English

A ternary square-free sequence avoiding factors equivalent to $abcacba$

Formal Languages and Automata Theory 2016-03-11 v1

Abstract

We solve a problem of Petrova, finalizing the classification of letter patterns avoidable by ternary square-free words; we show that there is a ternary square-free word avoiding letter pattern xyzxzyxxyzxzyx. In fact, we: (1) characterize all the (two-way) infinite ternary square-free words avoiding letter pattern xyzxzyxxyzxzyx (2) characterize the lexicographically least (one-way) infinite ternary square-free word avoiding letter pattern xyzxzyxxyzxzyx (3) show that the number of ternary square-free words of length nn avoiding letter pattern xyzxzyxxyzxzyx grows exponentially with nn.

Cite

@article{arxiv.1603.03059,
  title  = {A ternary square-free sequence avoiding factors equivalent to $abcacba$},
  author = {James D. Currie},
  journal= {arXiv preprint arXiv:1603.03059},
  year   = {2016}
}

Comments

7 pages, 1 figure

R2 v1 2026-06-22T13:07:37.565Z