(;
AB[pd][oo][ei][fi][fh][fg][ef][de][cd][cc][be][cf][af]
AW[dp][ci][eh][eg][dg][cg][bh][bf][ag][ff][fe][dc][cb][eb]
TR[bf]
C[Black's response to the marked ko capture?

Source:
American Go Journal, Vol. 31, No. 4, pp. 14-15
Commentary:  Michael Redmond 8P
Black:  Gin-hua Peng 5P
White:  Michael Redmond 8P
1997-02-23, IGS game]
(;
B[bb]
C[In the game, Black played this purely defensive ko threat, which is not good enough.];
W[ae]
C[Now Black has to play defense for a few moves, while White squeezes from the outside.];
B[ca];W[db];B[ad];W[df];B[bc];W[ee];B[dd];W[fc]
C[Black could have done much better.  White goes on to win the game.]
)
    (;
    B[ed]
    C[With this ko threat, Black could have had a much better position.]
    (;
    W[ae];B[fd];W[he];B[gd];W[hf];B[gb]
    C[Compare this position to the game line.]
    )
        (;
        W[fd]
        C[If White blocks here instead, ...];
        B[bg];W[ah]
        C[... White has no ko threat.];
        B[bb];W[ba];B[bc]
        (;
        W[bf];B[ec];W[fc];B[df];W[ae];B[ad];W[cl]
        C[White's groups are separated.  This result is still better for Black than the game.]
        )
            (;
            W[df];B[ee];W[ec];B[dd];W[bf];B[gc];W[fc];B[bg];W[di]
            C[Again White has no ko threat.  This result is also better than the game for Black.]
            )
        )
    )
)

