Ōhashi Hirofumi 7p has kindly pointed out to us that it would be technically correct to fill an empty bulky-five eye shape with a squared shape, but not with a pyramid one.

This advice may be helpful for your own games; in Igo Hatsuyōron 120 itself there is no effect.

Lets enter the analysis room ...

: (A 2040) ( 2022MainLine)
is a technically correct continuation for occupying the internal liberties of White's left-hand group.

Alternatively, this move could be played at , resulting in a change in the order of moves.

Ōhashi Hirofumi's advice never to use for further filling a nakade of the bulky five type should be seen independent of the very special Main Semeai of Igo Hatsuyōron 120.

would also do the job, but should be avoided as well, as it would provide White with a ko-threat (giving atari with e.g. ) unnecessarily.

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White will continue somewhere else on the board.

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Black's next move that White will not answer locally.

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Black gives atari at White's group.

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White captures a square shape of four Black stones.

Seen in isolation, there is now nothing more that Black has to do at the moment.

The points of and are miai, as are and .

VAR

: ( 2040)
Seen in isolation, this move can be considered a technical mistake.

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Again, White plays elsewhere on the board.

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The occupation of internal liberties of White's group contiues.

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Black gives atari.

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White captures a pyramid shape of four Black stones.

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Black is forced to play the oki of if he wants to prevent White's group from coming to life by playing at the same point.

This implies that White's previous move can be utilised as a ko-threat - in principle.
This is the decisive difference to the square shape above and the cause for Ōhashi Hirofumi's disadvantageous valuation of the pyramid shape.

2040)

Let's return to the dawn of time for a final conclusion ...

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The "classical" technical mistake (at left) does not have any negative impact in Igo Hatsuyōron 120, because it was played at a time when there are no more ko-fights of any kind.

Black is forced to take White's left-hand group a liberty anyway (even in the square shape at right), due to the Main Semeai with his large group in the upper right.

2022MainLine