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 Post subject: Two-space extensions - a mini-lesson from Shirae
Post #1 Posted: Thu Dec 05, 2013 5:51 am 
Oza

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Where are there good moves for White to play here? Try to rank the alternatives.

Click Here To Show Diagram Code
[go]$$ White’s best plays?
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , X . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]


Do the same here.

Click Here To Show Diagram Code
[go]$$ White’s best plays?
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]


In the first position, actual pro records indicate that White’s preferred move by far is to approach high at A below. This is a little more than twice as popular as a restrained approach at B. This in turn is twice as popular a low approach at C and a wedge at D. In other words, the ratio A:B:C:D is roughly 4:2:1:1. All other moves are very infrequent, but when they happen the focus is mainly on the open skirt on the left side.

Click Here To Show Diagram Code
[go]$$ White’s commonest plays ranked
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . d . . b c . . . . |
$$ | . . . , . . . . . , . . . . a , X . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]


Just as an historical sidelight, the Great Plasterer Komatsu Kaizen offers us the first example of A in the 18th century, but its popularity stems from Yasui Chitoku early in the following century – especially as Chitoku’s great friend and rival Honinbo Genjo took it up, too. Chitoku had first assayed it against him.

In a book on the two-space extension, pro Shirae Haruhiko (who is one of the most experienced and popular presenters) says that one idea to consider is to eschew a corner approach altogether on the grounds that Black’s high enclosure on the left is just begging to play a pincer against a White approach. In that case the right wedge would be D. As we have seen, in practice other pros agree.

I think it would be safe to say that amateurs in general are also comfortable with the theory that the left-side enclosure emphasises the upper left side and that a pincer there would be ideal for Black. I assume they also accept that one reason for a high approach is to make a pincer somewhat less problematical, and similar reasoning explains a preference for B over C.

In short, White’s wedge at D is indeed a move very worthy of consideration.

However, if you do accept all that, how do explain the database results below for the low left-side enclosure?

Click Here To Show Diagram Code
[go]$$ White’s commonest plays ranked
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . d . . c b . . . . |
$$ | . . . , . . . . . , . . . . a , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]


In this case White A (introduced by Honinbo Jowa) is even more popular, even though White has less reason to be concerned about a Black pincer. At least, it seems we can infer that from the fact that his second most popular choice in this case is now the low (and highly pincerable) approach at B.

Furthermore, the justification for the distant approach at C seems to fall away slightly, and making a position on the side by starting with a wedge at D could be seen as being more attractive now that Black has a less threatening low enclosure on the left.

But the GoGoD ratios of A:B:C:D are now 1906:565:320:65. A big movement! If this were election night, the psephologists would be getting very excited about the once marginal constituency of C+D changing radically because of a small boundary change. And possibly change in an unexpected direction?

I think the explanation lies in another example from Shirae. Try this: where is White’s best play on the right, A or B? (And why, of course!)

Click Here To Show Diagram Code
[go]$$ White A or B?
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X X X . X . . . . . . . . . . . . . |
$$ | . X O O O . . . . , . . . . . X . . . |
$$ | . O O . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . a . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . b . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . , . . . . X , X . . |
$$ | . . . . . . O . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


Shirae recommends White 1 below. He doesn’t give a game reference, but we have two and in both cases the pros agreed with him – no less than Takemiya Masaki and Yi Ch’ang-ho. The reason for the recommendation was a general rule he gives that amateurs can easily apply: never play a two-space extension unless it has a sharp follow-up (nerai). In this case, Shirae points to the nerai at A. Playing White B above as the two-space extension is, by contrast just wishy washy.

Click Here To Show Diagram Code
[go]$$W White 1 is best
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X X X . X . . . . . . . . . . . . . |
$$ | . X O O O . . . . , . . . . . X . . . |
$$ | . O O . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 6 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . 1 . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 4 . . . . . . . . . . . . . . . . |
$$ | . . 2 O . . . . . , . . . . X , X . . |
$$ | . b 3 5 . . O . . . X . a . . c . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


The Takemiya game continued as here and White did then indeed invade at once at A. In the other game, Yi played at B instead of 5, emphasising the left side first, but he likewise later exploited a nerai in the lower right, in his case at C.

In passing note a bit of psychology. It is fairly obvious that Black will want to play on the left side after White 1, but the inevitable consequence of that is to strengthen White’s lower-left position – which in turn makes the bull’s-eye at A pulse even stronger.

If we now apply Shirae’s rule to the initial positions, we can see that White’s two-space extension does indeed have nerai (which are, remember, sharp follow-ups – applying a scalpel, not a sticking plaster), at A and several points northwards.

Click Here To Show Diagram Code
[go]$$ White’s best plays?
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . c . . . . . . . . . . . . . . . |
$$ | . . . X . . . O . . O . . . X . . . . |
$$ | . . . , . . . . . , . . . . . , X . . |
$$ | . . b X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . a . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]


But in the same position with Black’s enclosure shifted to B, there are no such nerai. The best White has (and seen in several of the games recorded) is a wishy-washy probe at C. Reasons for White to overcome the much greater reluctance to play the two-space in this case presumably have to be sought in the positions on the rest of the board.


This post by John Fairbairn was liked by 6 people: asura, Boidhre, Dusk Eagle, hyperpape, Phoenix, VincentCB
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 Post subject: Re: Two-space extensions - a mini-lesson from Shirae
Post #2 Posted: Thu Dec 05, 2013 11:28 am 
Gosei
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Thanks for this!

I wonder how big of a concern the pincer really is though, in my experience white usually attaches underneath like so:

Click Here To Show Diagram Code
[go]$$Wcm1 followup
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . a . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . 3 2 4 . . . |
$$ | . . . , . . . . . , . . . . 1 , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]


"a" has been discussed here and on SL as a trendy probe now. I can't do a DB search right now, does anyone have a feeling about this vs. the pincer? What about in high shimari case?

Click Here To Show Diagram Code
[go]$$Wcm1 A or B?
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . a . . . . |
$$ | . . . , . . . . . , . b . . 1 , X . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

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