(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PW[White]PB[Black to play and make a Ko to capture]AW[pp][qp][kq][lq][oq][qq][rq][mr][or][qr][ms][ns]AB[rn][mo][po][qo][np][op][rp][mq][nq][sq][lr][nr][rr]
(;B[ps]C[This looks like it might cause White problems.]
(;W[pr]C[However White makes this eye and is hard to attack.]
(;B[ls]
;W[os])
(;B[qs]
;W[kr]
;B[rs]
;W[os]))
(;W[qs]C[This also defends White by making an eye, but
also threatening the corner.]
(;B[ls]
;W[os]
;B[pr]
;W[pq]
;B[rs]
;W[sr])
(;B[sr]
;W[kr])))
(;B[ls]
;W[os]
;B[qs]
;W[pr]C[Again White can make an eye.]
;B[rs]
;W[kr])
(;B[os]C[This sacrifice does not help.]
;W[ps]
;B[ls]
;W[os])
(;B[qs]C[The correct attacking move is this hane.]
(;W[ps]C[White can try making the eye this way.]
(;B[ls]
;W[os]
;B[ss]
(;W[kr]
;B[pq]
;W[rs]C[White has to fight this ko.])
(;W[rs]C[White can also start the ko earlier.]))
(;B[ss]C[This is too early for the ko as white traps the Black stone to the left.]
;W[kr]
;B[pr]
;W[pq]))
(;W[pr]C[If White makes this eye to avoid the ko then there is shortage of liberties.]
;B[os]
;W[ps]
;B[ls]C[Connecting these three stones will cause White to lose all.]
;W[rs]C[However White can live in the corner at the expense of the
bottom edge stones.]
;B[os]
;W[sr])))
