Believe it or not, but in the game white wasn't able to kill the black group! Please show him how to do it...
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[19]KM[1.00]TM[]
AW[cb][eb][fb][ac][bd][ed][fd][be][ce][de]AB[ca][ab][db][bc][dc][cd][dd]C[White to move!]PL[W]
(;W[ba]CR[ba]
;B[da]CR[da]
;W[bb]CR[bb]C[Black is dead! RIGHT])
(;W[bb]CR[bb]
;B[ba]LB[cc:B][ad:A]CR[ba]C[White can't play B because of the snapback, so this is only a ko! B A or B B instead of B B19 would allow white to play B19 himself and kill black as in the solution.])
(;W[ad]CR[ad]
;B[bb]CR[bb]C[The A 17 stone is not important!])
(;W[da]CR[da]
;B[ea]CR[ea]
(;W[ba]CR[ba]
;B[bb]CR[bb]C[This is only a ko!])
(;W[bb]CR[bb]
;B[ba]CR[ba]C[Only ko!])))
