The Magic of Go Yomiuri Shimbun / Problem 2 Solution

Black to play.  

One basic problem with this and other yose problems is that they are not well defined. What lies to the left of the diagram? It matters.

There are some standard assumptions.


We can assume that the surrounding area is Black's territory (or almost so). That is a natural assumption, and the answers to yose problems bear out that the authors are making it. (If not, we would see some White stones outside.)

But how strong is Black outside? In this variant black+circle prevents White from intruding too far into Black's territory. In this case the solution is very like the solution given.

Variant solution  

The placement of B1 aims at White's shortage of liberties. W2 protects.

Now the local temperature has dropped to 1 point.

B1 is a three-point sente.

White's follow-up  

Thanks to the black+circle/white+circle exchange, White has nothing better than W1.

Black's follow-up  

Because of shortage of liberties, after B1 White must play at W2.

Black's follow-up (ii)  
Black's follow-up (iii)  

Without the stone to the left[1] (in the variant) W1 below threatens to make a significant incursion into Black's territory.

White to play.  

Normally in yose problems such a move is treated as sente. Let's do that here. After B2, White has 10 points of territory. Since playing a sente play does not change the count, let's take that as the original count.

Black to play.  

B1 is tesuji. W2 may be surprising, but it takes sente.
After B3 the local temperature has dropped to 1 point. W6 - B7 is sente.

B1 - B3 is a five-point reverse sente play.

That assumes, of course, that W1 at 3 would be sente, eliciting B7. Does that make sense?

White sente?  

B2 elsewhere.

If Black fails to answer W1, W3 - B4 is sente, then later W5 - B8, and later W9 - B10. So B2 at 3 would be a 7 point reverse sente play. That confirms that W1 is a 5 point sente play.




Note: The absence of a stone to the left, as in the variant, indicates that there is no such stone to prevent a deep incursion. If there were, it would have been shown.

This is not just an apparent convention with yose problems. It follows general principles of interpretation shared by many cultures.

The Magic of Go Yomiuri Shimbun / Problem 2 Solution last edited by Bill on April 1, 2006 - 20:06
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