On
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[go]$$Wcm16
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Ed Lee suggested

. Here is one way to see that it is a good play.
- Click Here To Show Diagram Code
[go]$$Wcm8
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$$ | . . . . . . . . . . . . . . . 8 7 . . |
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Suppose that the game had gone this way, with Black replying at

instead of the pincer (probably not best play). Through

is joseki. Then the attachment,

, is unusual.

is solid. Maybe a little slow, but you can't say that it is a bad play.
- Click Here To Show Diagram Code
[go]$$Wcm16
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$$ | . . . . . . . . . . . . . . . X 2 . . |
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$$ | . . . O . . . . . X . . . X . , O . . |
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By contrast, if Black gets

in he is building strength on the right side, preventing White from making the normal extension in the bottom right, and putting pressure on the White group there. This position is not good for White.
- Click Here To Show Diagram Code
[go]$$Wcm14
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$$ | . . . . . . . . . . . . . . . X 2 . . |
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$$ | . . . . . X . . . . . . . . . X W . . |
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All of which means that Black should have played

in response to

. Which, in turn, means that White should not have played

. And if you are not going to make a base with

, why play the attachment at

earlier? (Not that pros have not played the

attachment. But then they followed up with more sophisticated play.

)
When I was learning go the textbooks said not to extend from a corner (except one with a 4-4 stone) without making an enclosure first. But even at that time, the idea was being revived — such extensions had been played in earlier centuries.
- Click Here To Show Diagram Code
[go]$$Bc
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$$ | . . . . . . . . . . . d c b . 8 . . . |
$$ | . . . O . . . . . X e . . . . , . . . |
$$ | . . . . . X . . . . . . . . a X . . . |
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$$ +---------------------------------------+[/go]
The high approach,

, was supposed to be the refutation. But it turns out that after the pincer,

, this is not such an easy position for White.

is outnumbered locally and it has no base. Furthermore, as we have seen, making a base is problematical.
In this kind of situation White generally wants to play lightly, to reduce Black's framework, possibly sacrificing a stone or two — or more.

Moves which have been tried include "a", which usually leads to complicated fighting, and the jumps, "b", "c", and "d". "d" is quite light.

With the advent of AlphaGo, perhaps we will see "e", as well.
N. B.: White can also play elsewhere, such as approaching the top right corner. With so many choices on the bottom side, it is often a good idea to play elsewhere and see how the game develops. An opening pincer is not sente.
- Click Here To Show Diagram Code
[go]$$Bc
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$$ | . . O . . . . . . . . . . . . a 8 . . |
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$$ +---------------------------------------+[/go]
White may also approach at

or "a", which are easier for White to handle.

Black does not have a severe pincer.