The "b" should be pretty easy, too...
Please find the best result for White!
(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]AB[aa][ab][ac][cc][ad][bd]C[White to move - what*s the best he can do?]PL[W]
(;W[dc]CR[dc]
(;B[db]CR[db]
;W[da]CR[da]
;B[ba]CR[ba]
(;W[bc]CR[bc]
;B[cd]CR[cd]C[Seki, White wins by one point (the prisoner) RIGHT])
(;W[ca]CR[ca]C[Seki, White wins by one point (the prisoner) RIGHT])
(;W[db]CR[db]C[Seki, White wins by one point (the prisoner) RIGHT])
(;W[dd]CR[dd]
;B[cd]CR[cd]
(;W[db]CR[db]C[Seki, White wins by one point (the prisoner) RIGHT])
(;W[bc]CR[bc]
;B[db]CR[db]
;W[dc]CR[dc]C[Black wins by one point!]))
(;W[cd]CR[cd]
;B[dd]CR[dd]
(;W[bc]CR[bc]
;B[db]CR[db]C[Black wins!])
(;W[db]CR[db]
;B[cd]CR[cd]C[Seki & Jigo!])))
(;B[ba]CR[ba]
;W[bc]CR[bc]
;B[cd]CR[cd]
;W[ca]CR[ca]C[White wins big!])
(;B[ca]CR[ca]
;W[ba]CR[ba]C[White wins!]))
(;W[db]CR[db]
;B[ba]CR[ba]
(;W[bc]CR[bc]
;B[ca]CR[ca]
;W[dc]CR[dc]
;B[cd]CR[cd]C[Seki!])
(;W[dc]CR[dc]
;B[ca]CR[ca]C[Seki & jigo!]))
(;W[bc]CR[bc]
;B[db]CR[db]
(;W[ca]CR[ca]
;B[dc]CR[dc]
;W[cd]CR[cd]
;B[dd]CR[dd]C[Seki, Black wins by one point (the prisoner)])
(;W[cd]CR[cd]
;B[dd]CR[dd]
;W[ca]CR[ca]C[Seki, Black wins by one point (the prisoner)])
(;W[dc]CR[dc]
;B[dd]CR[dd]
;W[ca]CR[ca]C[Seki, Black wins by one point (the prisoner)])))