# Events & Seminars

# T&G: Anton Khoroshkin (HSE), Compactified moduli spaces of rational curves with marked points as homotopy quotients of operads

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# T&G: Jesse Kass (University of South Carolina), How to count lines on a cubic surface arithmetically

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Salmon and Cayley proved the celebrated 19th century result that a smooth cubic surface over the complex numbers contains exactly 27 lines. By contrast, the count over the real numbers depends on the surface, and these possible counts were classified by Segre. A number of researchers have recently made the striking observation that Segre’s work shows a certain signed count is always 3. In my talk, I will explain how to extend this result to an arbitrary field.

# Game Theory & Math Economics: Sergiu Hart - "Too Much Two Good To Be True: The Complexity of Auctions"

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We consider the problem of maximizing the revenue from selling a number of goods (or items). In this talk we will focus on approximation results and on the "menu-size" as a measure of auction complexity which affects the revenue. * All the relevant concepts will be introduced in the talk.* The talk is mostly independent of the talk given earlier this year.

# Game Theory & Math Economics: Philip J. Reny (University of Chicago) - "Sequential Equilibria of Multi-Stage Games with Infinite Sets of Types and Actions," (joint work with Roger Myerson)

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Guided by several key examples, we formulate a definition of essential sequential equilibrium for multi-stage games with infinite type sets and infinite action sets, and we prove its general existence.

# Game Theory & Math Economics: Fuad Aleskerov (National Research University "Higher School of Economics" and Institute of Control Sciences, Moscow) - "Power Distribution: Theory and Applications"

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# Game Theory & Math Economics: Sergui Hart - "Much Too Good To Be True: Lotteries and the Complexity of Auctions"

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We consider the problem of maximizing the revenue from selling a number of goods to a single buyer. In this talk we will focus on the need for randomization (which arises only when there are multiple goods), and on the "menu-size" as a measure of auction complexity which affects the revenue. (All the relevant concepts will be introduced in the talk.) Read more about Game Theory & Math Economics: Sergui Hart - "Much Too Good To Be True: Lotteries and the Complexity of Auctions"

# Analysis seminar: Fanny Augeri (WIS) "On some heavy-tail phenomena occurring in large deviations"

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# Topology & geometry, Matan Prasma (Radboud University), "Model-categorical cotangent complex formalism"

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# Topology & Geometry Seminar: Serap Gurer (Galatasaray University), "(Co)homology theories on diffeological spaces".

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# Topology and Geometry Seminar: Alexander Caviedes Castro (Tel-Aviv University), "Symplectic capacities and Cayley graphs"

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# Combinatorics: Imre Leader (Cambridge) "Decomposing the Complete r-Graph"

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Title: Decomposing the Complete r-Graph

Abstract:

The Graham-Pollak theorem states that to decompose the complete graph K_n into complete bipartite subgraphs we need at least n−1 of them. What happens for hypergraphs? In other words, suppose that we wish to decompose the complete r-graph on n vertices into complete r-partite r-graphs; how many do we need?

In this talk we will report on recent progress on this problem.

This is joint work with Luka Milicevic and Ta Sheng Tan.