No.697(Answers)

Black 1 is crucial to get a Ko with 3 after White 2.

Black 1 allows White to live with 2 to 6.

Black 1 is crucial.
If White 2, Black lives with 3.
If White 4 at 5, Black lives with 4.

If White 2 and 4, Black lives with 3 and 5.
If White 6 at 7, Black lives with 6.