Nominal Unification from a Higher-Order Perspective

  • Authors:
  • Jordi Levy;Mateu Villaret

  • Affiliations:
  • IIIA - CSIC;Universitat de Girona

  • Venue:
  • ACM Transactions on Computational Logic (TOCL)
  • Year:
  • 2012

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Abstract

Nominal logic is an extension of first-order logic with equality, name-binding, renaming via name-swapping and freshness of names. Contrarily to lambda-terms, in nominal terms, bindable names, called atoms, and instantiable variables are considered as distinct entities. Moreover, atoms are capturable by instantiations, breaking a fundamental principle of the lambda-calculus. Despite these differences, nominal unification can be seen from a higher-order perspective. From this view, we show that nominal unification can be quadratically reduced to a particular fragment of higher-order unification problems: higher-order pattern unification. We also prove that the translation preserves most generality of unifiers.