(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PB[Black to play]AW[bn][fn][co][do][eo][go][bp][fp][hp][cq][fq][hq][br][hr][hs]AB[dp][ep][gp][dq][gq][cr][dr][fr][gr][gs]C[This is the problem position. Black to play.]
(;B[cs]C[If black tries to widen the eye space]
;W[es]C[White here stops the nose black needs between two eyes.])
(;B[eq]C[If black ataris the two stones...]
;W[es]C[.. white again takes the nose point]
;B[fo]
;W[fp]C[Capturing the two white stones doesn't make an eye
when white recaptures one.])
(;B[er]C[This move clearly fails to make two eyes,
white doesn't need to play hear again,
the black group is just dead.])
(;B[es]C[The diagonal move is right on the nose point.
This is the correct answer.]
(;W[cs]
;B[eq]C[If white plays on the edge then there is a second eye
on the second line]
;W[bs]
;B[ds])
(;W[eq]C[It looks a bit like white can push in...]
;B[cs]C[But when black makes the second edge eye...]
(;W[er]C[.. white here is self-atari!]
;B[fo]
;W[fp]
;B[fq]C[Three eyes.])
(;W[fo]C[Connecting is not fast enough]
;B[er]C[Two eyes.]))))
