Conference announcement: 30 Years of Game Theory at Institut Henri Poincaré, October 06-10, 2025, Paris.

Welcome

The Séminaire parisien de Théorie des Jeux is an open, inter-institutional, multi-disciplined seminar which covers all fields of game theory. It takes place on Monday from 11:00 to 12:00 am at Institut Henri Poincaré, 11 rue Pierre et Marie Curie, Paris 5ème. MAP

You will find the program for the current academic year on the page 2025/2026 and the program for past years on the page Archives.

The junior seminar welcomes PhD students in game theory to present their work.  You will find the program for the current academic year on the page Junior Seminar 2025/2026.

Next seminar:  

December 8, 2025 (room Maryam Mirzakhani): 

Claire Mathieu (CNRS) 

will present : Apportionment with Parity Constraints (Victor Verdugo)

Abstract: In the classic apportionment problem the goal is to decide how many seats of a parliament should be allocated to each party as a result of an election. The divisor methods provide a way of solving this problem by defining a notion of proportionality guided by some rounding rule. Motivated by recent challenges in the context of electoral apportionment, we consider the question of how to allocate the seats of a parliament under parity constraints between candidate types (e.g. equal number of men and women elected) while at the same time satisfying party proportionality. We consider two different approaches for this problem. The first mechanism, that follows a greedy approach, corresponds to a recent mechanism used in the Chilean Constitutional Convention 2021 election. We analyze this mechanism from a theoretical point of view. The second mechanism follows the idea of biproportionality introduced by Balinski and Demange [Math. Program. 1989, Math. Oper. Res. 1989]. In contrast with the classic biproportional method by Balinski and Demange, this mechanism is ruled by two levels of proportionality: Proportionality is satisfied at the level of parties by means of a divisor method, and then biproportionality is used to decide the number of candidates allocated to each type and party. We provide a theoretical analysis of this mechanism, making progress on the theoretical understanding of methods with two levels of proportionality. A typical benchmark used in the context of two-dimensional apportionment is the fair share (a.k.a matrix scaling), which corresponds to an ideal fractional biproportional solution. We provide lower bounds on the distance between these two types of solutions, and we explore their consequences in the context of two-dimensional apportionment. 

Organizers

Frédéric Koessler (CNRS, HEC Paris), frederic.koessler[at]gmail[dot]com

Maël Letreust  (CNRS,  IRISA Rennes), mael.le-treust[at]cnrs[dot]fr

Chantal Marlats (LEMMA, Université Paris Panthéon-Assas), chantal.marlats[at]u-paris2[dot]fr

Yannick Viossat (CEREMADE, PSL), viossat[at]ceremade[dot]dauphine[dot]fr

To join (or unsuscribe from) our mailing list, please contact Chantal Marlats at chantal.marlats[at]assas-universite[dot]fr. 

Former organizers

Joseph Abdou; Bernard De Meyer; Françoise Forges; Olivier Gossner;  Marie Laclau; Rida Laraki; Lucie Ménager; Vianney Perchet; Jérôme Renault; Dinah Rosenberg; Sylvain Sorin; Tristan Tomala; Xavier Venel; Nicolas Vieille; Guillaume Vigeral; Bruno Ziliotto