(;
AB[qq][qp][qn][pp][op][np][mp][kp][lq][lr]
AW[qr][rq][pq][oq][nq][mq]
C[Black plays.]
(;
B[os]
C[Bad timing.];
W[rs]
C[White takes the vital point.];
B[sr]
C[Otherwise White immediately makes 2 eyes here.];
W[ps]
C[But Black can do nothing to prevent White from making the 2nd eye on the bottom.]
)
    (;
    B[sr]
    C[A nice try, but the incorrect 2-1 point.];
    W[rr];B[os];W[ps];B[ns];W[rs]
    C[White easily makes 2 eyes.]
    )
    (;
    B[rs]
    C[The vital point.]
    (;
    W[sr]
    C[White's toughest defense.];
    B[os];W[ps];B[ns]
    C[White defended the bottom edge in sente.  Now can White make a 2nd eye on the right side?];
    W[rp];B[ro];W[sp]
    C[White has 2 eyes, yes?];
    B[rr]
    C[Answer:  no!

If you saw Black's move here from the original position, give yourself a pat on the back.

White cannot immediately capture the 2 stones because of a liberty shortage.  ];
    W[pr]
    C[White doesn't have time to fix the liberty shortage.];
    B[so]
    C[R.I.P.]
    )
        (;
        W[rr]
        C[Connecting to eliminate the problem in the previous variation doesn't help either.];
        B[os];W[ps]
        C[White seems to be able to make eye-space in sente, but ...];
        B[ns]
        C[... Black only needs to prevent White from making an eye at A to kill.]
        LB[pr:A]
        (;
        W[rp]
        C[For example ...];
        B[ro];W[sp];B[sr]
        C[A classic bent four shape.  White is dead.]
        )
            (;
            W[ss]
            C[Also fails.];
            B[sr];W[sq];B[ss]
            C[White still only has one eye.]
            )
        )
    )
)

