Long L group
The standard 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.
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
This diagram is a modified one with extra liberty at a for the black group. Note that Black is unconditionally alive.
The attack by and
fails. Black has an excellent way to live - by playing at
, aiming to play at a . . .
If White answers at , Black will play at
. The result is a gote seki for Black - the same as living unconditionally when considered in terms of life and death.
( at 6)
The strongest attempt for White is to play atari at in this diagram. But Black sacrifies yet another stone at
, and takes back with
. . .
If White plays at ,
will cause White to be caught in a connect-and-die (a kind of shortage of liberties).
here won't start a ko either. After
, White at a, Black at 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)
White has descended to the edge with . If Black doesn't answer, he dies unconditionally.
Black's attempt at a ko lacks liberties instead.
Note that can also be played at
.
Kanazawa Problem 18 / Solution includes this variation. creates a defect: now
is atari, making the previous diagram fail.
( at
)
Subsequently, if White plays at , Black lives with
and
.
The long L group with a descent outside (2)
White descends the other way. It is still the case that White to play can kill Black unconditionally.
This is also shortage of liberties. Black can't play at a after .
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