(;GM[1]FF[4]SZ[19]CA[utf-8]AP[SmartGo One:2.0.1]GN[208bx]AB[np][nq][op][kq][mq][pq][pr][qq]AW[oo][pp][qp][rp][oq][or][rq][nr]C[Black to play and rescue three stones.]
(;B[ps]C[This is the correct play.]
(;W[qr]C[This is White's toughest response.];B[rr]
(;W[rs]
(;B[mr]C[Black must fill this liberty now.])
(;B[qs]C[This is wrong - White gets a ko.];W[sr]
(;B[ss])
(;B[mr];W[qr]))
(;B[sr]C[With this Black runs out of liberties];W[os];B[qs];W[qr]))
(;W[sr]
(;B[rs]C[Black must play here.])
(;B[qs]C[This is wrong - White gets a ko.];W[rs])))
(;W[qs]C[This is often a tesuji.];B[rr];W[os];B[qr];W[sr]
;B[rs]C[Playing atari below white 6 would be  self-atari, so Black wins the race.];W[sq];B[mr]))
(;B[mr]
;W[qr]C[Just filling a liberty fails.])
(;B[rr]C[This also fails.];W[ps];B[qr];W[sr];B[rs];W[sq])
(;B[qs]C[As does this.];W[rr];B[mr];W[qr]))
