WQO-BQO: What is up?



 21-23 February 2023, Lyon, France  


Location · Schedule · Abstracts · Contact and Registration (the event is free)


The topic of the workshop are the notions of well-quasi order and a strengthening, better quasi ordering. A conjecture of Abraham, Bonnet, Kubis (ABK) asking if every wqo is a countable union of bqo, motivated the formation of an online seminar ABK - Abkhazian seminar, which met regularly during the Covid times.

The conjecture remains open, however several results have been obtained.

The workshop will report on the progress of the Abkhazian seminar, including two recently submitted papers, and will include talks on recent research by other specialists in wqo.

The meeting will give us an occasion to celebrate 80 years of life and many years of activity of the mathematician Robert Bonnet, an important contributor to the theory of wqo and to the mathematical life in Lyon.

The presentations will be organised in the hybrid mode, with live Zoom transmission. Please register at wqo.bqo@math.univ-lyon1.fr and indicate if you require a Zoom link.

The workshop is funded by the Labex MILyon MathInfo.


Salle de Séminaire 2 Bâtiment Jean-Braconnier

Département de Mathématiques, Université Claude Bernard, Lyon, France


Morning, Tuesday 21/02/2O23

·       09:45 − 10:00. Opening.

·       10:00 − 11:00. Maurice Pouzet A topological interpretation of de Jongh-Parikh theorem.

·       11:00 − 12:00. Wieslaw Kubis (Czech Academy of Sciences, Prague): A scattered rank on mathematical structures. (via Zoom)


12:00 − 14:00 - Lunch


Afternoon, Tuesday 21/02/2O23

·       14:00 - 15:00. Mirna Džamonja IRIF (CNRS et Université Paris-Cité, France): On the ABK Conjecture and α-well Quasi Orders.

·       15:00 - 16:00. Aliaume Lopez IRIF (CNRS et Université Paris-Cité, France): The Silence of the Powersets.

·       16:00-16:30. Coffee and Discussion.

·       16:30 - 17:30. Robert Woodrow (University of Calgary, Canada): Counting siblings.


Morning, Wednesday 22/02/2O23

·       10:00 − 11:00. Philippe Schnoebelen (ENS Paris-Saclay, France): WQOs and BQOs in automated program verification (via Zoom).

·       11:00 − 12:00  Uri Abraham (Ben Gurion University, Beer Sheva, Israel): Covering of Posets with Chains.


12:00 − 14:00— Lunch



Afternoon, Wednesday 22/02/2O23

·       14:00 - 15:00. Sylvain Schmitz (IRIF (CNRS et Université Paris-Cité, France): A width function theorem.

·       15:00 - 16:00. Gregory McKay (Babylon Health, London): Better-quasi-ordering classes of partial orders.


·       16:00-16:30. Coffee and Discussion

·       16:30 - 17:30. Imed Zaguia Royal Military College of Canada : Minimal prime ages, words and permutation graphs.


Morning, Thursday 23/02/2O23

·       10:00 − 11:00. Isa Vialard (ENS Paris-Saclay, France): Elementary, Dr Powerset !

·       11:00 − 12:00. Ambroise Baril (Loria, Université de Nancy) : Linear equivalence between component twin-width and clique-width with algorithmic applications.


12:00 − 14:00— Lunch



Afternoon, Thursday 23/02/2O23

·       14:00 - 15:00. Stephan Thomassé (ENS Lyon): Gaps in tournament profiles

·       15:00 - 16:00. Robert Bonnet (Université de Mont Blanc-Savoie, Le Bourget-du-Lac, France ): Skula spaces over a well-quasi-ordering.



Abstracts of talks can be found here