This section is dedicated to KataGo's third new discovery, the Bad-Shape Move in the left centre, which in combination with KataGo's Atari wins another point for White.

After a presentation of the subsequent moves, especially on the left side of the board, we focus on another idea of Joachim Meinhardt to gain by a tenuki into the right centre, as KataGo's third discovery loses a tempo in the Main Semeai in principle.

KataGo's original version was based on area scoring and at the time favoured the arguably "safer" of two therefore equivalent alternatives (which we then mistakenly used as "Our Solution" for some time), of which the "unsafe" one involved a complicated ko-fight and ultimately gave White -- albeit only under territory scoring – a one-point advantage.

KataGo's current 2021 version uses territory scoring and consequently finds even more approaches for clarification.

Let's go back a few years and enter the world of KataGo ...

: ( 2022MainLine)
This is the position from lightvector's initial KataGo version (as of 2019).

White plays KataGo's Bad-Shape Move in the left centre.

Please note that this move loses one tempo in the Main Semeai, in principle, as it does not occupy one of the liberties of Black's large group at the right.

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Black is one over par with the Punishment Semeai Liberty Level, and so can afford to reduce White's territory at the top with this move, in sente.

This push must not be played if Black is par with the Punishment Semeai Liberty Level.
White would answer by occupying a crucial liberty of Black's large group at the right, e.g. with , and win the Punishment Semeai thereafter.
Giving atari at thereafter would be of no use for Black, as he would be unable to divide White's centre group after she connected with .

Please also note that answering KataGo's Bad-Shape Move by immediately occupying one of White's Main Semeai Liberties with will not benefit Black, due to his weakness of the cutting point in the lower left centre. Please refer to the subvariation below.

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White's block is forced.

: (A 2039a)
It is best for Black to give atari at White's two stones in the lower left.

Connecting at , instead, will result in a change in the order of moves.

Immediately occupying White's liberty at the left with , instead, would be possible, but could be considered a technical mistake, as White would gain in the Semeai Variation unnecessarily.

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White's connection, which loses two tempi in the Main Semeai, is forced.

Please note that the AI-typical kikashi of , is of no use here, as it reduces Black's territory inside the Main Semeai Area, and Black could easily compensate for this temporary loss in the upper right through also reducing White's territory there.

: (124 2039b)
KataGo favours this solid connection in the left centre, which erases his weakness below.

Playing tenuki to , instead, follows a suggestion of Joachim Meinhardt, which (mistakenly, as we now know) resulted in our KataGo-based 2019 solution to the problem.
Please note that KataGo's 2019 version was fine with this alternative line of play that ended with White winning the game by only one point.

But this implies that the 2019 version was not able to handle Joachim's Tenuki "correct" (with regard to territory scoring; at least on our not so very powerful hardware), which was flying below the radar of area scoring (utilised by KataGo at that time).
Under area scoring, a territory scoring result of "White + 1" cannot be distinguished from a "White + 2" one (komi = 1 assumened).

Black will not win the forthcoming ko-fight in the left centre after this tenuki here, so we analysed it entensively without all of Black's kikashi (, ) played beforehand (intending to use these as additional ko-threats). The exchange of for has been taken place before (erasing potential ko-threats of both sides in this area).
However, we had to conclude finally that there was no way to success for Black ...
513a

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Black is able to take profit outside the Main Semeai Area by capturing White's single stone at the upper edge.

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White's immediate atari takes profit outside the Main Semeai Area as well and will benefit White in the Semeai Varation.

Please note that KataGo likes to let Black occupy this point, which will not affect the overall result of the game, but enhance Black's score in the Semeai Variation only.

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Black is able to connect.

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The Main Semeai continues.

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Black plays 1/1 reduction.

Capture Variation:

Compared to our 2021 solution, ...

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

In total, gains and losses compensate for each other.

White + 2 => White + 2

Semeai Variation:

Compared to our 2021 solution, ...

• White got an additional point of territory at the upper edge.
• White captured an additional Black stone in the upper right.

In total, White gained two points.

Black + 6 => Black + 4

2022MainLine