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]AB[aa][ba][dc][ad][dd]C[White to play - what's the best he can do?]PL[W]
(;W[cb]CR[cb]
;B[bc]CR[bc]
(;W[cc]CR[cc]
(;B[bb]CR[bb]
;W[cd]CR[cd]
;B[ca]CR[ca]
;W[db]CR[db]
;B[bd]CR[bd]C[Seki, White wins by two points (2 prisoners against 0) RIGHT CHOICE ])
(;B[cd]CR[cd]
(;W[bb]CR[bb]
;B[ab]CR[ab]
(;W[db]CR[db]
;B[ca]CR[ca]
;W[bd]CR[bd]
;B[cd]CR[cd]C[Seki, White wins by 2 points (3 prisoners against 1) RIGHT CHOICE])
(;W[ca]CR[ca]
;B[db]CR[db]
;W[ac]CR[ac]
;B[ab]CR[ab]C[Seki, White wins by two points (3 prisoners against 1) RIGHT CHOICE]))
(;W[db]CR[db]
;B[bb]CR[bb]
;W[bd]CR[bd]
;B[cd]CR[cd]
(;W[ca]CR[ca]
;B[dc]CR[dc]
;W[dd]CR[dd]
;B[bd]CR[bd]
(;W[ac]CR[ac]
;B[dc]CR[dc]C[Black wins])
(;W[ab]CR[ab]
;B[dc]CR[dc]C[Black wins]))
(;W[ac]CR[ac]
;B[bd]CR[bd]
;W[ca]CR[ca]
;B[ab]CR[ab]C[White wins by one point (3 prisoners against 2). Not bad, but 1 point worse than the correct solution!]))))
(;W[bb]CR[bb]
(;B[cc]CR[cc]
;W[ab]CR[ab]
;B[db]CR[db]
;W[ca]CR[ca]
;B[ac]CR[ac])
(;B[ab]CR[ab]
(;W[cc]CR[cc]
;B[cd]CR[cd]
(;W[db]CR[db]
;B[ca]CR[ca]
;W[bd]CR[bd]
;B[cd]CR[cd]C[Seki, White wins by two points (3 prisoners against 1) RIGHT CHOICE])
(;W[ca]CR[ca]
;B[db]CR[db]
;W[ac]CR[ac]
;B[ab]CR[ab]C[Seki, White wins by two points (3 prisoners against 1) RIGHT CHOICE]))
(;W[ca]CR[ca]
;B[cc]CR[cc]
;W[ac]CR[ac]
;B[ab]CR[ab]
(;W[bd]CR[bd]
;B[ac]CR[ac]
;W[db]CR[db]
;B[cd]CR[cd]C[Seki, White wins by one point (3 prisoners against 2). Not bad, but one point worse than the correct solution!])
(;W[db]CR[db]
;B[ba]CR[ba]
;W[aa]CR[aa]
;B[ac]CR[ac]
(;W[bd]CR[bd]
;B[ba]CR[ba]C[Black wins])
(;W[cd]CR[cd]
;B[ba]CR[ba]C[Black wins]))))))
(;W[bc]CR[bc]
;B[cb]LB[ac:A][bd:B]CR[cb]C[If you want to play A or B now, please choose A.]
;W[ac]CR[ac]
(;B[cc]CR[cc]
;W[bd]CR[bd]
;B[bb]CR[bb]
;W[da]CR[da]
;B[ab]CR[ab]
(;W[ca]CR[ca]
;B[db]CR[db]
(;W[ca]CR[ca]
;B[da]CR[da]C[Seki, Black wins by 2 points (3 prisoners against 1)])
(;W[da]CR[da]
;B[ca]CR[ca]C[Seki, Black wins by 2 points (3 prisoners against 1)]))
(;W[db]CR[db]
;B[ca]CR[ca]
(;W[da]CR[da]
;B[db]CR[db]C[Seki, Black wins by 2 points (3 prisoners against 1)])
(;W[db]CR[db]
;B[da]CR[da]C[Seki, Black wins by 2 points (3 prisoners against 1)])))
(;B[bd]CR[bd]
(;W[cd]CR[cd]
;B[cc]CR[cc]
;W[bd]CR[bd]
;B[bb]CR[bb]C[Black wins! But B B1 was a mistake, and only succeeded because White answered with a mistake on his own (W C1 instead of W C2).])
(;W[cc]CR[cc]
;B[db]CR[db]
;W[cd]CR[cd]
;B[bb]CR[bb]C[Seki, White wins by two points (2 prisoners against 1). B B1 was a mistake, and if White answers correctly with W c2 instead of W C1, he can win.]))))