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L+2 group
Path: LifeAndDeath   · Prev: L1Group   · Next: LongLGroup
    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
Second hane: failure
Difference game
Answer
Second hane: failure?
Second hane: failure?
Snapback
Lives, but...
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

[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.


[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]
Second hane: failure

Answering this hane at 1-2 leads to disaster. Black can't play 8 at a because of shortage of liberties. If Black 6 at a, White 7 at 6 kills: see rectangular six in the corner.

I may be missing the bleeding obvious here - but doesn't Black 6 at 7 give life for black?


RichardHunter: A Japanese book I have says this B2 also lives but is thin. The reason is at both b and c are sente, which is not the case if Black plays the 2-2 point as above.

Bill: I set up a difference game, but the advantage of the 2-2 is not so clear to me.

[Diagram]
Difference game

For instance, B1 threatens to kill, but W2 protects the group. Now Black would have an advantage if he could play B3 with sente, but White plays W4, probably leading to mutual damage.




[Diagram]
Answer

Good question. If B1 here, White makes a bulky five inside Black's eyespace. Black can not play at a because of shortage of liberties. What I said is wrong !! --Dieter

Dieter -- black will not play at a, but capture -- white 4 is a snapback. I still see this as black lives. Dieter: Yes I noticed, but didn't have the time to re-edit my stuff. Hence the exclamation above.



[Diagram]
Second hane: failure?

Bill: How about B 6? Dieter: see above (though you were first). Maybe a white stone at b is appropriate to prevent escape. WRONG. Needs edit Dieter


[Diagram]
Second hane: failure?

[Diagram]
Snapback

[Diagram]
Lives, but...

In this case I added the marked stone. 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.



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

In many of the variations above, Black suffers from shortage of liberties as soon as one of the circled points is filled by White.

[Diagram]
L+2 group


4. Weak leg

[Diagram]
L+2 group with a weak leg

If Black has a weak leg, White can kill with a rogue ko.


[Diagram]
White makes a rogue ko

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



Path: LifeAndDeath   · Prev: L1Group   · Next: LongLGroup
This is a copy of the living page "L+2 group" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.