In this not too difficult problem, the difference between a good move and the best one is two points. It's also the difference between victory and defeat!
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[7]KM[0.50]
AW[da][eb][dc][dd][ed][be][ce][ee][ef]AB[ca][cb][cc][bd][cd][de][af][df][dg]C[No komi, no prisoners - Black to play and win!]
(;B[bg]CR[bg]
;W[eg]CR[eg]
;B[db]CR[db]
;W[ea]CR[ea]C[Black wins by one point! RIGHT])
(;B[cf]CR[cf]
;W[eg]CR[eg]
(;B[bf]CR[bf]
;W[db]CR[db]C[White wins by one point])
(;B[ae]CR[ae]
;W[db]CR[db]C[White wins by one point!]))
(;B[bf]CR[bf]
;W[eg]CR[eg]
(;B[cf]CR[cf]
;W[db]CR[db]C[White wins by one point!])
(;B[ae]CR[ae]
;W[db]CR[db]C[White wins by one point!]))
(;B[ae]CR[ae]
;W[eg]CR[eg]
(;B[cf]CR[cf]
;W[db]CR[db]C[White wins by one point!])
(;B[bf]CR[bf]
;W[db]CR[db]C[White wins by one point!]))
(;B[eg]CR[eg]
;W[cf]CR[cf]C[White will capture the black stones!])
(;B[db]CR[db]
;W[cf]CR[cf]C[The four black stones are lost!]))