Now showing items 11-21 of 21

    • Infinite words containing squares at every position 

      Currie, James; Rampersad, Narad (EDP Sciences, 2010)
      Richomme asked the following question: what is the infimum of the real numbers α > 2 such that there exists an infinite word that avoids α-powers but contains arbitrarily large squares beginning at every position? We resolve ...
    • Least Periods of Factors of Infinite Words 

      Currie, James D.; Saari, Kalle (EDP Sciences, 2009)
      We show that any positive integer is the least period of a factor of the Thue-Morse word. We also characterize the set of least periods of factors of a Sturmian word. In particular, the corresponding set for the Fibonacci ...
    • The minimal automaton recognizing mN in a linear numeration system 

      Charlier, Émilie; Rampersad, Narad; Rigo, Michel; Waxweiler, Laurent (Integers, 2011-12-02)
      We study the structure of automata accepting the greedy representations of N in a wide class of numeration systems. We describe the conditions under which such automata can have more than one strongly connected component ...
    • Multi-dimensional sets recognizable in all abstract numeration systems 

      Charlier, Émilie; Lacroix, Anne; Rampersad, Narad (EDP Sciences, 2011)
      We prove that the subsets of Nd that are S-recognizable for all abstract numeration systems S are exactly the 1-recognizable sets. This generalizes a result of Lecomte and Rigo in the one-dimensional setting.
    • On avoidability of formulas with reversal 

      Currie, James D.; Mol, Lucas; Rampersad, Narad (EDP Sciences, 2018-02-13)
      While a characterization of unavoidable formulas (without reversal) is well-known, little is known about the avoidability of formulas with reversal in general. In this article, we characterize the unavoidable formulas ...
    • Overlap-Free Words and Generalizations 

      Rampersad, Narad (University of WinnipegUniversity of Waterloo, 2007)
      The study of combinatorics on words dates back at least to the beginning of the 20th century and the work of Axel Thue. Thue was the first to give an example of an infinite word over a three letter alphabet that contains ...
    • Shuffling and unshuffling 

      Henshall, Dane; Rampersad, Narad; Shallit, Jeffrey (Bulletin of the European Association for Theoretical Computer Science, 2012)
      We consider various shuffling and unshuffling operations on languages and words, and examine their closure properties. Although the main goal is to provide some good and novel exercises and examples for undergraduate formal ...
    • Squares and overlaps in the Thue-Morse sequence and some variants 

      Brown, Shandy; Rampersad, Narad; Shallit, Jeffrey; Vasiga, Troy (EDP Sciences, 2006)
      We consider the position and number of occurrences of squares in the Thue-Morse sequence, and show that the corresponding sequences are 2-regular. We also prove that changing any finite but nonzero number of bits in the ...
    • Suffix conjugates for a class of morphic subshifts 

      Currie, James D.; Rampersad, Narad; Saari, Kalle (Cambridge University Press, 2015-09)
      Let A be a finite alphabet and f: A^* --> A^* be a morphism with an iterative fixed point f^\omega(\alpha), where \alpha{} is in A. Consider the subshift (X, T), where X is the shift orbit closure of f^\omega(\alpha) and ...
    • Words with many palindrome pair factors 

      Borchert, Adam; Rampersad, Narad (The Electronic Journal of Combinatorics, 2015-10-30)
      Motivated by a conjecture of Frid, Puzynina, and Zamboni, we investigate infinite words with the property that for infinitely many n, every length-n factor is a product of two palindromes. We show that every Sturmian word ...