[bbeonx]

You're presuming that every phrase was worded _just so_. This could very well have been from the author refactoring their sentence and not simplifying everything. They probably were thinking in these terms (the author is a PL guy from MSR who's pretty heavy into a lot of the formalism) and this sounds like a not-perfectly-polished formal thought.

It's technical, and sometimes technical writing isn't written perfectly. That doesn't mean it's due to willful obtusity, or trying to sound smart.