[gnugo-devel] A thrashing dragon

[bump]

I added a test in trash.tst (the last one) that looks quite
interesting. Look at the position at move 204 in the game
uno-gnugo-3.3.16-200302050206.sgf.

There is a semeai going on at the bottom but GNU doesn't
recognize it. GNU believes that the W dragon at M8 is
dead and therefore the B dragon at L8 is alive.

The reason for this is that after B fills one liberty
at M5 during do_owl_attack, the M8 string has four liberties
while the L8 string has eight. The M8 string is classified
as a lunch and is considered not owl lively.

Yet the M8 string has a lot of life in it. It takes 7 moves 
to take it off the board and there is a ko to fight.

At stackp==0, the M8 string has 5 liberties and no
attack point is found though some attack threat points
are given. The owl_attack status is DEAD and the owl_attack
point is PASS.

If only GNU recognized the semeai,  --decide-semeai L8/M8 -o vars.sgf
finds:

After black at O4, L8 is ALIVE, M8 is DEAD (11 nodes)
After white at H8, L8 is DEAD, M8 is ALIVE (12 nodes)

with an acceptable variation set.

Dan