This game is a classic of the Edo period and the one where Shusaku forced his last major rival to sen-ai-sen handicap.

Go Seigen's commentary calls the next move "A superb move which..."

Can you guess what it is?

B: Ota Yuzo
W: Honinbo Shusaku

Click Here To Show Diagram Code

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

I may do more of these if people like them.

Source: Invincible - The Games of Shusaku

The two lower corners are settled. The upper right corner requires a move by white ( probably Q14 ). It is urgent.
The upper left corner is almost played out, but white does not want to get locked in. It is big but not urgent.

The left side, right side, and bottom are all moderately big to big moves, but none is urgent. The top side is urgent, for there are several unsettled groups there.

White has two urgent areas to play with a lone stone in each. If he does either in gote, black takes the other. So he needs a sente move that strengthens one of his stones so that he can play the other next.

White plays this:

Click Here To Show Diagram Code

[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . X . . . . . . . . X . . . . |
$$ | . . O , O X . . . , O . . . . , O . . |
$$ | . . X . O X . 1 . . . . . . B . . . . |
$$ | . . . . O . 2 . . . . . . . . 3 . . . |
$$ | . . X O . . X . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . a . . . . . , . . . . . , b . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . X . . . . . . . . . O . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Now he has 'a' threatening a double attack, and 'b' grabbing territory. On top of that, black has to find eye space for his P15/P17 stones.

_________________
Help make L19 more organized. Make an index: https://lifein19x19.com/viewtopic.php?f=14&t=5207

Seigen: "White 22 is a superb move which forces Black into a low position on the left"

It should also be noted that B23 is called "painfully submissive." c18 is noted as an alternative.

The next 5 moves play out as follows. W is able to live up top without much difficulty after the cap.

Click Here To Show Diagram Code

[go]$$Wcm22
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . X . . . . . . . . X . . . . |
$$ | . . O , O X . . 5 , O . . . . , O . . |
$$ | . . X . O X . . . . . . . . B . . . . |
$$ | . . . . O . . . . . 4 . . . . . . . . |
$$ | . . X O . . X . . . . . . . . . 3 . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . 1 . . . . . . . . . . . . . . . |
$$ | . . 2 , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . X . . . . . . . . . O . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

The main motivation for posting this was that in problem books you are often given a category for the problem. If you know you are looking for a reducing move or forcing move or shape it is easier to find the proper move. I find it more interesting to see what type of move people think is called for in a whole board problem.

Thanks to Joaz for the response.

Wow, I was surprised to see this. I had similar, but less effective, thoughts to what Joaz came up with. If nothing else, I figured Shusaku would revert to Joaz's moves after the forcing move. I guess he's prioritizing his own group stability/base eyespace first?

_________________
Someday I want to be strong enough to earn KGS[-].

A couple things to note:

1) 26 complicates the connectivity of B's knights move to the left making it more difficult for B to attack W.

2) once 22 and 24 are played the influence B can get from the cap and ensuing attack is considerably less useful than in Joaz's proposed plan.

3) The joseki played in the top left, which includes the move at L16 was new to this game. Shusaku wrote later that he spent 6 hours thinking through the position. So this was new ground for both players. B should have fixed before his shape on the left before playing 21.

4) Far from me to critique Joaz but my guess is that the moves he proposed would allow B to strengthen himself, attack White and then take a move like e11 which would make the board look quite good for B. Exchanging 1 for 2 seems like it's helping b to fix shape and creating a new group behind enemy lines before move 30.

5) I'm 5k so....