: ( 648ay)
White bumps in the left centre. This move intends to stop Black from getting any territory below.

:
Black continues with the Main Semeai, and gives atari at White's two stones in the lower left.

Please note that Black is two over par with the Punishment Semeai Liberty level, so White is unable to play any gote move outside the Main Semeai area on her own initiative.

:
White chooses Dany's Sacrifice.

Black is comfortably ahead in the Capture Variation; therefore, connecting with would not really benefit White.

(Referenced by 648az)

: (136 648bc;  139 648bd)
Black however, does not have any good continuation, even without the cutting point at lA so late in the game. This connection in the left centre secures two points of territory.

Capturing with at the upper edge will not change the final scores.

Joachim found that - for the time being - doing nothing (i.e. following the Main Semeai) is best for Black.
Black is well ahead in the Capture Variation, so White is severely handicapped by the fact that the loss of another tempo in the Main Semeai will result in a disaster in the Semeai Variation.

:
White's connection at the upper edge has the same effect as Black's previous move.

Black plays ...

... 0/2 reductions.

Capture Variation:

Compared to the superordinate variation ...

• Black lost one point of territory in the left centre.

White gained one point.

Black + 4 => Black + 3

Semeai Variation:

Compared to the superordinate variation ...

• Black lost one point of territory in the left centre.

White gained one point.

White + 2 => White + 3