(;GM[1]FF[4]SZ[19]
GN[Black to make ko]
PC[https://senseis.xmp.net/?GokyoShumyoSection3Problem31/Solution]AP[GoWiki:2009]
DT[2023-01-21]
C[Diagram from https://senseis.xmp.net/?GokyoShumyoSection3Problem31/Solution

Black to make ko]
PL[B]

AB[bb][jb][ac][ec][kc][bd][ed][fd][hd][jd][ce][de][he][ke][bf]
AW[cb][db][eb][gb][bc][cc][fc][gc][ic][cd]
LB[ha:a]

;B[ga]C[B1]MN[1]
;W[hb]C[W2]MN[2]
;B[ea]C[B3]MN[3]
;W[fa]C[W4]MN[4]

;LB[ha:a]
)
