Could someone recommend me a paper that discusses the relation between Girard's System F and Hindley-Milner type systems? I've been studying system F lately (and Haskell's semantics is still somewhat mysterious to me), and in System F existential types can be built from the basic operations, while in Haskell it seems that one needs language extensions to be able to use them... Thanks & cheers, Eduardo Ochs http://angg.twu.net/ edrx@inx.com.br