Quantifier Elimination and Parametric Polymorphism in Programming Languages

We present a simple and easy to understand explanation of ML type inference and parametric polymorphism within the framework of type monomorphism, as in the rst order typed lambda calculus. We prove the equivalence of this system with the standard interpretation using type polymorphism, and extend the equivalence to include polymorphic xpoints. The monomorphic interpretation gives a purely combinatorial understanding of the type inference problem, and is a classic instance of quantiier elimination, as well as an example of Gentzen-style cut elimination in the framework of the Curry-Howard propositions-as-types analogy.