Check out the latest game in the 31st Ryusei. Iyama 9-dan beat Kato Atsushi 9-dan by W+3.5. But both players overlooked a very simple life for an undead Black group in one corner, and for quite a long time.

Kato should have won, but once players agree the game is over there's no going back.

On the face of it, it's sheer nincompoopery, but I wonder whether a White stone was slightly displaced and appeared to be on a crucial empty hoshi point. If that point had been filled, Black really was dead. Had the stone been displaced, it would not have affected the rest of the final position, so there would be no special reason to notice it.

This is the game:



The situation is really strange. Not only black's status was unclear, but also white captured a group in atari when it could wait. So I think that there is a mistake in the record.
There was a ko fight previous to this. Perhaps some threat+answer are missing?

The game record is correct, as published, and the White capture at T15 is also correct if you start from the illusion that both players had (otherwise Black T17 has a real effect). There were no written comments by the players (the game, after all, was played in September did not comment - the procedure is that two games are played by the first winner on the same day and the losers just scarper - but Takao Shinji suggested that both players thought that Black R19 failed against P19. That is why I wondered whether the stone at P16 had drifted towards Q16 enough to make the players think Black truly suffered shortage of liberties. Anyone who watched the broadcast might have a better view, in both senses!

It was evidently noticed at the time, though, because of the comment that both players had agreed that the whole upper-right corner was White territory and so the game was completely over. There was no mention of any dispute.

Edit: corrected quote location

My first theory was that they played something like the diagram instead of capturing the 5 stones at move 190 but it is still odd since would have been sente if .

Click Here To Show Diagram Code

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

My second theory is that they played as in the next diagram. That is white played the ko threat but black plays before finishing the ko, then white kills the corner in gote. White could play differently but this way eliminates black's ko threats. It could be some nine-dan-shenanigans, black making a good forcing move when white won't maximize the points locally.

Click Here To Show Diagram Code

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

If there was no concern about ko threats, white could respond to as follows.

Click Here To Show Diagram Code

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

The schedule of the tournament suggests that the games were first played and then broadcasted later. That is gotoeveryone displays two dates as with NHK cup. Maybe there is some chance of finding a recording? It would be rather interesting, especially if it is the case that the stones slide, it is hard for me to imagine how white could think he could simply capture the 5 stones and already have killed the corner. The remaining moves are also much smaller than living the corner. I guess anything could be possible if the stones start moving