Günter M. Ziegler

  1. Optimal bounds for the colored Tverberg problem.

    Authors: Günter M. Ziegler, Pavle V. M. Blagojević
    Subjects: Combinatorics
    Abstract

    We prove a "Tverberg type" multiple intersection theorem. It strengthens the
    prime case of the original Tverberg theorem from 1966, as well as the
    topological Tverberg theorem of Barany et al. (1980), by adding color
    constraints. It also provides an improved bound for the (topological) colored
    Tverberg problem of Barany & Larman (1992) that is tight in the prime case and
    asymptotically optimal in the general case. The proof is based on relative
    equivariant obstruction theory.

  2. Polyhedral Surfaces in Wedge Products.

    Authors: Thilo Rörig, Günter M. Ziegler
    Subjects: Metric Geometry
    Abstract

    We introduce the wedge product of two polytopes. The wedge product is
    described in terms of inequality systems, in terms of vertex coordinates as
    well as purely combinatorially, from the corresponding data of its
    constituents. The wedge product construction can be described as an iterated
    ``subdirect product'' as introduced by McMullen (1976); it is dual to the
    ``wreath product'' construction of Joswig and Lutz (2005).

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