(No. 169: July 19, 1999)
Elementary level: Answer
Black 1 is the vital point to cut and capture the White stones.
Elementary level: Wrong Answer
Black 1 is wrong.
After Black 3, White plays 4 to 6.
Black cannot live.
Intermediate level: Answer
Black 1 is the vital point.
If White 2, Black lives with 3.
If White 2 at 3, Black lives with 2.
Intermediate level: Wrong Answer
Black 1 allows White to play at the vital point 2.
After Black 3 and White 4, Black cannot do anything further.
White can get a Ko at A whenever he likes.