Below is a problem from the Elementary Go Series book, "Tesuji." This is problem 7 from the end of Chapter 2: Black to play and capture the cutting stones. I have shown the given answer as the first variation/branch, but I don't understand why the second variation isn't also correct. I don't see anywhere white can give double atari, at least not until the white group is already in atari itself. Am I missing something with this problem? Could it merely be that black ends up with a more preferable shape with the given answer, compared to the result of capturing with variation 2?
I remember considering the variation you posted, but didn't see the white clamping move at N5 -- I clearly didn't read far enough ahead. It seems so obvious now that I've seen it.
[go]$$W :w1: = atari
$$ . . . . . . .
$$ . . . . . . .
$$ . . 1 X O . .
$$ . X X O X X .
$$ . . . O . . .
$$ . . O . O . .
$$ . . . . . . .[/go]
Okay, thanks for the correction. I was debating on whether to use the word "clamp" with my post, since I wasn't quite sure if the atari mentioned could also be called a clamp (as it sort of "squeezes" the stone from opposite side), but I knew the top example you gave is clearly a clamp.
The sequence that speedchase showed to escape is really useful to remember. It was played against me in probably half my games when I was a ddk. Also that chapter in the book ('knights move tesuji') is just to show a way to avoid this escaping sequence.
