question about tsumego (GoChild)

[dohduhdah]

Hi.

Again, I have a question about a go problem:

Dong-Dong grouping > (1) ~10k_6350 > (1) ~30k > (1) > 0062

Found at GoChild:http://gochild2009.appspot.com/?locale=en_US

http://bayimg.com/PAlFNaAdf

The solution given is for black to capture directly by playing at E7, but I was wondering
if an alternate solution for black would be to capture indirectly by playing at F7 as shown
in the screenshot.

Is there any reason why one of these two solutions is to be preferred over the other?

greetings and thanks in advance for any feedback, Niek

[Bill Spight]

Let me answer a simpler, but related question. In the given position all that is at stake are the two White stones and the single Black stone. Then the solid capture is better.

(;AP[GOWrite:2.2.21]ST[2]CA[ISO8859-1]FF[4]SZ[19]GM[1]AW[dd][ed][df][dg][eg][ff][fh][gf]PW[ ]PB[ ]AB[cc][dc][ec][fb][fd][gd][cd][ce][cf][de][ef]GN[ ]PM[2]FG[259:]
(
;C[*** Black has 4 points in the area of interest.]B[ee]
)
(
;C[*** In a sense, Black has captured the White stones. But let us look at the sequels.]B[fe]
(
;W[ee]
;B[ef]
;W[ee]C[*** Black has captured two net stones, taking three while White has taken one. However, he does not have two points of territory. ]
)
(
;C[*** Now Black has 4 points, but it took two moves to get it.]B[ee]
)

)

)

However, there are situations where the gain from the indirect capture is greater than the local comparative loss of a little more than a point. Then the indirect capture would be preferable. Keep looking for those alternative plays.

[dohduhdah]

Ok, that seems to make sense. But generally speaking, is it usually better to capture directly in case there is also an alternative way to capture via snapback or is it equally likely that either the direct or indirect capture will be better depending on the context and possible continuations?

Here are a few similar tsumego that involve the choice between a direct and indirect capture via snapback (where snapback capture is displayed in the screenshot):

http://bayimg.com/GAljIAADf

http://bayimg.com/iAljPaadF

http://bayimg.com/jalJNaadF

If I recall correctly it's usually better to capture directly if the alternative way to capture indirectly involves using a ladder.

[Bill Spight]

Ok, that seems to make sense. But generally speaking, is it usually better to capture directly in case there is also an alternative way to capture via snapback or is it equally likely that either the direct or indirect capture will be better depending on the context and possible continuations?

Wrong question. You should always consider the alternatives, averages be damned.

[Toge]

http://bayimg.com/GAljIAADf

http://bayimg.com/iAljPaadF

http://bayimg.com/jalJNaadF

- In first case, it's bad to capture with snapback as white can rescue her two stones in corner. In second case it is also wrong to capture with snapback, as black can place the group in atari. This can be used to help right side development or as a ko threat. Third case is the only really beneficial one. Exchange A5-A8 leaves white with weakness at B5.

Tesuji like the snapback are only tools. When you internalize them, they help in planning your tactics.

[dohduhdah]

Wrong question. You should always consider the alternatives, averages be damned.

But this is not always an option. For instance in a blitz game where there is no time to consider all possible continuations and you might be better off with general heuristics.

[jts]

If I recall correctly it's usually better to capture directly if the alternative way to capture indirectly involves using a ladder.

What you say here is a little ambiguous. As a rule of thumb, if there are some stones you can capture, and it's vital that you capture them, and you have an option about how to capture them, your preference should be...

1. Remove the stones from the board
2. Net the stones in a way that reduces their liberties ("firm")
3. Net the stones in a way that doesn't reduce their liberties ("loose")
4. Ladder the stones
5. Fight a ko to capture the stones

This can vary, though. If you can win all kos, then it might be better to fight a ko than to make a net. Very rarely, it might be better to give a ladder breaker than 2+ peeps at your net. If the life and death of groups are affected, all the rules are out the window... you might want to capture in a net rather than securely because it pokes out an eye, for example. If you are falling behind your opponent, you might start to play moves that you know are suboptimal because you need to make up points somewhere to win.

http://bayimg.com/GAljIAADf

This is probably a mistake. The direct capture at d7 relieves c10's shortage of liberties, and thereby cuts off b10; after e7, White can save the corner. However, if the situation on the rest of the board were such that cutting at either f6 or f8 were extremely valuable, damaging White's shape like this might make sense.

http://bayimg.com/iAljPaadF

Doesn't look like k10 accomplishes anything. Now W can choose between a free atari at k9 or favorable endgame around f12.

http://bayimg.com/jalJNaadF

This could be smart. The key thing to understand is that if Black just captures at a8 directly, she can later play a7 in sente. If White eventually has to take gote to play a7 himself, Black is equally happy. However, if the endgame moves around a7/a5 are already the biggest thing on the board, Black wants to play a7 immediately; whether she plays a7 or a8 the capture will be sente, but if she captures with a7 she gets an extra 4 points.

[Bill Spight]

Wrong question. You should always consider the alternatives, averages be damned.

But this is not always an option. For instance in a blitz game where there is no time to consider all possible continuations and you might be better off with general heuristics.

What is your goal? To play bad blitz? Or to play good go? You started out with some good questions. Keep that up.

[dohduhdah]

Wrong question. You should always consider the alternatives, averages be damned.

But this is not always an option. For instance in a blitz game where there is no time to consider all possible continuations and you might be better off with general heuristics.

What is your goal? To play bad blitz? Or to play good go? You started out with some good questions. Keep that up.

Well, basically my goal is to help improve gochild. Hence, I try to find alternative solutions when solving tsumego, but the problem I encounter is that it often seems that solutions are rather arbitrarily accepted or rejected. Hence I'm looking for arguments in favor of or against accepting or rejecting certain solutions, to improve overall consistency across the site.

In some sections of the site, it might be ok to accept alternative suboptimal solutions for didactical purposes, but I think it's important to try and maintain some kind of consistency across various batches of exercises, so people can figure out the logic behind the exercises which implies whether or not they should pay attention to certain aspects (like finding the most optimal solution or simply learning about alternative ways to capture stones).

--

Of the 4 examples I've referred to in this thread, only the last two accept both the direct and indirect capture as a solution at gochild, so my main concern at this point is whether or not there is a kind of logic behind this distinction between the former two and the latter two or whether it's more or less arbitrary.

http://bayimg.com/PAlFNaAdf

http://bayimg.com/GAljIAADf

http://bayimg.com/iAljPaadF

http://bayimg.com/jalJNaadF

[dohduhdah]

The last two tsumego were modified in response to my question about when an indirect capture via snapback might be an alternative for direct capture.

Setting up a snapback is now only an alternative for direct capture in the last tsumego.

(;GM[1]FF[4]CA[UTF-8]SZ[13]C[Dong-Dong grouping > (1) ~10k_6350 > (1) ~30k > (1) > 0062]AB[cb][db][dc][ec][cd][ce][cf][ef][fd][gd]AW[bb][bc][cc][dd][ed][df][dg][eg][fc][fb];B[de];W[ff];B[ee])

(;GM[1]FF[4]CA[UTF-8]SZ[13]C[Dong-Dong grouping > (1) ~10k_6350 > (1) ~30k > (2) > 0294
]AB[cb][cc][dd][bd][be][bf][cg]AW[bb][bc][dc][ec][cd][ce][cf][ef];B[df];W[ed];B[de])

(;GM[1]FF[4]CA[UTF-8]SZ[13]C[
Dong-Dong grouping > (1) ~10k_6350 > (1) ~30k > (3) > 0564
]AW[kb][kc][kd][ib][hc][hd][gc][fd][ed][ec][ff]AB[gd][ge][he][ie][ic][fc][fb][gb];B[hb];W[jc];B[id])

(;GM[1]FF[4]CA[UTF-8]SZ[13]C[Dong-Dong grouping > (1) ~10k_6350 > (1) ~30k > (3) > 0586
]AB[ab][bb][db][cb][bd][ce][de][ec][fc][fe][dd]AW[eb][fb][gb][dc][cd][cc][bc][ac][be][bf][cf][df][ef](;B[ad])(;B[ae];W[af];B[ad]))

[Dusk Eagle]

The difference between capturing directly and capturing via snapback can be subtle. Having said that, here's my take on the appropriate move in each case:

$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | . O X X . W . c c
$$ | . O O X X W . c c
$$ | . . X O O X X . .
$$ | . . X 1 a b . . .
$$ | . . X O B 2 . . .
$$ | . . . O O . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .

Click Here To Show Diagram Code

[go]$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | . O X X . W . c c
$$ | . O O X X W . c c
$$ | . . X O O X X . .
$$ | . . X 1 a b . . .
$$ | . . X O B 2 . . .
$$ | . . . O O . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

Here I think it is better to capture at 'a' then to make the snapback at 'b'. For one, by making the snapback at 'b', black has left a bit of endgame for white by initiating the snapback sequence, followed by recapturing the black stone. Note that in some types of snapbacks this is not possible, but in this shape it is. But there is more to why I think it is better to capture solidly. Notice that if white plays the White 'a' - Black - White 'a' sequence, it is a threat to cut off the three black stones on the right. This may not seem like such a big deal immediately, as black can capture the two marked white stones, but consider if white gets a move in the 'c' area at any point in the future - suddenly, black must respond to white's recapture at 'a', making the sequence sente for white. White will be able to improve his shape in the center in sente.

$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | . O X . . . . . .
$$ | . O X O O . . . .
$$ | . X O X 2 . . . .
$$ | . X O a b . . . .
$$ | . X O 1 O . . . .
$$ | . . X . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .

Click Here To Show Diagram Code

[go]$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | . O X . . . . . .
$$ | . O X O O . . . .
$$ | . X O X 2 . . . .
$$ | . X O a b . . . .
$$ | . X O 1 O . . . .
$$ | . . X . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

Here, I would play the snapback shape at 'b' instead of 'a'. By playing 'b', you introduce an additional cutting points into white's shape.

$$B
$$ ------------------
$$ . . . . . . . . .|
$$ . X X 1 O . O . .|
$$ O X O O X 2 O . .|
$$ O O X O a b O . .|
$$ . . X X X c . . .|
$$ . . . . . . . . .|
$$ . . . . . . . . .|
$$ . . . . . . . . .|
$$ . . . . . . . . .|
$$ . . . . . . . . .|

Click Here To Show Diagram Code

[go]$$B
$$ ------------------
$$ . . . . . . . . .|
$$ . X X 1 O . O . .|
$$ O X O O X 2 O . .|
$$ O O X O a b O . .|
$$ . . X X X c . . .|
$$ . . . . . . . . .|
$$ . . . . . . . . .|
$$ . . . . . . . . .|
$$ . . . . . . . . .|
$$ . . . . . . . . .|[/go]

This one's subtle, but I would play 'a' as I see no reason to give white a free move at 'c'.

$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | X X X X O O O . .
$$ | O O O O X X c . .
$$ | a X O X . d . . .
$$ | b O X X e B . . .
$$ | . O O O O . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .

Click Here To Show Diagram Code

[go]$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | X X X X O O O . .
$$ | O O O O X X c . .
$$ | a X O X . d . . .
$$ | b O X X e B . . .
$$ | . O O O O . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

If black's shape on the outside was better, I would take 'b' over 'a' for the endgame profit. However, black has shortage of liberty problems on the outside, so he should clear this issue up by capturing solidly with 'a'. To see what I mean by liberty problems, imagine white getting a stone at 'c'. Then moves like 'd' and 'e' work to cut off the lone black stone. This is the kind of aji black doesn't want to deal with, so capturing solidly is better.

I'm not sure if this is what you were looking for, but I hope it helps somewhat .

[dohduhdah]

This is from the forum at GoChild ("Question correction records 5" thread), regarding the first three problems:

http://bayimg.com/FalpKAAdf

GoSharpLite created GoChild.

[shapenaji]

This is from the forum at GoChild ("Question correction records 5" thread), regarding the first three problems:

http://bayimg.com/FalpKAAdf

GoSharpLite created GoChild.

The analysis of the second problem on there is incorrect, the left diagram DOES look better, but that's because white has made one less move than in the right diagram.

[dohduhdah]

The difference between capturing directly and capturing via snapback can be subtle. Having said that, here's my take on the appropriate move in each case:

$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | . O X . . . . . .
$$ | . O X O O . . . .
$$ | . X O X 2 . . . .
$$ | . X O a b . . . .
$$ | . X O 1 O . . . .
$$ | . . X . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .

Click Here To Show Diagram Code

[go]$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | . O X . . . . . .
$$ | . O X O O . . . .
$$ | . X O X 2 . . . .
$$ | . X O a b . . . .
$$ | . X O 1 O . . . .
$$ | . . X . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

Here, I would play the snapback shape at 'b' instead of 'a'. By playing 'b', you introduce an additional cutting points into white's shape.

But is introducing those additional cuttingpoints worth allowing white to save its two stones in the corner (as mentioned by Toge and jts earlier in this thread)?

[Dusk Eagle]

Like this?

$$B
$$ ------------------
$$ | . . 4 . . . . . .
$$ | . O X 6 . . . . .
$$ | . O X O O . . . .
$$ | . X O X 2 . . . .
$$ | . X O 5 3 7 . . .
$$ | . X O 1 O . . . .
$$ | . . X . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .

Click Here To Show Diagram Code

[go]$$B
$$ ------------------
$$ | . . 4 . . . . . .
$$ | . O X 6 . . . . .
$$ | . O X O O . . . .
$$ | . X O X 2 . . . .
$$ | . X O 5 3 7 . . .
$$ | . X O 1 O . . . .
$$ | . . X . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

Those two stones in the corner are not worth the horrible price white pays when black plays . White loses a lot of potential on the top side and is cut off from the center. Black's power radiates into the center and onto the left side of the board. Even if black doesn't play , the fact that white can no longer atari at to get into the center and left side costs white a lot of power.