(;GM[1]FF[4]SZ[19]AP[SmartGo:0.8.8]CA[UTF-8]
GN[182bx]
AB[np:sp][lq][nq][qq][mr][pr:ps]
AW[oq:or][pq][rq:rr][sq][nr][qr]
C[Black to play and kill.]
(;B[os]
C[Black can play here to trap four stones but the corner lives.];W[qs];B[ns]
;W[ss])
(;B[qs]
C[This is not fast enough.];W[rs])
(;B[sr]
C[This is the tesuji that leaves White short of liberties.];W[ss];B[qs]
C[It is self-atari for White on both sides.])
(;B[rs];W[ss];B[sr]
C[This is a Ko which is a failure for Black.]))

