(;AW[pq]AW[qo]AW[oq]AW[mq]AW[qp]AB[pr]AB[qq]AB[rq]AW[rp]TR[rp]AP[goproblems]
(;B[rr]C[];W[or]
(;B[qs]C[RIGHT])
(;B[ps];W[os]
(;B[qs]C[RIGHT])
(;B[rs]C[RIGHT])
(;B[ss];W[qs])
(;B[qr];W[sq])
(;B[sq];W[rs]
(;B[ss];W[sr]C[Ko])
(;B[qs];W[qr])
(;B[qr];W[ss]))
(;B[sr];W[rs]))
(;B[rs];W[ps])
(;B[os];W[qs]
(;B[ps];W[ns]
(;B[qr];W[sq])
(;B[rs];W[qr])
(;B[sq];W[qr]))
(;B[rs];W[ps]
(;B[qr];W[ps])
(;B[ns];W[ms]
(;B[qr];W[ps])
(;B[nr];W[mr])
(;B[mr];W[nr])))
(;B[ns];W[ps]
(;B[rs];W[ms]
(;B[qr];W[ps])
(;B[nr];W[mr])
(;B[mr];W[nr]))
(;B[qr];W[ms]
(;B[rs];W[ps])
(;B[nr];W[mr]))
(;B[sq];W[qr]))
(;B[sq];W[ps])
(;B[qr];W[ps]
(;B[rs];W[ps])
(;B[ns];W[ms]
(;B[rs])
(;B[nr];W[mr]))))
(;B[sq];W[ps]C[This leads to ko, black can do better.])
(;B[sr];W[qs]))
(;B[or];W[rr]
(;B[qr];W[sq]
(;B[nq];W[np];B[nr];W[lr])
(;B[nr];W[lr])
(;B[mr];W[lr]
(;B[nr];W[lp])
(;B[nq];W[np];B[nr];W[lp])
(;B[ms];W[lp];B[qs];W[sr];B[nq];W[np];B[nr];W[os]))
(;B[qs];W[sr])
(;B[rs];W[sr])
(;B[sr];W[ss];B[qs];W[sp]))
(;B[sq];W[qr]))
(;B[rs]C[This lives, but with less points than the correct solution.]
(;W[sq]C[CHOICE]
(;B[sr];W[qr]
(;B[rr];W[or]
(;B[qs]C[RIGHT])
(;B[ps]C[RIGHT]))
(;B[sp];W[ps])
(;B[ps];W[rr]))
(;B[or];W[rr];B[qr];W[sr])
(;B[rr];W[sr]
(;B[or];W[nr])
(;B[qs];W[or]))
(;B[qr];W[sr])
(;B[ps];W[rr]))
(;W[qr];B[rr]C[RIGHT])
(;W[or];B[ps]C[RIGHT]))
(;B[sr];W[rs]
(;B[qs]C[See problem 4779 for how white can kill.])
(;B[or];W[qr]C[If the marked stone were absent, black might be able to get a second eye by crawling out. However, if this were the case, white would have blocked at P2 instead of S4.]TR[mq]))
(;B[sq];W[or]
(;B[rs];W[ps])
(;B[ps];W[rs]C[This leads to ko, black can do better.])
(;B[qs];W[rr])
(;B[rr];W[ps]C[This leads to ko, black can do better.]))
(;B[qs];W[sr]
(;B[rr];W[sq]C[White gets a ko this way, black can do better.])
(;B[sq];W[rr])
(;B[rs];W[or])
(;B[or];W[rr]))
(;B[qr];W[or])
(;B[ps];W[sr]
(;B[sq];W[rr];B[qr];W[rs])
(;B[rr];W[sq])
(;B[rs];W[sq])))