Shared subtypes: subtyping recursive parametrized algebraic data types.

Ki Yung Ahn Tim Sheard Shared subtypes: subtyping recursive parametrized algebraic data types. 75-86 2008 Haskell http://doi.acm.org/10.1145/1411286.1411297 conf/haskell/2008 db/conf/haskell/haskell2008.html#AhnS08