I think that volcanic air is getting to you Tom, This question is way over most of our heads - a really hard question. No amount of googling seemed able to turn up any clues. And... well, once you see the answer its no easier to work it out.

I got the not null part. And its probably not the primary key, (otherwise why call it an elementary key). The middle one long complex answer I chose this because it was long and complex - don't pretent to understand it even now, and random choice for the other one.