(;AB[rr]AB[rq]AB[sq]AB[pr]AB[qp]AW[rp]AW[ro]AW[qo]AW[po]AW[pp]AW[oq]AW[or]AW[os]AW[sr]C[Black to live]AP[goproblems](;B[ps];W[rs](;B[qs];W[qq];B[qr]C[CHOICERIGHT])(;B[qr];W[ss])(;B[ss](;W[op]C[White plays a ko threat. Play at A (P5) to answer it or play in the corner if necessary.CHOICE]TR[oo](;B[oo]C[FORCE];W[sr](;B[qs];W[qq](;B[qr]C[RIGHT])(;B[ss];W[qr])(;B[pq];W[qr]))(;B[qq];W[pq];B[ss]C[Ko])(;B[qr];W[ss]))(;B[qs]C[Unnecessary.FORCE])(;B[qq]C[Unnecessary.FORCE])(;B[pq]C[Unnecessary.FORCE])(;B[qr]C[Unnecessary.FORCE]))(;W[qq]C[CHOICE];B[qr];W[sr];B[qs]C[RIGHT]))(;B[qq];W[pq];B[ss]C[Ko.]))(;B[pq];W[ps];B[qs];W[qq];B[qr];W[ss]C[Black has just one eye and dies])(;B[ss];W[qs];B[ps];W[qr])(;B[qr];W[ps])(;B[qq];W[ps];B[qs];W[pq];B[ss];W[qr]C[ko])(;B[qs];W[qq](;B[ss];W[qr])(;B[qr];W[ss])))