The unification problem for confluent right-ground term rewriting systems

  • Authors:
  • Michio Oyamaguchi;Yoshikatsu Ohta

  • Affiliations:
  • Faculty of Engineering, Mie University, 1515 Kamihama-cho, Tsu-shi, 514-8507, Japan;Faculty of Engineering, Mie University, 1515 Kamihama-cho, Tsu-shi, 514-8507, Japan

  • Venue:
  • Information and Computation - RTA 2001
  • Year:
  • 2003

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Abstract

The unification problem for term rewriting systems (TRSs) is the problem of deciding, for a given TRS R and two terms M and N, whether there exists a substitution θ such that Mθ and Nθ are congruent modulo R (i.e., Mθ ↔R* Nθ). In this paper, the unification problem for confluent right-ground TRSs is shown to be decidable. To show this, the notion of minimal terms is introduced and a new unification algorithm for obtaining a substitution whose range consists of minimal terms is proposed. Our result extends the decidability of unification for canonical (i.e., terminating and confluent) right-ground TRSs given by Hullot [Proceedings of the 5th Conference on Automated Deduction, LNCS, vol. 87, 1980, p. 318] in the sense that the termination condition can be omitted.