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.
Black cannot play at a to secure the second eye as Nick Sibicky demonstrated in May of 2023.
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)