Capturing Race Exercise 10 / Solution

David: My attempt (see a better solution below):

8 at 3  

W1 prevents an immediate play at B7 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).

The atari at W3 forces the capture at B4. After W5, Black can approach at B6. White's atari at W7 forces a black connection at B8. Another atari at W9 wins the race for White.

If B2 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 W7 is sente, it's okay to reverse the order of W5 and W7, although I suppose W5 at W7, followed by B6 at W5 (or one to the left) and White capturing at W3 might leave aji in the top left. (In my game, I was strong enough on the left that it didn't matter).

Bill: W1, while saving White's stones, risks letting Black's stones on the left make at least ko. First, let me show my solution. (See here for a better one.[1])


W1 wins the fight with the Black stones on the right, despite the fact that Black appears to have one more liberty. After W9, 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 W1, above:

Black has chances on the left  

If White does not take, Black can get a ko for everything.

Black makes ko  

W3 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.

Bill: It looks like you would have crushed him, anyway.

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.

David: Thanks, Bill. I see that your B2 is a cleverer response to my W1. What happens, though, when White plays W3 at B4? Does Black have a defense that I don't see?

Black is dead on the left?  

Bill: Remember how often my play is the opponent's? Since White did not play at W5, Black does.

White dies in the middle.  

After B2, White must throw in at B4 to reduce Black's liberties.

David: Thanks again.


Better solution  

After W5, 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.

Reference diagram: Black still loses  

If B3 is at W4, 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.

-- Bill

Capturing Race Exercise 10

Capturing Race Exercise 10 / Solution last edited by CharlesMatthews on October 3, 2003 - 10:13
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