The seminar takes place biweekly on Tuesdays at 15:00 Paris time. In summer, it means 6:00 in California, 9:00 in New-York or Waterloo, 14:00 in London, 15:00 in Paris, 16:00 in Moscow and 22:00 in Tokyo. In winter, some of these numbers change. Please check in advance the time in your time zone.
The address of the Zoom meeting is https://zoom.us/j/92245493528 . The password is distributed in announcements. If you want to receive them, or receive them and want to unsubscribe, please write to Anna Frid.
All recorded talks are also available here.
Anna E. Frid, Aix-Marseille Université, Narad Rampersad, University of Winnipeg, Jeffrey O. Shallit, University of Waterloo, Manon Stipulanti, Université de Liège.
If you are interested in giving a talk, you are welcome to contact Narad Rampersad and Manon Stipulanti.
February 17 2026: Steven Robertson
March 03 2026: Ingrid Vukusic
March 17 2026: Gwenael Richomme
March 31 2026: Paulina Cecchi Bernales
April 14 2026: Idrissa Kaboré On modulo-recurrence and window complexity in infinite words
In this talk, first, I will recall the notions of modulo-recurrent words and of window complexity. These notions are introduced in 2007. Then, I present some properties of these notions. After that, I will present the notions of uniform modulo-recurrence and of strong modulo-recurrence. These notions are defined recently in a joint work with Julien Cassaigne. Sturmian words are uniformly (resp. strongly) modulo-recurrent words. Then, I will address the window complexity of the Thue-Morse. To finish, I will present a recurrent aperiodic word with bounded window complexity.
April 28 2026: Ľubomíra Dvořáková Attractors of sequences coding beta-integers
May 12 2026: Léo Vivion
May 26 2026: Reem Yassawi
July 7 2026: Delaram Moradi
February 3 2026: Annika Huch A Word Reconstruction Problem for Polynomial Regular Languages
The reconstruction problem concerns the ability to uniquely determine an unknown word from querying information on the number of occurrences of chosen subwords. In the joined work with M. Golafshan and M. Rigo we focused on the reconstruction problem when the unknown word belongs to a known polynomial regular language, i.e., its growth function is bounded by a polynomial. Exploiting the combinatorial and structural properties of these languages, we are able to translate queries into polynomial equations and transfer the problem of unique reconstruction to finding those sets of queries such that their polynomial equations have a unique integer solution.
January 20 2026: Savinien Kreczman Factor complexity and critical exponent of words in a Thue-Morse family
The Thue-Morse, Fibonacci-Thue-Morse and Allouche-Johnson words are related to the binary, Zeckendorf and Narayana numeration systems respectively, as they count the parity of the number of ones in representations of natural numbers in those systems. These three numeration systems can be seen as the special cases for k=1,2,3 of a positional numeration system based on the recurrence relation $U_n=U_{n-1}+U_{n-k}$. As such, the three words above can be seen as the first elements in a family of binary words related to those numeration systems.
In a recent preprint, J.Shallit put forth two conjectures on words of this family, the first concerning the first difference of their factor complexity and the second concerning their asymptotic critical exponent. In this talk, we will prove both conjectures by studying bispecial factors within those words. We will highlight a method by K.Klouda allowing us to fully list those bispecial factors and show how this list allows us to attack the conjectures in question. Joint work with L'ubomíra Dvořáková and Edita Pelantová.
January 6 2026: Louis Marin Maximal 2-dimensional binary words of bounded degree
(Authors: Alexandre Blondin Massé, Alain Goupil, Raphael L'Heureux, Louis Marin)
Let $d$ be an integer between $0$ and $4$, and $W$ be a $2$-dimensional word of dimensions $h \times w$ on the binary alphabet $\{0, 1\}$, where $h, w \in \mathbb Z > 0$. Assume that each occurrence of the letter $1$ in $W$ is adjacent to at most $d$ letters $1$. We provide an exact formula for the maximum number of letters $1$ that can occur in $W$ for fixed $(h, w)$. As a byproduct, we deduce an upper bound on the length of maximum snake polyominoes contained in a $h \times w$ rectangle.
The talks of 2025 are available here.
The talks of 2024 are available here.
The talks of 2023 are available here.
The talks of 2022 are available here.
The talks of 2021 are available here.
The talks of 2020 are available here.
Several starting lectures by Anna Frid are available here.