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[go]$$Wc White to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X . O . . . . . O . . b . X . . . . |
$$ | . . . , . O . . . , . . . . . , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . X . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . X . O . |
$$ | . . . O . . O . . a . . X . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Neither 'a' nor 'b' is the top answer, but of the 2, I preferred 'a', as:

It is in a bigger gap; and
The 2 stones on its left look weaker that the 3 stones to the left of 'b'.

Why did the book rate 'b' much higher?

_________________
Regards,

Peter

Because it stops black playing in that area, and black's move there is better than black's move on the lower side as it threatens the invasion at c. White could defend against that by jumping to d, but that means black got to make the extension in sente which is nice for him. Also the white move on the bottom is rather flat and doesn't really threaten anything nasty to black's lower right corner (white's move at the top doesn't really threaten that corner much either).

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[go]$$Wc White to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X . O . . . c . O . 2 . . X . . . . |
$$ | . . . , . O . . . , . . . . . , X . . |
$$ | . . X . . . . . . d . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . X . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . X . O . |
$$ | . . . O . . O . . 1 . . X . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Here is a good opportunity to develop your own judgement.

Compare these two diagrams.

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[go]$$Wc White a, Black b
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X . O . . . . . O . B . . X . . . . |
$$ | . . . , . O . . . , . . . . . , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . X . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . X . O . |
$$ | . . . O . . O . . W . . X . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

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[go]$$Wc White b, Black a
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X . O . . . . . O . . W . X . . . . |
$$ | . . . , . O . . . , . . . . . , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . X . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . X . O . |
$$ | . . . O . . O . . B . . X . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

OC, "a" and "b" do not refer to specific points.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

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[go]$$Wc White to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X . O . . . . . Q . . b . X . . . . |
$$ | . . . , . O . . . , . . . . . , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . X . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . X . O . |
$$ | . . . O . . @ . . a . . X . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

OK. Is it the fact that the white stone with the triangle is weaker than the one with the square?

_________________
Regards,

Peter

Sort of, but not really. Both white groups will feel a little unhappy if black approaches, and white will feel he owes a move in each case (I think); both can strengthen themselves with a silly little flat extension on the 3rd line, but it's not worth many points. And don't forget that white will take one and black will take the other. So the question is really: which is more profitable for black? Both are also little flat extensions for black. But notice that the lower one has little potential to build from, whereas the upper one forms a double wing (even if a rather tight one), and black can expect to gain not only a few tiny points on the side, but also more inside the double wing formation.

Because the triangled stone is three spaces away, the connection is more open to invasion than the two space. White might want to reply to both black moves at some point to strengthen his groups or connection, but...

The other thing about black's extension to B is that black already has an extension down the right side and a strong corner, so it's easy and natural for black to expand outwards and make a nice moyo if white defends in some way. Black's group on the bottom has less potential for continued expansion because of white's group on the right side.

That's not a thought that consciously crosses my mind when preferring the move on the top side (I think "black's m17 aims at h17", but I suppose yes it is weaker in that it is 3 spaces away from its nearest support, and thus there is the h17 invasion to worry about, whereas the lower side stone is only 2 spaces away so black moves in that area don't aim at anything. Neither of them are weak groups though. The weak groups here are black's two stones in the lower left and white's on the left side so that is the most important place to play. One idea would be c4 to stop those black stones making eyes in the corner and get the corner profit for ourselves, but as g3 is low it doesn't look so easy to attack black severely, which is why I like c13 which makes it harder for black to invade at c10 (the same middle point of a 3 space extension from 3rd to 4th line as h17 on top) as he can no longer link up to his group above, and c13 itself is pretty much sente on the black group above.

A key point about checking extensions as on the top side is not just what they achieve now, but what they aim at in the future, and this needs to be taken into account when judging how big they are.

I'd note that the bottom left group isn't in as much trouble as it might appear at first, because the black stones above it aren't strong either. If we reimagine the position to strengthen black there:

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[go]$$Wc White to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X . O . . . . . O . . . . X . . . . |
$$ | . . . , . O . . . , . . . . . , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . X . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . X . O . |
$$ | . . . O . . O . . . . . X . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Then I'd be much more worried about white giving black profit trying to handle the bottom group. Playing c4 to try to enclose the corner really helps black, escaping to the center black can also expand his profit on that side.

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[go]$$Wc Black to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . X . O . . . . . O . . O . X . . . . |
$$ | . . . , . O . . . , . . . . . , X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X a . X . . . . . . . . . . . . . |
$$ | . b 1 , . . . . . , . . . . . X . O . |
$$ | . c . O . . O . . X . . X . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

As it stands, this looks like a reasonable response to the approach. If black doesn't respond, his side stones will be split. If he responds at a, he's not obviously in a better position and white has helped her corner in sente so she can be happy. If black plays b, white plays c and wherever it goes from there the white corner seems quite solid.

On the left black doesn't have much room for a base, and the two stone jump means he has a cut to worry about. The stones feel a little vulnerable. Which means you'd like to threaten them and get something in return. Securing a group is a great thing to get in return, so even without the big move at the top, you'd almost like black to force you to attack him with k3.

I second Uberdude's C13. Of all the white groups on the board, the left side one looks the weakest. C13 helps make it stronger, and at the same time weakens the top-left black group. I didn't understand this for a long time, but a lot of Go is simply about making your groups strong and your opponent's groups weak.

_________________
We don't know who we are; we don't know where we are.
Each of us woke up one moment and here we were in the darkness.
We're nameless things with no memory; no knowledge of what went before,
No understanding of what is now, no knowledge of what will be.

This is quite an interesting question if you've not seen it before. If black ignores c13, how does white attack the black group? Someone was asking about studying shape, this is a great lesson in it.

Ah, nice, I never thought about it this way. I have only seen this one =)

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[go]$$Bc elsewhere - Black to settle his shape
$$ ------------------
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . 4 . . 2 . . .
$$ | . 3 . O . . . . .
$$ | . . . . . . . . .
$$ | . . 1 . . . . . .
$$ | . . . . . . . . .
$$ | . . 6 . . . . . .
$$ | . . . . . . . . .[/go]

_________________
My "guide" to become stronger in Go

There is also another problem here: if White plays a instead of 3, how does Black make sabaki?