L+2 group

    Keywords: Life & Death

The L+2 group is an L group with a leg on both sides.

Table of contents Table of diagrams
L+2 group
First hane
First hane: failure
Second hane
Lives, but...
When Black ignores the sente move
When Black ignores the sente move
Attack at 1-2
Attack at other 1-2
Attack at 1-3
Attack at 2-2
L+2 group
L+2 group with a weak leg
White makes a rogue ko
L+2 group with a weak leg
L+2 group with a weak leg
Follow up (1) after W's attack.
Follow up (2) after W's attack.
The ko I saw: B6 threat, W7 answer
After Black 1...
After Black 1...
After Black 1...

[Diagram]
L+2 group  

The L+2 group is alive. The corner territory can be reasonably counted as 6 points. We will have a look at: the defense against the hane from either side; how to deflect attacks from within; and the status of this group when White has a stone on either of the marked points.


1. Defence against a hane

[Diagram]
First hane  

Against the hane from the short side, one should defend at the 1-2 point. Now there are two sure eyes at the circled points.

See also /Discussion

[Diagram]
First hane: failure  

Answering at the 2-2 point leads to seki - or to ko if that is what Black really wants (see bent four in the corner).

[Diagram]
Second hane  

Against the hane from the long side, one should defend at the 2-2 point. Now there are two sure eyes at the circled points.

[Diagram]
Lives, but...  

Suppose the marked stone is added. Now W3 is sente. If B2 was played at a then the addition of white stones at W3 and b would not be sente at all.

[Diagram]
When Black ignores the sente move  

Black cannot play at a to secure the second eye.

[Diagram]
When Black ignores the sente move  

One eye to none, White wins the capturing race.



See also /Discussion.


2. Attacks from within

[Diagram]
Attack at 1-2  
[Diagram]
Attack at other 1-2  
[Diagram]
Attack at 1-3  

Here a and b become miai.

[Diagram]
Attack at 2-2  

Here a and b become miai.


3. An extra stone

If white has the descent marked by the circle in the diagram, the L+2 group is no longer unconditionally alive. However, a white descent at the point marked by a square in the diagram does not affect the status of the group.

[Diagram]
L+2 group  



See L+2 group with descent.


4. Weak leg

[Diagram]
L+2 group with a weak leg  

If Black has a weak leg, White can kill with a rogue ko (in this case, also a two-stage ko).

[Diagram]
White makes a rogue ko  

Black cannot play atari at a because of a shortage of liberties.


5. Weak leg (2)

[Diagram]
L+2 group with a weak leg  

In this shape, white can make ko fight with White a.


[Diagram]
L+2 group with a weak leg  

B2 and B4 is best response of black.

[Diagram]
Follow up (1) after W's attack.  
[Diagram]
Follow up (2) after W's attack.  

This is the ko fight.

Tapir: Forcing with B6, B8, B10 before fighting the Ko, is a waste of internal ko threats.

^Tapir is erroneous and should not write comments so confidently lest he not only make himself look like a fool, but worse, miseducate others. It does NOT waste Ko threats. In fact, you can't even start the Ko without playing B6,B8,B10. Either of the immediate ataris are a lot worse. If doubt remains on the matter, this has been played in pro games multiple times. (Someone stronger than Tapir)

tapir: Please be so nice and simply correct, best with explanation, and move on next time. It is a wiki, after all. My thought process probably was: Black can fight a ko in the corner already after W5, B6 threat, W7 answer, B8 recaptures the corner stone.

[Diagram]
The ko I saw: B6 threat, W7 answer  

I see now that this ko is not worth fighting for, but this needs explaining. (Fighting the approach ko is better for Black than fighting a direct ko over the corner stone.)


[Diagram]
After Black 1...  

Above shape can be made by black's probing move - B1, in real games.


[Diagram]
After Black 1...  

Andy: Why make the B3/W4 exchange? Wouldn't it be usual to play B3 at B5 with tripod or sabaki options instead?

unkx80: This B3 is common as well. When to play B3 and when to play directly at B5 is difficult to answer.

[Diagram]
After Black 1...  

unkx80: In this result, Black gets slightly less and White has sente. Which is better for Black?

tapir: It is white's choice isn't it. If Black plays B6 before B3, I've seen White changing directions and taking the corner. (in professional games)


See also


L+2 group last edited by tapir on July 28, 2016 - 15:18
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