(Referenced by 498; 509)

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In the professional publications about the problem so far, Black fills in the five-point-nakade on the left side with the sequence from to , creating a pyramid shape.

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After White has captured Black's four stones with , Black is forced to play oki with , in the centre of White's eye-shape. This is necessary not only to occupy a liberty of White's group in the course of the current semeai, but also to prevent a white move on this point, which would create a living shape for her group.

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However, from on, it is technically correct to use the sequence shown here, which creates a square shape. Ōhashi Hirofumi 6p was kind enough to point this out to us.

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After White captures Black's stones with , serves only to take a liberty of White's group. White would need two consecutive moves to get two eyes here, so is not sente locally. This means that capturing Black's stones cannot be used as a ko-threat.

It is important to note that, in this problem, Black does not have any use for his sente, won by the "correct" filling-in sequence. So, as far as the outcome of the semeai is concerned, the order of moves does not really matter. This may be the reason, why the pyramid shape was chosen originally.