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The Weak Point (Seki)
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Author:  Ian Butler [ Mon Apr 30, 2018 6:31 am ]
Post subject:  The Weak Point (Seki)
Okay in Level Up 9 there is a lesson that I don't quite understand and there is no additional information.

It's all about taking/choking the weak point to make a seki (I think).

Here are two exercises where I couldn't find the right answer.



Why is the answer of problem 1 at A and for example not at B? Can't you catch those white stones at B? I guess you get a 3-stone dead shape, then. But then why A? I thought they were connected anyway because it's diagonal so they can't be cut.

Problem 2 is even more of an enigma for me. I see 4 cuts (one diagonal so let's say for our sake 2 cuts, C & D). Why is the one cut more important than the other?
The right answer should be C. I have no idea why, though.

Thanks for the help.

EDIT: is it C because white couldn't cut at D because he'd made a 4 space shape to catch and make us alive?
Author:  Shenoute [ Mon Apr 30, 2018 6:36 am ]
Post subject:  Re: The Weak Point (Seki)
Problem 1
If white takes A then playing at a5 will put the black stones in atari, forcing black to connect at c3 which leads to a dead shape. With black playing at A first, all the black stones are connected and white cannot do anything except play inside to give atari but then that leads to black being alive with points instead of seki.

Problem 2
More or less the same. Playing D leads to the same result as playing c3 in problem 1, black is filling a intersection he desperately needs to make seki. After black D, white will be able to atari the whole black group and black can only capture three white stones which leads to a dead shape.

Edit. Here are a few variations


Attachments:
cead9ad8d962ce15e0f0f4e79db5b6702e61ba88.sgf [1.41 KiB]
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Author:  Bill Spight [ Mon Apr 30, 2018 9:16 am ]
Post subject:  Re: The Weak Point (Seki)
Ian Butler wrote:
Okay in Level Up 9 there is a lesson that I don't quite understand and there is no additional information.

It's all about taking/choking the weak point to make a seki (I think).

Here are two exercises where I couldn't find the right answer.



Why is the answer of problem 1 at A and for example not at B? Can't you catch those white stones at B? I guess you get a 3-stone dead shape, then. But then why A? I thought they were connected anyway because it's diagonal so they can't be cut.

Problem 2 is even more of an enigma for me. I see 4 cuts (one diagonal so let's say for our sake 2 cuts, C & D). Why is the one cut more important than the other?
The right answer should be C. I have no idea why, though.

Thanks for the help.

EDIT: is it C because white couldn't cut at D because he'd made a 4 space shape to catch and make us alive?


Small confession. When I was 4 kyu I once played a move like D. My opponent, a 2 dan, made me take my move back. ;)
Author:  Uberdude [ Mon Apr 30, 2018 9:37 am ]
Post subject:  Re: The Weak Point (Seki)
Bill Spight wrote:
Small confession. When I was 4 kyu I once played a move like D. My opponent, a 2 dan, made me take my move back. ;)

Bigger confession: ~2 years ago as a 4d I died in gote with a dead shape, I think it was a bulky five, thinking it was a seki. I kept on playing for a while before realising.
Author:  ez4u [ Mon Apr 30, 2018 4:02 pm ]
Post subject:  Re: The Weak Point (Seki)
Uberdude wrote:
Bill Spight wrote:
Small confession. When I was 4 kyu I once played a move like D. My opponent, a 2 dan, made me take my move back. ;)

Bigger confession: ~2 years ago as a 4d I died in gote with a dead shape, I think it was a bulky five, thinking it was a seki. I kept on playing for a while before realising.

Been there done that! :D
Author:  ez4u [ Mon Apr 30, 2018 4:23 pm ]
Post subject:  Re: The Weak Point (Seki)
Problem 2 is the more interesting here. The thematic variation is "c". Look at Shenoute's third variation where Black places "c" and White adds a stone at R17. Inside the shape both strings of black stones share two liberties with the white stones. There is no way for White to force Black to play further inside. Thus we end up with a seki. This type of seki is frequently the key in tsumego problems. The play at "c" prevents White from isolating one of the black strings such that it has only one internal liberty.

In problem 1 we create a single string with sufficient internal space for seki by playing Shenoute's "a". If we choose "b" instead, then White can play "a" and create a black string with only one internal liberty. Any such string can be put in atari from the outside later, reducing the space inside.
Author:  Knotwilg [ Mon Apr 30, 2018 4:38 pm ]
Post subject:  Re: The Weak Point (Seki)
The fact that you don't find these solutions, even after going through the trouble of editing them for us, tells me that you are looking at the spaces and not at the chains surrounding them. If you think "chain", "liberty", "connection", then the difference between A/B and C/D should be glaring. But if you think "empty points", "eyespace", "territory", then you probably don't.
Author:  Bill Spight [ Mon Apr 30, 2018 6:43 pm ]
Post subject:  Re: The Weak Point (Seki)
ez4u wrote:
Uberdude wrote:
Bill Spight wrote:
Small confession. When I was 4 kyu I once played a move like D. My opponent, a 2 dan, made me take my move back. ;)

Bigger confession: ~2 years ago as a 4d I died in gote with a dead shape, I think it was a bulky five, thinking it was a seki. I kept on playing for a while before realising.

Been there done that! :D


Hey guys! We could form a club. ;)

The Been There Done That Society. :D
Author:  Bill Spight [ Mon Apr 30, 2018 7:01 pm ]
Post subject:  Re: The Weak Point (Seki)
Knotwilg wrote:
The fact that you don't find these solutions, even after going through the trouble of editing them for us, tells me that you are looking at the spaces and not at the chains surrounding them. If you think "chain", "liberty", "connection", then the difference between A/B and C/D should be glaring. But if you think "empty points", "eyespace", "territory", then you probably don't.


Good point. :) There are two main aspects to life and death problems: 1) empty points and eyes; 2) chains and liberties. They literally require different ways of looking. Both are necessary here. First, you have to see (or know) that the 3 pt. eye which would be formed if the three White stones are captured is half alive. White to play can kill. That tells you that seki is the best outcome for Black. Second, you have to see the two shared liberties of the seki and that one connection is necessary to keep from having to fill one of them. (Actually, you won't have to fill, will you, you'll just be dead. ;))
Author:  Ian Butler [ Tue May 01, 2018 12:28 am ]
Post subject:  Re: The Weak Point (Seki)
Knotwilg wrote:
The fact that you don't find these solutions, even after going through the trouble of editing them for us, tells me that you are looking at the spaces and not at the chains surrounding them. If you think "chain", "liberty", "connection", then the difference between A/B and C/D should be glaring. But if you think "empty points", "eyespace", "territory", then you probably don't.


Well, yes and no. If you look at the 2nd problem, my reasoning was that the black stones are all connected anyway. Because of the diagonal move, both C & D connect the entire string of black stones.
Why it is C, then, is probably because D takes away one of white's liberties and it forces a capture, both disadvantagous for black (let's say lethal).

Same goes for problem 1, where I also saw that A was "unnecessary" because black is connected anyway because it's a diagonal stone and if white takes one space, back takes the other.

But now we probably come to a point of mutual liberties? So in seki, is the rule not to take away mutal liberties? At least it seems so in these examples.
Author:  Knotwilg [ Tue May 01, 2018 2:27 am ]
Post subject:  Re: The Weak Point (Seki)
Ian Butler wrote:
Knotwilg wrote:
The fact that you don't find these solutions, even after going through the trouble of editing them for us, tells me that you are looking at the spaces and not at the chains surrounding them. If you think "chain", "liberty", "connection", then the difference between A/B and C/D should be glaring. But if you think "empty points", "eyespace", "territory", then you probably don't.


Well, yes and no. If you look at the 2nd problem, my reasoning was that the black stones are all connected anyway. Because of the diagonal move, both C & D connect the entire string of black stones.
Why it is C, then, is probably because D takes away one of white's liberties and it forces a capture, both disadvantagous for black (let's say lethal).

Same goes for problem 1, where I also saw that A was "unnecessary" because black is connected anyway because it's a diagonal stone and if white takes one space, back takes the other.

But now we probably come to a point of mutual liberties? So in seki, is the rule not to take away mutal liberties? At least it seems so in these examples.


I see ... Indeed, your "equivalent" moves are not equivalent: one connects while maintaining the eyespace intact, the other connects but decreases the eyespace.
Author:  Ian Butler [ Tue May 01, 2018 2:38 am ]
Post subject:  Re: The Weak Point (Seki)
Knotwilg wrote:
Ian Butler wrote:
Knotwilg wrote:
The fact that you don't find these solutions, even after going through the trouble of editing them for us, tells me that you are looking at the spaces and not at the chains surrounding them. If you think "chain", "liberty", "connection", then the difference between A/B and C/D should be glaring. But if you think "empty points", "eyespace", "territory", then you probably don't.


Well, yes and no. If you look at the 2nd problem, my reasoning was that the black stones are all connected anyway. Because of the diagonal move, both C & D connect the entire string of black stones.
Why it is C, then, is probably because D takes away one of white's liberties and it forces a capture, both disadvantagous for black (let's say lethal).

Same goes for problem 1, where I also saw that A was "unnecessary" because black is connected anyway because it's a diagonal stone and if white takes one space, back takes the other.

But now we probably come to a point of mutual liberties? So in seki, is the rule not to take away mutal liberties? At least it seems so in these examples.


I see ... Indeed, your "equivalent" moves are not equivalent: one connects while maintaining the eyespace intact, the other connects but decreases the eyespace.


Oh yes.
It's probably a blindspot in my game right now that one day will just fall into place and then I'll see it clearly :D
Those exercises in Level Up will be good practise for me, in that case.

Thanks.
Author:  dfan [ Tue May 01, 2018 5:10 am ]
Post subject:  Re: The Weak Point (Seki)
Ian Butler wrote:
Those exercises in Level Up will be good practise for me, in that case.

It is cool that you have gotten to a point in Level Up where you are learning new things in addition to getting a review of existing knowledge! These books are great for learning and drilling basic vocabulary and grammar.
Author:  ez4u [ Tue May 01, 2018 6:33 am ]
Post subject:  Re: The Weak Point (Seki)
@Ian - you have learned the wrong lesson. You understand that two diagonal stones are connected. However, that is only true when the shared points are empty. Then, if your opponent plays one, you can play the other and stay connected. In other words, two diagonal stones are "connected" because there are two possible connecting plays that are miai. Here if the opponent plays on the outside point and you are forced to connect on the inside point, you are filling the empty space necessary to maintain the seki.

Another case where the miai connection can become problematical is in a ko. We can play one of the miai points as a ko threat, threatening to cut the "connected" stones. In order to sustain the "connection" the opponent has to answer the ko threat by playing the other miai point.
Author:  Uberdude [ Tue May 01, 2018 6:56 am ]
Post subject:  Re: The Weak Point (Seki)
ez4u wrote:
@Ian - you have learned the wrong lesson. You understand that two diagonal stones are connected. However, that is only true when the shared points are empty. Then, if your opponent plays one, you can play the other and stay connected. In other words, two diagonal stones are "connected" because there are two possible connecting plays that are miai. <snip> Another case where the miai connection can become problematical is...

Problem time: White to play. Black has 2 diagonal shapes, which when considered separately are connected by miai. But how about when considered together, is black connected from end to end?
Go Diagram
Click Here To Show Diagram Code
[go]$$B
$$ -----------------
$$ . . . . . . . . .
$$ . O X . O . . . .
$$ . O X . O . . . .
$$ . O . X O , . . .
$$ . O X . O . . . .
$$ . O X . O . . . .
$$ . O X . O . . . .
$$ . . . . . . . . .
$$ . . . . . . . . .[/go]
Author:  Ian Butler [ Tue May 01, 2018 9:35 am ]
Post subject:  Re: The Weak Point (Seki)
These things I know. In both problems the diagonal stones I was talking about are the ones with both points empty :)

In the problem above you cut them on the left!
Author:  Ian Butler [ Tue May 01, 2018 11:32 am ]
Post subject:  Re: The Weak Point (Seki)
dfan wrote:
Ian Butler wrote:
Those exercises in Level Up will be good practise for me, in that case.

It is cool that you have gotten to a point in Level Up where you are learning new things in addition to getting a review of existing knowledge! These books are great for learning and drilling basic vocabulary and grammar.


Level Up is great. Only downside is they're rather low on explaining. For example now there's a section on solid connection/hanging connection and you get exercises on both of them but there's no real explanation on what connection you should pick in which situation. Or maybe that's too hard to make a rule of and it's just different in every case :)
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