Existential Type Systems with No Types in Terms

  • Authors:
  • Ken-Etsu Fujita;Aleksy Schubert

  • Affiliations:
  • Gunma University, Kiryu, Japan 376-8515;The University of Warsaw, Warsaw, Poland 02-097

  • Venue:
  • TLCA '09 Proceedings of the 9th International Conference on Typed Lambda Calculi and Applications
  • Year:
  • 2009

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Abstract

We study type checking, typability, and type inference problems for type-free style and Curry style second-order existential systems where the type-free style differs from the Curry style in that the terms of the former contain information on where the existential quantifier elimination and introduction take place but omit the information on which types are involved. We show that all the problems are undecidable employing reduction of second-order unification in case of the type-free system and semiunification in case of the Curry style system. This provides a fine border between problems yielding to a reduction of second-order unification problem and the semiunification problem. In addition, we investigate the subject reduction property of the system in the Curry-style.