Re: [gnugo-devel] Owl mistake and thrashing dragons.

[bump]

> White is struggling to live on the right edge. Now GNU Go finds the S8
> dragon critical with both attack and defense points at T7! This is
> just horrible. T7 has no effect whatsoever on the life of the group.
> In fact it shouldn't even spend any time at all trying it.

The underlying problem is that if the ko is removed from
the board, the position paradoxically looks better to
owl for whichever player does not have sente.  Thus the
ko is taken to throw away sente.

If B has sente, A1124 proposes B:P10, after which D319
proposes W:P9. 

On the other hand, if W has sente, W:P9 is never considered.

We can remove the paradoxical situation where W:P9 is only
considered if B:P10 is present by adding a pattern:

Pattern D321

...X       move out, making some eyeshape
.*.O
X.Oo

:8,-,value(80)

Then B plays at P9 which is after all the best move on the
board, though undervalued at 6.27 points. This is a classic
thrashing dragon, and P9 should be valued big. This pattern
could be combined with D319.

The second move considered by B is to take the ko (proposed
by A1201). If W has sente, D1316 proposes filling the
ko. In either case, the reason the move seems to work is
that the position looks better to owl for whomever moves
second.

Dan