Bonjour, ce mardi 20 mars 2018 à 10h30 en B107, Sergey Dovgal nous parlera de : Pólya enumeration theorem from scratch III Résumé : I am going to talk about very popular combinatorial connection between ordinary and exponential generating functions which is called cycle index function. I am going to define the combinatorial species according to the book "Theory of Species" by Bergeron, Labelle, Leroux, and present their beautiful proof of the cycle index composition theorem. The proof relies on the theory of symmetric functions in infinitely many variables. This proof is a beautiful example of Grothendieck's concept: in order to prove something particular, one should make a more general statement and prove it. L'après-midi, à 14h00 en B107, Antoine Deza nous parlera de : On lattice polytopes, convex matroid optimization, and degree sequences of hypergraphs Résumé : We introduce a family of polytopes, called primitive zonotopes, which can be seen as a generalization of the permutahedron of type Bd. We discuss connections to the largest diameter of lattice polytopes and to the computational complexity of multicriteria matroid optimization. Complexity results and open questions are also presented. In particular, we answer a question raised in 1986 by Colbourn, Kocay, and Stinson by showing that deciding whether a given sequence is the degree sequence of a 3-hypergraph is computationally prohibitive. Based on joint works with Asaf Levin (Technion), George Manoussakis (Paris Sud), Shmuel Onn (Technion). À demain, Thierry