The reasons for it are several and left as an exercise to the reader. That's a damn funny parody of scientific literature. I can't remember how many time I've seen that in Physics books or lecture notes.

Or its less instructive cousin: "... the reasons for which should be intuitively obvious to the reader." I had a professor who would use that during lecture, and just stare down anyone who dared raise their hand and claim otherwise. (He liked to move fast, and actually doing intermediate steps in derivations hindered that, so he just proclaimed them all not worth doing explicitly.)

As for "left as an exercise", I think it's often the better answer in terms of 'growing' better players, but it's often an unpopular answer, and I could see why people would avoid it, especially if they're busy.

valguarnera@carrionfields.com