[Haskell] Request for review of a GADT tutorial draft

Dear Haskell community, I have recently written an introductory-level tutorial article about GADTs in GHC (inspired by LASER 2012 summer school and to be submitted to their proceedings). I have already send this draft to the "Haskell Cafe" mailing list, but I was also advised to use these mailing lists, so I would like to ask for your feedback: http://anton-dergunov.ru/publications/gadts_draft_v4.pdf Any opinion about this article and any suggestions are very welcome! -- Best Regards, Anton Dergunov