Abstract
It is commonly admitted that the origin of combinatorics on words goes back to the work of Axel Thue in the beginning of the twentieth century, with his results on repetition-free words. Thue showed that one can avoid cubes on infinite binary words and squares on ternary words. Up to now, a large part of the work on the theoretic part of combinatorics on words can be viewed as extensions or variations of Thue’s work, that is, showing the existence (or nonexistence) of infinite words avoiding, or limiting, a repetition-like pattern. The goal of this chapter is to present the state of the art in the domain and also to present general techniques used to prove a positive or a negative result. Given a repetition pattern P and an alphabet, we want to know if an infinite word without P exists. If it exists, we are also interested in the size of the language of words avoiding P, that is, the growth rate of the language. Otherwise, we are interested in the minimum number of factors P that a word must contain. We talk about limitation of usual, fractional, abelian, and k-abelian repetitions and other generalizations such as patterns and formulas. The last sections are dedicated to the presentation of general techniques to prove the existence or the nonexistence of an infinite word with a given property.
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsReferences
Aistleitner, C., Becher, V., Scheerer, A.M., Slaman, T.: On the construction of absolutely normal numbers. Acta Arith. (to appear), arXiv:1702.04072
Badkobeh, G., Crochemore, M.: Finite-repetition threshold for infinite ternary words. In: WORDS. EPTCS, vol. 63, pp. 37–43 (2011)
Badkobeh, G., Crochemore, M.: Fewest repetitions in infinite binary words. RAIRO Theor. Inform. Appl. 46(1), 17–31 (2012)
Badkobeh, G., Crochemore, M., Rao, M.: Finite repetition threshold for large alphabets. RAIRO Theor. Inform. Appl. 48(4), 419–430 (2014)
Baker, K.A., McNulty, G.F., Taylor, W.: Growth problems for avoidable words. Theor. Comput. Sci. 69(3), 319–345 (1989)
Bean, D.R., Ehrenfeucht, A., McNulty, G.: Avoidable patterns in strings of symbols. Pac. J. Math. 85, 261–294 (1979)
Berstel, J.: Axel Thue’s papers on repetitions in words: a translation. In: Monographies du LaCIM, vol. 11, pp. 65–80. LaCIM (1992)
Berthé, V., Rigo, M. (eds.): Combinatorics, automata and number theory. Encyclopedia of Mathematics and Its Applications, vol. 135. Cambridge University Press, Cambridge (2010)
Berthé, V., Rigo, M. (eds.): Combinatorics, words and symbolic dynamics. Encyclopedia of Mathematics and Its Applications, vol. 159. Cambridge University Press, Cambridge (2016)
Carpi, A.: On abelian power-free morphisms. Int. J. Algebra Comput. 03(02), 151–167 (1993)
Carpi, A.: On the number of abelian square-free words on four letters. Discret. Appl. Math. 81(1–3), 155–167 (1998)
Cassaigne, J.: Motifs évitables et régularité dans les mots. Ph.D. thesis, Université Paris VI (1994)
Cassaigne, J., Currie, J.D., Schaeffer, L., Shallit, J.: Avoiding three consecutive blocks of the same size and same sum. J. ACM 61(2), 10:1–10:17 (2014)
Chalopin, J., Ochem, P.: Dejean’s conjecture and letter frequency. RAIRO Theor. Inform. Appl. 42(3), 477–480 (2008)
Clark, R.J.: Avoidable formulas in combinatorics on words. Ph.D. thesis, University of California, Los Angeles (2001)
Clark, R.J.: The existence of a pattern which is 5-avoidable but 4-unavoidable. Int. J. Algebra Comput. 16(02), 351–367 (2006)
Currie, J.D.: The number of binary words avoiding abelian fourth powers grows exponentially. Theor. Comput. Sci. 319(1), 441–446 (2004)
Currie, J.D., Rampersad, N.: Fixed points avoiding abelian k-powers. J. Comb. Theory Ser. A 119(5), 942–948 (2012)
Currie, J.D., Visentin, T.I.: Long binary patterns are abelian 2-avoidable. Theor. Comput. Sci. 409(3), 432–437 (2008)
Dejean, F.: Sur un théorème de Thue. J. Comb. Theory Ser. A 13(1), 90–99 (1972)
Dekking, F.M.: Strongly non-repetitive sequences and progression-free sets. J. Comb. Theory Ser. A 27(2), 181–185 (1979)
Edlin, A.E.: The number of binary cube-free words of length up to 47 and their numerical analysis. J. Differ. Equ. Appl. 5(4–5), 353–354 (1999)
Entringer, R.C., Jackson, D.E., Schatz, J.A.: On nonrepetitive sequences. J. Comb. Theory Ser. A 16(2), 159–164 (1974)
Erdős, P.: Some unsolved problems. Mich. Math. J. 4(3), 291–300 (1957)
Erdős, P.: Some unsolved problems. Magyar Tud. Akad. Mat. Kutató Int. Közl. 6, 221–254 (1961)
Evdokimov, A.A.: Strongly asymmetric sequences generated by a finite number of symbols. Dokl. Akad. Nauk SSSR 179, 1268–1271 (1968)
Fiorenzi, F., Ochem, P., Vaslet, E.: Bounds for the generalized repetition threshold. Theor. Comput. Sci. 412(27), 2955–2963 (2011)
Fraenkel, A.S., Simpson, R.J.: How many squares must a binary sequence contain? Electron. J. Comb. 2, R2, 9pp. (1995)
Gamard, G., Ochem, P., Richomme, G., Séébold, P.: Avoidability of circular formulas (2016). ArXiv:1610.04439
Georgiadis, L., Goldberg, A.V., Tarjan, R.E., Werneck, R.F.: An Experimental Study of Minimum Mean Cycle Algorithms, pp. 1–13. SIAM (2009)
Guégan, G., Ochem, P.: A short proof that shuffle squares are 7-avoidable. RAIRO Theor. Inform. Appl. 50(1), 101–103 (2016)
Huova, M., Karhumki, J., Saarela, A.: Problems in between words and abelian words: k-abelian avoidability. Theor. Comput. Sci. 454, 172–177 (2012)
Ilie, L., Ochem, P., Shallit, J.: A generalization of repetition threshold. Theor. Comput. Sci. 345(2), 359–369 (2005)
Karhumäki, J.: Generalized Parikh mappings and homomorphisms. Inf. Control 47(3), 155–165 (1980)
Karhumäki, J., Saarela, A., Zamboni, L.Q.: On a generalization of Abelian equivalence and complexity of infinite words. J. Comb. Theory Ser. A 120(8), 2189–2206 (2013)
Karhumäki, J., Shallit, J.: Polynomial versus exponential growth in repetition-free binary words. J. Comb. Theory Ser. A 105(2), 335–347 (2004)
Karp, R.: A characterization of the minimum mean cycle in a digraph. Discret. Math. 23, 309–311 (1978)
Keränen, V.: Abelian squares are avoidable on 4 letters. In: ICALP, pp. 41–52 (1992)
Keränen, V.: New abelian square-free DT0L-languages over 4 letters. Manuscript (2003)
Keränen, V.: A powerful abelian square-free substitution over 4 letters. Theor. Comput. Sci. 410(38), 3893–3900 (2009)
Khalyavin, A.: The minimal density of a letter in an infinite ternary square-free word is 883/3215. J. Integer Seq. 10, Art. 07.6.5 (2007)
Kolpakov, R.: Efficient lower bounds on the number of repetition-free words. J. Integer Seq. 10, Art. 07.3.2 (2007)
Kolpakov, R., Kucherov, G., Tarannikov, Y.: On repetition-free binary words of minimal density. Theor. Comput. Sci. 218, 161–175 (1999)
Kolpakov, R., Rao, M.: On the number of Dejean words over alphabets of 5, 6, 7, 8, 9 and 10 letters. Theor. Comput. Sci. 412(46), 6507–6516 (2011)
Kucherov, G., Ochem, P., Rao, M.: How many square occurrences must a binary sequence contain? Electron. J. Comb. 10(1), R12 (2003)
Ochem, P.: A generator of morphisms for infinite words. RAIRO Theor. Inform. Appl. 40, 427–441 (2006)
Ochem, P.: Letter frequency in infinite repetition-free words. Theor. Comput. Sci. 380(3), 388–392 (2007)
Ochem, P.: Doubled patterns are 3-avoidable. Electron. J. Comb. 23(1) (2016)
Ochem, P., Reix, T.: Upper bound on the number of ternary square-free words. In: Workshop on Words and Automata (2006)
Ochem, P., Rosenfeld, M.: Avoidability of formulas with two variables (2016). ArXiv:1606.03955
Ochem P., Rao M.: Minimum frequencies of occurrences of squares and letters in infinite words. In: Mons Days of Theoretical Computer Science. Mons, August 27–30 (2008)
Pirillo, G., Varricchio, S.: On uniformly repetitive semigroups. Semigroup Forum 49(1), 125–129 (1994)
Pleasants, P.A.B.: Non-repetitive sequences. Math. Proc. Camb. Philos. Soc. 68, 267–274 (1970)
Rao, M.: Last cases of dejeans conjecture. Theor. Comput. Sci. 412(27), 3010–3018 (2011)
Rao, M.: On some generalizations of abelian power avoidability. Theor. Comput. Sci. 601, 39–46 (2015)
Rao, M., Rigo, M., Salimov, P.: Avoiding 2-binomial squares and cubes. Theor. Comput. Sci. 572, 83–91 (2015)
Rao, M., Rosenfeld, M.: Avoidability of long k-abelian repetitions. Math. Comput. 85(302), 3051–3060 (2016)
Rao, M., Rosenfeld, M.: Avoiding two consecutive blocks of same size and same sum over \(\mathbb {Z}^2\). Manuscript (2016). ArXiv:1511.05875
Rigo, M., Salimov, P.: Another Generalization of Abelian Equivalence: Binomial Complexity of Infinite Words, pp. 217–228. Springer, Berlin/Heidelberg (2013)
Rosenfeld, M.: Every binary pattern of length greater than 14 is Abelian-2-avoidable. In: MFCS 2016. LIPIcs, vol. 58, pp. 81:1–81:11 (2016)
Shur, A.M.: Growth rates of complexity of power-free languages. Theor. Comput. Sci. 411(34), 3209–3223 (2010)
Shur, A.M., Gorbunova, I.A.: On the growth rates of complexity of threshold languages. RAIRO Theor. Inform. Appl. 44(1), 175–192 (2010)
Tarannikov, Y.: The minimal density of a letter in an infinite ternary square-free word is 0.2746…. J. Integer Seq. 5(2), Art. 02.2.2 (2002)
Thue, A.: Über unendliche Zeichenreihen. Norske vid. Selsk. Skr. Mat. Nat. Kl. 7, 1–22 (1906). Reprinted in Selected Mathematical Papers of Axel Thue, T. Nagell, editor, Universitetsforlaget, Oslo, 1977, pp. 139–158
Thue, A.: Über die gegenseitige Lage gleicher Teile gewisser Zeichenreihen. Norske vid. Selsk. Skr. Mat. Nat. Kl. 1, 1–67 (1912). Reprinted in Selected Mathematical Papers of Axel Thue, T. Nagell, editor, Universitetsforlaget, Oslo, 1977, pp. 413–478
Tunev, I.N., Shur, A.M.: On Two Stronger Versions of Dejean’s Conjecture, pp. 800–812. Springer, Berlin/Heidelberg (2012)
Zimin, A.: Blocking sets of terms. Math. USSR Sbornik 47(2), 353–364 (1984)
Author information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2018 Springer International Publishing AG, part of Springer Nature
About this chapter
Cite this chapter
Ochem, P., Rao, M., Rosenfeld, M. (2018). Avoiding or Limiting Regularities in Words. In: Berthé, V., Rigo, M. (eds) Sequences, Groups, and Number Theory. Trends in Mathematics. Birkhäuser, Cham. https://doi.org/10.1007/978-3-319-69152-7_5
Download citation
DOI: https://doi.org/10.1007/978-3-319-69152-7_5
Published:
Publisher Name: Birkhäuser, Cham
Print ISBN: 978-3-319-69151-0
Online ISBN: 978-3-319-69152-7
eBook Packages: Mathematics and StatisticsMathematics and Statistics (R0)