Endgame tesuji from 20th Judan game 2

[xela]

$$B Cho Chikun (W) vs Otake Hideo on 1982-03-11, position after white 196 $$ --------------------------------------- $$ | . . O X X X X X X . . . . . . . . . . | $$ | . O O X X O O X . X . . . . . . . . . | $$ | . . X O X O . O X X . . . . X . . . . | $$ | . X . O O O . O O X . . X . . X X . . | $$ | . O O . . . . O O X . . . O . X . X . | $$ | . . . . . . X O X X . . . . . O X . X | $$ | . . . . . . O . O O X X X X . X X X O | $$ | . . X . X . X O X O X O X O . O O O . | $$ | . O O O O O . X . . O O O O . O X . O | $$ | . . . , . . O O O , . . . . O , X . . | $$ | . X c X X X X X X X . . X O X O O O O | $$ | . a . X O . . . . O O O X X X X X X . | $$ | . . O O O O . . . . . X O O . . X . . | $$ | b . . O X X X X . O . O X O . X . X . | $$ | . O O . O O X . O O O O X O . . X . X | $$ | O . . O O X X . X O X X X O . O O X . | $$ | X O O X X . . X X O O O X . O . . O . | $$ | X X X . . . . . . X X X X O . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------

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[go]$$B Cho Chikun (W) vs Otake Hideo on 1982-03-11, position after white 196 $$ --------------------------------------- $$ | . . O X X X X X X . . . . . . . . . . | $$ | . O O X X O O X . X . . . . . . . . . | $$ | . . X O X O . O X X . . . . X . . . . | $$ | . X . O O O . O O X . . X . . X X . . | $$ | . O O . . . . O O X . . . O . X . X . | $$ | . . . . . . X O X X . . . . . O X . X | $$ | . . . . . . O . O O X X X X . X X X O | $$ | . . X . X . X O X O X O X O . O O O . | $$ | . O O O O O . X . . O O O O . O X . O | $$ | . . . , . . O O O , . . . . O , X . . | $$ | . X c X X X X X X X . . X O X O O O O | $$ | . a . X O . . . . O O O X X X X X X . | $$ | . . O O O O . . . . . X O O . . X . . | $$ | b . . O X X X X . O . O X O . X . X . | $$ | . O O . O O X . O O O O X O . . X . X | $$ | O . . O O X X . X O X X X O . O O X . | $$ | X O O X X . . X X O O O X . O . . O . | $$ | X X X . . . . . . X X X X O . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Black to play the best endgame move on the left side.

In the actual game, Otake played 'a'. I wondered about the monkey jump at 'b' instead, but it doesn't work because of the weakness at 'c'. KataGo found a surprising tesuji which is better than the game move.

[kvasir]

I think it is like this.

$$B $$ +--------------------------------------+ $$ | . . O X X X X X X . . . . . . . . . .| $$ | . O O X X O O X . X . . . . . . . . .| $$ | . . X O X O . O X X . . . . X . . . .| $$ | . X . O O O . O O X . . X . . X X . .| $$ | . O O . . . . O O X . . . O . X . X .| $$ | . . . . . . X O X X . . . . . O X . X| $$ | . . . . . . O . O O X X X X . X X X O| $$ | 6 8 X . X . X O X O X O X O . O O O .| $$ | 5 O O O O O . X . . O O O O . O X . O| $$ | 7 1 . 3 . . O O O , . . . . O , X . .| $$ | . X . X X X X X X X . . X O X O O O O| $$ | . 4 2 X O . . . . O O O X X X X X X .| $$ | . . O O O O . . . . . . O O . . X . .| $$ | . . . O X X X X . O . O X O . X . X .| $$ | . O O . O O X . O O O O X O . . X . X| $$ | O . . O O X X . X O X X X O . O O X .| $$ | X O O X X . . X X O O O X . O . . O .| $$ | X X X . . . . . . X X X X O . . O . .| $$ | . . . . . . . . . . . . . . . . . . .| $$ +--------------------------------------+

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[go]$$B $$ +--------------------------------------+ $$ | . . O X X X X X X . . . . . . . . . .| $$ | . O O X X O O X . X . . . . . . . . .| $$ | . . X O X O . O X X . . . . X . . . .| $$ | . X . O O O . O O X . . X . . X X . .| $$ | . O O . . . . O O X . . . O . X . X .| $$ | . . . . . . X O X X . . . . . O X . X| $$ | . . . . . . O . O O X X X X . X X X O| $$ | 6 8 X . X . X O X O X O X O . O O O .| $$ | 5 O O O O O . X . . O O O O . O X . O| $$ | 7 1 . 3 . . O O O , . . . . O , X . .| $$ | . X . X X X X X X X . . X O X O O O O| $$ | . 4 2 X O . . . . O O O X X X X X X .| $$ | . . O O O O . . . . . . O O . . X . .| $$ | . . . O X X X X . O . O X O . X . X .| $$ | . O O . O O X . O O O O X O . . X . X| $$ | O . . O O X X . X O X X X O . O O X .| $$ | X O O X X . . X X O O O X . O . . O .| $$ | X X X . . . . . . X X X X O . . O . .| $$ | . . . . . . . . . . . . . . . . . . .| $$ +--------------------------------------+[/go]

But if white blocks on the other side then the monkey jump is coming.

$$W $$ +--------------------------------------+ $$ | . . O X X X X X X . . . . . . . . . .| $$ | . O O X X O O X . X . . . . . . . . .| $$ | . . X O X O . O X X . . . . X . . . .| $$ | . X . O O O . O O X . . X . . X X . .| $$ | . O O . . . . O O X . . . O . X . X .| $$ | . . . . . . X O X X . . . . . O X . X| $$ | . . . . . . O . O O X X X X . X X X O| $$ | . . X . X . X O X O X O X O . O O O .| $$ | 1 O O O O O . X . . O O O O . O X . O| $$ | . X . , . . O O O , . . . . O , X . .| $$ | . X 8 X X X X X X X . . X O X O O O O| $$ | 6 . 7 X O . . . . O O O X X X X X X .| $$ | 4 . O O O O . . . . . . O O . . X . .| $$ | 2 3 . O X X X X . O . O X O . X . X .| $$ | 5 O O . O O X . O O O O X O . . X . X| $$ | O . . O O X X . X O X X X O . O O X .| $$ | X O O X X . . X X O O O X . O . . O .| $$ | X X X . . . . . . X X X X O . . O . .| $$ | . . . . . . . . . . . . . . . . . . .| $$ +--------------------------------------+

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[go]$$W $$ +--------------------------------------+ $$ | . . O X X X X X X . . . . . . . . . .| $$ | . O O X X O O X . X . . . . . . . . .| $$ | . . X O X O . O X X . . . . X . . . .| $$ | . X . O O O . O O X . . X . . X X . .| $$ | . O O . . . . O O X . . . O . X . X .| $$ | . . . . . . X O X X . . . . . O X . X| $$ | . . . . . . O . O O X X X X . X X X O| $$ | . . X . X . X O X O X O X O . O O O .| $$ | 1 O O O O O . X . . O O O O . O X . O| $$ | . X . , . . O O O , . . . . O , X . .| $$ | . X 8 X X X X X X X . . X O X O O O O| $$ | 6 . 7 X O . . . . O O O X X X X X X .| $$ | 4 . O O O O . . . . . . O O . . X . .| $$ | 2 3 . O X X X X . O . O X O . X . X .| $$ | 5 O O . O O X . O O O O X O . . X . X| $$ | O . . O O X X . X O X X X O . O O X .| $$ | X O O X X . . X X O O O X . O . . O .| $$ | X X X . . . . . . X X X X O . . O . .| $$ | . . . . . . . . . . . . . . . . . . .| $$ +--------------------------------------+[/go]

There is a real surprise if white fails to protect with in the first diagram.

$$B $$ +--------------------------------------+ $$ | . . O X X X X X X . . . . . . . . . .| $$ | . O O X X O O X . X . . . . . . . . .| $$ | 5 . X O X O . O X X . . . . X . . . .| $$ | . X . O O O . O O X . . X . . X X . .| $$ | . O O . . . . O O X . . . O . X . X .| $$ | 4 3 . . . . X O X X . . . . . O X . X| $$ | 2 . . . . . O . O O X X X X . X X X O| $$ | O 1 X . X . X O X O X O X O . O O O .| $$ | X O O O O O . X . . O O O O . O X . O| $$ | X X . X . . O O O , . . . . O , X . .| $$ | . X . X X X X X X X . . X O X O O O O| $$ | . O O X O . . . . O O O X X X X X X .| $$ | . . O O O O . . . . . . O O . . X . .| $$ | . . . O X X X X . O . O X O . X . X .| $$ | . O O . O O X . O O O O X O . . X . X| $$ | O . . O O X X . X O X X X O . O O X .| $$ | X O O X X . . X X O O O X . O . . O .| $$ | X X X . . . . . . X X X X O . . O . .| $$ | . . . . . . . . . . . . . . . . . . .| $$ +--------------------------------------+

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[go]$$B $$ +--------------------------------------+ $$ | . . O X X X X X X . . . . . . . . . .| $$ | . O O X X O O X . X . . . . . . . . .| $$ | 5 . X O X O . O X X . . . . X . . . .| $$ | . X . O O O . O O X . . X . . X X . .| $$ | . O O . . . . O O X . . . O . X . X .| $$ | 4 3 . . . . X O X X . . . . . O X . X| $$ | 2 . . . . . O . O O X X X X . X X X O| $$ | O 1 X . X . X O X O X O X O . O O O .| $$ | X O O O O O . X . . O O O O . O X . O| $$ | X X . X . . O O O , . . . . O , X . .| $$ | . X . X X X X X X X . . X O X O O O O| $$ | . O O X O . . . . O O O X X X X X X .| $$ | . . O O O O . . . . . . O O . . X . .| $$ | . . . O X X X X . O . O X O . X . X .| $$ | . O O . O O X . O O O O X O . . X . X| $$ | O . . O O X X . X O X X X O . O O X .| $$ | X O O X X . . X X O O O X . O . . O .| $$ | X X X . . . . . . X X X X O . . O . .| $$ | . . . . . . . . . . . . . . . . . . .| $$ +--------------------------------------+[/go]

[xela]

I think it is like this.

Oh, that's nice!

To split hairs, KataGo thinks this way is about half a point better. This is all a bit above my level; I'm just posting it because the first move is so striking.

$$B $$ --------------------------------------- $$ | . . O X X X X X X . . . . . . . . . . | $$ | . O O X X O O X . X . . . . . . . . . | $$ | . . X O X O . O X X . . . . X . . . . | $$ | . X . O O O . O O X . . X . . X X . . | $$ | . O O . . . . O O X . . . O . X . X . | $$ | . . . . . . X O X X . . . . . O X . X | $$ | . . . . . . O . O O X X X X . X X X O | $$ | a . X . X . X O X O X O X O . O O O . | $$ | 1 O O O O O . X . . O O O O . O X . O | $$ | . . . , . . O O O , . . . . O , X . . | $$ | . X . X X X X X X X . . X O X O O O O | $$ | . . . X O . . . . O O O X X X X X X . | $$ | . . O O O O . . . . . X O O . . X . . | $$ | . . . O X X X X . O . O X O . X . X . | $$ | . O O . O O X . O O O O X O . . X . X | $$ | O . . O O X X . X O X X X O . O O X . | $$ | X O O X X . . X X O O O X . O . . O . | $$ | X X X . . . . . . X X X X O . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------

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[go]$$B $$ --------------------------------------- $$ | . . O X X X X X X . . . . . . . . . . | $$ | . O O X X O O X . X . . . . . . . . . | $$ | . . X O X O . O X X . . . . X . . . . | $$ | . X . O O O . O O X . . X . . X X . . | $$ | . O O . . . . O O X . . . O . X . X . | $$ | . . . . . . X O X X . . . . . O X . X | $$ | . . . . . . O . O O X X X X . X X X O | $$ | a . X . X . X O X O X O X O . O O O . | $$ | 1 O O O O O . X . . O O O O . O X . O | $$ | . . . , . . O O O , . . . . O , X . . | $$ | . X . X X X X X X X . . X O X O O O O | $$ | . . . X O . . . . O O O X X X X X X . | $$ | . . O O O O . . . . . X O O . . X . . | $$ | . . . O X X X X . O . O X O . X . X . | $$ | . O O . O O X . O O O O X O . . X . X | $$ | O . . O O X X . X O X X X O . O O X . | $$ | X O O X X . . X X O O O X . O . . O . | $$ | X X X . . . . . . X X X X O . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

The point, according to my limited understanding, is that for white to reply at 'a' really is too passive (as opposed to your first variation, which is the better option for white). So KataGo's idea of best play for both sides is:

$$B $$ --------------------------------------- $$ | . . O X X X X X X . . . . . . . . . . | $$ | . O O X X O O X . X . . . . . . . . . | $$ | . . X O X O . O X X . . . . X . . . . | $$ | . X . O O O . O O X . . X . . X X . . | $$ | . O O . . . . O O X . . . O . X . X . | $$ | . . . . . . X O X X . . . . . O X . X | $$ | . . . . . . O . O O X X X X . X X X O | $$ | 4 . X . X . X O X O X O X O . O O O . | $$ | 1 O O O O O . X . . O O O O . O X . O | $$ | 2 3 . , . . O O O , . . . . O , X . . | $$ | . X . X X X X X X X . . X O X O O O O | $$ | . . . X O . . . . O O O X X X X X X . | $$ | . . O O O O . . . . . X O O . . X . . | $$ | 5 . . O X X X X . O . O X O . X . X . | $$ | . O O . O O X . O O O O X O . . X . X | $$ | O . . O O X X . X O X X X O . O O X . | $$ | X O O X X . . X X O O O X . O . . O . | $$ | X X X . . . . . . X X X X O . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------

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[go]$$B $$ --------------------------------------- $$ | . . O X X X X X X . . . . . . . . . . | $$ | . O O X X O O X . X . . . . . . . . . | $$ | . . X O X O . O X X . . . . X . . . . | $$ | . X . O O O . O O X . . X . . X X . . | $$ | . O O . . . . O O X . . . O . X . X . | $$ | . . . . . . X O X X . . . . . O X . X | $$ | . . . . . . O . O O X X X X . X X X O | $$ | 4 . X . X . X O X O X O X O . O O O . | $$ | 1 O O O O O . X . . O O O O . O X . O | $$ | 2 3 . , . . O O O , . . . . O , X . . | $$ | . X . X X X X X X X . . X O X O O O O | $$ | . . . X O . . . . O O O X X X X X X . | $$ | . . O O O O . . . . . X O O . . X . . | $$ | 5 . . O X X X X . O . O X O . X . X . | $$ | . O O . O O X . O O O O X O . . X . X | $$ | O . . O O X X . X O X X X O . O O X . | $$ | X O O X X . . X X O O O X . O . . O . | $$ | X X X . . . . . . X X X X O . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Black's loss with letting be captured is more than made up for by the monkey jump, so this is a full point better than the game move.

[kvasir]

I wanted to find a way to make that move work but I tricked myself somewhere in the variations and thought I had found a way for white to resist the monkey jump.