(;
AB[rn][sn][qo][qm][po][pp][pq][or][os][nq]
AW[qr][pr][qq][qp][rp][ro]
C[Black plays.]
(;
B[so]
C[Too slow.];
W[sr]
C[White lives easily, and with 4 points of territory.]
)
    (;
    B[sq]
    C[Better than the previous variation, but ...];
    W[rr];B[sr]
    C[... Black only has a seki.]
    (;
    W[ps];B[so];W[sp];B[rs]
    )
        (;
        W[so]
        C[Mistake.];
        B[ps];W[qs];B[rs]
        C[Black has the option for this ko.]
        )
    )
    (;
    B[sr]
    C[Sometimes the vital point, but not with this shape.];
    W[rr];B[sq]
    C[Transposes to the previous variation, i.e., White has a seki.]
    )
    (;
    B[rr]
    C[The vital point, and the best move.]
    (;
    W[rs]
    (;
    B[sr];W[ps]
    (;
    B[sp]
    C[Black has the option to force a ko here.];
    W[so];B[rq]
    C[White takes 1st.]
    )
        (;
        B[so]
        C[Another possibility.];
        W[sp];B[ss]
        C[A 10000 year ko.]
        )
    )
        (;
        B[sq]
        C[Inferior.];
        W[ps];B[ss]
        LB[qs:A]
        C[Now Black only has a 2 stage ko, i.e., after ignoring a ko threat, Black still has to fight the ko at A.]
        )
    )
        (;
        W[sr]
        C[Mistake.];
        B[rs]
        C[Now White doesn't even have a ko.  For example ...]
        (;
        W[ps]
        C[Maybe White's best practical chance.];
        B[sq];W[rq];B[ss];W[sp]
        C[Black can create a dead bulky 5.  Note however, that if White can separate any of Black's surrounding stones, White will have a lot of internal liberties for such a semeai.]
        )
            (;
            W[rq];B[ps];W[qs];B[so]
            )
            (;
            W[so];B[ps];W[qs];B[rq]
            )
        )
    )
)

