Tsumego Questions

Dontbtme · Post by **Dontbtme** » Wed Jul 15, 2015 6:31 am

Hi everybody.
I found some time ago a Chinese website where you can find many tsumego problems among other things: 101weiqi.com
I'm presently going through the Segoe Tsumego Dictionary and I've some trouble with the solution they gave for one tsumego in particular.
Here's the problem:

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

On the website, they give this solution:

My question is: can't White choose a ko she would take first with something like this?

Because if Black avoids this one ko by connecting...

... and then destroys the eye on the right...

... then it looks like if Black seals White in with a, White makes a second eye at b. But if Black prevents the second eye with b, White escapes with d.
So it seems Black can only play c to try to kill White but isn't this ko way too risky for Black? Plus if White has helping stones farther on the side...
Anyway, I suppose there is something I missed which would justify the website's solution. Does anyone know what that might be?

Kirby · Post by **Kirby** » Wed Jul 15, 2015 10:26 pm

Dontbtme wrote:
$$ Black can't stop White
$$ -----------------------
$$ . c 4 X 2 . O . 1 . O |
$$ a d X O . O O O 3 O O |
$$ . . X b O X O O O X X |
$$ . , . . . X X X X . . |
$$ . . . X . . . . . X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
Click Here To Show Diagram Code
[go]$$ Black can't stop White $$ ----------------------- $$ . c 4 X 2 . O . 1 . O | $$ a d X O . O O O 3 O O | $$ . . X b O X O O O X X | $$ . , . . . X X X X . . | $$ . . . X . . . . . X . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . |[/go]
... then it looks like if Black seals White in with a, White makes a second eye at b. But if Black prevents the second eye with b, White escapes with d.

Maybe it depends on the rest of the board, but is 'd' much of an escape?

As a side note, I have been reflecting (whining?) about go lately, and I think maybe, more important than if your answer is right or wrong, the fact that you are personally thinking about the problem is good.

ez4u · Post by **ez4u** » Wed Jul 15, 2015 10:40 pm

Note that in the solution diagram, White has two internal ko threats on the right edge by throwing in to put two stones in atari and, if Black captures, playing atari again against the resulting three stones. As a result, the solution looks like a better ko for White than your alternative.

Dontbtme · Post by **Dontbtme** » Thu Jul 16, 2015 1:04 am

ez4u wrote:Note that in the solution diagram, White has two internal ko threats on the right edge by throwing in to put two stones in atari and, if Black captures, playing atari again against the resulting three stones. As a result, the solution looks like a better ko for White than your alternative.

Thank you ez4u

This problem gave me a headache but your explanation is clear and simple. I knew I missed something

So, on the website, a more definite answer for slow old me should have been:

Click Here To Show Diagram Code: [go]$$W White takes back the ko $$ ----------------------- $$ . . . X 3 X X X O . . | $$ . . X O X O . O . O O | $$ . . X . O X O O O X X | $$ . , . . . X X X X 1 2 | $$ . . . X . . . . . X a | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . |[/go]

Since White has a ko threat at 'a' against none in my variation, this sequence is definitely better for her (and I'm kind of

I couldn't find it).
You have my gratitude ez4u: I'll sleep better at night thanks to you

Uberdude · Post by **Uberdude** » Thu Jul 16, 2015 6:13 am

Dontbtme, one advantage of your variation though is that if white wins the ko, black doesn't lose so many points. Also in the solution diagram if black wins the ko white has one ko threat to live remaining for use in another ko, versus none in yours. There's no rule like needing an extra ko threat is equivalent to potentially losing 4 more points in the ko, it depends on the rest of the board so much. But these subtleties might be interesting to ponder about. There will be few games where it makes a difference, though I guess Shusaku and co from years gone by probably got it right when they spent weeks on a single game, but pros these days might not. One thing like this though that does crop up reasonably often is which 2-1 you should play in answer to the 2-2 attack on your carpenters square. If the attacker is trying to make territory on one or both of the sides surrounding your corner then you should play the attach which means after the corner ko you damage his bigger territory if you win the ko (i.e. the 2-1 not on the side you want to damage).

Dontbtme · Post by **Dontbtme** » Thu Jul 16, 2015 6:33 am

Kirby wrote: As a side note, I have been reflecting (whining?) about go lately, and I think maybe, more important than if your answer is right or wrong, the fact that you are personally thinking about the problem is good.

While I agree that thinking about a problem should in itself be good, I'm willing to build my Life&Death tesuji arsenal by reviewing problems exemplifying each one of them. For this to be efficient, I need to (think I) fully understand those problems, which wasn't the case with this one, until ez4u shed some light on it.

When I found the Segoe Tsumego problems were already classified into tesuji types, I was very glad, but a lot of those problems were way above my head... But in 101weiqi.com the users rated their difficulty, and I found out that I could reasonably try to solve those up to what they call '1D+' (since I already know what kind of tesuji is used in the first place, and need only to read out all variations from there on)... which means I could just skip those rated above that rank for the time being, and keep going through the collection, honing my reading skills and my understanding of each tesuji while feeling a sense of accomplishment instead of utter despair.

The tsumego given above was rated as a 1D problem on the website, so I really wanted it to be included in my personal collection...

Anyway. If I encounter another problem which solution doesn't convince me, I plan to seek tactical help in this thread as well, which is why I named it 'Tsumego Questions' in the plural.

I don't know if there is already such a general thread, but if not, anyone with an inquiry on a particular tsumego can and should use it freely.

Dontbtme · Post by **Dontbtme** » Thu Jul 16, 2015 7:23 am

Uberdude wrote:Also in the solution diagram if black wins the ko white has one ko threat to live remaining for use in another ko, versus none in yours.

I'm not sure I follow you, since if Black wins the ko, that means White used all local threats, right? I mean, the resulting local shape should look like something like this:

Click Here To Show Diagram Code: [go]$$ Black wins the ko $$ ----------------------- $$ . . a X . X X X O . . | $$ . . X O X . X O . O O | $$ . . X . O X O O O X X | $$ . , . . . X X X X . X | $$ . . . X . . . . . X . | $$ . . . . . . . . . . X | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . |[/go]

The atari at 'a' doesn't seem like a ko threat to me, plus White doesn't have space for two eyes in the corner no matter what... Did I misread something?

Uberdude wrote:There's no rule like needing an extra ko threat is equivalent to potentially losing 4 more points in the ko, it depends on the rest of the board so much. But these subtleties might be interesting to ponder about. There will be few games where it makes a difference, though I guess Shusaku and co from years gone by probably got it right when they spent weeks on a single game, but pros these days might not. One thing like this though that does crop up reasonably often is which 2-1 you should play in answer to the 2-2 attack on your carpenters square. If the attacker is trying to make territory on one or both of the sides surrounding your corner then you should play the attach which means after the corner ko you damage his bigger territory if you win the ko (i.e. the 2-1 not on the side you want to damage).

I'm reading once again James Davies' "Life and Death" and was surprised to see something along those lines in chapter #23 'The L+2 group', where he explained that the choice between the solid connection and a tiger mouth was really about 'which side do you want to keep open?'.
It's very interesting to see how many layers of understanding there are in this game... But first thing first: if I could kill or live every time it's indeed possible, even in a suboptimal way, I would be more than happy already!

Uberdude · Post by **Uberdude** » Thu Jul 16, 2015 8:01 am

Dontbtme wrote:
Uberdude wrote:Also in the solution diagram if black wins the ko white has one ko threat to live remaining for use in another ko, versus none in yours.
I'm not sure I follow you, since if Black wins the ko, that means White used all local threats, right? I mean, the resulting local shape should look like something like this:
$$ Black wins the ko
$$ -----------------------
$$ . . a X . X X X O . . |
$$ . . X O X . X O . O O |
$$ . . X . O X O O O X X |
$$ . , . . . X X X X . X |
$$ . . . X . . . . . X . |
$$ . . . . . . . . . . X |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
Click Here To Show Diagram Code
[go]$$ Black wins the ko $$ ----------------------- $$ . . a X . X X X O . . | $$ . . X O X . X O . O O | $$ . . X . O X O O O X X | $$ . , . . . X X X X . X | $$ . . . X . . . . . X . | $$ . . . . . . . . . . X | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . |[/go]
The atari at 'a' doesn't seem like a ko threat to me, plus White doesn't have space for two eyes in the corner no matter what... Did I misread something?

Nope, I did!

I had assumed black captured the other stone and then there is a threat at a:

Click Here To Show Diagram Code: [go]$$ Black wins the ko in a bad way $$ ----------------------- $$ . . . X . X X X O . . | $$ . . X . X O a O . O O | $$ . . X X O X O O O X X | $$ . , . . . X X X X . X | $$ . . . X . . . . . X . | $$ . . . . . . . . . . X | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . |[/go]

But I think the other stuff I wrote is correct!

Dontbtme · Post by **Dontbtme** » Thu Jul 16, 2015 9:21 am

Uberdude wrote: Nope, I did! I had assumed black captured the other stone and then there is a threat at a:
$$ Black wins the ko in a bad way
$$ -----------------------
$$ . . . X . X X X O . . |
$$ . . X . X O a O . O O |
$$ . . X X O X O O O X X |
$$ . , . . . X X X X . X |
$$ . . . X . . . . . X . |
$$ . . . . . . . . . . X |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
Click Here To Show Diagram Code
[go]$$ Black wins the ko in a bad way $$ ----------------------- $$ . . . X . X X X O . . | $$ . . X . X O a O . O O | $$ . . X X O X O O O X X | $$ . , . . . X X X X . X | $$ . . . X . . . . . X . | $$ . . . . . . . . . . X | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . |[/go]
But I think the other stuff I wrote is correct!

That's the problem with Life and Death situations: one misstep and it's all over

-though in your case it resulted in just one ko threat difference, which isn't such a big deal when playing against someone like me who avoids playing ko like the plague

Life In 19x19

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