(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PB[Black to play]AW[rn][po][qo][so][pp][rp][oq][sq][or][pr][rr]AB[np][op][qp][mq][pq][qq][rq][nr][qr][qs]C[This is the problem position. Black to play]
(;B[os]C[Black cannot win the semeai directly]
;W[rs]
;B[ps]
;W[ns])
(;B[nq]C[This doesn't work]
;W[rs]
;B[os]
;W[ps])
(;B[ps]C[Nor this]
;W[os]
;B[ns]
;W[rs])
(;B[sr]C[This move is often a tesuji]
(;W[ss]C[But white can simple capture and black loses a point.]
;B[nq]C[He can now play here and win the semeai - white has
to play three times before the black stones can be put
in atari.])
(;W[rs]C[Black cannot expect white go here as the kos
are too dangerous for white to risk everything,
so white will just capture the one stone as before.]
(;B[ss]
;W[rr]
;B[sp])
(;B[sp])))
(;B[rs]C[Simply playing here is the correct move to win the
semeai as white is short of liberties to play the 
corner point now.]
(;W[ps]
;B[sr]C[This way black lives in the corner])
(;W[sr]C[So white must play here - though it may be quite
small for white to do so immediately.]
(;B[nq]C[And this wins the semeai - as white would
play into self-atari if he tries to atari black.]
;W[sp]C[So white has to connect here first.]
;B[os]
;W[ss]
;B[ps])
(;B[os]C[This would also win the semeai -
but leaves behind a worse shape
if black ever has to abandon the black stones
in a ko fight.])
(;B[ps]C[Likewise.]))))
