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Type Inference for the Mixture of Matching and Implicit Subtyping

We present a type inference system for a language with object-oriented features such as polymorphic record access and subtyping. We separate the notion of matching and subtyping in order to avoid di culties caused by recursive type constraints. We will use two kinds of type constraints | record (variant) constraints and subtyping constraints. Then, we discuss simpli cation of such mixed type constraints and show that simpli cation becomes much easier by the separation.