Please find the best result for Black!
(japanese rules)
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[4]KM[0.00]
PW[Weiß]PB[Schwarz]AW[bb][cb][dc]AB[aa][ab][ac][bd][cd][dd]C[Black to play - what's the best he can do?]
(;B[db]CR[db]
(;W[bc]CR[bc]
;B[cc]CR[cc]
;W[ca]CR[ca]C[Seki, Black wins by one point ( 1 prisoner against 0) RIGHT])
(;W[cc]CR[cc]
;B[ca]CR[ca]
;W[da]CR[da]
;B[ba]CR[ba]C[White is lost])
(;W[da]CR[da]
;B[cc]CR[cc]
;W[db]CR[db]
(;B[ba]CR[ba]C[White is lost ])
(;B[bc]CR[bc]C[White is lost])))
(;B[bc]CR[bc]
;W[ba]CR[ba]C[Black is dead!])
(;B[cc]CR[cc]
;W[db]CR[db]
(;B[ba]CR[ba]
;W[bc]CR[bc]C[Black is dead!])
(;B[ca]CR[ca]
;W[bc]CR[bc]C[Black is dead!]))
(;B[ca]CR[ca]
;W[ba]CR[ba]
;B[cc]CR[cc]
;W[db]CR[db]C[Seki, White wins by one point (1 prisoner against 0)])
(;B[ba]CR[ba]
;W[ca]CR[ca]
;B[cc]CR[cc]
;W[db]CR[db]C[Seki, and jigo!]))