http://homepages.inf.ed.ac.uk/wadler/papers/class/class.ps
http://www.haskell.org/haskellwiki/Typeclassopedia
http://book.realworldhaskell.org/read/using-typeclasses.html
http://www.haskell.org/tutorial/classes.html
http://ropas.snu.ac.kr/~bruno/papers/TypeClasses.pdf
http://typeclassopedia.bitbucket.org/
https://docs.google.com/present/view?id=0AVWqzioOIq3IZGM4ZGJrbWJfNGZmYjQ4bWN0&pli=1
http://plastic-idolatry.com/typcls/#title
http://dibblego.wordpress.com/2007/05/23/the-power-of-type-classes-with-scala-implicit-defs/
http://debasishg.blogspot.de/2010/06/scala-implicits-type-classes-here-i.html