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MoonShadow: I came across the following position in a game with Nagi today.


..o...
.o..o.
o.oox.
..ox.x
.ox.o.
.oxx..
  White is thick around the middle and left corner, since  black is attacking deep in white's territory (board size 13x13).
 
  Black to play and keep the corner alive.



Thoughts?


AlexChurchill:
Initially, I couldn't tell for sure.  It *seems* like Black ought to be able to live.  But on analysis, I think White can kill the Black stones no matter what.


..o...
.o..o.
o.oox.
..ox.x
.ox.o.
.oxx..








If Black can get both (a) and (b), and also defend the stones left and right of (c), he'll have two eyes (one around the central White stone, and one in the bottomright corner).

So I think (a), (b) or (c) is Black's best play.

But playing (a) seems suicidal on reflection, because of this:

..o...
.o..o.
o.oox.
..ox.x
.ox.ox
.oxxo.








Black loses the three on the left.  Playing (d) would just let White take them all.


(b) is different from (a) in that it leaves the Black stones one more liberty:

..o...
.o..o.
o.oox.
..ox.x
.ox.oo
.oxxx.







It seems that White's going to lose the internal stones.  However, he might well do so in a way that leaves the Black group with only one eye.  (c) or (d) seem Black's best moves, but I think in both cases, the corner dies.  If Black plays (c):


..o...
.o..o.
o.oox.
..oxxx
.oxooo
.oxxxx







At this point, the White stones are captured, but White can reduce the Black formation to one eye:


..o...
.o..o.
o.oox.
..oxxx
.ox.o.
.oxxxx








If instead Black plays (d):

..o...
.o..o.
o.oox.
..oxox
.oxxoo
.oxxxx







Again the Whites are captured, but Black is left with only one eye.

..o...
.o..o.
o.oox.
..ox.x
.oxxo.
.oxxxx










And finally, if in the initial position Black plays (c):

..o...
.o..o.
o.oox.
..oxxx
.oxoo.
.oxx..








then the black group on the left is dead.  Unless black plays (a), then white (a) kills them; if black plays (a), white (b) kills them.

Conclusion: ye're all DOOMED :)
--AlexChurchill

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Last edited November 22, 2002 5:23 pm (viewing revision 4, which is the newest) (diff)
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