On the Repetition Threshold for Large Alphabets

  • Arturo Carpi
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4162)

Abstract

The (maximal) exponent of a finite non-empty word is the ratio among its length and its period. Dejean (1972) conjectured that for any n ≥5 there exists an infinite word over n letters with no factor of exponent larger than n/(n–1). We prove that this conjecture is true for n ≥38.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    Berstel, J.: Axel Thue’s papers on repetition in words: a translation, Publications du LaCIM, Université du Québec á Montréal 20 (1995)Google Scholar
  2. 2.
    Berstel, J., Karhumäki, J.: Combinatorics on words: a tutorial. Bulletin of the EATCS 79, 178–228 (2003)MATHGoogle Scholar
  3. 3.
    Brandenburg, F.-J.: Uniformly growing k-th power-free homomorphisms. Theoret. Comput. Sci. 23, 69–82 (1983)MATHCrossRefMathSciNetGoogle Scholar
  4. 4.
    Carpi, A.: On the repetition threshold for large alphabets, Dipartimento di Matematica e Informatica dell’Università di Perugia, Tech. rep. no. 5-2006 (2006)Google Scholar
  5. 5.
    Crochemore, M., Goralcik, P.: Mutually avoiding ternary words of small exponent. Int. J. Alg. Comp. 1, 407–410 (1991)MATHCrossRefMathSciNetGoogle Scholar
  6. 6.
    Dejean, F.: Sur un théorème de Thue. J. Combin. Th. A 13, 90–99 (1972)MATHCrossRefMathSciNetGoogle Scholar
  7. 7.
    Ilie, L., Ochem, P., Shallit, J.: A generalization of repetition threshold. In: Fiala, J., Koubek, V., Kratochvíl, J. (eds.) MFCS 2004. LNCS, vol. 3153, pp. 818–826. Springer, Heidelberg (2004)CrossRefGoogle Scholar
  8. 8.
    Karhumäki, J., Shallit, J.: Polynomial versus exponential growth in repetition-free binary words. J. Comb. Theory Ser. A 105, 335–347 (2004)MATHCrossRefGoogle Scholar
  9. 9.
    Mignosi, F., Pirillo, G.: Repetitions in the Fibonacci infinite word. RAIRO Inf. Theor. and Appl. 26, 199–204 (1992)MATHMathSciNetGoogle Scholar
  10. 10.
    Mohammad-Noori, M., Currie, J.D.: Dejean’s conjecture and Sturmian words. European J. Comb. (to appear)Google Scholar
  11. 11.
    Moulin-Ollagnier, J.: Proof of Dejean’s conjecture for alphabets with 5, 6, 7, 8, 9, 10 and 11 letters. Theoret. Comput. Sci. 95, 187–205 (1992)MATHCrossRefMathSciNetGoogle Scholar
  12. 12.
    Pansiot, J.-J.: A propos d’une conjecture de F. Dejean sur les répétitions dans les mots. Discr. Appl. Math. 7, 297–311 (1984)MATHCrossRefMathSciNetGoogle Scholar
  13. 13.
    Shallit, J.: Simultaneous avoidance of large squares and fractional powers in infinite binary words. Int. J. Found. Comput. Sci. 15, 317–327 (2004)MATHCrossRefMathSciNetGoogle Scholar
  14. 14.
    Thue, A.: Uber unendliche Zeichenreihen. Norske Vid. Selsk. Skr. I. Mat. Nat. Kl., Christiania 7, 1–22 (1906); reprinted in: Nagell, T. (ed.) Selected Mathematical Papers of Axel Thue, pp. 139–158. Universitetsforlaget, Oslo (1977)Google Scholar
  15. 15.
    Thue, A.: Uber die gegenseitige Lage gleicher Teile gewisser Zeichenreihen. Norske Vid. Selsk. Skr. Mat. Nat. Kl., Christiania 1, 1–67 (1912); reprinted in: Nagell, T. (ed.) Selected Mathematical Papers of Axel Thue, pp. 413–478. Universitetsforlaget, Oslo (1977)Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2006

Authors and Affiliations

  • Arturo Carpi
    • 1
  1. 1.Dipartimento di Matematica e InformaticaUniversità di PerugiaItaly

Personalised recommendations