Completeness and Soundness Results for X with Intersection and Union Types

  • Authors:
  • Steffen van Bakel

  • Affiliations:
  • Department of Computing, Imperial College London, 180 Queen's Gate, London SW7 2BZ, UK. svb@doc.ic.ac.uk

  • Venue:
  • Fundamenta Informaticae - Intersection Types and Related Systems ITRS
  • Year:
  • 2012

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Abstract

With the eye on defining a type-based semantics, this paper defines intersection and union type assignment for the sequent calculus X, a substitution-free language that enjoys the Curry-Howard correspondence with respect to the implicative fragment of Gentzen's sequent calculus for classical logic. We investigate the minimal requirements for such a system to be complete i.e. closed under redex expansion, and show that the non-logical nature of both intersection and union types disturbs the soundness i.e. closed uder reduction properties. This implies that this notion of intersection-union type assignment needs to be restricted to satisfy soundness as well, making it unsuitable to define a semantics. We will look at two confluent notions of reduction, called Call-by-Name and Call-by-Value, and prove soundness results for those.