(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[9]KM[0.00]
PB[Noir]AW[ad][bd][cd][de][df][eg][eh][di][ei]AB[af][cf][bh][dh][ci]
;B[]
(;W[ah]
(;B[ai]
(;W[be]C[This incredible exchange is necessary]
(;B[bf]
;W[cg]
;B[bg]
(;W[ch]C[the other hard move]
;B[dg]
;W[ch]
;B[cg]
;W[bi]C[Ko, black must find the first threat])
(;W[dg]
;B[ch]
;W[bi]
;B[ag]C[The ko iscrushed]))
(;B[ag]
;W[bg]
(;B[bf]
;W[cg]C[false eyes])
(;B[cg]
;W[bf]C[false eyes])))
(;W[cg]
;B[bg]
;W[ch]
;B[dg]
;W[ch]
;B[cg]
;W[bi]
;B[ch]
;W[ai]
;B[ag]
;W[ai]
;B[be]C[Noir vit ]))
(;B[ag]
;W[cg]
;B[bg]
;W[dg]
;B[ch]
;W[ai]C[death without ko])
(;B[bg]
;W[dg]
;B[ai]
;W[bi]
(;B[ch]
;W[ai]
;B[ag]
;W[ai]
;B[be]
;W[ce]C[death without ko])
(;B[fd]
;W[fe]
;B[ai]
;W[ch]C[no ko])))
(;W[cg]
;B[bg]
;W[bf]
(;B[be]
;W[ce]
(;B[ch]
;W[bf]C[looks like a favorable ko for white, but]
;B[ai]C[well-hidden move, working as a inner ko threat]
;W[ag]
;B[cf]C[so this is a better ko for black than the correct answer])
(;B[bf]
(;W[ah]
;B[ai]
(;W[dg]
;B[ch]
;W[bi]C[ko,  good for white])
(;W[bi]
;B[ch]
;W[dg]
;B[ai]C[ko , good for black]))
(;W[dg]
;B[ah])))
(;B[ag]
;W[ai]
;B[be]
;W[dg]
;B[ch]C[already dead])))