(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2] RU[Japanese]SZ[19]KM[0.00]TM[] PW[Weiß]PB[Schwarz]AW[mb][ob][mc][nc][pc][qc][qd][re]AB[kb][nb][lc][oc][ld][md][od][pd][qe][qf][rf]C[Black to play]PL[B] (;B[pb]CR[pb] ;W[na]CR[na] ;B[qb]CR[qb] ;W[rb]CR[rb] ;B[rc]CR[rc] ;W[rd]CR[rd] (;B[sb]CR[sb] (;W[sc]CR[sc] ;B[ra]CR[ra]C[This is a two step ko RIGHT CHOICE]) (;W[ra]CR[ra] ;B[sd]LB[sc:A]CR[sd]C[ This is a direct ko. White should have played S19 at A! RIGHT CHOICE])) (;B[ra]CR[ra] ;W[sb]LB[sc:A]CR[sb]C[Of course white doesn't allow a ko by playing T18 at A !])) (;B[rd]CR[rd] ;W[rc]CR[rc]C[This is not small, but black can do better]) (;B[rc]CR[rc]C[This only works if white makes a mistake ] (;W[rd]CR[rd]C[This is a mistake, black can reach the solution now. White shouldn't connect!] ;B[pb]CR[pb] ;W[na]CR[na] ;B[qb]CR[qb] ;W[rb]CR[rb] ;B[sb]CR[sb] (;W[sc]CR[sc] ;B[ra]CR[ra]C[After the white mistake earlier, the same position as in the solution is reached, a two step ko for black. CHOICE]) (;W[ra]CR[ra] ;B[sd]CR[sd]C[After the white mistake earlier, the same end position as in the solution is reached. W S19 was another mistake: W T17 is better! Now black has a direct ko. CHOICE])) (;W[rb]CR[rb]C[This W2 ist better than connecting] ;B[rd]CR[rd] ;W[pb]CR[pb]C[ White lost some points in the corner, but there is no danger of losing the whole group now. CHOICE])))