Problem diagram.
Black's response to the marked play?

Source:
American Go Journal, Vol. 16, No. 3, Sept. 1981
Pro vs. Pro, "A four stone game", Miyamoto Naoki

Solution follows    (or click here to download SGF)

Correct.
Black sacrifices two stones with 1 and 3. The key point of Black 5 keeps White off balance. If White tries to cause corner trouble with 6, Black 11 uses the sacrifice stones to capture White's two stones.

Variation.
If White tries to watari immediately with 2, Black 3 extends and causes unacceptable problems for White on the left side.

Inferior.
Normally Black 1 would be joseki, but White 2 strengthens a base for future operations against the lower right side.

Wrong move order.
Without the Black sacrifice of two stones, White 8 declines the Black sacrifice to eliminate any further problems.

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