[gnugo-devel] ladder problem sc18

[Yoshikawa Takeshiro]

I want to measure the time to solve a ladder problem.
But I can not succeed it.
The position is shown below:

 

(;GM[1]FF[4]RU[Japanese]SZ[19]
PW[CCC]PB[BBB]
KM[6.5]GN[aaa]SY[Cgoban 1.9.12]
AW[ab][ac][ad][ah][ai][aj][al][an][ao][ap][aq][ar][ba][bd][bf][bg][bi][bo][bs][ca][cd][cf][cg][ci][cs][da][df][dg][di][dm][dr][eb][ed][eg][ei][el][em][er][fb][fd][fe][fj][fk][fn][fq][gb][gd][gk][go][gp][ha][hm][hr][ia][id][ij][im][in][io][jd][jn][ka][ko][ks][ld][li][lj][lm][lq][lr][ls][mb][mg][mh][mi][mk][mp][mq][nb][ns][od][og][oh][oi][or][pc][ph][ps][qb][qd][qg][qn][qp][qs][rb][rc][rg][ri][rj][rk][rs][sg][sh][sm][sn][sp][sq][sr]
AB[af][ag][bc][be][bh][bj][bn][bp][bq][cc][ce][ch][cj][cm][cn][cp][cr][db][dc][dd][de][dh][dj][dl][dn][dq][ec][ej][ek][eo][ep][fg][fh][fi][gc][gf][gi][hb][hc][hd][he][hf][hg][hh][hi][hn][ho][hp][ic][ie][ih][il][ip][is][jc][je][jg][jm][jp][js][ke][ki][kq][kr][lf][lg][lh][mj][ml][na][nh][ni][nj][nk][nl][nm][no][np][nq][nr][oa][oj][pa][pe][pi][pl][po][pq][qa][qe][qh][qi][qk][qm][qo][qr][ra][rd][rh][rl][rm][rp][rr][sb][sc][si][sj][sk]
)

Target to be attacked is the white string R18 at upper right corner.
This problem is referred  from the book  Nakayama's
"ladder of the world".

 

I am not quite sure about the operation and to get least time
to solve.

 

Takeshiro Yoshikawa