This section is dedicated to KataGo's second new discovery, the Immediate Crosscut after Yamada Shinji's Tsuke, which can be successfully played "early", i.e. before the consolidation of the border of Black's upper left corner.

We compare KataGo's new endgame sequence on the left side with Yamada Shinji's original line of play, in order to identify the individual value of KataGo's Immediate Crosscut.

Then we turn to determining the individual values of KataGo's further new discoveries.

Finally, we will explain some failures in deviations from the continuation proposed by KataGo.

Referenced by ( 2022MainLine), ( 2037), ( 2037)

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

: (A 2038) ( 2022MainLine)
This is the position from lightvector's initial 2019 version of KataGo.

KataGo's Immediate Crosscut cannot be played "late", i.e. after Black's corner has been solidified by his moves at during the mutual occupation of opponent's liberties in the Main Semeai.

This has already been shown in section "Yamada Shinji's Tsuke" ( 2037) above.

Additional variations for a later played Tsuke can be found in section "Prof. Jeong SooHyun's Advice to Start the Endgame Early" ( 2043)

Yamada Shinji found his Tsuke at a time when the endgame at the left side of the board was played after the dissolving of the hanezeki, i.e. "extremely late".
Since White's move at was consequently not possible, he had to continue with drawing back to . We will try to evaluate the value of KataGo's Immediate Crosscut in the respective subvariation.

: (106 2038a)
Black gives atari in the corner, capturing White's just played stone.

Black is unable to resist.
He would lose one point overall, if he captured the other White stone (i.e. Yamada Shinji's Tsuke) with a move at .

:
White's atari at the upper edge is sente.

:
Thereafter, White retreats with this move, capturing Black's single stone at the top as well as saving her initially played tsuke stone.

: (A 2038b)
Black defends his territory in the upper left corner, also giving atari at White's single stone at the upper edge.

I found that Black could defend his lower left corner by descending to , instead, without affecting the overall result of the game.
However, the result of the Semeai Variation will be worse for him (whilst the Capture Variation remains unaffected).

:
White continues with the endgame in the lower left corner.

:
It is best for Black to play tenuki, in order to strengthen his formation in the upper left corner.

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KataGo likes to play this kikashi "early".

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

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This connection loses two tempi in the Main Semeai.

:
KataGo's Solid Connection in the left centre.

The comparison with the original sequence after Yamada Shinji's Tsuke will become a bit difficult.
KataGo's new moves at the left side of the board dramatically affect the internal dependencies on the board, especially because Black is no longer par with the Punishment Semeai Level now, and has thus been given the opportunity to become active on the right side of the board, and at the top, himself.

In order to simplify the determining of the individual effect of KataGo's Immediate Crosscut, we will briefly interrupt here and present the move sequence first that we utilised for so long.

We will discuss KataGo's further move sequence and some subvariations therein later, at the end of this section.

Let's go back in time and enter the world of amateurs ...

: ( 2038)
White draws back.

Since Prof. Jeong SooHyun's kind advice, the endgame was started "early" by us, i.e. after the termination of the Nakade Sequence.

For further details, please refer to section "Prof. Jeong SooHyun's Advice to Start the Endgame Early" ( 2043).

Without much thought, we simply used the move sequence shown to us by Yamada Shinji for his "late" Tsuke even at this earlier moment in the game, after the exchange of for in the Nakade Sequence of the classical line of play, which ended with White's sente.

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Black's hane stops White from reducing Black's corner territory at the upper edge.

:
The "late" crosscut at is used as a kikashi here, ...

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... forcing Black to accept gote in the upper left corner.

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White continues with the endgame in the lower left corner.

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It is best for Black to play tenuki, in order to defend his territory in the upper left.

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White gives atari, ...

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... forcing Black to capture her cutting stone.

:
The rest of the game will follow the well-known path of Our Solution (2015 / 2017)..

The final scores of the game will become Black + 5 / Black + 3

2038

After a short detour to KataGo's first new finding, the analysis continues in the world of amateurs ...

:
KataGo's Immediate Crosscut.

:
The sequence in the upper left corner continues as usual.

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White's hasami-tsuke starts the reduction of Black's lower left corner.

:
We only want to determine the value of KataGo's Immediate Crosscut and therefore choose an amateurish continuation of the endgame on the left side, in order to simplify the presentation.

Black must not play any reduction.

After her decision point, White will connect her single stone at the upper edge with .
Thereafter, Black will push at at the top, forcing White to block at .

Capture Variation:

Compared to the previous variation, ...

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

In total, White gained three points.

Black + 5 => Black + 2

Semeai Variation:

Compared to the previous variation, ...

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

In total, White gained three points.

Black + 3 => Jigo

( 2038)
Another stopover in KataGo's world leads to a changed scenario in the world of amateurs ...

: ( A 2038)
White connects her single stone in the right centre, so continuing with the Main Semeai.

The value of her connection with in the lower left (which is the correct line of play) will be derived in the following subvariation.
We will find there that 3 + 3 + 2 = 7!

:
Black captures White's two stones in the lower left.

:
In order to simplify the presentation, we let White occupy another one of Black's Main Semeai Liberties here.

:
KataGo's Solid Connection in the left centre.

:
Some White kikashi for reducing Black's territory in the left centre.

Black must not play any reduction.

After her decision point, White will connect her single stone at the upper edge with .
Thereafter, Black will push at at the top, forcing White to block at .

Capture Variation:

Compared to the previous variation, ...

• White destroyed one point of Black's territory in the left centre.
• White destroyed two points of Black's territory in the lower left (both sides captured one opponent stone each).

In total, White gained three points.

Black + 2 => White + 1

KataGo's Atari (seen exclusively for itself) has a value of two points, KataGo's Bad-Shape Move has a value of one point.

Semeai Variation:

Compared to the previous variation, ...

• White destroyed one point of Black's territory in the left centre.
• White destroyed two points of Black's territory in the lower left (both sides captured one opponent stone each).
• Black captured two White stones more at the left side, so gaining four points.

In total, White lost one point.

Jigo => Black + 1

Ultimately, the amateurs use all of KataGo's new findings to complete their analysis ...

: ( 2038)
White follows KataGo's solution by connecting her two stones in the lower left.

In principle, this connection loses two tempi in the Main Semeai, but gains four points (in the Capture Variation), so the net effect expected is two points in White's favour - in principle.

However, it will turn out that the sum of three (KataGo's Immediate Crosscut), three (KataGo's Atari and Bad-Shape Move), and two (KataGo's Connection) is only seven!

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KataGo's Solid Connection in the left centre.

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White's connection in the right centre prevents Black from gaining three points (in the Capture Variation) at the cost of only one Main Semeai Liberty.

However, there is still something left with added value for Black at the upper edge ...

:
Black is able to push at the top in sente.

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Black is two over par with the Punishment Semeai Liberty Level, and can afford to capture White's single stone at the upper edge without falling prey to the Punishment Semeai..

This move gains one prisoner and destroys an additional point of White's territory, at the cost of only one tempo in the Main Semeai. Therefore, the net gain of this capture is one point.
This benefit is the cause of the strange-seeming calculation above.

:
It is best for White to give atari immediately.

:
Black simply connects.

:
Some White kikashi for reducing Black's territory in the left centre.

Black plays 1/1 reduction.

Capture Variation:

Compared to the previous variation, ...

• Black captured one White stone at the upper edge, so gaining one point.
• Black destroyed one point of White's territory at the upper edge.
• Black destroyed one point of White's territory in the right centre.
• Black did not capture White's two stones in the lower left, so losing four points.

In total, White gained one point.

White + 1 => White + 2

Semeai Variation:

Compared to the previous variation, ...

• Black captured one White stone at the upper edge, so gaining one point.
• Black destroyed one point of White's territory at the upper edge.
• Black destroyed one point of White's territory in the right centre.
• Black captured one White stone more in the lower left, so gaining two points.
• White captured one Black stone more in the right centre, so gaining two points.

In total, White lost three points.

Black + 1 => Black + 4

2038

Let's return to the world of KataGo ...

: (123 2038c; 125 2038d)
White continues by connecting her single stone in the right centre.

Blocking at , instead, would be one point worse; connecting at two points.

:
Black is two over par with the Punishment Semeai Liberty Level, so he can affort to push at the top, in sente.

If he played this move otherwise, White would reply by connecting at , occupying a crucial liberty of Black's large group at the right.

:
White is forced to connect, in order to prevent a Black atari at her three stones below with .

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Black gains two points by capturing White's single stone at the upper edge, but also loses one tempo in the Main Semeai, so the net gain of this move is one point.

:
KataGo likes to continue with the Main Semeai, ...

:
... allowing Black to take further profit outside the Main Semeai Area, but which will affect the Semeai Variation only.

If would have been technically correct for White to block with immediately, letting Black destroy one point of her territory at the right in the further process of the mutual occupation of opponent's liberties in the Man Semeai.

:
White must capture.

:
Black is able to connect, losing his last surplus Main Semeai Liberty.

As we already know, ...

White will win the game by two points.

Please note that Black will win the Semeai Variation by six points here, due to White's deviation at the upper edge.

2022MainLine