(No. 163: Jun. 7, 1999)
Elementary level: Answer
Black 1 is the vital point. After White 2,
Black plays 3 and 5 to win the race. White dies.
Elementary level: Wrong Answer
Black 1 first allows White to capture Black with 2 and 4.
Intermediate level: Answer
The combination of Black's moves 1 to 5 is crucial.
Black gets a Ko with the moves to 13.
(This is the same shape as the problem No.162 elementary level.)
Intermediate level: Reference Diagram
If White 6, Black kills White with 7 to 11.