(;
AB[rb][mb][rd][qd][pd][od][nd][nc][nb]
AW[ra][oc][pc][qc][rc][sc]
C[Black plays.]
(;
B[qb]
C[Black seems able to run out, but ...];
W[sb]
C[... White can calmly take the 2-1 point for an eye.]
(;
B[pb]
C[Black cannot connect out.];
W[ob];B[oa];W[pa]
C[White catches the 3 stones in a snapback.]
)
    (;
    B[qa]
    C[No better.];
    W[pb];B[sa];W[pa]
    )
)
    (;
    B[qa]
    C[Also fails.  White now has multiple ways to live.];
    W[pa]
    C[For example ...];
    B[sa];W[qb];B[ra];W[sb];B[ra];W[ob]
    )
    (;
    B[sb]
    C[Correct.  To kill White without a ko, Black has to keep White from taking the 2-1 point.];
    W[ob]
    C[Now White's only hope is to expand the eye-space hoping for at least a seki.]
    (;
    B[qb]
    C[Also the only move.];
    W[pa]
    (;
    B[na]
    C[White seems to have a seki, but Black has this innocent looking move.];
    W[oa];B[qa]
    LB[sd:A]
    C[White has a liberty shortage, and can do nothing to stop the atari at A.]
    )
        (;
        B[sd]
        C[Fails.];
        W[qa]
        C[White lives in seki.]
        )
    )
        (;
        B[oa]
        C[Bad timing.];
        W[pa];B[qb];W[na]
        (;
        B[ma];W[qa]
        C[Black only has a ko.]
        )
            (;
            B[qa]
            C[This move doesn't work, because ...];
            W[pb]
            C[... White has an extra outside liberty.]
            )
        )
    )
)

