(;
AB[pb][nb][nc][rd][qd][pd][od][nd]
AW[ob][rc][qc][pc][oc][lc]
C[Black plays.

Source:  a mid-kyu problem from Maeda's Tsumego Vol. 2];
B[oa]
C[Simple is correct.];
W[pa]
C[Best defense.];
B[qa]
(;
W[qb];B[sc]
LB[sb:A]
C[Now with no outside liberties, White cannot defend at A.];
W[pa]
C[Does White have a ko for life?];
B[sb]
C[No.]
(;
W[rb];B[ra];W[sa];B[ra]
C[White has only one eye.]
)
    (;
    W[na];B[mb]
    )
)
    (;
    W[ra]
    C[In some dan level problems, this tesuji can save White's group with a ko, but ...];
    B[sb];W[qb];B[sc];W[pa];B[rb];W[na];B[mb]
    C[... White can still only make one eye.]
    )
)

