Endgame Problem 39 / Solution

Solution  

You might think this is 'obvious'; but one does have to think about Black playing at a first. And for that you have to read on.

Making a ko?  

As Bill pointed out, here is better than connecting, which would get an immediate shunt to capture. So will this be a ko?

Ko line  

If White contests this ko, Black has a useful threat at a. Suppose Black wins the ko.

Winning the ko (1)  

One has to imagine this position, right at the start, to see how serious it is, when Black connects with . This is shown with the / exchange made.

Winning the ko (2)  

And without it. Here will end in sente, because there is now a weakness at b. But can White afford ?

Winning the ko (3)  

Yes, that's OK in fact; Black has nothing after .

So, in conclusion, not only shouldn't Black play atari blindly here, it is better not to play it unless Black will also lose the ko. (Another example of a local threat that diminishes the ko, If I'm not wrong.)

Shunt  

For reference, if connects, then and captures some White stones. The term shunt referred to in this problem is .

White avoids shunt  

Hal9666 This could just be because I'm not very good, but it seems white 4 in this diagram would be better.

Conceding  

In practice White may well concede with . White ends in sente. There is no reason for Black to waste ko threats with an atari here.

Conceding not sente ( elsewhere)  

Tapir: Isn't it better to concede with somewhere else. This leaves the ko for later and doesn't take away a liberty. has a certain thank you feeling and is gote... I had a very similar situation in a game a week ago. I suppose it isn't uncommon. Black can't capture after tenuki since white has liberties at both a and b and can't be cut either. (Or , for the same result)

Doesn't this work for Black if White tenuki?  

Sorry, but it seems like White ends up in gote after this (otherwise Black could capture something). Could someone stronger check the above comment?-Illluck

The white group suffers from Oiotoshi after - René