Playing as white here, what is the standard 'good shape' way of responding to black's slide, if your main objective is to block his progress across the top of the board? Is it 'a'?

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[go]$$W
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . B . . . . . . . . . |
$$ | . . . . . . . X . . . a . . . . . . . |
$$ | . . . X . . . . . O . . . . . O . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

_________________
Regards,

Peter

I would play the diagonal if my only objective were to stop Black from getting more of the top. In general, don't allow Black to play that slide if you care about the territory there, though (and don't stop it by playing the diagonal kick, which is bad style) because there's not really a great option.

In a broader sense, by playing the white stone high, white has committed to a more center based strategy instead of asking for territory there, so it shouldn't come as a surprise that black slides under and takes territory of his own. White's goal should be to use that stone to help with fighting elsewhere, and to be consistent with that, pressing black low, like to the 2nd line, works. That said, depending on how the rest of the board is and how late in the game it is, this aim doesn't always hold, but the moral is that you shouldn't really count the area under it as territory until you play moves to block black from sliding under (and even then it may or may not work, of course).

By now many readers must know that when ol' EZ answers a post like this chances are good that he has been checking his database.

In this case, though the results are quite interesting IMHO. I plugged the position below into GoGoD/Kombilo and hit the search button.

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[go]$$B Search Pattern
$$+ - - - - - - - - - - - - - - - - - - - +
$$| . . . . . . . . . . . . . . . . . . . |
$$| . . . . . . . . . . . . . . . . . . . |
$$| . . . . . . . X . . . . . . . . . . . |
$$| . . . X . . . . . O . . . . . O . . . |
$$| . . . . . . . . . . . . . . . . . . . |
$$| . . . . . . . . . . . . . . . . . . . |
$$| . . . . . . . . . . . . . . . . . . . |
$$| . . . . . . . . . . . . . . . . . . . |
$$[/go]

I turned up 300 examples. Before you look, what do you think the results were?
Next play by White and then by Black:

_________________
Dave Sigaty
"Short-lived are both the praiser and the praised, and rememberer and the remembered..."
- Marcus Aurelius; Meditations, VIII 21

Taking away the corner stones to just focus on the sliding shape, if you are going to respond then the usual move would be the kosumi but like Shaddy says it's kind of sucky to get into such a position of black's slide being a move you want to answer to keep the territory. One other option that is worth mentioning to add to your Go vocabulary is this attachment. If black timidly pulls back then you can defend too and get more points than the kosumi (it's like you played the kosumi first and then later you played at 1 and black answered at 2 which is a nice sente endgame for you, whereas what should happen in the endgame is black gets to push at 1 and white blocks/jumps: black's push there has a bigger followup of diving further into white's territory than white's block (which can next capture with the clamp at 2) so it is black's privilege to get the yose in this area).

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

Black doesn't need to be so obedient but can go for the trade below. Black is separated and has hurt his stone to the left, but has a ponnuki on the right. Whether this is good or bad or a disaster depends on the surroundings: white loses a lot to the right (unless he is so strong in that area anyway he can kill the ponnuki (e.g. at a) but if he can do something awesome to the left now black is cut then it might be playable.

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

Also black might choose this. Depending on the surroundings next he could cut at a, bulge at b, or tenuki.

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

White would need to consider all these options (and others but those are the normal choices) and confirm they are all (as it's black's choice) good for him before playing the attachment. It's a risky move that stands to go horribly wrong, but if it works it's nice.

One idea to stop black playing the trade line would be this inside attachment: if black answers at 2 then he can't hane at 4:

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[go]$$W White's dream
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . 1 B 3 . . . . . . . . |
$$ | . . . . . . . X 2 5 4 . . . . . . . . |
$$ | . . . , . . . . . O . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

But probably black can do this, what happens next is a fight that will depend on the surrounding position, but without help it's trouble for white.

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[go]$$W Wakey wakey
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . 1 B . . . . . . . . . |
$$ | . . . . . . . X 3 2 . . . . . . . . . |
$$ | . . . , . . . . 4 O . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

However, if we add one more white stone as shown (a shape which does actually occur in games if there are black and white walls respectively along the triangles and squares) then black's push up no longer works:

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[go]$$W Extra stone
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . B . . . . . . . . . |
$$ | . . . . . T T X . . . . . . . . . . . |
$$ | . . . , . S S S W O . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

Click Here To Show Diagram Code

[go]$$W Extra stone, black's push up fails
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . 1 B . . . . . . . . . |
$$ | . . . . . T T X 3 2 . . . . . . . . . |
$$ | . . . , . S S S W O . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

So black has to cut off 1 which means white can then attach on the outside and black can't hane but must connect and white blocks off the area to the right. As before black might next tenuki, or cut at a or play endgame at b.

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[go]$$W Extra stone, black's push up fails
$$ +---------------------------------------+
$$ | . . . . . . . . . . b . . . . . . . . |
$$ | . . . . . . . . 1 B 3 . . . . . . . . |
$$ | . . . . . T T X 2 4 5 . . . . . . . . |
$$ | . . . , . S S S W O a . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

White has lost some points though in giving the sacrifice stone of 1 to ensure he can block at 3. So if you can play 3 directly (even with the extra marked white stone) it's better, but you have to take into consideration the trade lines where black hanes on the outside.

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

Is the kosumi? Is not bad for white if he was intending most of the upper right to become his territory? It doesn't seem to have blocked black.

_________________
Regards,

Peter

The main lesson here is that if the intent was to take upper side territory, White should have either played on the third line or responded to Black's original stone. Your best bet in this situation is to force Black in a way that will help you obtain territory somewhere else.

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

Yes



Yes, if you want the points 2 is annoying, but it is bad shape:

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[go]$$W
$$ +---------------------------------------+
$$ | . . . . . . . . . 8 4 d b . . . . . . |
$$ | . . . . . . . . 5 B 3 2 a 0 . . . . . |
$$ | . . . . . . . X 6 7 1 c 9 . e . . . . |
$$ | . . . , . . . . . O . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

Black can continue jumping along the 2nd line whilst white builds a wall. In the early stages of the game this is great for white, but in the endgame if white wants the territory to the right it is indeed good for black.

The bad shape is the lack of eyes along the edge and liberty shortage if black tries things like this push:

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[go]$$Bm10
$$ +---------------------------------------+
$$ | . . . . . . . . 4 X X 2 3 . . . . . . |
$$ | . . . . . . . 7 O X O X 1 6 . . . . . |
$$ | . . . . . . . X X O O 8 O . . . . . . |
$$ | . . . , . . . . . O . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

If you really really want the points then you could even do things like this if you don't care about your hoshi stone:

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[go]$$W
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . B . 1 . . . . . . . |
$$ | . . . . . . . X . . 2 3 . . . . . . . |
$$ | . . . , . . . . . O 4 5 . . . , . . . |
$$ | . . . . . . . . . . 6 7 . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

Or the knight's move of your first post and then fall back again hurting the hoshi stone:

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[go]$$W
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . B . 2 3 . . . . . . |
$$ | . . . . . . . X . . 4 1 . . . . . . . |
$$ | . . . , . . . . . O 6 5 . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

Basically there is not a good way to keep the points once black slides (anything is profit in sente for black), so don't let him slide if you want the points.

P.S. some food for thought, shifting things over to the corner:

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

It's probably worth pointing out that the jump on the second line ( below) doesn't work for black any more:

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