What’s the best way for black to protect this cut?

dany · Post by **dany** » Thu May 25, 2023 11:37 am

cool problem found on the web

Click Here To Show Diagram Code: [go]$$c Black to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . X X O O . . | $$ | . . . O . . . . . X . X . O . X O . . | $$ | . . O , O . . X . O . . . . . X O . . | $$ | . . X . . X . . . . . . . . . X . . . | $$ | . . . X . . . . . . . . . . . . O . . | $$ | . . . . . X . . . . . . . . . . . . . | $$ | . . O O O . . . . . . . . . . . . . . | $$ | . . . X 2 . O . . . . . . . . . . . . | $$ | . X . , . . . . . , . . . . . , . . . | $$ | 1 . X a . . . . . . . . . . . . . . . | $$ | . X O X . . . . . . . . . . . . . . . | $$ | . O O X . . . . . . . . . . . . . . . | $$ | . . O X . . . . . . . . . . . . . . . | $$ | . O X X . . . . . . . . . . . . . . . | $$ | . . O X . X O . . , . . . . X , X . . | $$ | . . O O . O . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

"Black took the stone at 1 and white protected at 2.

Black wants to attack white, but there’s an obvious cut at A that black needs to take note of.

White may not cut immediately, but black will always need to worry about the cut and this will impact the attack.

What’s the best way for black to protect this cut?"

"Hint: The move is beautiful

"

ez4u · Post by **ez4u** » Fri May 26, 2023 2:04 am

I cheated and checked with katago, so I won't post an answer for now. But I think this really is a beautiful idea that is more generally relevant than just this position. I learned something new. Good find!

ez4u · Post by **ez4u** » Sun May 28, 2023 2:17 am

Since no one else posted...

Here is katago's answer. I am used to the idea of throwing in at "b" below to start a ko to capture White's four marked stones. However, here the immediate throw in would be met by simply descending at "d" instead of capturing at "c". But, Black has other resources due to a defect in White's position. Black can cut at 3. Notice that after 3 the throw in at "b" is atari on both sides so White has to capture. Black gets to start a ko with "d". Furthermore, if Black waits until White cuts at "a", there are three internal ko threats from playing atari against the cutting stone. With that in hand, katago turns away to 5 after 3. This 5 is a forcing move before attacking the 5 White stones in the center.

BTW - this is not some super AI move. It is just better than my level of thinking.

I tried it on one of my teachers (one of the top amateurs in Tokyo, ex-insei) and he got it immediately. At least he got it faster than I could lay out the stones. Either way, it is indeed a beautiful move.

Click Here To Show Diagram Code: [go]$$c Black to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . X X O O . . | $$ | . . . O . . . . . X . X . O . X O . . | $$ | . . O , O . . X . O . . . . . X O . . | $$ | . . X . . X . . . . . . . . . X . . . | $$ | . . . X . . . . . . . . . . . . O . . | $$ | . . . . . X . . . . . . . . . . . . . | $$ | . . O O O . . . . . . . . . . . . . . | $$ | . . . X 2 . O . . . . . . . . . . . . | $$ | . X . , . . . . . , . . . . . , . . . | $$ | 1 . X a . . . . . . . . . . . . . . . | $$ | . X W X . . . . . . . . . . . . . . . | $$ | d W W X . . . . . . . . . . . . . . . | $$ | c b W X . . . . . . . . . . . . . . . | $$ | . O X X . . 5 . . . . . . . . . . . . | $$ | . 3 O X . X O . . , . . . . X , X . . | $$ | . 4 O O . O . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

The fun part is here. White would like to connect here but the gap at "b" in the diagram gives Black surprising resources in the corner. If White answers 7 by capturing the two stones, Black will play atari at "b" and split White's corner apart.

Click Here To Show Diagram Code: [go]$$c White tries to resist $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . X X O O . . | $$ | . . . O . . . . . X . X . O . X O . . | $$ | . . O , O . . X . O . . . . . X O . . | $$ | . . X . . X . . . . . . . . . X . . . | $$ | . . . X . . . . . . . . . . . . O . . | $$ | . . . . . X . . . . . . . . . . . . . | $$ | . . O O O . . . . . . . . . . . . . . | $$ | . . . X 2 . O . . . . . . . . . . . . | $$ | . X . , . . . . . , . . . . . , . . . | $$ | 1 . X a . . . . . . . . . . . . . . . | $$ | . X O X . . . . . . . . . . . . . . . | $$ | . O O X . . . . . . . . . . . . . . . | $$ | . 4 O X . . . . . . . . . . . . . . . | $$ | . O X X . . . . . . . . . . . . . . . | $$ | . 3 O X . X O . . , . . . . X , X . . | $$ | . 5 O O b O . . . . . . . . . . . . . | $$ | 9 6 7 8 . . . . . . . . . . . . . . . | $$ | . . 0 . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

After 1 below, White has to resort to ko anyway. This one is much bigger and Black even takes first.

Click Here To Show Diagram Code: [go]$$c White tries to resist cont'd $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . X X O O . . | $$ | . . . O . . . . . X . X . O . X O . . | $$ | . . O , O . . X . O . . . . . X O . . | $$ | . . X . . X . . . . . . . . . X . . . | $$ | . . . X . . . . . . . . . . . . O . . | $$ | . . . . . X . . . . . . . . . . . . . | $$ | . . O O O . . . . . . . . . . . . . . | $$ | . . . X O . O . . . . . . . . . . . . | $$ | . X . , . . . . . , . . . . . , . . . | $$ | X . X a . . . . . . . . . . . . . . . | $$ | . X O X . . . . . . . . . . . . . . . | $$ | . O O X . . . . . . . . . . . . . . . | $$ | . O O X . . . . . . . . . . . . . . . | $$ | 1 O X X . . . . . . . . . . . . . . . | $$ | 2 X O X . X O . . , . . . . X , X . . | $$ | 3 X O O b O . . . . . . . . . . . . . | $$ | X O . O . . . . . . . . . . . . . . . | $$ | 4 5 O . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

jlt · Post by **jlt** » Sun May 28, 2023 2:41 am

Thanks... I didn't post because I was clueless. I initially thought about "b" but saw after a while that it didn't work because of "d", and didn't find anything better.

kvasir · Post by **kvasir** » Sun May 28, 2023 7:55 am

I looked at this on Thursday but had some other things on my mind, then I had deja vu about it on Friday, maybe this was posted on L19 before?

I was mainly thinking about starting the ko immediately or playing G5. The solution is really good timing. I'm not sure I'd say black is attacking white in the center as opposed to defending. The proverb is that offense is the best defense. However, in Go it's often that the best offense is good defense.

dany · Post by **dany** » Tue Jun 06, 2023 12:22 pm

Original post https://www.reddit.com/r/baduk/comments ... beautiful/

Problem

Solution with great explanation

the game
Byun Sangil 9p (Black) vs. Weon Seongjin 9p (White) B+R
http://go4go.net/go/games/sgfview/109260

Life In 19x19

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Re: What’s the best way for black to protect this cut?