This is really an easy problem! How should White answer the marked stone?
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[7]KM[0.50]TM[]
AW[ca][fa][ab][cb][eb][cc][ec][fc][ad][bd][ed][gd][fe]AB[da][ea][db][gb][dc][cd][dd][ae][be][de][ee][cf][ef][ff]TR[gb]C[No komi, no prisoners - White to play and win!]PL[W]
(;W[gf]CR[gf]
(;B[fg]CR[fg]
(;W[fb]CR[fb]
;B[gg]CR[gg]
;W[ge]CR[ge]C[White wins by one point! RIGHT])
(;W[ge]CR[ge]
;B[gg]CR[gg]
(;W[fb]CR[fb]C[White wins by one point! RIGHT])
(;W[gc]CR[gc]C[White wins by one point! RIGHT]))
(;W[gc]CR[gc]
;B[gg]CR[gg]
;W[ge]CR[ge]C[White wins by one point! RIGHT]))
(;B[fb]CR[fb]
;W[gc]CR[gc]
;B[ga]CR[ga]
;W[fa]CR[fa]
;B[fg]CR[fg]C[White wins by two points! RIGHT]))
(;W[fb]CR[fb]
;B[gf]CR[gf]
;W[ge]CR[ge]C[Black wins by one point!])
(;W[gc]CR[gc]
;B[gf]CR[gf]
;W[ge]CR[ge]C[Black wins by one point!]))