I have a problem with the following position where GNU Go generates an illegal suicide move:
-- file PbSuicide.sgf
(
;SZ[19]
AB[ja][ka][na][oa][pa][jb][sb][dc][ec][fc][gc][hc][ic][jc][mc][nc][oc][rc][bd][cd][kd][ld][md]
[pd][qd][rd][sd][me][pe][ff][gf][hf][if][jf][kf][lf][mf][bg][eg][bh][eh][bi][ei][fi][gi][hi][ii][ji]
[qi][ri][cj][jj][kj][lj][mj][nj][nk][ok][el][fl][gl][hl][il][jl][kl][ll][ml][nl][ol][sl][dm][em][sm]
[dn][en][on][pn][rn][sn][eo][oo][so][ep][fp][gp][hp][ip][jp][kp][op][pp][qp][rp][sp][cq][lq]
[mq][nq][cr][hr][pr]
AW[la][ra][kb][lb][mb][nb][ob][pb][qb][rb][kc][lc][pc][qc][be][ce][bf]
[df][pg][ch][dh][qk][rk][pl][rl][pm][qm][rm][qn][po][qo][ro][eq][pq][qq][dr][fr][rr]
PL[W]
)
-- end of file PbSuicide.sgf
This strange position has been obtained when verifying the ability of my Drago free software (you can see it at www.geocities.com/wwwdrago) to:
- draw a random position
- start a game from the current position.
In that case, GNU Go was playing with White. I know, this was very unfair.
You can retrieve the problem with the following gtp commands:
>Gnugo –mode gtp
loadsgf pbsuicide.sgf
= white
genmove w
= T17
T17 is a suicide move although GNU Go is playing with Japanese rules. Note that this move doesn't appear in the list of legal moves obtained from the commands:
>Gnugo –mode gtp
loadsgf pbsuicide.sgf
= white
all_legal
= …
Apart to reporting this problem, I am also interested in the solution to handle illegal moves. Next version of Drago will implement the following one:
- detect illegal moves,
- undo them
- generate a new move from the list of legal moves
In that case, GNU Go plays a PASS in the above position.