Shallow confluence of conditional term rewriting systems

  • Authors:
  • Claus-Peter Wirth

  • Affiliations:
  • Department of Computer Science, Saarland University, D-66123 Saarbrücken, Germany

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 2009

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Abstract

Recursion can be conveniently modeled with left-linear positive/negative-conditional term rewriting systems, provided that non-termination, non-trivial critical overlaps, non-right-stability, non-normality, and extra variables are admitted. For such systems we present novel sufficient criteria for shallow confluence and arrive at the first decidable confluence criterion admitting non-trivial critical overlaps. To this end, we restrict the introduction of extra variables of right-hand sides to binding equations and require the critical pairs to have somehow complementary literals in their conditions. Shallow confluence implies [level] confluence, has applications in functional logic programming, and guarantees the object-level consistency of the underlying data types in the inductive theorem prover QuodLibet.