(;
AB[bb][bc][ae][be][ce][de][ee][fd][gd][fb][gb]
AW[ab][cb][cd][bd][ad][dd]
C[Black plays.

Source:
    51st Judan Title promotional tsumego]
(;
B[db]
C[Fails.];
W[ba]
C[White has a defensive resource here.];
B[cc]
C[Black seems to be able to run out, but ...];
W[dc];B[ca];W[ac]
C[... White catches the stones in a liberty shortage.  White has a ko.]
)
    (;
    B[ba]
    C[Black takes away the vital point, but this move is bad timing.]
    (;
    W[dc]
    C[A funny-looking, but effective move to give White enough space to create a seki.];
    B[da]
    C[For example ...];
    W[eb];B[ea];W[ca];B[ec];W[db];B[fa];W[ac]
    )
        (;
        W[db]
        C[Looks normal, but the wrong defense!];
        B[dc]
        C[Black takes the vital point to reduce White's eye-space.];
        W[cc];B[da]
        C[White cannot both capture the marked stone and cut off the 3 corner stones.];
        W[ec];B[ca]
        )
    )
    (;
    B[dc]
    C[Correct.  Black takes the vital point.];
    W[cc];B[ba]
    C[Now Black has time to destroy the eye-space in the corner.]
    (;
    W[db];B[da]
    C[White cannot avoid a dead shape in the corner.]
    (;
    W[ec];B[ca]
    )
        (;
        W[ea];B[eb]
        )
        (;
        W[ca];B[ec]
        )
    )
        (;
        W[eb];B[ec];W[db];B[ea];W[da];B[ac]
        C[Now White is the one with the liberty shortage.];
        W[fa];B[ed]
        )
    )
)

