White to play. Please note that white has no ko threats available and black has.
Thanks to Henry, Greywulf, Flame, Kochi and Andre Engels for their comments :)
(;AB[ns]AB[nr]AB[nq]AB[np]AB[pn]AW[om]AW[no]AW[mo]AW[mp]AW[mq]AW[mr]AW[ms]AB[op]AW[qm]AW[pm]AB[qn]AB[sn]AB[rn]AW[oo]AB[po]AW[on]AW[pp]AW[qp]AB[pq]AB[rm]AW[ql]AB[rl]AW[rk]AW[sl]AW[qk]AB[qq]AW[sk]C[Remember, Black wins any ko. Avoid ko at all cost.]AB[or]AP[goproblems]
(;W[ro];B[rp])
(;W[rq];B[rp])
(;W[rp]
(;B[rq]
(;W[sm];B[sp])
(;W[so];B[ro]
(;W[sm];B[sp])
(;W[sp];B[sq])
(;W[qo];B[sp])
(;W[sq];B[sr]))
(;W[sp];B[sq]C[Seki! Best for both, but Black has taken it easy here.CHOICERIGHT])
(;W[sq];B[sp]C[Black sets up a possible ko]
(;W[ro];B[sr])
(;W[so];B[sr]
(;W[sm];B[sp]C[Ko, and black captures due to more ko threats])
(;W[ro];B[sp]C[Ko, and black captures due to more ko threats])
(;W[sp];B[ro])
(;W[qo];B[sp]C[Ko, and black captures due to more ko threats]))
(;W[rr];B[sr])
(;W[sm];B[sr])
(;W[sr];B[so]))
(;W[ro];B[sp];W[sm];B[so])
(;W[qo];B[sp]))
(;B[sp]C[Rauli suggested this move. Black is prepared to incur a loss just to make unconditional life hard on White.]
(;W[rq];B[rr]
(;W[sr];B[rs]
(;W[qr];B[pr]
(;W[ro];B[so]
(;W[sm];B[qs];W[sq]C[Correct! Black now loses the upper part as punishment for underestimating your strength.CHOICERIGHT])
(;W[sq]C[Correct! Black now loses the upper part as punishment for underestimating your strength.RIGHT])
(;W[qs];B[ps])
(;W[ps];B[sq]))
(;W[sm];B[ro];W[sq]C[Ko])
(;W[sq];B[ro]C[Ko])
(;W[qo];B[ro])
(;W[so];B[ro]
(;W[sq]C[Ko])
(;W[sm];B[qs];W[sq]C[Ko])))
(;W[ro];B[so]
(;W[sq];B[ss])
(;W[qr];B[sq])
(;W[sm];B[ss]))
(;W[sq];B[ro]
(;W[so]C[Ko])
(;W[qr];B[qo]C[Ko])
(;W[sm];B[ss]C[Ko]))
(;W[so];B[ro]
(;W[sq]C[Ko])
(;W[sm];B[ss])))
(;W[sq];B[sr]
(;W[so];B[ro]C[Ko])
(;W[ro];B[so])
(;W[qo];B[ro])
(;W[sm];B[ro]C[Ko]))
(;W[qr];B[pr]
(;W[sr];B[qs]
(;W[sq];B[ro]
(;W[so];B[rs]
(;W[sm];B[sp]C[Ko])
(;W[sp];B[ss])
(;W[qo];B[sp]C[Ko])
(;W[ss];B[sp]C[Ko]))
(;W[rs];B[ss]
(;W[so];B[rs];W[sm];B[sp]C[Ko])
(;W[sm];B[qo]))
(;W[ss];B[rs]C[Ko])
(;W[qo];B[ss])
(;W[sm];B[rs]C[Ko]))
(;W[rs];B[ss]
(;W[sq];B[rs]
(;W[so];B[ro];W[sm];B[sp]C[Ko])
(;W[ro];B[so])
(;W[qo];B[ro])
(;W[sm];B[ro]C[Ko]))
(;W[ro];B[sq])
(;W[so];B[ro]
(;W[rs]C[Ko])
(;W[sm];B[sq]))
(;W[qo];B[sq]))
(;W[ss];B[ro]
(;W[sq];B[rs]C[Ko])
(;W[sm];B[rs]))
(;W[ro];B[so]
(;W[sq];B[ss]C[Ko])
(;W[rs];B[ss]C[Ko])
(;W[ss];B[rs])
(;W[sm];B[ss]C[Ko]))
(;W[so];B[ro]
(;W[sq];B[rs]C[Ko])
(;W[rs];B[ss]C[Ko])
(;W[ss];B[rs])
(;W[sm];B[rs];W[sq]C[Ko]))
(;W[sm];B[ro]
(;W[sq];B[rs]C[Ko])
(;W[ss];B[rs])
(;W[rs];B[ss]C[Ko])))
(;W[qs];B[sq])
(;W[sq];B[sr]
(;W[so];B[ro];W[sm];B[sp]C[Ko])
(;W[ro];B[so])
(;W[qo];B[ro])
(;W[sm];B[ro]C[Ko]))
(;W[ro];B[sq])
(;W[so];B[sr]
(;W[sq];B[ro];W[sm];B[sp]C[Ko])
(;W[ro];B[sq])
(;W[sm];B[ro])
(;W[qo];B[ro]))
(;W[rs];B[sr]
(;W[sq];B[qs]
(;W[so];B[ro]C[Ko])
(;W[ro];B[so])
(;W[qo];B[ro])
(;W[sm];B[ro]C[Ko]))
(;W[ro];B[sq])
(;W[so];B[ro])
(;W[sm];B[sq])))
(;W[ro];B[sq])
(;W[so];B[ro]
(;W[sq];B[sr]C[Ko])
(;W[sr];B[qo])
(;W[sm];B[sq]))
(;W[sm];B[sq]))
(;W[sq];B[rq]
(;W[so];B[sr]
(;W[sm];B[sp]C[Ko, and black captures due to more ko threats])
(;W[ro];B[sp]C[Ko, and black captures due to more ko threats])
(;W[sp];B[ro])
(;W[qo];B[sp]C[Ko, and black captures due to more ko threats]))
(;W[ro];B[sr])
(;W[sm];B[sr])
(;W[rr];B[sr])
(;W[sr];B[so]))
(;W[rr];B[rq])
(;W[ro];B[rq];W[sm];B[so])
(;W[so];B[ro]
(;W[rq];B[rr]
(;W[sq];B[sr]C[Ko])
(;W[sr];B[qo])
(;W[sm];B[sq]))
(;W[sq];B[rq]
(;W[so];B[sr])
(;W[sm];B[qo]))
(;W[sm];B[rq]))
(;W[sm];B[rq])))
(;W[sm];B[rp])
(;W[qo];B[rp])
(;W[so];B[rp])
(;W[sp];B[rp]))