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.
As Bill pointed out, here is better than connecting, which would get an immediate shunt to capture. So will this be a 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.)
For reference, if connects, then and captures some White stones. The term shunt referred to in this problem is .
Hal9666 This could just be because I'm not very good, but it seems white 4 in this diagram would be better.
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.
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)