Snapback Problem 6 / Solution

I dunno about this..  

Scartol: Insofar as this is a snapback workshop, I feel like the question in question is about whether to extend to a or capture immediately at . If black extends to a, white will descend to b and Black can't take the marked white stone because then White can immediately take Black in the snapback. But it still looks like White can make two eyes, so I expect that I'm missing the point entirely. Oh well.

Dieter: The problem diagram says it is yose time. So White making two eyes is not the issue here. Well, some pro games of course ...

Jasonred I don't see how White can fail to make an eye, even giving Black two moves in a row, I see a solid eye at c, an easy eye when White eventually extends up to b (or almost anywhere... there's space for four eyes if Black and White conspire to let White exercise some artistic judgement). In any case, isn't there a basic rule or something about this shape?

The "side triangle" as I call it  

That rule being... never extend to a... unless it's a sacrificial move or something or if you have stones on both b and c... or... well, mostly, don't extend to a, you're just making things worse...