(;
AB[bd][pd][cf][ci][ql][om][po][pp][pq][ip][fq]
AW[cc][jc][dd][fd][cn][qn][rn][dp][qp][qq][kq]
TR[kq]
C[Black's response to the marked invasion?

Source:
    American Go Journal, v36 #3, pp. 17-18
    Adapted originally from "Baduk Monthly".]
(;
B[ko]
C[Capping makes any escape to the center very difficult.  So ...];
W[ir]
C[... White must seek life by sliding here.];
B[hq]
C[Black can tighten the attack with this kosumi.];
W[hr];B[gr];W[gp];B[gq];W[mq]
C[However, White has no problem securing life.];
B[mo];W[nr]
C[If White lives with such a big territory, the game is over for Black.]
)
    (;
    B[iq]
    C[Black can also try this "iron pillar".];
    W[jo]
    (;
    B[hn]
    C[If Black tries to stay ahead, ...];
    W[jm]
    C[... White simply flies away with this jump.]
    )
        (;
        B[jp]
        C[Note that the following push and cut is not a good idea for Black.];
        W[kp];B[ko];W[lo];B[kn];W[ln];B[km];W[lm];B[kl];W[ll]
        C[White pushes through into the center.

Because White's marked stones are so solid, Black's middle wall does not have much influence.  Moreover, Black's wall to the right reduces in strength.]
        TR[cn][dp]
        )
    )
    (;
    B[jq]
    C[In the actual game between Cho Hunhyun (Black) and Lee Changho, the following sequence appeared.];
    W[ko]
    C[The proper response.]
    (;
    B[jn]
    (;
    W[no]
    C[Before jumping out, White takes time for this sente play.];
    B[pn];W[lm]
    C[White runs out ahead of Black.];
    B[lk]
    C[Here, Cho decides to start a complicated fight.  Lee goes on to win the game.]
    )
        (;
        W[lm]
        C[Note that White could also extend without first forcing to the right, because ...]
        (;
        B[kn]
        C[... White is not afraid of this push and cut.];
        W[ln];B[lo];W[mo];B[lp];W[mp];B[lq];W[mq];B[lr];W[nn]
        C[White is out into the center, and Black's wall to the right has become a floating group.]
        )
            (;
            B[kl]
            C[If Black keeps pushing, ...];
            W[mk]
            C[... so does White.];
            B[lj];W[mj]
            C[A thick move.  Again, White is weakening Black's stones to the right.]
            )
        )
    )
        (;
        B[kr]
        C[What about this hane, which removes White's base to tighten the attack?];
        W[lq];B[lr];W[jn]
        C[White cannot be dissatisfied with this kosomi.]
        )
    )
)

