: ( 648aa)
Black captures White's single stone at the upper edge.

:
Here, White blocks at the top, letting Black play the atari of at the upper edge.
These two points are miai.

Black must not play any reduction.

Capture Variation:

Compared to the superordinate variation ...

• Black destroyed one point of White's territory at the upper edge.
• White got an additional point of territory at the top.

In total, gains and losses compensate for each other.

White + 2 => White + 2

Semeai Variation:

Compared to the superordinate variation ...

• Black destroyed one point of White's territory at the upper edge.
• White got an additional point of territory at the top.

In total, gains and losses compensate for each other.

Black + 4 => Black + 4