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][cc]AB[aa][ba][ca][bd][cd][dd]C[Black to play - what's the best he can do?]
(;B[bc]CR[bc]
;W[cb]CR[cb]
;B[ab]CR[ab]
;W[ac]CR[ac]
;B[ad]CR[ad]
;W[db]CR[db]C[Seki, Black wins by one point (the prisoner). RIGHT])
(;B[cb]CR[cb]
;W[bc]CR[bc]
;B[dc]CR[dc]
;W[db]CR[db]
;B[da]CR[da]
;W[ac]CR[ac]C[Seki, Black wins by one point (the prisoner). RIGHT])
(;B[dc]CR[dc]
;W[cb]CR[cb]
;B[db]CR[db]
;W[ab]CR[ab]
;B[da]CR[da]
;W[ac]CR[ac]C[Seki & jigo!])
(;B[ab]CR[ab]
;W[bc]CR[bc]
;B[ac]CR[ac]
;W[dc]CR[dc]
;B[ad]CR[ad]
;W[db]CR[db]C[Seki & jigo!])
(;B[db]CR[db]
;W[cb]CR[cb]
;B[dc]CR[dc]
;W[ab]CR[ab]
;B[da]CR[da]
;W[ac]CR[ac]C[Seki & jigo!])
(;B[ac]CR[ac]
;W[bc]CR[bc]
;B[ab]CR[ab]
;W[dc]CR[dc]
;B[ad]CR[ad]
;W[db]CR[db]C[Seki & jigo!]))