BQM 264

Ishida Yoshio vs Oeda Yusuke, 50 moves  

This game between Ishida and Oeda is the subject of the first chapter of The 1971 Honinbo Tournament. The book explains that Oeda (white) could not play at a for move 56 ( in diagram) using the following diagram:

Ishida Yoshio vs Oeda, alternate sequence  

This White 56 ( in diagram) is not possible. The White stones on the top are not settled as Black a forces White b which is followed by Black c and White d.

Why can't White respond to Black a with White c ?

 

My best guess is the atari at .

8 at marked stone  

If at a, then Black b kills.

 

Due to shortage of liberties, connects all the stones, and White has hardly any eye space.

Ishida Yoshio vs Oeda, alternate sequence (continued)  

The book provides this sequence as the continuation should White use move 56 to engulf the black stone rather than extending. White must find eye space on the upper edge while Black strenghtens his center group preventing White from being able to attack it further.