(;
AB[ir][eq][jq][cp][dp][ep][fp][np][pp][ho][jo][dn][en][em][gm][cj]
AW[er][fr][cq][fq][hq][bp][gp][co][fo][cn][qn][dm][dl]
C[Black plays.

Source:
    Tesuji Dictionary, by Segoe Kensaku & Go Seigen]
(;
B[dr]
C[This move looks promising, but fails.]
(;
W[dq]
C[If White thoughtlessly cuts, ...];
B[bq];W[cr];B[br];W[ds];B[bo]
C[... this result is a disaster for White.]
)
    (;
    W[cr]
    LB[bq:A][bo:B]
    C[White can simply descend here to keep the connection.  The reader can verify that Black's cut at A and B do not threaten the bulk of White's stones.]
    )
)
    (;
    B[cr]
    C[This attachment prevents White from descending to connect, but ...];
    W[bq]
    C[... White can cut off the stone this way.];
    B[dr];W[dq]
    C[Captures the 2 stones.]
    )
    (;
    B[bq]
    C[Correct.  Now White is going to lose something important.]
    (;
    W[br]
    C[For example ...];
    B[cr];W[aq];B[dr]
    C[Black captures the 6 stones to the right.]
    )
        (;
        W[cr];B[bo]
        C[Another big loss for White.]
        )
    )
)

