(;AP[goproblems]AB[qr]AB[qq]AB[pq]AB[oq]AB[op]AB[lp]AB[lq]AB[lr]AB[ls]AW[ks]AW[kr]AW[kq]AW[kp]AW[ko]AW[lo]AW[mo]AW[no]AW[oo]AW[pp]AW[qp]AW[rq]AW[rr]AW[ro]AW[nq]C[Black to live.](;B[nr];W[mq](;B[mr](;W[ps]C[CHOICE](;B[qs];W[ns](;B[or];W[os]C[Seki.RIGHT])(;B[os];W[or];B[pr];W[os]))(;B[os];W[qs]))(;W[qs]C[Wrong white move. Black is alive with points.];B[ps](;W[or];B[os])(;W[rs];B[or])(;W[ns];B[or])))(;B[os];W[mr](;B[pr];W[qs])(;B[qs];W[pr]))(;B[ps];W[mr](;B[or];W[ns])(;B[ns];W[or])))(;B[np]C[Pushing at O4 reduces black liberties. In some situations this is a bad idea...];W[mp](;B[nr];W[mq];B[mr];W[qs];B[ps];W[or](;B[pr];W[os])(;B[rs];W[ns])(;B[ns];W[pr]))(;B[mq];W[nr]TR[ls]TR[lr]TR[lq]TR[lp]TR[mq]C[The tirangle stones are captured.]))(;B[or];W[nr];B[np];W[mp](;B[mq];W[ms])(;B[ns];W[mq]))(;B[mq];W[nr];B[np];W[mp])(;B[os];W[nr];B[np];W[mp];B[mq];W[ms])(;B[mp];W[np])(;B[mr];W[nr])(;B[ps];W[nr]))