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Offline paullik
 Post subject: Why only after two black moves is white dead?
Post #1 Posted: Wed Aug 26, 2015 8:56 am 
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I was reading about ko, and ko threats at Sensei's Library and I found this diagram:

Image

If I take it in isolation and consider this paragraph:
Quote:
In this diagram black can play at a. White must respond at b. If white neglects to respond black will kill all the white stones by playing at b himself.


Well, isn't white already dead? Since he's surrounded and cannot make eyes?
Why should black play at a and b in order to consider white dead? Or is this just for illustration purposes for the entire article?


Original article:
http://senseis.xmp.net/?Ko
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Offline leichtloeslich
 Post subject: Re: Why only after two black moves is white dead?
Post #2 Posted: Wed Aug 26, 2015 9:07 am 
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its a simple seki
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Offline paullik
 Post subject: Re: Why only after two black moves is white dead?
Post #3 Posted: Wed Aug 26, 2015 9:44 am 
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I cannot see it...
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Offline Abyssinica
 Post subject: Re: Why only after two black moves is white dead?
Post #4 Posted: Wed Aug 26, 2015 9:51 am 
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KGS: STOP STALKING ME
Even though white has no eyes, when the liberties on the outside get filled, black cannot fill in the liberties on the inside to capture white without making it so that white will be able to live.

Simple example:

In order for white to capture black, white would have to play a move inside. Yet if white plays a move here, it creates a straight 4 shape, black captures, and then black has the 4 space eye shape to live with. If black wants to capture white well then that's self-atari and he dies.

Click Here To Show Diagram Code
[go]$$c Seki
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . O O O O O O O O O . . . . . |
$$ | . . . . . O X X X X X X X O . . . . . |
$$ | . . . , . O X . O O O . X O . , . . . |
$$ | . . . . . O X X X X X X X O . . . . . |
$$ | . . . . . . O O O O O O O . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

This post by Abyssinica was liked by: daal
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Offline xed_over
 Post subject: Re: Why only after two black moves is white dead?
Post #5 Posted: Wed Aug 26, 2015 10:03 am 
Oza

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paullik wrote:
I cannot see it...

well then... let's play it out...

Click Here To Show Diagram Code
[go]$$B Ko threat
$$ -------------------
$$ | . X X X . b 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]

Black makes the ko threat.
If White ignores the threat to win the ko (elsewhere on the board, and not shown), then black plays again to kill the white stones.
Click Here To Show Diagram Code
[go]$$B White ignores the Ko threat
$$ -------------------
$$ | . X X X . 3 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]

Now there is no way for white to make two eyes here. Black will just continue to fill in all the liberties until he can capture all of white's stones.

However, if White responds to the threat, white is alive in seki.
Click Here To Show Diagram Code
[go]$$B Seki
$$ -------------------
$$ | . X X X . 2 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]


Once all the outside liberties are filled, neither side want to play at a or b. Seki.
Click Here To Show Diagram Code
[go]$$B Seki
$$ -------------------
$$ | a X X X b O X X .
$$ | O O O O O O O X .
$$ | 7 O 1 X X X X X .
$$ | X O O 3 X . . . .
$$ | X O X X X . . . .
$$ | 5 X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]

If black plays at a or b, then white can live with territory.
If white plays at a or b, then black can capture all of whites stones for lots of territory.
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Offline paullik
 Post subject: Re: Why only after two black moves is white dead?
Post #6 Posted: Wed Aug 26, 2015 10:10 am 
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xed_over wrote:
well then... let's play it out...

[...]

However, if White responds to the threat, white is alive in seki.
Click Here To Show Diagram Code
[go]$$B Seki
$$ -------------------
$$ | . X X X . 2 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]



Ok, so the seki is after white responds to the threat, that makes more sense.

Thanks for the clarifications.

This post by paullik was liked by: xed_over
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Offline Bill Spight
 Post subject: Re: Why only after two black moves is white dead?
Post #7 Posted: Wed Aug 26, 2015 10:18 am 
Honinbo

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One more point about this position.

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


If White plays :w1: the :bc: stones are dead. :)

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At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.
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Offline paullik
 Post subject: Re: Why only after two black moves is white dead?
Post #8 Posted: Wed Aug 26, 2015 10:54 am 
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Bill Spight wrote:
One more point about this position.

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


If White plays :w1: the :bc: stones are dead. :)


Since they are inside white's territory, right?
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Offline skydyr
 Post subject: Re: Why only after two black moves is white dead?
Post #9 Posted: Wed Aug 26, 2015 11:43 am 
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paullik wrote:
Bill Spight wrote:
One more point about this position.

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


If White plays :w1: the :bc: stones are dead. :)


Since they are inside white's territory, right?

Yes, in a sense, but do you understand why it's white's territory now and not before?

This post by skydyr was liked by: Bill Spight
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Offline paullik
 Post subject: Re: Why only after two black moves is white dead?
Post #10 Posted: Wed Aug 26, 2015 12:27 pm 
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skydyr wrote:
paullik wrote:
Since they are inside white's territory, right?

Yes, in a sense, but do you understand why it's white's territory now and not before?

Because it's only now that the :bc: are surrounded.
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Offline skydyr
 Post subject: Re: Why only after two black moves is white dead?
Post #11 Posted: Wed Aug 26, 2015 12:38 pm 
Oza

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paullik wrote:
skydyr wrote:
paullik wrote:
Since they are inside white's territory, right?

Yes, in a sense, but do you understand why it's white's territory now and not before?

Because it's only now that the :bc: are surrounded.


Well...
Click Here To Show Diagram Code
[go]$$B Seki
$$ -------------------
$$ | . X X X . 2 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]

In this diagram, black's three stones are also surrounded, but they're alive in seki. So what's the difference between the this one and the following that makes it different?
Click Here To Show Diagram Code
[go]$$W White lives outright
$$ -------------------
$$ | . X X X . . 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]
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Offline paullik
 Post subject: Re: Why only after two black moves is white dead?
Post #12 Posted: Wed Aug 26, 2015 1:21 pm 
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skydyr wrote:
Well...
Click Here To Show Diagram Code
[go]$$B Seki
$$ -------------------
$$ | . X X X . 2 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]

In this diagram, black's three stones are also surrounded, but they're alive in seki. So what's the difference between the this one and the following that makes it different?
Click Here To Show Diagram Code
[go]$$W White lives outright
$$ -------------------
$$ | . X X X . . 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]


The number of liberties of the white stones, which in fact lead to seki or to killing the three black stones.
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Offline skydyr
 Post subject: Re: Why only after two black moves is white dead?
Post #13 Posted: Wed Aug 26, 2015 2:03 pm 
Oza

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paullik wrote:
skydyr wrote:
Well...
Click Here To Show Diagram Code
[go]$$B Seki
$$ -------------------
$$ | . X X X . 2 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]

In this diagram, black's three stones are also surrounded, but they're alive in seki. So what's the difference between the this one and the following that makes it different?
Click Here To Show Diagram Code
[go]$$W White lives outright
$$ -------------------
$$ | . X X X . . 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]


The number of liberties of the white stones, which in fact lead to seki or to killing the three black stones.

Well, if black plays here:
Click Here To Show Diagram Code
[go]$$W White lives outright
$$ -------------------
$$ | . X X X 2 . 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]

Isn't the number of liberties the same as before? White has 5 liberties in this and the other diagram.
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Offline Joaz Banbeck
 Post subject: Re: Why only after two black moves is white dead?
Post #14 Posted: Wed Aug 26, 2015 4:28 pm 
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http://senseis.xmp.net/?DeadEyeshapes

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Offline gowan
 Post subject: Re: Why only after two black moves is white dead?
Post #15 Posted: Thu Aug 27, 2015 6:37 am 
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In this diagram

Click Here To Show Diagram Code
[go]$$W White lives outright
$$ -------------------
$$ | a X X X 2 b 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]


White has three "outside" liberties so white can play at a and b (if necessary) so in the end the shape will be

Click Here To Show Diagram Code
[go]$$W White lives with territory
$$ -------------------
$$ | O . . . . O O X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]


The empty points inside White's group make four in a line which is alive.

If Black plays first as in the next diagram, White lives in seki, as do the three surrounded black stones.

Click Here To Show Diagram Code
[go]$$B White lives in seki (no territory)
$$ -------------------
$$ | . X X X . 2 1 X .
$$ | O O O O O O O X .
$$ | . O . X X X X X .
$$ | X O O . X . . . .
$$ | X O X X X . . . .
$$ | . X . . . . . . .
$$ | . X . X . . . . .
$$ | . . . . . . . . .[/go]


So in either case, White lives. In one case White gets points, in the other no points, but White lives in both cases.
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Offline paullik
 Post subject: Re: Why only after two black moves is white dead?
Post #16 Posted: Thu Aug 27, 2015 6:44 am 
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gowan wrote:
So in either case, White lives. In one case White gets points, in the other no points, but White lives in both cases.


I wouldn't have thought about this, since I was still looking at the problem from the point where black dies or not, not considering the fact that white remains alive.
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Offline EdLee
 Post subject:
Post #17 Posted: Thu Aug 27, 2015 9:10 pm 
Honinbo
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Off topic:
Quote:
I was still looking at... not considering...
Hi Paul,

Isn't it nice that Go teaches us...
To:
  • Look more deeply (not just the surface);
  • Look more broadly (the big and bigger pictures);
  • Look at not only our own situation, but our opponent's;
  • See the reality as it is (objectively; not subjectively, biased by our blindness, selfishness, over-confidence, cowardice, convenience, prejudices, jealousy, anger, stupidity, immaturity, impatience, greed, etc.)
:)

( The same can be said about chess, many genuine martial arts, and other disciplines. :mrgreen: )
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