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This discussion was part of the 2013 LG Cup thread ( viewtopic.php?f=13&t=8474&p=152713#p152713 ).
IMO, it is interesting enough that it deserves its own thread.
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I just replayed the Chen-Iyama game and I ask myself whether Iyama misread the Aji before he decided to double-Hane on move ? The result up to Black 101 seems horrible for White - Black settling his weak-ish group and taking away almost all territory White had. The cut at White 106 also seems to hint that White needs to make something happen.
To back up a bit, I feel by move White is behind. I for one already didn't like the Joseki outcome in the bottom right for White (and styler-points for Black for not playing the large avalanche in the top left : D) and Black's Tenuki on for a patient defensive move seems to me like Black is confident he can keep White's left in check, although White got - for a moment - a nice double attack.

In the end White lost both - I guess - last resort Kos, that's also quite something.


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SoDesuNe, I do not like the bottom right joseki from white's perspective either. But Iyama used it in aother important game before with opposite color (http://www.go4go.net/go/games/sgfview/27071/33) so perhaps he has done his homework.

I don't like his , after playing from outside, it looks an inconsistent decision to attack from inside.

Click Here To Show Diagram Code

[go]$$Wm58
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . O O X . . . . . . . . X . . . . . |
$$ | . . O X . X . X . O . . . . . , X . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . O . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . 6 O 5 . . . . . . . . . . . . . . . |
$$ | . 8 4 . . . . . . . . . . . . . X . . |
$$ | . 7 . X . 1 . . . , . . . . . , . X . |
$$ | . . . . . . . . . . . . . . . X X O . |
$$ | . 9 . 2 . 3 . . . . . . . . . X O O . |
$$ | . . . . . . . . . . . . . . O O X . . |
$$ | . . . . . . . . . . . . X X X O X O . |
$$ | . . a . . . O . . . . . . O X O . . . |
$$ | . . O , O . O X . , . . . O X O O . . |
$$ | . . . . O X X . . . . . X X O X O . . |
$$ | . . . . . . . . . . . . . . O X X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

White's shape does not look solid enough for effective attacking. And black always has tesuji 'a'.

I would do something differently, such as:

Click Here To Show Diagram Code

[go]$$W
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . O O X . . . . . . . . X . . . . . |
$$ | . . O X . X . X . @ . . . . . , X . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . @ . . . . . . . . . |
$$ | . . . . 3 . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . 2 . . . . . . . . . . . X . . |
$$ | . . a X . . . . . , . . . . . , . X . |
$$ | . . . . . . . . . . . . . . . X X O . |
$$ | . . . 1 . . . . . . . . . . . X O O . |
$$ | . . . . . . . . . . . . . . O O X . . |
$$ | . . . . . . . . . . . . X X X O X O . |
$$ | . . . . . . O . . . . . . O X O . . . |
$$ | . . O , O . O X . , . . . O X O O . . |
$$ | . . . . O X X . . . . . X X O X O . . |
$$ | . . . . . . . . . . . . . . O X X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

is to prevent the connection at 'a'. Then separates the two groups, at the same time helping the group. If black run into the central area, white can naturally reduce black's bottom potential.

Is the 'tesuji at a(c5)' that you mentioned something any strong player would be aware of? I was very surprised by it.

That is a common tesuji to break the connection. The basic shape is like this:

Click Here To Show Diagram Code

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

is a following tesuji. Depending on what white does next, black either cuts off the stone inside, or benefits from something outside (in this basic shape, that means killing the outside stone by a ladder).

Thanks, Macelee, it's good to know about that tesuji. It was a fun game, and the big exchange was quite thrilling. An Youngil at GoGameGuru said w82 was the mistake, but your idea about w58 seems logical too.

The latest Weekly Go from Japan covers a bit of the game and agrees that 82 was the mistake.