the tsumego comes from classic work "xuanxuan qijing" published in 1340s
(;C[black first,black kills white.a classic tsumego was created in 1340s,chinaCHOICE]AB[rb]AB[qc]AB[pc]AB[mc]AB[lc]AB[od]AB[nd]AW[md]AW[ld]AW[kc]AW[kd]AW[nc]AW[oc]AW[pb]AP[goproblems]
(;B[mb]
(;W[na];B[oa];W[ob];B[kb];W[jb];B[nb];W[pa];B[la]C[RIGHT])
(;W[ob];B[kb];W[jb];B[nb];W[na];B[la];W[ja];B[qb]C[RIGHT]))
(;B[nb];W[ob];B[mb];W[na];B[ma];W[la];B[oa];W[lb]))