(;
AB[qd][pq][de][hd][ce][fe][gd][gf][od][nc][ob][dq][ep][qk][pc]
AW[dp][dc][dh][cd][cb][bc][fc][fd][cm][eq][qc][pd][pe][pb]
PL[W]
TR[ep]
C[White's response to the marked play?

Source:
    Go World #17, p. 13
    Sonoda 9P v. Yamshiro 6P, 5th Meijin
    Commentary:  Kobayashi Koichi 9P]
(;
W[fq]
C[In the game, White pulled back here.

White's problem is that ...]
(;
B[rc]
C[... Black is encouraged to expand the ko here.];
W[oc];B[cp]
TR[fq]
C[Because of White's marked play, Black now has this one absolute ko threat.];
W[do];B[pc];W[cq]
C[White's best ko threat, but ...];
B[qb]
C[... Black is happy to dissolve the ko.  The exchange of the top right corner for the lower left is favorable for Black, because White invested more stones in the top right than Black in the lower left.

And Black goes on to win the game by resignation after move 119.]
)
    (;
    B[qb]
    C[Note that Black should not atari here, because ...];
    W[oc];W[pc]
    TR[qb]
    C[... if White wins the ko, and connects here, Black's marked stone has no aji whatsoever.]
    )
)
    (;
    W[cp]
    C[Kobayashi Koichi suggested this extension as a better move relating to the ko in the top right.]
    (;
    B[fq]
    C[If Black plays here immediately, ...];
    W[er];B[fp];W[dr]
    C[... unlike in the game, Black would be left with no ko threat in the lower left corner.]
    )
        (;
        B[]
        C[On the other, if Black plays a ko threat other than in the lower left, ...];
        W[oc];B[fq]
        C[... now if Black plays this ko threat, ...];
        W[pc]
        C[... White will connect the ko.];
        B[er]
        C[Black captures in the lower left, but does not threaten White's other stones.]
        )
    )
)

