Any a play is answered by either b; and vice versa. Thus Black secures eyes on the left group. So White attacks on the right. It looks like Black won't have enough eye space. But the cutting point (circled) proves fatal to White's plans.
threatens to capture and thus connect the groups, so White must fill. makes the necessary eyes.
ABortz: What about playing 2 for white? Black is forced to play 3 (or lose both vital points of the bent 4), and White's response of 4 leaves black with only 1 eye in the right group (Sorry if this is not the right way to edit. I'm a new visitor)
in the previous diagram is a mistake. Black should play atari instead, and then make two eyes with .
why can't black play at the cutting point?
The Count: Which point, when?
point 4 on the previous diagram become black's first move.
The Count: If was played at , White could immediately capture by playing one point higher.
How does this work? The ko threat at forces White to respond by filling in the ko, allowing Black to play a and secure the second eye. Anything I missed in this sequence?
Superdave: White would play at a, taking away the second eye. Why do you consider a ko threat?
Because of the ko. Black threatens recapturing the ko which puts the marked group in atari. But yeah, obviously white has sente which allows for the kill at a.
Superdave: White would just connect when Black takes back the ko, and it still wouldn't make an eye. In any case, a sure thing is better than a ko.