Generalised fine and Wilf's theorem for arbitrary number of periods

  • Authors:
  • Sorin Constantinescu;Lucian Ilie

  • Affiliations:
  • Department of Computer Science, University of Western Ontario, London, Ont., Canada N6A 5B7;Department of Computer Science, University of Western Ontario, London, Ont., Canada N6A 5B7

  • Venue:
  • Theoretical Computer Science - Combinatorics on words
  • Year:
  • 2005

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Abstract

The well known Fine and Wilf's theorem for words states that if a word has two periods and its length is at least as long as the sum of the two periods minus their greatest common divisor, then the word also has as period the greatest common divisor. We generalise this result for an arbitrary number of periods. Our bound is strictly better in some cases than previous generalisations. Moreover, we prove it optimal. We show also that any extrenal word is unique up to letter renaming and give an algorithm to compute both the bound and a corresponding extremal word.