(;AP[goproblems]AW[eb]AW[db]AW[cb]AW[bb]AW[ac]AW[cc]AW[ea]AB[fa]AB[fb]AB[ec]AB[dc]AB[gc]AB[cd]AB[bd]AB[bc]AB[be]C[Black to kill.](;B[ab](;W[aa]C[CHOICE](;B[ca]C[RIGHT])(;B[ad];W[ca];B[ab]C[Only ko.]))(;W[ca]C[CHOICE](;B[ad]C[RIGHT])(;B[aa];W[ba](;B[ab];W[aa]C[RIGHT])(;B[ad];W[ab]))))(;B[ba];W[ca](;B[ab];W[aa])(;B[ad];W[ab]))(;B[ca](;W[ba]C[CHOICE](;B[ab]C[RIGHT])(;B[ad];W[ab]))(;W[ab]C[CHOICE](;B[ba]C[RIGHT])(;B[ad];W[ba])(;B[da];W[ba])(;B[aa];W[ba])))(;B[aa];W[ab])(;B[ad];W[ab]))