Subtyping Recursive Types modulo Associative Commutative Products

Abstract

We study subtyping of recursive types in the presence of associative and commutative products---that is, subtyping modulo a restricted form of type isomorphisms. We show that this relation, which we claim is useful in practice, is a composition of the usual subtyping relation with the recently proposed notion of equality up to associativity and commutativity of products, and we propose an efficient decision algorithm for it. We also provide an automatic way of constructing coercions between related types