Explanation of this Python language feature? [x for x in x for x in x] (to flatten a nested list)

[Chris Angelico]

On Fri, Mar 28, 2014 at 3:37 AM, Mark H Harris <harrismh777 at gmail.com> wrote:
> For the purposes of this list, a "normal" user is a reasonably intelligent
> college educated non "computer professional" non "computer scientist" non
> "expert" who for the moment has an interest in leveraging computer science
> and|or programming to solve everyday or other scientific problems (without)
> having to first become a computer professional, computer scientist, or
> expert.

Now you have to justify: Why is this person considered normal?

ChrisA