(;GM[1]FF[4]SZ[19]PL[B]C[Black to kill.]
AW[ab][bb][cb][db][da]AB[ac][bc][cc][dc][ec][eb][ea]
(;B[ba]TE[1]C[Correct: the vital point.]
(;W[aa];B[ca])
(;W[ca];B[aa]C[White has only one eye.]))
(;B[aa]BM[1]C[Wrong: White lives.];W[ba])
(;B[ca]C[Wrong.];W[ba]))