[The Zipper]: http://www.st.cs.uni-saarland.de/edu/seminare/2005/advanced-fp/docs/huet-zipper.pdf "paper by Gérard Huet" [Type-indexed data types]: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1.6342 "paper by Ralf Hinze, Johan Jeuring, and Andres Löh" [functor-combo]: http://hackage.haskell.org/package/functor-combo "Hackage entry: functor-combo" [Differentiation of higher-order types]: http://conal.net/blog/posts/differentiation-of-higher-order-types/ "blog post" [Semantic edito More

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