Structural Rules and Algebraic Properties of Intersection Types

Abstract: In this paper we define several notions of term expansion, used to define terms with less sharing, but with the same computational properties of terms typable in an intersection type system. Expansion relates terms typed by associative, commutative and idempotent intersections with terms typed in the Curry type system and the relevant type system, terms typed by non-idempotent intersections with terms typed in the affine and linear type systems and terms typed by non-idempotent and non-commutative intersections with terms typed in an ordered type system. Finally, we show how idempotent intersection is related with the contraction rule, commutative intersection with the exchange rule and associative intersection with the lack of structural rules in a type system.