Guillaume Aubian's

Who am I ?

I am a postdoc at Charles University, under the supervision of Zdeněk Dvořák. Before that, I was a PhD student under the supervision of Pierre Aboulker and Pierre Charbit in the TALGO team at École Normale Supérieure and in the IRIF lab at Paris University. I’m mainly interested in graph theory, optimization and algorithmics, and I’m fond of algorithmic contests.

In a past life, I have worked for almost two years as a Google Software Engineer in Zürich, Switzerland, and have attended École Normale Supérieure Paris-Saclay before that.

Why are you here ?


My research interests revolve around graph theory, in particular directed graph theory. I focus on digraph colouring, a notion which arised lately and consists in partitioning directed graphs into acyclic subgraphs. You can find my PhD thesis here.

I am an author of the following published papers and preprint:

I have also presented in the following conferences and workshops :

  • ANR Digraphs 2021, presenting a Decomposition theorem for locally in-transitive tournaments
  • JGA 2020, presenting Brooks’ theorem on digraphs
  • EUROCOMB’21, presenting Decomposing and Colouring Locally Out-Transitive Oriented Graphs
  • JGA 2021, presenting Vizing’s and Shannon’s Theorems for edge-defective colouring
  • ICGT 2022, presenting Heroes in Orientations of Complete Multipartite Graphs
  • JGA 2022, presenting (P_6, triangle)-free digraphs have bounded dichromatic number
  • ANR Digraphs 2023, presenting Maximum local arc-connectivity and dichromatic number
  • Charles University seminars, presenting Colouring Digraphs
  • Séminaire Bordeaux 2024, présenting Clique number of tournaments

I was in the organizing committee of JGA 2022, along with Pierre Aboulker and Thomas Bellitto.


I am responsible for the tutorials at Charles University for Combinatorics and Graph Theory III. List of exercise sheets:

And here is the homework to handout by November 30:

Before that, I was a teaching fellow at Paris University. I have been in charge of :

  • Practical works for Initiation to Python Programming (IP1 Python) in 2020-2021 and 2022-2023
  • Practical works for Web and tools (IO2 Internet et Outils) in 2020-2021
  • Practical works for Initiation to Java Programming (IP1 Java) in 2021-2022 and 2022-2023
  • Practical and theoretical works for Principles of operation of binary machines (PF1 Principes de fonctionnement des machines binaires) in 2021-2022
  • Practical works for Introduction to Operating Systems (IS1 Initiation aux Systèmes d’Exploitation) in 2022-2023

Algorithmic Contests

Since 2023, I am a judge at ICPC SWERC, and before that I was a coach for ENS Paris-Saclay, and a contestant before that.

I used to train on Codeforces, currently am ranked master, and hope to someday get the motivation to get to grandmaster. I have alse reached twice the third round of Google Code Jam, once the offline finals of Google Hash Code, have won two editions of Battle Dev and also have won Codin’Night.

How to contact me ?

My mail address is but you can also contact me on Discord under username LeCaRiBoU#3837 or aubian on irc.{,,}.