Charles As was suggested, start like this.
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.
JoelR: It doesn't matter to the shunt line, but
has evaporated in all the diagrams below. Do we mind?
As Bill pointed out, here is better than connecting, which would get an immediate shunt to capture. So will this be a ko?
If White contests this ko, Black has a useful threat at a. Suppose Black wins the ko.
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.
And without it. Here will end in sente, because there is now a weakness at b. But can White afford
?
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.)
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.