(;AB[qd]AB[pd]AB[oc]AB[ob]AW[nb]AW[nc]AW[od]AW[pe]AW[qe]AW[re]AB[rd]AB[rb]AW[qb]C[Black to live]AW[nd]AW[ra]AW[rf]AW[mb]AP[goproblems]
(;B[rc];W[pa]
(;B[oa];W[pc])
(;B[pb];W[oa]))
(;B[qc];W[pb]C[]
(;B[pa];W[qa]
(;B[pc];W[oa])
(;B[oa];W[sd]
(;B[pc];W[sb]
(;B[sa];W[sc])
(;B[rc];W[sc]))
(;B[sc];W[na])
(;B[sb];W[na]))
(;B[sc];W[oa])
(;B[sb];W[oa]))
(;B[oa];W[sd]C[]
(;B[sc];W[pc];B[se];W[na]
(;B[sa];W[sb]C[a 2-step ko (b needs 2 external ko threats to win)RIGHT])
(;B[qa];W[pa]))
(;B[pa];W[sb];B[rc];W[sc])
(;B[qa];W[sb];B[sa];W[sc]))
(;B[sc];W[pc];B[sa]C[RIGHT]))
(;B[pa];W[rc]
(;B[sb];W[sd])
(;B[qc];W[sb]
(;B[qa];W[sd])
(;B[sd];W[sc]
(;B[qa];W[pb])
(;B[pb];W[qa]))))
(;B[pb];W[rc]
(;B[sb];W[sd])
(;B[sd];W[sb])
(;B[qc];W[sb])
(;B[sc];W[sb]))
(;B[pc];W[rc]
(;B[sb];W[pa]
(;B[oa];W[sc]
(;B[sd];W[sa];B[pb];W[qa])
(;B[qc];W[sa]
(;B[pb];W[sd])
(;B[sd];W[pb])))
(;B[qc];W[oa]))
(;B[qc];W[sb]))
(;B[sb];W[pa]
(;B[oa];W[pc])
(;B[pb];W[oa]))
(;B[sc];W[pa]
(;B[oa];W[pc]
(;B[qc];W[na]
(;B[sa]C[];W[sb]C[a 2-step ko (b needs 2 external ko threats to win)RIGHT])
(;B[pb];W[pc]))
(;B[sa];W[qc];B[qa];W[na]))
(;B[pb];W[oa])
(;B[pc];W[oa])
(;B[qc];W[oa])
(;B[sa];W[qc]
(;B[oa];W[pc])
(;B[pc];W[oa])
(;B[rc];W[oa])))
(;B[qa];W[pa])
(;B[sa];W[sb];B[rc];W[pa];B[oa];W[pc]))
