(;
AB[eb][db][cb][dc][fc][bd][cd][ce][bf][cf][ch][eg][dg][ei]
AW[bb][bc][cc][dd][ec][de][df][fe][ff][cg][bg][bh][ci][cl]
C[From this common avalanche joseki position, play some moves to reach this week's problem.];
W[ad]
C[White starts a famous trick play.  You probably won't find a pro playing this move!];
B[ae];W[ab]
C[What is Black's best response?]
(;
B[ba]
C[A very easy mistake to make!];
W[ag]
LB[af:A]
TR[df][de][fe][ff][dd]
C[Now White has an unfavorable 2 step ko -- after White ignores a ko threat to play at A, the ko becomes direct.

However, note that White risks almost nothing locally with this ko, whereas Black risks a big corner and White's marked stones become strong.  White can give up a lot elsewhere on the board in order to win this ko.]
)
    (;
    B[ag]
    C[Correct!];
    W[ah];B[ba]
    C[Black lives in double ko!]
    )
)

