(;
AB[er][nr][or][eq][oq][dp][jp][pp][dn][gn][pn][hm][hl][rl][hk][ik][kk][nk][ok][pk][qk][lj][mj]
AW[fr][mr][fq][nq][gp][np][ho][hn][mn][im][cl][il][kl][ll][rk][nj][oj][pj][qj][rj]
C[Black plays.

Source:
    Tesuji Dictionary, Vol. 1, Hasami-tsuke #26];
B[lr]
C[Everybody knows the clamp tesuji, right?

This problem is a great example of how this clamp can be catastrophic for the clampee, when the clamper has even a minimum of nearby support.]
(;
W[ms]
C[Black must always have a response ready for this descent.  Otherwise, don't play the clamp!];
B[lp]
C[Every situation is different.  In this position, this is the killer move.];
W[lq];B[kq];W[mq];B[no]
C[Black cuts off the White group.];
W[mo];B[mp];W[kr];B[jr]
C[And even though White can capture the stone, White's one-eyed group will lose the semeai.  White collapses]
)
    (;
    W[lq]
    C[When White cannot descend, this play is the usual fallback strategy.];
    B[ms]
    (;
    W[kq];B[mq];W[mp];B[kr];W[jq]
    C[With the Black stone above, White cannot block.];
    B[jr]
    C[But Black can keep forcing with pushes.];
    W[iq]
    C[Again White must extend or Black will play here and destroy almost all of White's territory.

In any event, Black has already destroyed almost half of White's territory, and in sente!]
    )
        (;
        W[kr]
        C[Dangerous];
        B[mq];W[mp];B[kq]
        C[And if Black wins the ko, almost all of White's territory evaporates.]
        )
    )
)

