(;AB[ao]AB[bo]AB[bp]AB[bq]AB[dq]AB[cq]AB[eq]AB[er]AB[es]AW[br]AW[cr]AW[an]AW[bn]AW[co]AW[cn]AW[dp]AW[ep]AW[en]AW[fq]AW[fr]AW[fs]AW[fo]C[How can White kill the corner?]AP[goproblems]
(;W[ar];B[aq]C[Seki.])
(;W[aq];B[ar]
(;W[as];B[cs]C[Seki.])
(;W[bs];B[ds]C[Seki.])
(;W[cs];B[as]C[Seki.])
(;W[dr];B[ds]C[Seki.])
(;W[ds];B[dr]
(;W[as];B[cs]C[Seki.])
(;W[bs];B[cs]C[Please play a ko threat at A.FORCE]LB[gm:A];W[gm];B[gn];W[ds];B[hn]C[(black tenuki)]
(;W[as];B[cs]C[White will need two more ko threats.])
(;W[cp];B[cs]C[Ko is best. White needs one more threat.RIGHT])))))