This is a problem that occurred in one of my games.
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PW[White]PB[Black]AW[am][an][bo][do][ap][cp][dp][cq][br]AB[ck][bl][bn][cn][dn][en][co][eo][ep][eq][dr][er]C[Black to get the best result.]
(;B[bs]
(;W[cs]
;B[cr]
(;W[as]
(;B[bq]
;W[aq]
;B[ds]
;W[bp]
;B[bs]C[Black gets a ko for the life of White's group. White can get a better ko in other variations (see branching paths). RIGHT])
(;B[aq]
;W[bq])
(;B[ds]
;W[bq]))
(;W[bq]
;B[ar]
;W[as]C[Black gets a ko for the life of White's group. White starts the ko. RIGHT]))
(;W[bq]
;B[ar]
;W[cs]
;B[cr]
;W[as]C[Black gets a ko for the life of White's group. White starts the ko. RIGHT]))
(;B[aq]
;W[cr]
(;B[cs]
;W[bs])
(;B[ar]
;W[cs])
(;B[bq]
;W[cs]))
(;B[bq]
;W[cr]
(;B[aq]
;W[cs])
(;B[cs]
;W[bs]))
(;B[cr]
;W[bs]
(;B[bq]
;W[aq])
(;B[aq]
;W[bq])))