(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PB[Black to play]AW[fo][go][dp][ep][gp][eq][fq][gq][cr][dr][gr][gs]AB[fn][gn][co][do][eo][ho][cp][hp][bq][dq][hq][br][er][hr][hs]C[This is the problem position. Black to play.]
(;B[es]C[This is the tesuji. White cannot live now.]
(;W[cq]C[If white takes the stone...]
;B[cs]C[Then black connects underneath bacause white oon the edge is self-atari, and the second eye is false.])
(;W[ds]C[This clearly fails.]
;B[cq])
(;W[fr]
;B[cq]C[Black simply connects and white cannot
atari from either side without self-atari.]))
(;B[cq]
;W[es]
;B[cs]
;W[fr]C[This is easy eyes for white])
(;B[fs]C[This is sometimes a clever move, as white cannot atari the 
last black stone without self-atari.]
(;W[cs]C[white can get a ko now.]
;B[cq]
;W[es]
;B[ds])
(;W[cq]C[But this is better for white]
(;B[ds]C[Or this sets up another ko]
(;W[cs]
;B[bs]
(;W[es])
(;W[dq]C[But if white connects it's a ko black can never win.]))
(;W[fr]C[Or white can now play here and live.]))
(;B[cs]C[This is a mistake for black.]
(;W[ds]C[This is not a seki.]
;B[bs]
;W[dq]
;B[bp]
;W[es]C[white has one eye so beats no eyes of black.])
(;W[fr]C[in fact white can play here now and live easily.])))))
