Deleting string rewriting systems preserve regularity

  • Authors:
  • Dieter Hofbauer;Johannes Waldmann

  • Affiliations:
  • Mühlengasse 16, D-34125 Kassel, Germany;Hochschule für Technik, Wirtschaft und Kultur (FH) Leipzig, Fachbereich IMN Postfach 301166, D-04251 Leipzig, Germany

  • Venue:
  • Theoretical Computer Science - Developments in language theory
  • Year:
  • 2004

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Abstract

A string rewriting system is called deleting if there exists a partial ordering on its alphabet such that each letter in the right-hand side of a rule is less than some letter in the corresponding left-hand side. We show that the rewrite relation induced by a deleting system can be represented as the composition of a finite substitution (into an extended alphabet), a rewrite relation of an inverse context-free system (over the extended alphabet), and a restriction (to the original alphabet). Here, a system is called inverse context-free if the length of the right-hand side of any rule does not exceed one. The decomposition result directly implies that deleting systems preserve regularity and that inverse deleting systems preserve context-freeness. The latter result was already obtained by Hibbard (J. ACM 21(3) (1974) 446-453).