Enumerating outer narrowing derivationsfor constructor-based term rewriting systems

  • Authors:
  • Jia-Huai You

  • Affiliations:
  • -

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 1989

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Abstract

Narrowing has been used as a mechanism for reasoning about equations and evaluatingequational logic programs, where enumeration of all narrowing derivations is often necessary in order to generate complete sets of solutions. In this paper, a special type of narrowing derivations, called outer narrowing derivations, is examined for the class of constructor-based term rewriting systems. It is shown that every narrowing derivation in this class is subsumed by an outer narrowing derivation. This result is applied to a matching problem in equational theories, i.e., whether an arbitrary term is E-matchable to a term composed of constructors and disjoint variables. It is shown that outer narrowing derivations generate complete and minimal sets of E-matchers. An E-matching procedure is presented which enumerates all and only outer narrowing derivations for the E-matching problem considered in this paper.