(;
AB[da][eb][cc][dc]
AW[fb][gb][ec][bd][cd][dd][fd]
C[Black plays.]
(;
B[ab]
C[A vital point, but doesn't fix Black's weakness.];
W[ba];B[bb];W[fa];B[ca];W[db]
C[Classic tesuji.  Black dies.]
)
    (;
    B[bb]
    C[Looks like the vital point, but amazingly, Black's weakness is still open.];
    W[fa]
    C[This calm descent kills Black.]
    (;
    B[bc];W[ac];B[ab];W[ba];B[ca];W[db]
    )
        (;
        B[ca];W[bc];B[ab];W[db]
        )
    )
    (;
    B[cb]
    C[Correct.  Black makes a solid eye.  White now has several ways to make a ko for Black's second eye.]
    (;
    W[fa]
    C[One possibility.];
    B[ea];W[bb];B[bc];W[ac];B[ab];W[aa];B[ba]
    C[White takes the ko 1st.]
    )
        (;
        W[ab];B[ac];W[bc];B[bb];W[ba];B[aa];W[ea]
        C[White has a local ko threat.]
        )
        (;
        W[bb]
        C[Another possibility.];
        B[bc];W[ac];B[ab];W[aa];B[ba]
        C[White takes the ko 1st.]
        )
    )
)

