Fedya wrote:
I assume there's a reason why 7 at 8 is wrong:
$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . X . . . . . . 6 8 X 9 . . . . |
$$ | . . . X O . . . O X X 7 X O X X X . . |
$$ | . . . X . . . . O , O X . O O O X . . |
$$ | . . X . . . . . . . O X O . X . X O . |
$$ | . . . . . . . 5 . 3 4 O O X . X X . . |
$$ | . . . . . c . . . 1 O . . X X O . X . |
$$ | . . . . . . . . a O X X . X O O O . . |
$$ | . . . . . . . . 2 b O X . . O X O . . |
$$ | . . . , . . . . X O O X . X X X O . . |
$$ | . . . . . . . . O O O X . . . X X O . |
$$ | . . O O . . . . O O X O X O O O X O . |
$$ | . . X O X X X X . O X O . . . X O . . |
$$ | . O O X . X O X . O X . O . O . . . . |
$$ | . . . . X O O X . O X . O X . . . . . |
$$ | . . O , X . . O X O X X X O O O O . . |
$$ | . . . O X . O . X O X O O X O . X . . |
$$ | . . . . X . . . X O O O . X X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------
- Click Here To Show Diagram Code
[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . X . . . . . . 6 8 X 9 . . . . |
$$ | . . . X O . . . O X X 7 X O X X X . . |
$$ | . . . X . . . . O , O X . O O O X . . |
$$ | . . X . . . . . . . O X O . X . X O . |
$$ | . . . . . . . 5 . 3 4 O O X . X X . . |
$$ | . . . . . c . . . 1 O . . X X O . X . |
$$ | . . . . . . . . a O X X . X O O O . . |
$$ | . . . . . . . . 2 b O X . . O X O . . |
$$ | . . . , . . . . X O O X . X X X O . . |
$$ | . . . . . . . . O O O X . . . X X O . |
$$ | . . O O . . . . O O X O X O O O X O . |
$$ | . . X O X X X X . O X O . . . X O . . |
$$ | . O O X . X O X . O X . O . O . . . . |
$$ | . . . . X O O X . O X . O X . . . . . |
$$ | . . O , X . . O X O X X X O O O O . . |
$$ | . . . O X . O . X O X O O X O . X . . |
$$ | . . . . X . . . X O O O . X X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
That's a good question, and a variation that needs to be read and evaluated too. Black doesn't die or anything catastrophic like that, but white gets a better / more sente squeeze. White gets both 3 and 5 in sente here, 5 is useful to connect in the centre, 3 could be useful to make some eyespace in the g18 area (and gain liberties). With my variation it appears that could also be true if white starts with L18 to make the sacrifice larger not just starting at k16. However, the important point is the "in sente" is for what threat if ignored? With m17 connection the answer is white is threatening to capture the entire black group of 5 stones. With my sequence it's just the tail of 2 stones.
$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . 6 . 4 . . . . . . |
$$ | . . . . X . . . 3 2 1 O O X X . . . . |
$$ | . . . X O . . . O X X X X O X X X . . |
$$ | . . . X . . . . O 5 O X . O O O X . . |
$$ | . . X . . . . . . . O X O . X . X O . |
$$ | . . . . . . . X . X O O O X . X X . . |
$$ | . . . . . . . . . X O . . X X O . X . |
$$ | . . . . . . . . . O X X . X O O O . . |
$$ | . . . . . . . . O . O X . . O X O . . |
$$ | . . . , . . . . X O O X . X X X O . . |
$$ | . . . . . . . . O O O X . . . X X O . |
$$ | . . O O . . . . O O X O X O O O X O . |
$$ | . . X O X X X X . O X O . . . X O . . |
$$ | . O O X . X O X . O X . O . O . . . . |
$$ | . . . . X O O X . O X . O X . . . . . |
$$ | . . O , X . . O X O X X X O O O O . . |
$$ | . . . O X . O . X O X O O X O . X . . |
$$ | . . . . X . . . X O O O . X X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------
- Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . 6 . 4 . . . . . . |
$$ | . . . . X . . . 3 2 1 O O X X . . . . |
$$ | . . . X O . . . O X X X X O X X X . . |
$$ | . . . X . . . . O 5 O X . O O O X . . |
$$ | . . X . . . . . . . O X O . X . X O . |
$$ | . . . . . . . X . X O O O X . X X . . |
$$ | . . . . . . . . . X O . . X X O . X . |
$$ | . . . . . . . . . O X X . X O O O . . |
$$ | . . . . . . . . O . O X . . O X O . . |
$$ | . . . , . . . . X O O X . X X X O . . |
$$ | . . . . . . . . O O O X . . . X X O . |
$$ | . . O O . . . . O O X O X O O O X O . |
$$ | . . X O X X X X . O X O . . . X O . . |
$$ | . O O X . X O X . O X . O . O . . . . |
$$ | . . . . X O O X . O X . O X . . . . . |
$$ | . . O , X . . O X O X X X O O O O . . |
$$ | . . . O X . O . X O X O O X O . X . . |
$$ | . . . . X . . . X O O O . X X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
So for example if white goes for the squeeze/sacrifice immediately instead of g15, black could consider ignoring and going for the outside. It's also worth noting capturing 2 stones is not an 100% alive shape so 4 here is annoying, whereas the 5 stones is 100% alive.
$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . X . . 4 . 3 1 O X X . . . . . |
$$ | . . . X O . . . O X X O X O X X X . . |
$$ | . . . X . . 2 . O , O X X O O O X . . |
$$ | . . X . . . . . . . O X O . X . X O . |
$$ | . . . . . . . X . X O O O X . X X . . |
$$ | . . . . . . . . . X O . . X X O . X . |
$$ | . . . . . . . . . O X X . X O O O . . |
$$ | . . . . . . . . O . O X . . O X O . . |
$$ | . . . , . . . . X O O X . X X X O . . |
$$ | . . . . . . . . O O O X . . . X X O . |
$$ | . . O O . . . . O O X O X O O O X O . |
$$ | . . X O X X X X . O X O . . . X O . . |
$$ | . O O X . X O X . O X . O . O . . . . |
$$ | . . . . X O O X . O X . O X . . . . . |
$$ | . . O , X . . O X O X X X O O O O . . |
$$ | . . . O X . O . X O X O O X O . X . . |
$$ | . . . . X . . . X O O O . X X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------
- Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . X . . 4 . 3 1 O X X . . . . . |
$$ | . . . X O . . . O X X O X O X X X . . |
$$ | . . . X . . 2 . O , O X X O O O X . . |
$$ | . . X . . . . . . . O X O . X . X O . |
$$ | . . . . . . . X . X O O O X . X X . . |
$$ | . . . . . . . . . X O . . X X O . X . |
$$ | . . . . . . . . . O X X . X O O O . . |
$$ | . . . . . . . . O . O X . . O X O . . |
$$ | . . . , . . . . X O O X . X X X O . . |
$$ | . . . . . . . . O O O X . . . X X O . |
$$ | . . O O . . . . O O X O X O O O X O . |
$$ | . . X O X X X X . O X O . . . X O . . |
$$ | . O O X . X O X . O X . O . O . . . . |
$$ | . . . . X O O X . O X . O X . . . . . |
$$ | . . O , X . . O X O X X X O O O O . . |
$$ | . . . O X . O . X O X O O X O . X . . |
$$ | . . . . X . . . X O O O . X X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
Fedya wrote:
I also assume in your variation, capturing the P16 stones with O15 is small.
Yes, it's small for now as gote and just connects n16 to o15, stones which are already connected around the corner. But at ~10 points it's a moderate sized endgame move and white did incur a loss (of ~5 points, because that's half of 10 and 50% chance black gets to cut) by giving black a stone at n16 to use the m18 tesuji. That's another reason n18 connect is the better answer to m18 peep.