Empowering Union and Intersection Types with Integrated Subtyping
summary
Framework implements a decision procedure that combines a simple, textbook reductive subtyping kernel with user-specified extensions to recognize distributivity and domain-specific relationships like disjointness; it requires proving DNF preservation and a promotion property plus small proofs about an intersector and an intersectedness predicate for literals. Produces a sound, complete algorithm (Coq library) used to model Ceylon features (nullable types, ADTs, principled instantiation), composes multiple extensions, and notes exponential blowup from full DNF expansion.
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