According to AlphaGo Teach, there is a potentially serious human blind spot in a later position in this joseki. That is, humans prefer, by a ratio of 5 to 1 (49 to 10 by Waltheri's database), a play that is likely to be a mistake.
- Click Here To Show Diagram Code
[go]$$Bcm11 Obvious wedge
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , 8 . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . . . X . 1 . . . . 7 . . . . . . |
$$ | . . . O . . . O X 3 5 . . . . X . . . |
$$ | . . . . . X . O 2 4 . 6 . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
Given Black's thickness on the bottom side, this wedge,
, has to be a good play, right? Lee Changho played it agains Cho Hunhyun in 1996. Well, AlphaGo doesn't like it. It gives Black an estimated win rate of 44.6%, 3.2% higher (worse for White) than its chosen play. That difference suggests that
is a mistake.
What's the problem with it?
- Click Here To Show Diagram Code
[go]$$Bcm19 Attack
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 3 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . . . X 1 X . . . . X . . . . . . |
$$ | . . . O . . . O X X X . . . . X . . . |
$$ | . . . . . X . O O O . O . 2 . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
Cho Hunhyun continued with a sequence AlphaGo likes. He connected at
with sente and then
attacked White in the bottom left.
What should White have played instead of the wedge?
- Click Here To Show Diagram Code
[go]$$Wcm18 Connect
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . d b . . |
$$ | . . . O . . . . . , . . . . . X c . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . a 6 . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . 2 4 . . . . . . . . . . . |
$$ | . . . . . X 1 X . . . . X . . . . . . |
$$ | . . . O . 5 3 O X X X . . . . X . . . |
$$ | . . . . . X . O O O . O . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
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connects White's groups, obviously forestalling an attack against either one. Then
takes a big point on the right side. This actually is in line with the go proverb to make urgent plays before big plays, but humans haven't particularly seen it that way. In Waltheri's database only two humans, Kato Masao and Zhang Wengdong picked AlphaGo's play. Then their opponents played at "a", but that's another question.
BTW, how does AlphaGo Teach continue from here, to deal with Black's imposing moyo? With the 3-3 invasion of at "b", of course.
But doesn't that allow Black to build up his moyo with a block at "c"? Maybe so, but AlphaGo blocks at "d".
Like I said, I don't understand this game.
BTW, AlphaGo doesn't particularly like
, the 5th line keima, giving it a winrate of only 41.5%. Well, that kind of makes sense, if the moyo isn't that big a deal. What does AlphaGo like? Why, the 3-3 invasion in the top left corner, of course!
It gives it a winrate of 44.0%, 2.5% better than the keima.
is another potential human blind spot, chosen by humans more than 95% in Waltheri's database. Needless to say, humans chose the 3-3 invasion 0% of the time. That will change.
Edit: And if the moyo isn't that big a deal, so that the keima is at least questionable, then maybe playing the press to build thickness isn't that big a deal, either. So maybe the pincer is better, eh?