(;AB[qb]AB[pb]AB[pc]AB[pe]AB[oe]AB[nf]AB[mf]AB[kf]AB[kd]AB[jb]AB[kb]AW[pa]AW[ob]AW[oc]AW[od]AW[ne]AW[me]AW[le]AW[ld]AW[lc]AW[lb]AW[la]AB[oa]AB[nb]AB[ma]AB[lf]AB[ke]AB[kc]AB[pd]C[White to do his best.]AP[goproblems]
(;W[na]
(;B[rf]LB[sf:K]C[Please answer the ko threat at K.CHOICE];W[sf];B[oa]LB[se:K]C[Play at K if you want to use a Ko threat.]
(;W[nc];B[mc];W[na]C[Great! Now black has to find a second ko threat.RIGHT])
(;W[se]C[No need to start wasting Ko threats yet.])
(;W[mb];B[nd];W[na];B[nc];W[oa];B[qa]))
(;B[nc]
(;W[nd];B[oa];W[mb];B[qa];W[mc]C[RIGHT])
(;W[mb];B[nd];W[oa];B[qa];W[ma]C[Dead shape.]))
(;B[mb];W[nc];B[oa];W[mc];B[qa];W[na]C[RIGHT])
(;B[nd]
(;W[nc];B[oa];W[md]C[RIGHT])
(;W[mb];B[nc];W[oa];B[qa];W[ma]C[Dead shape.])))
(;W[nc];B[mc]
(;W[na];B[rf]LB[sf:K]C[Please answer the ko threat at K.];W[sf];B[oa]C[And if you don't have any Ko threats?];W[nd];B[mb]C[White is dead.])
(;W[nd];B[mb]C[White has a dead shape.]))
(;W[mb];B[nd];W[na];B[nc];W[oa];B[qa];W[ma]C[Dead shape.])
(;W[mc];B[qa]C[Black wins.])
(;W[md];B[qa]C[Black wins.])
(;W[nd];B[qa]C[Black wins.]))