• 2020 Feb 25

    Logic Seminar - Martin Hils

    2:00pm to 4:00pm


    Ross building - Room 63,
    Martin Hils will speal about Classification of imaginaries in valued fields with automorphism.

    Title: Classification of imaginaries in valued fields with automorphism

    Abstract: The imaginaries in the theory ACVF of non-triviallally valued algebraically closed
    valued fields are classified by the so-called 'geometric' sorts. This is a fundamental
    result due to Haskell-Hrushovski-Macpherson. We show that the imaginaries in
    henselian equicharacteristic 0 valued fields may be reduced, under rather general
  • 2020 Jan 30

    Basic Notions: Cy Maor (HUJI) "Infinite dimensional Riemannian geometry in hydrodynamics and shape analysis".

    4:00pm to 5:15pm


    Ross 70
    In the mid-18th century,Euler derived his famous equations of motion of an incompressible fluid, one ofthe most studied equations in hydrodynamics. More than 200 years later, in1966, Arnold observed that they are, in fact, geodesic equations on the(infinite dimensional) Lie group of volume-preserving diffeomorphisms of amanifold, endowed with a certain right-invariant Riemannian metric.
  • 2020 Jan 30

    Groups & Dynamics Seminar. Chloe Perin (HUJI): Homogeneity of torsion-free hyperbolic groups

    10:00am to 11:00am


    Ross 70 a
    A countable group is said to be homogeneous if whenever tuples of elements u, v satisfy the same first-order formulas there is an automorphism of the group sending one to the other. We had previously proved with Rizos Sklinos that free groups are homogeneous, while most surface groups aren't. In a joint work with Ayala Dente-Byron, we extend this to give a complete characterization of torsion-free hyperbolic groups that are homogeneous.
  • 2020 Jan 29

    Logic Seminar - Yatir Halevi

    9:45am to 11:45am


    Ross building - Room 63
    Yatir Halevi will speal about Coloring Stable Graphs.

    Title: Coloring Stable Graphs

    Abstract: Given a graph G=(V,E), a coloring of G in \kappa colors is a
    map c:V\to \kappa in which adjacent vertices are colored in different
    colors. The chromatic number of G is the smallest such \kappa.
    We will briefly review some questions and conjectures on the chromatic
    number of infinite graphs and will mainly concentrate on the strong
    form of Taylor's conjecture:
  • 2020 Jan 28

    Benjamin Weiss (HUJI) On the construction of measure distal transformations

    2:00pm to 3:00pm


    Ross 70

    Abstract: I will explain what measure distal transformations are
    and describe some new constructions obtained with Eli Glasner.
    These answer, inter alia, a question recently raised by Ibarlucia and Tsankov
    concerning the existence of strongly ergodic non compact distal actions of the
    free group.
  • 2020 Jan 27

    Combinatorics: Chaya Keller (Ariel)

    10:00am to 12:00pm


    C-400, CS building

    Title: The epsilon-t-net problem


    In this talk we study a natural generalization of the classical \eps-net problem (Haussler-Welzl 1987), which we call 'the \eps-t-net problem': Given a hypergraph on n vertices and parameters t and \eps , find a minimum-sized family S of t-element subsets of vertices such that each hyperedge of size at least \eps n  contains a set in S. When t=1, this corresponds to the \eps-net problem.