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.
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.


[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


This is a copy of the living page "L+2 group" at Sensei's Library.
(OC) 2014 the Authors, published under the OpenContent License V1.0.
[Welcome to Sensei's Library!]
StartingPoints
ReferenceSection
About