prevents an immediate play at and makes an approach move necessary before Black can play at a. It also forces Black to connect on the left (see the variation below).
If is the approach move:
Once the white group has secured life, the black group on the right is dead as well. Black is left with a ko threat at a.
Reading positions like the one in this exercise is one of my major weaknesses. I would like very much for others to comment on my solution.
Alex Weldon: Perfect marks. Now, as I said on the page for the example itself, I'm only 12k* IGS, so I may have made a mistake, but I don't think so. This is the solution I had in mind, and I believe it to be correct. If you would be likely to see this solution in the course of an actual game, your reading skills are up to scratch for at least 15k* IGS, probably better, I'd say (I often notice that my opponents often miss such tesujis, and I'm sure I miss some, too).
Oh, and since is sente, it's okay to reverse the order of and , although I suppose at , followed by at (or one to the left) and White capturing at might leave aji in the top left. (In my game, I was strong enough on the left that it didn't matter).
wins the fight with the Black stones on the right, despite the fact that Black appears to have one more liberty. After , Black loses by me ari me nashi. He cannot play atari on White without putting himself in atari.
Black is dead on the left.
The danger of , above:
holds Black to one eye in the corner, maybe bent four. (Black does better to make the ko at his first opportunity, I think.)
Alex Weldon: Thanks Bill. I had a feeling my solution wasn't perfect. Yours is clearly better. Thankfully, during the actual game, my opponent didn't see that he could get ko in the upper left.
Alex Weldon: Yes, I would have. :) It was a very one-sided game. He should have resigned long before this capturing race occurred, but IGS players never seem to resign, except right before the dame are filled.
After , White must throw in at to reduce Black's liberties.
David: Thanks again.
After , the Black group on the left still does not have an eye, nor does it have enough liberties to slug it out with White.
Even if Black makes the eye with Black at a, it threatens nothing.
If is at , Black will have only one external liberty on the left, and will not be able to capture the White group, even if White tenukis. This is not seki, because White can capture the Black group on the right.
This solution is better, because Black has fewer ko threats.