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[go]$$Bcm15 Black to play
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . c . . . . . . . . . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . O X . . . . . . . . . . . . . |
$$ | . . . . X O O . . . . . . . . . . . . |
$$ | . . X . X . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . a . O . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . b . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . d . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . O . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

I've been lurking for a long time, but Bill's excellent series and ready access to a desktop brought me out.

Like Robert my first reaction was that black played 'a'. After more reflection I figured that, with the two adjacent corners for support, 'b' or 'c' was more likely. Based on Uberdude's bible, however, I'd wager that the computer would play 'd'.

The game is GoGoD 2003-02-19g, the 4th game of the Kisei final between O Rissei (W) and Yamashita Keigo.

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[go]$$Bcm15 Thick and slow
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . a . . . . . . . . . . . . . |
$$ | . . 2 , O . . . . , . . . . . X . . . |
$$ | . . X . O X . . . . . . . . . . . . . |
$$ | . . . . X W W . . . . . . . . . . . . |
$$ | . . X . X 1 . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . O . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Yamashita's was new to me. When I was learning go, a was the tesuji to know, played as a sacrifice to weaken or even capture the stones. Elf reckons that loses 15½% to par, while a loses only 15%. The correct answer is none of the above. O replied with securing the corner and threatening the Black group. Elf reckons that loses 18½% to par!

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[go]$$Wcm16 Mainline for
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . O X . . . . . . . . . . . . . |
$$ | . . . . X O O . . . . . . . . . . . . |
$$ | . . X . X X . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . W . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . b a . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 9 . . . . . . . . . . . . . . . . |
$$ | . . 1 6 . . . . . . . . . . . . . . . |
$$ | . 5 4 7 3 . . . . , . . . . . O . . . |
$$ | . . 8 X . 0 . . . . . . . 2 . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

approaches the bottom left corner, with as backup. approaches the bottom right corner. (a and b are also playable, in order of preference.) plays the press. does not crawl on the 3d line, but resists. An AI joseki follows.

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[go]$$Wcm26 Mainline for , continued
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . O X . . . . . . . . . . . . . |
$$ | . . . . X O O . . . . . . . . . . . . |
$$ | . . X . X X . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . O X . . . 5 7 . . . . . . . . . . |
$$ | . O X O O 1 3 4 6 8 . . . . . O . . . |
$$ | . . X X . X 2 . . . . . . 2 . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

White pushes to build a wall in exchange for territory.

Better play for . Enclose the bottom left corner.

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[go]$$Bcm15 The Black group is OK.
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . b . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . O X . . . . . . . . . . . . . |
$$ | . . . . X O O . . . . . . . . . . . . |
$$ | . . X . X . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 1 a . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . O . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Elf's top choice is to play the large knight's enclosure of the bottom left corner, with a in second place, and certainly playable. No other play is on Elf's radar, i.e., gets more than 1.5k rollouts. I would not be too surprised if another top bot chose b. In any event, it is not urgent to do anything about the Black group in the top left corner.

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[go]$$Bcm15 Mainline for
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . 3 . . 2 . . . . . |
$$ | . . . , O . . 4 . , . . . . . X . . . |
$$ | . . X . O X . . . . . . . . . . . . . |
$$ | . . . . X O O . . . . . . . . . a . . |
$$ | . . X . X . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 1 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . O . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

This same position occurs in GoGoD 2000-01-29b, between Cho Chikun (W) and Kataoka Satoshi. I chose to use its variations, as they have many more rollouts (26.4k) than those in the O vs. Yamashita game.

After encloses the bottom left corner, the top right corner becomes important. (White could also approach at a.) approaches from the top side, pincers, and bolsters White's position there, in a nice flow of the stones.

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[go]$$Bcm15 Variation 2
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . 6 8 . . . . . . . . . . . . . . . . |
$$ | . 3 7 O . . . 9 . . . . . . . . . . . |
$$ | . . . , O . 0 . . , . . . . . X . . . |
$$ | . . X . O X . . . . . . . . . . . . . |
$$ | . . . . X O O . . . . . . . . . . . . |
$$ | . 5 X . X . . . . . . . . . . . . . . |
$$ | . . 4 . . 2 . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 1 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . O . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Starting with White boxes Black in, but then gets to play on the top side with sente. Not that getting boxed in is good, but in exchange Black gets and takes sente.

Current position:
1. D6 comes to mind as a pincer shimari. B's group in the upper left already has a one space extension and access to corner and side, though it is short on liberties.
2. G16 to fight might be exciting but W F12 seems dangerous especially as W still has C16 or B16. In that case perhaps F17 is a tesuji. Or just sacrifice with H17?
3. F12 is proper but seems too slow when W can settle comfortably on left.

Opp to play
1. In lower left, W cut is a move but not very efficient when already on 2nd line. My instinct is C11/D12 ish

Past:
1. By memory, I think this joseki is meant to be good for B but I haven't seen it for many years.

Check:
1. close enough