index n; clearance lifetime; LIO_b; Labeled \ell

- I think you're right in \ell and roman being a bit confusing, but
  I'm not sure it's woth amking the change now. Maybe when we get
  replies from JFP again?

- Index n: made some up-front clairification.

- Lifentime of data: didn't add too much. I think the interesting case
  is when privs come into play, but since we don't talk about privs
  in this paper it seems like we should just keep it brief. (I barely
  convinced Ale to be cool with the footnote on privs)

- LIO_True LIO_False: took suggestion