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LGroup

 

L+2 group
    Keywords: Life & Death

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

[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?


[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...

unkx80: For ease of comparison I added the marked stones. B2 lives but when white plays W3, black can only play at B4 to live, he cannot play at either a or b. This loses one point.


[Diagram]
A OK?

Bill: Maybe it's too late at night, but what's wrong with a (B4)?

unkx80: Oops, I am the one who has gone blur.

Bill: Rare for you. :-)

unkx80: No, not rare for me. I am blur all the time. =P


[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.



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.