(;
AB[qm][rm][pn][po][op][qp][oq][pq][qq][rr][sr]
AW[ql][om][pm][qn][rn][no][np][nq][rq][sq][or][pr][qr][rs]
C[Black plays.

Source:
    Xuan Xuan QiJing, a classic 14th century collection]
(;
B[sn]
TR[qm][rm][rr][sr]
C[The only move.

At first look, even this move looks hopeless.  White seems to be able to always capture both pairs of marked stones, which seems to mean that Black cannot make a 2nd eye on the right side.];
W[rl];B[sm]
(;
W[so]
C[Black seems to have lost both liberty races.  Now can you spot Black's saving sequence?];
B[sp]
C[Throw-in #1.];
W[rp];B[ro]
C[Throw-in #2!  If White captures this stone, Black takes the stones back in a snapback to live.];
W[sl]
C[White can capture the 4 stones above, but ...];
B[sp];W[qo];B[sn]
LB[oo:A][rq:B]
C[A and B are miai for Black to make 2 eyes.]
)
    (;
    W[sl]
    C[No better.];
    B[so];W[ro];B[rp]
    C[Again, Black has a double atari snapback.];
    W[sp];B[so]
    C[Black has 2 eyes.]
    )
)
    (;
    B[rl]
    C[Black can escape with the stones above, but ...];
    W[so]
    C[... White connects all the side stones.  The bulk of Black's stones die.]
    )
    (;
    B[sp]
    C[Bad timing.];
    W[ss]
    C[After White captures the 2 corner stones, Black loses the chance for the double atari in the correct sequence.];
    B[sn];W[rl];B[sm];W[sl]
    C[Black loses this semeai on the right edge and dies.]
    )
    (;
    B[rp]
    C[Same problem as the previous variation.];
    W[ss];B[so];W[rl]
    C[Black cannot make a 2nd eye.]
    )
    (;
    B[ro]
    C[Also bad timing.];
    W[rl]
    C[Again, Black loses the chance for a double atari, as in the correct sequence.]
    )
    (;
    B[sm]
    C[Fails.];
    W[sn]
    C[Black dies.]
    )
)

