(;GM[1]FF[4]SZ[19]
GN[Two-step ko]
PC[http://senseis.xmp.net/?XuanxuanQijingProblem41/Solution]AP[GoWiki:2009]
DT[2013-04-01]
C[Diagram from http://senseis.xmp.net/?XuanxuanQijingProblem41/Solution

Two-step ko]
PL[B]

AB[bk][bm][cm][cn][co][eo][dp][cq][eq][fq][gq][gr][ir]
AW[bn][bo][bp][cp][dq][dr][er][fr]

;B[br]C[B1]MN[1]
;W[ar]C[W2]MN[2]
;B[aq]C[B3]MN[3]
;W[cr]C[W4]MN[4]
;B[bq]C[B5]MN[5]
;W[bs]C[W6]MN[6]
;B[as]C[B7]MN[7]

;
)
