Problem diagram.
White plays.

Source:
Tesuji Dictionary, Vol. 1, Hasami-tsuke #3,
Segoe Kensaku & Go Seigen, Ishi Press

Solution follows    (or click here to download SGF)

Correct.
White 1 is the only way. Black 2 and 6 are the toughest defense. White 7 takes 1st in a ko that is enormous for both sides, but White also has internal ko threats at A followed by B.

Black variation.
If Black avoids the ko with 6, White 7 catches Black in a shortage of liberties.

Black variation.
If Black 2 tries to avoid the ko even earlier, White makes simple forcing moves through 9 to live outright.

Fails.
Forcing with White 1 is crude. After Black 6, White dies. White cannot even salvage a ko.

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