(;AW[ro]AW[lp]AW[np]AW[op]AW[pp]AW[qp]AW[kq]AW[mq]AW[rq]AW[sq]AW[jr]AW[lr]AW[mr]AW[nr]AW[qr]AW[ks]AB[nq]AB[oq]AB[pq]AB[qq]AB[or]AB[rr]AB[sr]AB[ls]AB[ms]AB[ns]AB[os]AB[ps]TR[qr]C[White has played the marked stone. Black to live.] (;B[rs];W[qs];B[pr];W[qr];B[qs]C[Right. Black was already alive after B S1. The last two moves from white should not be played but held in reserve as ko threats.RIGHT]) (;B[qs];W[rs] (;B[pr];W[qr]C[Oh no.]) (;B[ss];W[rs]C[Oh no.])) (;B[ss]C[White can tenuki and black remains dead.]) (;B[pr];W[qs]C[Oh no.]) (;B[rp];W[sp]C[This was a wasted ko threat.]))