On the context-freeness of the set of words containing overlaps

  • Authors:
  • Narad Rampersad

  • Affiliations:
  • David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, ON N2L 3G1, Canada

  • Venue:
  • Information Processing Letters
  • Year:
  • 2007

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Abstract

We show that the set of binary words containing overlaps is not unambiguously context-free and that the set of ternary words containing overlaps is not context-free. We also show that the set of binary words that are not subwords of the Thue-Morse word is not unambiguously context-free.