For a class A\mathcal{A} of convex sets (in not necessarily finite-dimensional) real vector spaces, let Sep A\mathcal{A} denote the class of all convex sets C such that the affine maps from C to elements of A\mathcal{A} separate points. If we restrict our attention to finite-dimensional convex sets, there are only four possibilities for SepfA:=Sep A∩{C:C finite-dimensional convex set}\mathrm{Sep}_\mathrm{f}\mathcal{A} := \mathrm{Sep}\,\mathcal{A} \cap \{\mathcal{C} : \mathcal{C} \text{ finite-dimensional convex set}\}. Similarly, restriction to absolutely convex sets yields only three possibilities. In the general case, there are many possibilities for Sep A\mathcal{A}, at least as many as cardinals. In particular, there is no line-free convex set C such that for all linearly bounded convex sets D the affine maps from D to C separate points.

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Reinhard Börger

Fachbereich Mathematik, Fernuniversität, 58084 Hagen, Germany

  1. R. Börger, R. Kemper: A cogenerator for pre-separated superconvex spaces, Applied Categorical Structures 4 (1996) 361–370.https://doi.org/10.1007/BF00122684Google Scholar
  2. J. B. Hiriart-Urruty, C. Lemaréchal: Convex Analysis and Minimazation Algorithms I, Grundlehren der mathematischen Wissenschaften 305, Springer-Verlag, Berlin et al., 1993.https://doi.org/10.1007/978-3-662-02796-7Google Scholar
  3. D. Pumplün, H. Röhrl: Banach spaces and totally convex spaces I, Comm. Algebra 12 (1984) 953–1019.https://doi.org/10.1080/00927878408823035Google Scholar
  4. R. Schneider: Convex Bodies: The Brunn-Minkowski Theory, Cambridge University Press, Cambridge (UK), 1993.https://doi.org/10.1017/CBO9780511526282Google Scholar

R. Börger. “When Can Points in Convex Sets be Separated by Affine Maps?.” Journal of Convex Analysis 8 (2001), No. 2, 409–415. https://doi.org/10.68381/jca08021