L+2 group
The L+2 group is an L group with a leg on both sides.
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
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
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).
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.
Suppose the marked stone is added. Now
is sente. If
was played at a then the addition of white stones at
and b would not be sente at all.
2. Attacks from within
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.
4. Weak leg
If Black has a weak leg, White can kill with a rogue ko (in this case, also a two-stage ko). see the discussion at BQM 507
5. Weak leg (2)
This is the ko fight.
Tapir: Forcing with
,
,
before fighting the Ko, is a waste of internal ko threats.
^Tapir is erroneous and should not write comments so confidently lest he not only make himself look like a fool, but worse, miseducate others.
It does NOT waste Ko threats. In fact, you can't even start the Ko without playing
,
,
. Either of the immediate ataris are a lot worse. If doubt remains on the matter, this has been played in pro games multiple times.
(Someone stronger than Tapir)
tapir: Please be so nice and simply correct, best with explanation, and move on next time. It is a wiki, after all. My thought process probably was: Black can fight a ko in the corner already after
,
threat,
answer,
recaptures the corner stone.
I see now that this ko is not worth fighting for, but this needs explaining. (Fighting the approach ko is better for Black than fighting a direct ko over the corner stone.)
Andy: Why make the
/
exchange? Wouldn't it be usual to play
at
with tripod or sabaki options instead?
unkx80: This
is common as well. When to play
and when to play directly at
is difficult to answer.
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
before
, I've seen White changing directions and taking the corner. (in professional games)
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is best response of black.
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, in real games.
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2024 the Authors,
published under the ![Sensei's Library [Welcome to Sensei's Library!]](../../images/stone-hello.png)