(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2] RU[Japanese]SZ[4]KM[0.00] PW[Weiß]PB[Schwarz]AW[cc][dd]AB[db][bc][ad][bd]C[White to play - what's the best he can do?]PL[W] (;W[bb]CR[bb] (;B[cb]CR[cb] (;W[ca]CR[ca] ;B[ab]CR[ab] ;W[ba]CR[ba]C[Seki & Jigo! Four groups on a 4x4 board.... B A3 was necessary, if White can play there, Black will have to sacrifice a stone, giving White a win. RIGHT]) (;W[ab]CR[ab] ;B[dc]CR[dc]C[W A3 is too slow])) (;B[dc]CR[dc] ;W[cb]CR[cb] ;B[cd]CR[cd] ;W[ab]CR[ab]C[White wins])) (;W[cb]CR[cb] (;B[bb]CR[bb] (;W[ba]CR[ba] ;B[cd]CR[cd] ;W[ca]CR[ca] ;B[dc]CR[dc] ;W[ab]CR[ab]C[Seki, Black wins by one point (the prisoner)]) (;W[ca]CR[ca] ;B[ba]CR[ba] ;W[ab]CR[ab] ;B[cd]CR[cd]C[Black wins big])) (;B[cd]CR[cd] ;W[bb]CR[bb] ;B[dc]CR[dc] ;W[ab]CR[ab]C[White wins, but B C1 was a mistake! This move should have been at B3.])))