(;AB[rq]AB[rp]AB[qq]AB[qr]AB[qs]AB[so]AB[ro]AW[sn]AW[rn]AW[qo]AW[qp]AW[pq]AW[pr]AW[ps]AW[op]AW[qn]AP[goproblems] (;W[sr] (;B[sq];W[rs]C[Seki. Neither side can play S2; the other side would capture all stones.RIGHT]MA[rr]) (;B[rr];W[sq] (;B[ss];W[rs]C[Black takes a huge risk by starting this ko. Black can gain just 5 points compared to the seki, and it will cost Black 2 extra moves. Losing the ko would lose Black 18 points compared to the seki.RIGHT]) (;B[on];W[ss]C[Black cannot ignore T3; White will play here and kill Black. This is not seki; White can play S1 and start a ko fight at the end of the game when there are no more threats. Under Japanese rules this is bent 4 in the corner and Black is dead by default.RIGHT];B[pn];W[rs];B[sp];W[sr];B[ss];W[rs]C[Tke ko in effect. White chooses the moment to start this (if need be).RIGHT]))) (;W[sq];B[sr]) (;W[rs];B[sr]) (;W[rr];B[sr]) (;W[ss];B[sr]) (;W[sp];B[sr]))