(;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.]))))