(;C[White to kill.]AB[ra]AB[sb]AB[rb]AB[qb]AB[pb]AB[na]AW[sc]AW[rc]AW[qc]AW[pc]AW[oc]AW[nb]AW[mb]AW[lb]AP[goproblems]
(;W[pa]
(;B[ob]C[This is the position shown in BostonGo Problem #4.]
(;W[oa];B[qa];W[oa]C[CHOICERIGHT])
(;W[ma];B[oa]C[Two eyes.]))
(;B[oa]C[]
(;W[ob]C[CHOICERIGHT])
(;W[ma];B[ob]))
(;B[qa]C[]
(;W[oa];B[ob];W[oa]C[CHOICERIGHT])
(;W[ob];B[oa]C[RIGHT])
(;W[ma]
(;B[oa];W[ob]C[CHOICERIGHT])
(;B[ob];W[oa];B[na];W[oa]C[RIGHT]))))
(;W[oa];B[pa]C[Two eyes.])
(;W[ob];B[pa]C[Two eyes.CHOICE]))