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][bd][dd]AB[ab][db][ac][dc]C[No komi, no prisoners - what is the best Black can do?]PL[B]
(;B[bc]CR[bc]
;W[cc]CR[cc]
;B[cd]CR[cd]
;W[aa]CR[aa]
(;B[ba]CR[ba]
;W[dd]CR[dd]
;B[ca]CR[ca]
;W[da]CR[da]
;B[db]CR[db]C[Three prisoners each - Seki & Jigo :) RIGHT])
(;B[ad]CR[ad]
;W[bd]CR[bd]C[White wins]))
(;B[cc]CR[cc]
;W[bc]CR[bc]C[White wins])
(;B[cd]CR[cd]
;W[bc]CR[bc]C[White wins]))