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Coherence and transitivity of subtyping as entailment
A LIENS(CNRS) and DMI, Ecole Normale Supérieure, 45 rue d'Ulm, 75005 Paris, France E-mail: longo@dmi.ens.fr, A2 NET, France Télécom, 28 chemin du Vieux Chêne, BP 98, 38243 Meylan Cedex, France E-mail: kathleen.milsted@cnet.francetelecom.fr, A3 IRIT, Université de Toulouse-III, 118 route de Narbonne, 31062 Toulouse, France E-mail: soloviev@irit.fr
The relation of inclusion between types has been suggested by the practice of programming as it enriches the polymorphism of functional languages. We propose a simple (and linear) sequent calculus for subtyping as logical entailment. This allows us to derive a complete and coherent approach to subtyping from a few, logically meaningful sequents. In particular, transitivity and anti-symmetry will be derived from elementary logical principles.
Keywords: second-order logic, Gentzen sequent calculus, polymorphism, coercive subtyping, cut-elimination