(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2] RU[Japanese]SZ[4]KM[0.00] PW[Weiß]PB[Schwarz]AW[db][cc]AB[bb][ad][bd][cd]C[White to play - what's the best he can do?]PL[W] (;W[bc]CR[bc] ;B[ac]CR[ac] (;W[ab]CR[ab] ;B[aa]CR[aa] (;W[dd]CR[dd] (;B[cb]CR[cb]C[Taking the ko is worse (see variations)] ;W[ab]CR[ab] ;B[ac]CR[ac] (;W[bd]CR[bd] ;B[ca]CR[ca]C[Seki! White wins by 2 points (4 prisoners against 2) RIGHT]) (;W[ca]CR[ca] ;B[bd]CR[bd]C[Seki! White wins by 2 points (4 prisoners against 2) RIGHT])) (;B[dc]CR[dc] ;W[cb]CR[cb] ;B[ca]CR[ca] ;W[dd]CR[dd]C[Black is completely lost])) (;W[cb]CR[cb] ;B[ca]CR[ca]C[It's to late to start the ko now - Black wins by one point (the prisoner)]) (;W[ca]CR[ca] ;B[cb]CR[cb] ;W[dc]CR[dc]C[Black wins by one point (the prisoner)])) (;W[cb]CR[cb] ;B[ca]CR[ca]C[White can't start the ko anymore and will lose by one point (he has to sacrifice a stone to prevent a black eye)]) (;W[ca]CR[ca] (;B[ba]CR[ba] ;W[ab]CR[ab] ;B[aa]CR[aa] ;W[cb]CR[cb]C[B4??! Stupid Black :) Instead of this big mistake, he should have played B C3 (see variations).]) (;B[cb]CR[cb] ;W[dc]CR[dc] (;B[ba]CR[ba] ;W[ab]CR[ab]C[B4??! Stupid, stupid Black :) Of course, if Black plays c3 himself instead, it's a seki (see variations)]) (;B[ab]CR[ab] ;W[ba]CR[ba]C[Seki & jigo!]))) (;W[dd]CR[dd] (;B[ab]CR[ab] ;W[cb]CR[cb] ;B[ca]CR[ca] ;W[ba]CR[ba] ;B[dc]CR[dc]C[Black wins!]) (;B[dc]CR[dc] ;W[cb]CR[cb] ;B[ca]CR[ca] ;W[dd]CR[dd] ;B[ab]CR[ab] ;W[ba]CR[ba] ;B[dc]CR[dc]C[Black wins!]))) (;W[cb]CR[cb] ;B[bc]CR[bc] ;W[ba]CR[ba] (;B[ab]CR[ab] ;W[ca]CR[ca]C[Seki & Jigo, but both can do better!]) (;B[ca]CR[ca] ;W[da]CR[da] ;B[ab]CR[ab]C[White is lost - 'one eye beats no eye'!])) (;W[ca]CR[ca] ;B[bc]CR[bc] (;W[cb]CR[cb] ;B[ba]CR[ba] ;W[ab]CR[ab] ;B[dd]CR[dd] ;W[ac]CR[ac] ;B[aa]CR[aa] ;W[ab]CR[ab] ;B[ac]CR[ac]C[Maybe Black can also play d2 instead of d1, but as usual I am not sure about the rules :) Anyway, this is a three point win for black.]) (;W[ba]CR[ba] ;B[cb]CR[cb] ;W[dc]CR[dc] ;B[ab]CR[ab]C[Black wins!])))