Kill corner?

Aidoneus · #1

Can Black kill this corner with my first move? Or maybe Bc1 not the key move?

Click Here To Show Diagram Code: [go]$$B $$ +---------------------------------------+ $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . X X X . . . . . , . . . . . , . . . | $$ | . O O O X X X . . . . . . . . . . . . | $$ | . . . . O O X . . . . . . . . . . . . | $$ | . . 1 . . . . . . . . . . . . . . . . | $$ +---------------------------------------+[/go]

Here is my read, mistakes and all.
1) If Wf1 (?) Bd1, forcing Wd2 then Bb2 threats to link out and WA2 or WA3 allows Black to play Bc2 followed by Bb1 to make bulky five, right?

2) If Wd1 Bc2 kills, right?

3) If Wc2 Bd1: then a) We1 (?) Ba3, Wa2 Bb1 kills, I think; but b) Wb1 lives, as far as I can tell, so I'm stuck here. Is Bd1 a mistake?

DrStraw · #2

Click Here To Show Diagram Code: [go]$$B $$ +---------------------------------------+ $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . X X X . . . . . , . . . . . , . . . | $$ | d O O O X X X . . . . . . . . . . . . | $$ | . . . b O O X . . . . . . . . . . . . | $$ | . e . c . a . . . . . . . . . . . . . | $$ +---------------------------------------+[/go]

There is a much easier way to approach this. The L+1 group lives or dies with sente. That means that in response to a white cannot play b and must play c. But then after d white cannot block, otherwise e kills. So, the two statements:

1. L+1 is sente.
2. After d the tesuji is e.

will, between them, pretty much answer all questions regarding this position. Of course, there are other moves to look at, but if you know these two things then everything becomes simple.

Uberdude · #3

A general piece of advice for how to approach tsumego. Start by playing from the outside to reduce the eyespace ("there is death in the hane"). Only after you have shown that doesn't work think about playing inside moves first.

moyoaji · #4

That move is incorrect. The corner is actually ko for life.

Aidoneus · #5

I started by looking at two hanes, but thought that Wc2 would make two eyes after Bb1--overlooking that Bg1 forces the right eye to be false since White can't protect with We1 because of Bc1.

Again, thank you both for the help. The corner tesujis give me so much trouble!

Aidoneus · #6

moyoaji wrote:

That move is incorrect. The corner is actually ko for life.

No, DrStraw is right. Bb1 is a nice killing tesuji!

moyoaji · #7

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

Are you guys sure this kills? It still looks like ko to me.

From what I read of DrStraw's post, he isn't saying that 'e' kills, he says it is a powerful combination after 'd'. Which is true and which is what I posted in my analysis.

EDIT: If you are speaking of this variation, here is what I read -

Click Here To Show Diagram Code: [go]$$B White lives $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . X X X . . . . . , . . . . . , . . . | $$ | 3 O O O X X X . . . . . . . . . . . . | $$ | 4 7 8 . O O X . . . . . . . . . . . . | $$ | . 5 6 2 . 1 . . . . . . . . . . . . . | $$ +---------------------------------------+[/go]

Click Here To Show Diagram Code: [go]$$B White lives $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . X X X . . . . . , . . . . . , . . . | $$ | 3 O O O X X X . . . . . . . . . . . . | $$ | 4 8 7 . O O X . . . . . . . . . . . . | $$ | . 5 6 2 . 1 . . . . . . . . . . . . . | $$ +---------------------------------------+[/go]

HermanHiddema · #8

After the hane, it is a JGroup, which dies like this:

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

moyoaji · #9

Right, sorry. I found it. :oops:

Click Here To Show Diagram Code: [go]$$W is the killing move. $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . O O O . . . . . $$ | 3 X X X O O O . . $$ | 4 7 8 . X X O . . $$ | . 5 6 2 . 1 9 . . $$ +------------------[/go]

HermanHiddema · **#10**

@moyaji: white should answer :b6:

with

immediately, otherwise capturing :w3:

is sente and black can get out.

moyoaji · **#11**

HermanHiddema wrote:

@moyaji: white should answer :b6:

with

immediately, otherwise capturing :w3:

is sente and black can get out.

If the possibility of getting out is included in this, then why does black not just capture :w3:

with

so he has enough liberties? Assuming that white has to block in some fashion then the variation at :b6:

will work after the capture.

Click Here To Show Diagram Code: [go]$$W Black lives? $$ | . 7 . . . . . . . $$ | . . . . . . . . . $$ | 6 O O O . . . . . $$ | 3 X X X O O O . . $$ | 4 9 0 . X X O . . $$ | . 5 8 2 . 1 . . . $$ +------------------[/go]

I do agree, however, that if black plays :b6:

that white should play :w9:

as

.

DrStraw · **#12**

moyoaji wrote:

From what I read of DrStraw's post, he isn't saying that 'e' kills,

Yes I was. It is a standard tesuji which any midkyu needs to know.

Uberdude · **#13**

HermanHiddema wrote:

After the hane, it is a JGroup, which dies like this:

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

Sorry to be picky Herman, but it's subtlety different as there are two stones not one at the lower right leg. In this case it doesn't make a difference to the status, but in other cases it can so this approach of simplifying to known corner shapes doesn't always work (though obviously it gives a good idea of things to try). For example:

Click Here To Show Diagram Code: [go]$$W Tripod group with extra leg = ko $$ | . O . . . . . . . $$ | . . . . . . . . . $$ | . O O . . . . . . $$ | . X O . . . . . . $$ | . X X O O . . . . $$ | . . . X O . O . . $$ | . . X . . . . . . $$ +------------------[/go]

Click Here To Show Diagram Code: [go]$$W Very similar to a tripod group with extra leg = alive $$ | . O . . . . . . . $$ | . . . . . . . . . $$ | . O O . . . . . . $$ | . X O . . . . . . $$ | . X X O O O . . . $$ | . . . X X O . . . $$ | . . X . O . . . . $$ +------------------[/go]

moyoaji · **#14**

Uberdude wrote:

Sorry to be picky Herman, but it's subtlety different as there are two stones not one at the lower right leg. In this case it doesn't make a difference to the status, but in other cases it can so this approach of simplifying to known corner shapes doesn't always work (though obviously it gives a good idea of things to try).

James Davies considers this a J-Group.

It's status problem 5 of the J-Group chapter in Life and Death. Page 111 in my copy.

DrStraw wrote:

Yes I was. It is a standard tesuji which any midkyu needs to know.

I see that now. I am sorry. I failed to read one move farther than what I needed to.

I did see the tesuji, but I did not see how it would succeed in that case. I was not familiar with this particular life and death problem.

HermanHiddema · **#15**

@moyoaji: You can prevent the escape and black still cannot live:

Click Here To Show Diagram Code: [go]$$W $$ | . . . . . . . . . $$ | . 7 . . . . . . . $$ | . . . . . . . . . $$ | 6 O O O . . . . . $$ | 3 X X X O O O . . $$ | 4 a c b X X O . . $$ | . 5 8 2 d 1 9 . . $$ +------------------[/go]

After

Black is out of options, because a is answered with b, and c is answered with d

@Uberdude: I am aware of that, but this is generally considered a J-Group, AFAIK, and is shown as such on the page I linked.

Aidoneus · **#16**

moyoaji wrote:

I did see the tesuji, but I did not see how it would succeed in that case. I was not familiar with this particular life and death problem.

I always tell my math students to not be afraid to ask questions. If one of them needs clarification, there are probably five more students too shy to ask.

So, I am glad if others--including those much stronger than me--benefited from my ignorance! :lol:

Edit: For those, like me, without Davies' book, you can find the J group discussed at: http://senseis.xmp.net/?JGroup

Uberdude · **#17**

Ok yeah, it's a J group in the sense of belonging to the J group family of related shapes. My point was the (basic) J group being dead:

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

doesn't logically imply that this one is:

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

In this case they are both dead with the same killing sequence, but the tripod group extra leg example shows a shape where this change changes the status. I remember being surprised by this in a game.

Kill corner?

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