | $$ | . . . . . O O f . . . . . . . . . . . | $$ | . . . . . . . . e . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

I had been thinking about the hane at d, and I regretted missing my chance once black played

, and then I rather aimlessly played at f. There are so many better moves here, I'm not sure which lesson is most important to learn, but:

If I were really so sad about missing d, I could just play d now instead of f, and it would be an improvement of about 0.4 points.

Or, if my plan is to prevent white from enclosing territory on the bottom, the knight's move slide at e would be a further 0.35 points better.

Or, if I want to damage the black stones, splitting at a would be a further 0.9 points better.

Or, if I want to learn a cool joseki followup, b would be a further 0.5 point improvement, threatening to either connect to the nearby white stones or jump into the corner.

Or, if I want to learn another cool joseki followup, the clamp at c is another 0.15 point improvement, mostly likely allowing white to build some center influence in sente.

All told, white can do about 2.3 points better than f.

hakuseki · Post by **hakuseki** » Thu Jan 07, 2021 12:04 am

This time I played black and lost about 34.8 points by move 80.

Game 18, position 1

Click Here To Show Diagram Code: [go]$$Bc Large knight's move extension $$ , . . . . . , . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . 1 . . | $$ . . . . . . . . . . | $$ , . . . . . O . . . | $$ . . . 2 . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

Time to learn about the large knight's move extension. In this game, I tried playing in much the same way I would play against the small knight's move:

Click Here To Show Diagram Code: [go]$$Bc Bad for black $$ , . . . . . , . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . 9 . . | $$ . . . . . . 8 X . . | $$ . . . . . . 6 4 7 . | $$ e c a . . . O 1 5 . | $$ . d b W f . . 2 3 . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

This is the game result. Although neither black nor white should play this way, black came out worse, losing 1.4 points overall. It seems that white's marked stone is more efficient than in the standard knight's move joseki. In fact, white's preferences for where to put the marked stone seem to be a, b, c, d, its current location, e, and f, in that order.

So what should be done differently?

Click Here To Show Diagram Code: [go]$$Bc Even better for white $$ , . . . . . , . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . X . . | $$ . . . . . . . . 5 . | $$ , . . . . . O 1 . . | $$ . . . O . . 4 2 3 . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

For white, this is an even better way to punish

. Black is more overconcentrated than white.

Click Here To Show Diagram Code: [go]$$Bc Into the corner $$ , . . . . . , . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . X . . | $$ . . . . . . . 8 6 . | $$ , . . . . 4 O 2 5 . | $$ . . . O . . 3 1 7 . | $$ . . . . 9 . . . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

So black should simply jump into the corner, resulting in something like this sequence.

(Game 18 to be continued?)

hakuseki · Post by **hakuseki** » Sun Jan 10, 2021 7:58 pm

I played black in this game and lost 27.9 points by move 80.

Game 19, position 1

Click Here To Show Diagram Code: [go]$$Wc :w3: elsewhere $$ -------------------- $$ | . . . . . . . . . . $$ | . . 8 . . . . . . . $$ | . . 4 1 7 . . c . . $$ | . . . 6 . a . b . , $$ | . . . 2 . . . . . . $$ | . . . . . . . . . . $$ | . . 9 . . . . . . . $$ | . . . . 5 . . . . . $$ | . . . . . . . . . . $$ | . . . , . . . . . ,[/go]

In this position I pincered at c, but covering at a is about 0.5 points better. Another good option is b.

Click Here To Show Diagram Code: [go]$$Bc Variation $$ -------------------- $$ | . . . . . . . . . . $$ | . . X . . . . . . . $$ | . . X O O . . 1 . . $$ | . . . X . b . . . , $$ | . . . X . a . . . . $$ | . . . . . . . . . . $$ | . . O . . . . . . . $$ | . . . . O . . . . . $$ | . . . . . . . . . . $$ | . . . , . . . . . ,[/go]

If black pincers, white is able to split at either a or b. While a appears less solid, white would be happy to sacrifice the two stones for shape should black try to cut.

Click Here To Show Diagram Code: [go]$$Bc Continuation $$ -------------------- $$ | . . . . . . . . . . $$ | . . X . . . . . . . $$ | . . X O O . . X . . $$ | . . . X . a . . . , $$ | . . . X . . 1 . . . $$ | . . . . . . . . . . $$ | . . O . . . . . . . $$ | . . . . O . . . . . $$ | . . . . . . . . . . $$ | . . . , . . . . . ,[/go]

In the game, white played elsewhere, so black was able to continue locally. Although I played at a in the game,

is the correct local move, about 0.5 points better.

Game 19, position 2

Click Here To Show Diagram Code: [go]$$Wc Asymmetric double apprach $$ | . . . a . . . . . $$ | . . . b . . . . . $$ | . . d . . . . . . $$ | . . . . . . . . . $$ | . . O e . . . . . $$ | . . . . . . . . . $$ | . c . X . . 1 . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ ------------------[/go]

With the stone-scoring AI, I see my 4-4 stones approached in several different ways; consequently, there is a great variety of double approaches.
In the game, I responded with the familiar contact play at e, any of the labeled counter-pincers would be much better; enclosing the corner at c is also superior to e.

Game 19, position 3

Click Here To Show Diagram Code: [go]$$Bc Mistake $$ | . . . , . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . O . . . . . $$ | . . O X X . 1 . . $$ | . O O . . . . . . $$ | . X O X . . O . . $$ | . . X . X O . . . $$ | . . . . a . . . . $$ | . . . . . . . . . $$ ------------------[/go]

In this game position, I jumped out at 1, neglecting the weakness at a. If white were to hane here, black would be forced to either leave the corner territory open or allow the two stones to be cut off. I was aware of this, but thought that a defensive move would be too slow.

Click Here To Show Diagram Code: [go]$$Bc Correct defense $$ | . . . , . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . O . . . . . $$ | . . O X X . . . . $$ | . O O . . . . . . $$ | . X O X . 1 O . . $$ | . . X . X O . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ ------------------[/go]

With

, black is able to fix the connection while simultaneously threatening white's cutting point. This is the correct move.

Game 19, position 4

Click Here To Show Diagram Code: [go]$$Bc Black [b]a[/b], [b]b[/b], or [b]c[/b]? $$ -------------------- $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ , . . . . . X . . . | $$ . . . . . . . . . . | $$ . . . . . . . c . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ . . . . . . . . . . | $$ , . . . . . , . . . | $$ . . . . . . O . . . | $$ . . . . . . . . . . | $$ . . . . . . . 8 a . | $$ . . . . . . . 4 7 . | $$ . . . . . . 6 5 . . | $$ , O . . . . O 3 . . | $$ . . . . . . 2 1 . . | $$ . . . . . . b . . . | $$ . . . . . . . . . . | $$ --------------------[/go]

My tenuki at c seems rather small, losing two points compared to b, which is slightly better than a.

Game 19, position 5

Click Here To Show Diagram Code: [go]$$Wc Defend or approach? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . 1 a . . . | $$ | . . X O O . . X . . . . . c . b . . . | $$ | . . . X . X . . . , . . . . . X . . . | $$ | . . . X . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . X . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . O . . . | $$ | . . . O . . . . . . . . . . . . . . . | $$ | . . . O . O . . . . . . . . . . O . . | $$ | . . O X X . . . . . . . . . . . O X . | $$ | . O O X . . . . . . . . . . . O X . . | $$ | . X O X O . O . O , O . . . . O X . . | $$ | . . X X X O . . . . . . . . . O X . . | $$ | . X . . O . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

In the game I responded to

with a. but c is a bit better and b is the best move, considering the whole board situation.
I guess the problem with a is that black has a moyo up top, and white would like to disrupt it. In this case, it is more important to make use of the moyo than to strongly defend the corner territory.
In another recent game of mine, the same local situation came up but the evaluation was different, so if I get a chance I would like to compare the two games.

hakuseki · Post by **hakuseki** » Thu Jan 14, 2021 9:57 pm

I played black in this game and lost 17.5 points by move 80.

Game 20, position 1

Click Here To Show Diagram Code: [go]$$Bc Should black follow up in the lower right? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . b . . . . . . . . . . . . . . . . | $$ | . . . 4 . . . . . , . . . . . 1 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . c . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . 6 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . d . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 3 . . . . . , . . . . . 2 . . . | $$ | . . . . . . . . . . . . . 5 . . a . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

was new to me. I thought about playing a local followup, such a 3-3 invasion at a or a double approach at d. I finally decided to tenuki at c, but I think a would have been a slightly better choice.
Afterwards, I reviewed various options for

and how black should respond to each of them, and came up with this rough guide:

Click Here To Show Diagram Code: [go]$$Bc Keima extension $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 4 . . . . . , . . . . . 1 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . 6 . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 3 . . . . . , . . . . . 2 . . . | $$ | . . . . . . . . . . . . . 5 . 7 8 . . | $$ | . . . . . . . . . . . . . . . . 9 . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

If white plays the keima extension at

, then black plays the familiar contact joseki.

Click Here To Show Diagram Code: [go]$$Bc One-space extension $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . b . . . . . . . . . . . . . . . . | $$ | . . . 4 . . . . . , . . . . . 1 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . 6 . . . | $$ | . . . . . . . . . . . . . . a . . . . | $$ | . . . 3 . . . . . , . . . . . 2 . . . | $$ | . . . . . . . . . . . . . 5 . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

If white plays the one-space extension, then a black follow-up is not so urgent and a tenuki such at b is fine. However, locally a followup at a is also a good option.

Click Here To Show Diagram Code: [go]$$Bc Loose extension or pincer $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 4 . . . . . , . . . . . 1 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . 6 6 . . | $$ | . . . . . . . . . . . . . . . 6 6 . . | $$ | . . . . . . . . . . . . . . . 6 6 . . | $$ | . . . . . . . . . . . . . . . 6 6 . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 3 . . . . . 6 6 6 . . . 2 . . . | $$ | . . . . . . . . . 6 6 . . 5 . . 7 . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

If white plays any of the loose extensions on the right, or a pincer on the bottom, then the 3-3 invasion is great. Basically a double approach is not good when one of the two approaching stones is already pincered.

Click Here To Show Diagram Code: [go]$$Bc Double approach $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . c . . . . . . . . . . . . . | $$ | . . . 4 . . . . . , . . . . . 1 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . b . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . a . . . . . . . . . . . . . 7 . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 3 . . . . . , . . . . . 2 . . . | $$ | . . . . . . . . . . . 6 . 5 . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

The one exceptional pincer is the low pincer.

is especially helpful for containing a 3-3 invasion, so in this case the double approach is preferred. It is also good when white tenukis, e.g. at a, b, or c.

Game 20, position 2

Click Here To Show Diagram Code: [go]$$Wc Double approach joseki $$ -------------------- $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . 5 c . X d . . . $$ | . . 4 O . 7 b . . , $$ | . . 6 a . . . . . . $$ | . . X 1 3 . . . . . $$ | . . . 2 . . . . . . $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . . , . . . . . ,[/go]

I think this is a pretty normal double-approach joseki, but I'm still not super familiar with

(which is also a slightly mistake in the game position).
At this point I was thinking about how to make use of my upper-side stone and considered moves like b, c, and d, but actually the push at a is considered the best move.

Click Here To Show Diagram Code: [go]$$Bc Continuation $$ -------------------- $$ | . . . . . . . . . . $$ | . 7 5 4 . . . . . . $$ | . 3 O 6 . X . c b . $$ | . . X O 2 O . . a , $$ | . . X 1 . . . . . . $$ | . . X O O . . . . . $$ | . . . X . . . . . . $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | . . . , . . . . . ,[/go]

After

, white will enclose the top with a move like a, b, or c, but black can continue to reduce white's top anyway (the exact technique depending on white's move). Or, if white tries to tenuki instead, then black may play something like c to help the isolated black stone.

Game 20, position 3

Click Here To Show Diagram Code: [go]$$Bc Double approach joseki $$ | . . . , . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . O . . . . . . $$ | . . . . . 3 4 . . $$ | . . . X . 1 2 . . $$ | . . . . 5 O . . . $$ | . . . . 6 . . . . $$ | . . . . . . . . . $$ ------------------[/go]

My own corner was double-approached, leading to this sequence.

seems like a group tax-style move.

Click Here To Show Diagram Code: [go]$$Bc Continuation from the game $$ | . . . , . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . O . . 3 . . . $$ | . . . . . X O . . $$ | . . . X . X O . . $$ | . . a . X O . . . $$ | . . . 1 O 2 . . . $$ | . . . . . . . . . $$ ------------------[/go]

I played this sequence, thinking to keep white separated and be able to attack the stone on the left side. However, black will be unable to make a severe attack given the aji in the corner e.g. at a. Therefore this is not a good plan.

Click Here To Show Diagram Code: [go]$$Bc Better idea $$ | . . . , . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . O . . 4 . . . $$ | . . . . . X O . . $$ | . . . X . X O . . $$ | . . . . X O 2 . . $$ | . . . 3 O 1 . . . $$ | . . . . . . . . . $$ ------------------[/go]

Instead, black should capture one stone and allow white to enclose with

. Now black is completely safe and can take sente to play elsewhere.

hakuseki · Post by **hakuseki** » Tue Jan 19, 2021 6:00 am

I played white in this game and lost 17.5 points by move 80.

Game 21, position 1

Click Here To Show Diagram Code: [go]$$Bc How should white respond to :b1:? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . , . . . . . O . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . a . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . b . X . . . | $$ | . . . O . d . . . , X . . . . X O . . | $$ | . . . . . 1 . . . . . . . O X X O . . | $$ | . . . . . . . . . . . . . c X O O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

I didn't want my stone on the lower-left to lose access to the center, so I played d. I think this was my first real mistake of the game, about 1 point worse than a. Of course, a is the most typical response to an approach, and this situation should not have been an exception.
A move like b or c would also be big. I've seen this kind of follow-up in lectures and reviews a few times, but still haven't gotten into the habit of actually playing it. Hopefully next time.

Game 21, position 2

Click Here To Show Diagram Code: [go]$$Wc Joseki continuation $$ | . . . X . . . . . . $$ | . . . , . . . . . , $$ | . . . . . . . . . . $$ | . . . d . . . . . . $$ | . . a c . . . . . . $$ | . . . . . b . . . . $$ | . . . . . 3 8 . . . $$ | . . . O . 1 2 . . , $$ | . . 5 4 . X . . . . $$ | . . 7 . 6 . . . . . $$ | . . . . . . . . . . $$ --------------------[/go]

I thought about playing a, as this looked to me like a pretty big extension for either player. However, I finally chose b in keeping with my original aim of maintaining access to the center. In fact, now would be a great time to tenuki, but locally it seems like c is the best and b is the worst (a difference of about half a point).

Game 21, position 3

Click Here To Show Diagram Code: [go]$$Wc Approaching black's corner $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . b . . 1 . . . . . . . . . . . . . | $$ | . . . X . a . . . , . . . . . O . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . O O . . . . . . . . . O . . | $$ | . . . . . O X . X . . . . . . X . . . | $$ | . . . O . O X . . , X . . . . X O . . | $$ | . . O X . X . . . . . . . O X X O . . | $$ | . . O . X . . . . . . . . . X O O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

In the game I played

. However, it seems in this case a is a particularly good local response, perhaps because it helps enlarge black's left side. I think this is the reason why

is considered a mistake -- white should invade directly at b.

Game 21, position 4

Click Here To Show Diagram Code: [go]$$Bc Upper-right joseki choice $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . 7 5 3 . . | $$ | . O O O . O . . . . . . . X 4 1 2 a . | $$ | . . X X X O . . . , . . . b 6 O . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . X . . . . . X . . . . | $$ | . . . . . O O . . . . . . . . . O . . | $$ | . X X . . O X . X . . . . . . X . . . | $$ | . O O O . O X . . , X . . . . X O . . | $$ | . . O X . X O X . . . . . O X X O . . | $$ | . . O . X . O X . . . . . . X O O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Without considering the whole board context, b is my usual instinct in the upper-right corner situation. However, given that white has very little potential on the right side, I (correctly) guessed that a might be a bit better here. But then I decided: why not both?

Click Here To Show Diagram Code: [go]$$Wc Mistake $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X X X . . | $$ | . O O O . O . . . . . . 2 X O X O 3 . | $$ | . . X X X O . . . , . . . 1 O O . . . | $$ | . . . . . 4 . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . X . . . . . X . . . . | $$ | . . . . . O O . . . . . . . . . O . . | $$ | . X X . . O X . X . . . . . . X . . . | $$ | . O O O . O X . . , X . . . . X O . . | $$ | . . O X . X O X . . . . . O X X O . . | $$ | . . O . X . O X . . . . . . X O O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

This isn't so good because

is gote, so black is able to play

.

Game 21, position 5

Click Here To Show Diagram Code: [go]$$Wc :w1: and :w3: are mistakes $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X X X . . | $$ | . O O O . O . . . . b . X X O X O O . | $$ | . . X X X O 5 3 . , . . . O O O . . . | $$ | . . . . . X 1 4 . . . . . . . . . . . | $$ | . . . . . 6 2 . . . . . . . . . O . . | $$ | . . a . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . X . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . X . . . . . X . . . . | $$ | . . . . . O O . . . . . . . . . O . . | $$ | . X X . . O X . X . . . . . . X . . . | $$ | . O O O . O X . . , X . . . . X O . . | $$ | . . O X . X O X . . . . . O X X O . . | $$ | . . O . X . O X . . . . . . X O O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

is losing about 0.8 points; it seems responding here isn't the biggest point on the board. Invading at a is the best; b is also good.
The more serious mistake is

. White should not play a hanging connection here.

at

would be a better move, which threatens to ladder the

stone.

hakuseki · Post by **hakuseki** » Wed Jan 20, 2021 2:33 am

I played white in this game and lost 59.3 points by move 80. However, I'm only covering the early mistakes here:

Game 22, position 1

Click Here To Show Diagram Code: [go]$$Wc Biggest move for white? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . a . . X . . . . . | $$ | . . . X . X . . . , . . . . . O . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . b . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . d . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . X . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . e . O . . . . . , . . . . X X X . . | $$ | . . . . . O . . . . . . c . . O O . . | $$ | . . . . . . . . . . . . . O . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

On move 16, white has a lot of options for big moves. The move I chose, e, is the smallest move depicted here -- about 0.7 points smaller than b, which is likely the biggest.
c is somewhat big, and I think it may threaten a follow-up like d later. The value of c will be reduced if black extends first, so now is a good time to play it.
b is a classic splitting move, with enough room for a two-space extension in either direction. Recently I've been playing this kind of move less, because I had gotten the impression that AIs do not like it. However, it is KataGo's recommendation here. I'm guessing it's good in this case because the available space is just wide enough that black's checking extension will be overconcentrated.

Game 22, position 2

Click Here To Show Diagram Code: [go]$$Wc How should white help the upper-left stones? $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . X . . . . . | $$ | . . . X . X . . . , . . . . . O . . . | $$ | . . . 6 5 . . . . . . . . . . . . . . | $$ | . . 3 7 8 . . . . . . . . . . . O . . | $$ | . . . . b . . . . . . . . . . . . . . | $$ | . . 4 a . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . 2 . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . X . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . 1 . O . . . . . , . . . . X X X . . | $$ | . . . . . O . . . . . . . . . O O . . | $$ | . . . . . . . . . . . . . O . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

,

, and

are all relatively small mistakes. At this point I was considering a and b. Well, often in this kind of situation a is recommended, but I never really though about why (so I played b -- oops).
The problem with b is that it sacrifices the

stone for little gain.

is a cutting stone which may become useful.
Also, a isn't weak as I feared; black needs to somehow protect both the

and the

stone in order to cut, each of which requires an extra move.
Overall, a is about 3.7 points better than b.

Comte · Post by **Comte** » Sat Jan 30, 2021 2:34 am

hakuseki wrote:A new 19x19 opening after a couple weeks of 9x9. I'm black. I lost about 40 points by move 80.

$$Bc Game 13, position 1
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . 5 . . . . . . . . . . 7 . . . . |
$$ | . . . , . . . . . , . . . 6 . , 1 . . |
$$ | . . 2 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . a . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . 3 . . . . . . . . . . . . 4 . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------
Click Here To Show Diagram Code
[go]$$Bc Game 13, position 1 $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . 5 . . . . . . . . . . 7 . . . . | $$ | . . . , . . . . . , . . . 6 . , 1 . . | $$ | . . 2 . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . a . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . 3 . . . . . . . . . . . . 4 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
I don't see the two-space high approach much. should be at a. The difference is about 0.15 points.

In position 1, move black 7 is incorrect and should be played at black a as mentioned or black R14. The black move 7 should only be played if black already has supporting stones somewhere below black 1.

Life In 19x19

Opening study with KataGo

Game 10, part 1

Game 11

Game 12

Game 13

Game 14

Game 15

Game 16

Re: Game 16

Game 17

Game 18

Game 19

Game 20

Game 21

Game 22

Re: Game 13