(;
AB[mc][nc][oc][pd][qd][re][qf][jd][jk][kl][ml][ll][oj][pj][pk][pq][qp][oq][np][no][mp][lp][kp][kq][jo][ir][pr][js][iq][hq][hp][jp]
AW[dc][ci][dp][dn][jn][in][lk][lm][mm][nm][lo][jq][kr][lq][mq][nq][op][ol][ok][qc][rc][rd][pc][ob][nb][io][ip][or][ns][lr][jr][gq]
TR[lr]
C[Black's response to the marked play?

Source:
    Go World #15, p. 17
    Kato Masao 9P vs. Rin Kaiho 9P
    34th Honinbo Title, game 1]
(;
B[ps]
C[Most amateurs, having this position against a pro, would probably leap at the chance to descend here.

White's bottom group has only 1 eye, and Black's surrounding outside groups have enough liberties to win any semeai.

By killing the pro's group, the amateur would then have something to tell his grandkids.  However, ...];
W[fq]
C[... White would squeeze as follows.];
B[gp];W[gn];B[fp];W[ep]
C[White still loses the bottom group.  But while squeezing from the outside here, White would be able to build good outside thickness and secure the lower left corner territory.

This result would be reasonable for White.]
)
    (;
    B[eq]
    C[In the game, Kato instead played this beautiful move, to which White does not have a good answer.

Now White can go back to make 2 eyes in gote on the bottom, but with sente Black would take an unsurmountable lead.]
    (;
    W[fq]
    C[If White tries to keep the squeeze option open here, ...];
    B[go];W[ep];B[gm]
    LB[ps:A][er:B]
    C[... Black simply moves out.  Now White's center group is weak.  And White still has to worry about Black's killing move at A.  To add insult to injury, Black even has the descent at B.]
    )
        (;
        W[ps]
        C[In the game, Rin Kaiho tried this desperate sequence.];
        B[qs];W[qr];B[os]
        C[But even for a pro, White has little chance of winning this ko.

Black went on to win this game.]
        )
    )
)

