Lambda the Ultimate

Hi Haskellers,

I have written a draft of an introductory-level tutorial paper about GADTs in Haskell (for submittion to proceedings of the recent LASER summer school) and I would like to seek initial feedback about its content: what information is probably missing? are there any subtle mistakes?

The main idea of this article was to serve as a starting point for learning GADTs (I was missing this kind of information myself some time ago), so I have collected several examples demonstrating common use cases.

Here is a link to the paper:
https://docs.google.com/open?id=0B9ZIIsDR0B7Hb1VBTFZOZEUzXzA