Game record:
The main story in the game to me was in this part.
$$W White takes territory instead of helping the stones in the center.
$$ +--------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O .|
$$ | . . O . . . . O . . . . . O . O X O X|
$$ | . O . O O . O . . . . . X . O O O X .|
$$ | . X O O X X O X . , . . . X . , X . .|
$$ | . X X X . . X O O O O O . . . X . X .|
$$ | . . . . . . X X X X X . 4 . . . . . .|
$$ | . . O . X . . . . . . . . . . . . . .|
$$ | . . . . . . O . . . . . . . . . . . .|
$$ | . . O . O O . X . . . . . . . . 2 . .|
$$ | . X . , X O . O . , . . . . . , . X .|
$$ | . . X . X O O . . . . . . . . X X O .|
$$ | . . X . O X X O . . . . . . . X O O .|
$$ | . . . O . O X X . . . . . . X O X O .|
$$ | . X X O . X X . . . . . . O O O . . .|
$$ | . . O . 1 . . . X . . . X X X O . . .|
$$ | . X O O . . O O X , . . . O X O O . .|
$$ | . X X O . O . X O X . . X X O X O . .|
$$ | . X O . . . O X O X . . 6 5 O X X 3 .|
$$ | . . . . . . . . . . . . . . . . 7 . .|
$$ +--------------------------------------+
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[go]$$W White takes territory instead of helping the stones in the center. $$ +--------------------------------------+ $$ | . . . . . . . . . . . . . . . . . O .| $$ | . . O . . . . O . . . . . O . O X O X| $$ | . O . O O . O . . . . . X . O O O X .| $$ | . X O O X X O X . , . . . X . , X . .| $$ | . X X X . . X O O O O O . . . X . X .| $$ | . . . . . . X X X X X . 4 . . . . . .| $$ | . . O . X . . . . . . . . . . . . . .| $$ | . . . . . . O . . . . . . . . . . . .| $$ | . . O . O O . X . . . . . . . . 2 . .| $$ | . X . , X O . O . , . . . . . , . X .| $$ | . . X . X O O . . . . . . . . X X O .| $$ | . . X . O X X O . . . . . . . X O O .| $$ | . . . O . O X X . . . . . . X O X O .| $$ | . X X O . X X . . . . . . O O O . . .| $$ | . . O . 1 . . . X . . . X X X O . . .| $$ | . X O O . . O O X , . . . O X O O . .| $$ | . X X O . O . X O X . . X X O X O . .| $$ | . X O . . . O X O X . . 6 5 O X X 3 .| $$ | . . . . . . . . . . . . . . . . 7 . .| $$ +--------------------------------------+[/go]
$$B Black attack is soft and from a distance.
$$ +--------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O .|
$$ | . . O . . . . O . . . . . O . O X O X|
$$ | . O . O O . O . . . . . X . O O O X .|
$$ | . X O O X X O X . , . . . X . , X . .|
$$ | . X X X . . X O O O O O . . . X . X .|
$$ | . . . . . . X X X X X . X . . . . . .|
$$ | . . O . X . . 5 . . . . . . . . . . .|
$$ | . . . . . . O 3 4 . . . . . . . . . .|
$$ | . . O . O O . X 2 . . . 7 . . . X . .|
$$ | . X . , X O . O . , 6 . . . . , . X .|
$$ | . . X . X O O . . . . 1 . . . X X O .|
$$ | . . X . O X X O . . . . . . . X O O .|
$$ | . . . O . O X X . . . . . . X O X O .|
$$ | . X X O . X X . . . . . . O O O . . .|
$$ | . . O . O . . . X . . . X X X O . . .|
$$ | . X O O . . O O X , . . . O X O O . .|
$$ | . X X O . O . X O X . . X X O X O . .|
$$ | . X O . . . O X O X . . X O O X X O .|
$$ | . . . . . . . . . . . . . . . . O . .|
$$ +--------------------------------------+
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[go]$$B Black attack is soft and from a distance. $$ +--------------------------------------+ $$ | . . . . . . . . . . . . . . . . . O .| $$ | . . O . . . . O . . . . . O . O X O X| $$ | . O . O O . O . . . . . X . O O O X .| $$ | . X O O X X O X . , . . . X . , X . .| $$ | . X X X . . X O O O O O . . . X . X .| $$ | . . . . . . X X X X X . X . . . . . .| $$ | . . O . X . . 5 . . . . . . . . . . .| $$ | . . . . . . O 3 4 . . . . . . . . . .| $$ | . . O . O O . X 2 . . . 7 . . . X . .| $$ | . X . , X O . O . , 6 . . . . , . X .| $$ | . . X . X O O . . . . 1 . . . X X O .| $$ | . . X . O X X O . . . . . . . X O O .| $$ | . . . O . O X X . . . . . . X O X O .| $$ | . X X O . X X . . . . . . O O O . . .| $$ | . . O . O . . . X . . . X X X O . . .| $$ | . X O O . . O O X , . . . O X O O . .| $$ | . X X O . O . X O X . . X X O X O . .| $$ | . X O . . . O X O X . . X O O X X O .| $$ | . . . . . . . . . . . . . . . . O . .| $$ +--------------------------------------+[/go]
$$W White quickly makes shape.
$$ +--------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O .|
$$ | . . O . . . . O . . . . . O . O X O X|
$$ | . O . O O . O . . . . . X . O O O X .|
$$ | . X O O X X O X . , . . . X . , X . .|
$$ | . X X X . . X O O O O O . . . X . X .|
$$ | . . . . . . X X X X X . X . . . . . .|
$$ | . . O 1 X . . X . . . . . . . . . . .|
$$ | . . . . . . O X O . . . . . . . . . .|
$$ | . . O . O O . X O . 4 . X . . . X . .|
$$ | . X . , X O . O . 5 O . . . . , . X .|
$$ | . . X . X O O . . 3 2 X . . . X X O .|
$$ | . . X . O X X O . . . . . . . X O O .|
$$ | . . . O . O X X . . . . . . X O X O .|
$$ | . X X O . X X . . . . . . O O O . . .|
$$ | . . O . O . . . X . . . X X X O . . .|
$$ | . X O O . . O O X , . . . O X O O . .|
$$ | . X X O . O . X O X . . X X O X O . .|
$$ | . X O . . . O X O X . . X O O X X O .|
$$ | . . . . . . . . . . . . . . . . O . .|
$$ +--------------------------------------+
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[go]$$W White quickly makes shape. $$ +--------------------------------------+ $$ | . . . . . . . . . . . . . . . . . O .| $$ | . . O . . . . O . . . . . O . O X O X| $$ | . O . O O . O . . . . . X . O O O X .| $$ | . X O O X X O X . , . . . X . , X . .| $$ | . X X X . . X O O O O O . . . X . X .| $$ | . . . . . . X X X X X . X . . . . . .| $$ | . . O 1 X . . X . . . . . . . . . . .| $$ | . . . . . . O X O . . . . . . . . . .| $$ | . . O . O O . X O . 4 . X . . . X . .| $$ | . X . , X O . O . 5 O . . . . , . X .| $$ | . . X . X O O . . 3 2 X . . . X X O .| $$ | . . X . O X X O . . . . . . . X O O .| $$ | . . . O . O X X . . . . . . X O X O .| $$ | . X X O . X X . . . . . . O O O . . .| $$ | . . O . O . . . X . . . X X X O . . .| $$ | . X O O . . O O X , . . . O X O O . .| $$ | . X X O . O . X O X . . X X O X O . .| $$ | . X O . . . O X O X . . X O O X X O .| $$ | . . . . . . . . . . . . . . . . O . .| $$ +--------------------------------------+[/go]
It is not so easy.
However, if you were to analyze what happens if black plays B or C then you could find it difficult to guarantee two eyes. It would appear to come down to the cut marked with a triangle and the wedge marked with a square. According to KataGo white will often be connecting on the first line to the upper left corner. It is not at all clear to me that works after black connects at the triangle point, maybe white would have to play A and go into the center anyway. It gets wildly complicated.
Basically, if white only gets to play A then it is a hard reading problem that can go on for many moves. I at least don't see a way to simplify it. But if black attack with C then the form appears alive, there aren't many variations to be checked and they seem to lead quickly to life, so quickly that I summarized it in only a few words.
I don't know how Leo approached thinking about this position but when black connected the triangle spot he defended the shape. That suggested that the relationship to this cut was clear to him.
$$B
$$ +--------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O .|
$$ | . . O . . . . O . . . . . O . O X O X|
$$ | . O . O O . O . . . . . X . O O O X .|
$$ | . X O O X X O X . , . . . X . , X . .|
$$ | . X X X . . X O O O O O . . . X . X .|
$$ | . . . . b . X X X X X T X . . . . . .|
$$ | . . O O X . . X . . . . . . . . . . .|
$$ | . . . . . . O X O . . . . . . . . . .|
$$ | . . O . O O d X O . X S X . . . X . .|
$$ | . X c , X O . O . O O . . . . , . X .|
$$ | . . X . X O O . . O X X . . . X X O .|
$$ | . . X . O X X O a . . . . . . X O O .|
$$ | . . . O . O X X . . . . . . X O X O .|
$$ | . X X O . X X . . . . . . O O O . . .|
$$ | . . O . O . . . X . . . X X X O . . .|
$$ | . X O O . . O O X , . . . O X O O . .|
$$ | . X X O . O . X O X . . X X O X O . .|
$$ | . X O . . . O X O X . . X O O X X O .|
$$ | . . . . . . . . . . . . . . . . O . .|
$$ +--------------------------------------+
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[go]$$B $$ +--------------------------------------+ $$ | . . . . . . . . . . . . . . . . . O .| $$ | . . O . . . . O . . . . . O . O X O X| $$ | . O . O O . O . . . . . X . O O O X .| $$ | . X O O X X O X . , . . . X . , X . .| $$ | . X X X . . X O O O O O . . . X . X .| $$ | . . . . b . X X X X X T X . . . . . .| $$ | . . O O X . . X . . . . . . . . . . .| $$ | . . . . . . O X O . . . . . . . . . .| $$ | . . O . O O d X O . X S X . . . X . .| $$ | . X c , X O . O . O O . . . . , . X .| $$ | . . X . X O O . . O X X . . . X X O .| $$ | . . X . O X X O a . . . . . . X O O .| $$ | . . . O . O X X . . . . . . X O X O .| $$ | . X X O . X X . . . . . . O O O . . .| $$ | . . O . O . . . X . . . X X X O . . .| $$ | . X O O . . O O X , . . . O X O O . .| $$ | . X X O . O . X O X . . X X O X O . .| $$ | . X O . . . O X O X . . X O O X X O .| $$ | . . . . . . . . . . . . . . . . O . .| $$ +--------------------------------------+[/go]
However, if you were to analyze what happens if black plays B or C then you could find it difficult to guarantee two eyes. It would appear to come down to the cut marked with a triangle and the wedge marked with a square. According to KataGo white will often be connecting on the first line to the upper left corner. It is not at all clear to me that works after black connects at the triangle point, maybe white would have to play A and go into the center anyway. It gets wildly complicated.
Basically, if white only gets to play A then it is a hard reading problem that can go on for many moves. I at least don't see a way to simplify it. But if black attack with C then the form appears alive, there aren't many variations to be checked and they seem to lead quickly to life, so quickly that I summarized it in only a few words.
I don't know how Leo approached thinking about this position but when black connected the triangle spot he defended the shape. That suggested that the relationship to this cut was clear to him.