Reduction and Unification in Lambda Calculi with a General Notion of Subtype


Reduction, equality and unification are studied for a family of simply typed lambda calculi with subtypes. The subtype relation is required to relate base types only to base types and to satisfy some order-theoretic conditions. Constants are required to have a least type, i.e. ``no overloading''. We define the usual beta- and a subtype-dependent eta-reduction. These are related to a typed equality relation and shown to be confluent in a certain sense. We present a generic algorithm for pre-unification modulo beta-eta-conversion and an arbitrary subtype relation. Furthermore it is shown that unification with respect to any subtype relation is universal.

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Zhenyu Qian