(;SZ[19]AW[rl]AW[on]AW[pn]AW[qn]AW[rn]AW[no]AW[so]AW[mp]AW[qp]AW[rp]AW[iq]AW[kq]AW[mq]AW[oq]AW[mr]AW[qr]AB[mo]AB[po]AB[qo]AB[ro]AB[np]AB[op]AB[pp]AB[nq]AB[pq]AB[nr]AB[pr]GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]RU[Japanese]KM[5.50]PW[White]PB[Black]
(;B[qq];W[rr];B[rq];W[sq])
(;B[rr];W[qq]
(;B[qs];W[rs]
(;B[ss];W[sq])
(;B[rq];W[sp];B[ss];W[sq])
(;B[sq];W[ps]
(;B[sp];W[ns])
(;B[os];W[rq])))
(;B[sq]
(;W[rs]
(;B[sp];W[sn]
(;B[ps];W[qs]
(;B[ss];W[sr]C[Correct - ko is the best black can get.RIGHT])
(;B[sr]))
(;B[ss];W[sr]LB[nn:A]C[Please play a ko threat at 'A'];B[nn];W[oo];B[ss];W[qs];B[ps];W[sr]C[This is close to correct, but worse than the correct solution because black has used up an extra ko threat.]))
(;B[ps];W[sp];B[qs];W[sn];B[ss];W[rq]))
(;W[sp];B[qs]
(;W[sn];B[rq]C[RIGHT])
(;W[rs];B[ss];W[sn];B[rq]C[RIGHT]))))
(;B[sq];W[rr]))