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!

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Best Regards,
Anton Dergunov