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LifeAndDeath

Referenced by
LGroup
TenThousandYearKo
KanazawaProblem18...
KanazawaProblem20
KanazawaProblem20B

 

Long L group
Path: LifeAndDeath   · Prev: L2Group   · Next: TripodGroup
    Keywords: Life & Death, Shape

Table of contents Table of diagrams
The long L group
a strange ko
With an extra liberty
Black can answer at 4
Variation 1: seki
Variation 2: still alive
Variation 2a: oiotoshi
Variation 2b: big capture
White descends to the edge (1)
White descends to the edge (1)
White descends to the edge (1, variation)
White descends to the edge (1, variation)
White descends to the edge (2)
White descends to the edge (2)

The standard long L group

[Diagram]
The long L group

The black shape in this corner is the long L group. It controls more corner space than the L group, and this greatly improves its chances for survival.


[Diagram]
a strange ko

This is White's best attack. She produces a somewhat strange ko in the corner. This is known as a ten thousand year ko.



The long L group with an extra liberty

[Diagram]
With an extra liberty

This diagram is a modified one with extra liberty at a for the black group. Note that Black is unconditionally alive.


[Diagram]
Black can answer at 4

The attack by W1 and W3 fails. Black has an excellent way to live - by playing at B4, aiming to play at a...


[Diagram]
Variation 1: seki

If White answers at W5, Black will play at B6. The result is a seki - the same as living unconditionally when considered in terms of life and death.


[Diagram]
Variation 2: still alive

(Black 8 at 6)

The strongest attempt for White is to play atari at W5 in this diagram. But B6 sacrifies yet another stone, and takes back at B8...


[Diagram]
Variation 2a: oiotoshi

If White plays at W9, B10 will cause White to be caught in a connect-and-die (a kind of shortage of liberties).


[Diagram]
Variation 2b: big capture

W9 here won't start a ko either. After B10, White a, Black b, it will be obvious that Black is unconditionally alive. The extra liberty comes in very handy here.



The long L group with a descent outside (1)

[Diagram]
White descends to the edge (1)

White with WC has descended to the edge. If White plays first, Black is unconditionally dead.


[Diagram]
White descends to the edge (1)

Black's attempt at a ko lacks liberties instead.

Note: W5 can also be played at W7.


[Diagram]
White descends to the edge (1, variation)

Kanazawa Problem 18 / Solution includes this variation. BC creates a defect, and now B4 is atari making the previous diagram fail.


[Diagram]
White descends to the edge (1, variation)

(W3 at WC)

Subsequently, if White plays at W1, Black lives with B2 and B4.



The long L group with a descent outside (2)

[Diagram]
White descends to the edge (2)

White descends the other way. It is still the case that White to play can kill Black unconditionally.


[Diagram]
White descends to the edge (2)

This is also shortage of liberties. Black can't play at a after W7.



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Path: LifeAndDeath   · Prev: L2Group   · Next: TripodGroup
This is a copy of the living page "Long L group" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.