(;
AB[pn][mo][no][qo][qp][kp][kq][kr][lp][mq][nq]
AW[mp][np][op][lq][lr][oq][mr]
C[Black plays.]
(;
B[qr]
C[Approaching solidly looks slack but is correct.]
(;
W[pr]
C[Blocking here looks good, but ...];
B[ps]
C[... Black can squeeze from the outside.];
W[os];B[nr]
C[White has room for only one eye.]
)
    (;
    W[ls]
    C[Expanding from the other direction also doesn't work.];
    B[ns]
    C[Black can take the vital point.];
    W[nr];B[pr]
    C[White has only one eye.]
    )
)
    (;
    B[pr]
    C[Looks good but is an overplay.];
    W[or]
    C[Descending here threatens 2 eyes to the left, while setting up corner aji.];
    B[ls];W[qr]
    C[For example, ...];
    B[pq];W[ps]
    (;
    B[rq];W[rr];B[sr];W[qq];B[pp];W[rp];B[sp]
    C[White has a ko.]
    )
        (;
        B[rs];W[qs];B[rq];W[qq];B[pp];W[rr];B[sr]
        C[Again, White has a ko.]
        )
    )
    (;
    B[ls]
    C[Also looks good, but lets White off the hook.];
    W[qr]
    C[White has this defensive resource.];
    B[nr];W[or];B[ms];W[qq];B[rq];W[rr];B[sr];W[rp];B[sp]
    C[White is happy to have a ko.]
    )
)

