L+2 group with descent

  Difficulty: Advanced   Keywords: Life & Death

Table of contents Table of diagrams
L+2 group with descent
The tesuji
White's mistake
White's best response
What many books say
The approach move
The two stage ko
The two stage ko
Hane first
When Black wins the ko
What many books do not say
L+2 group with descent
L+2 group with descent

L+2 group with descent I

[Diagram]
L+2 group with descent  

It is said that the L+2 group is alive. However, when there is a descent at black+circle, it is not exactly the case.



The tesuji

[Diagram]
The tesuji  

The tesuji of B1 and B3 exploits the black+circle stone.

[Diagram]
White's mistake  

What works for the L+2 group case does not work here. The atari at W4 is a mistake. After B7, due to shortage of liberties, White is unable to prevent Black from connecting the three stones at a.

[Diagram]
White's best response  

White's best response is W4. Black can play either a or b.



Method I: What many books say

[Diagram]
What many books say  

Many books suggest making the throw-in at B5 directly. This is a two stage one move approach ko.

[Diagram]
The approach move  

The required approach move is B7, converting it to a direct two stage ko.

[Diagram]
The two stage ko  

For White to win the ko, he must make two moves at W8 and W10.

[Diagram]
The two stage ko  

For Black to win the ko, he must make two moves at B9 and connect at white+circle.



Method II: A better method?

[Diagram]
Hane first  

Bill proposed that Black can hane with B5 and start a ko with B7. This is a two stage ko for Black, and White has a ko-threat at a. In most cases, this method is slightly better than the previous method.

[Diagram]
When Black wins the ko  

When Black wins the two kos, Black connects at B1 to finish White off.

Alex: Looks like a good way for a Moonshine Life position to arise. Now White just needs to arrange for a double ko somewhere else... :-)



Method III: When both sides have no ko threats

[Diagram]
What many books do not say  

When neither side has a ko threat, this is best. Note that both players threaten to make a ko. This is like a ten thousand year ko, either player can convert to a proper seki.


L+2 group with descent II

[Diagram]
L+2 group with descent  

The descent at black+circle does not affect the status of the group, which means that White is unconditionally alive. Defence against Black's attacks are identical to those listed in L+2 group.


Variation

[Diagram]
L+2 group with descent  

It is worth while to discuss this variation. The ko is White's best result, but inferior to the main line. B3 is the only move to avoid seki


L+2 group with descent last edited by Bill on March 22, 2009 - 03:18
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