(;
AB[qo][ro][so][jp][np][op][pp][qp][kq][lq][mq][rq][sq][nr][ps]
AW[rm][ln][nn][pn][qn][mo][mp][nq][oq][pq][qq][or][rr][sr][ns]
C[Black plays.]
(;
B[qr]
C[Correct.];
W[mr]
(;
B[os]
C[Black sets up the desired shape - White has a liberty shortage.]
(;
W[rs];B[ls]
C[White cannot approach from either side.  White dies - Black lives.]
)
    (;
    W[lr]
    C[No better.];
    B[kr];W[ls];B[rs]
    C[White cannot make a 2nd eye.]
    )
)
    (;
    B[rs]
    C[Bad timing.]
    (;
    W[pr]
    (;
    B[ss]
    (;
    W[lr]
    C[Black lives, but so does White.]
    )
        (;
        W[os]
        C[Mistake.];
        B[ls];W[rr];B[sr];W[qs];B[rr];W[rp];B[sp];W[lr];B[kr];W[rn];B[ks];W[no];B[ms];W[po];B[nr];W[mr];B[lr];W[sn]
        C[White is dead in double ko.]
        )
    )
        (;
        B[lr]
        C[To kill White now, Black has to fight a ko.]
        )
    )
        (;
        W[lr]
        C[White returns the favor.];
        B[kr];W[os];B[ls];W[pr];B[ss];W[rr];B[sr];W[qs];B[rr];W[rp];B[sp];W[rn];B[ks];W[no];B[ms];W[po];B[nr];W[mr];B[lr];W[sn]
        C[Black is alive in double ko.]
        )
    )
)
    (;
    B[os]
    C[Transposes.];
    W[mr];B[qr]
    )
)

