This is a position from one of my games. My opponent, who was white, didn't find the solution. In a review afterwards a observer showed us the the correct variation.
(;AB[rs]AB[qr]AB[pr]AB[os]AB[nr]AB[nq]AB[np]AB[op]AW[oq]AW[or]AW[pq]AW[qq]AW[rq]AW[rr]AB[om]AB[pm]AB[ol]AB[pk]AB[qk]AB[rl]AB[rm]AW[pl]AW[ql]AW[qm]AW[qn]AW[rn]AW[qo]AW[qp]AB[ro]AB[sr]C[White to live.]AB[ok]AP[goproblems]
(;W[so];B[sq]
(;W[sp];B[qs];W[ss];B[sr])
(;W[qs];B[ps];W[sp];B[ns];W[ss];B[sr])
(;W[ps];B[qs];W[sp];B[ns];W[ss];B[sr]))
(;W[sq]
(;B[ns];W[ss]C[Correct, Ko.Black cannot connect at A to prevent KoRIGHT]LB[ps:A])
(;B[qs];W[ss]C[Ko, but black would't play this way.RIGHT])
(;B[ps];W[ss]C[Correct, Ko is best, black cannot play A to prevent ko.RIGHT]LB[qs:A]))
(;W[rp];B[sq]
(;W[sp];B[qs];W[ss];B[sr])
(;W[qs];B[ps];W[sp];B[ns];W[ss];B[sr])
(;W[ps];B[qs];W[sp];B[ns];W[ss];B[sr]))
(;W[sm];B[rk];W[sq]C[Correct, but playing T7 just waste some threatsRIGHT])
(;W[sp];B[ns]
(;W[sq];B[qs];W[ss];B[ps])
(;W[qs];B[ps]))
(;W[qs];B[ps];W[sq];B[ns];W[ss];B[qs])
(;W[ps];B[qs];W[sq];B[ns];W[ss];B[ps]))