(;AB[ra]AB[rb]AB[qc]AB[qd]AB[pd]AB[od]AB[nd]AB[nc]AB[nb]AW[ob]AW[oc]AW[pc]AW[qb]AW[sb]AW[rc]AW[rd]AW[qe]AW[rf]C[Black to settle the corner.]AP[goproblems]
(;B[pa]C[Good.RIGHT])
(;B[oa];W[qa]C[White gains two stones when they could have been saved.])
(;B[qa];W[pa];B[pb]C[Ko is not necessary.]))