EMIS ELibM Electronic Journals Bulletin, Classe des Sciences Mathématiques et Naturelles, Sciences mathématiques naturelles / sciences mathematiques
Vol. CXXVII, No. 28, pp. 93–106 (2003)

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Universal minimal flows of automorphism groups

A. S. Kechris, V. Pestov and S. Todorcevic

Department of Mathematics, Caltech 253-37, Pasadena, CA 91125, kechris@caltech.edu
Department of Mathematics and Statistics, University of Ottawa, 585 King Edward Avenue, Ottawa, Ontario, Canada K1N6N5, vpest283@science.ottawa.ca
Institute of Mathematics, SANU, Knez Mihailova 15, 11000 Beograd, Yugoslavia, stevo@mi.sanu.ac.yu

Abstract: We investigate some connections between the Fra\"{i}sse theory of amalgamation classes and ultrahomogeneous structures, Ramsey theory, and topological dynamics of automorphism groups of countable structures. We show, in particular, that results from the structural Ramsey theory can be quite useful in recognizing the universal minimal flows of this kind of groups. As result we compute universal minimal flows of several well known topological groups such as, for example, the automorphism group of the random graph, the automorphism group of the random triangle-free graph, the automorphism group of the $\infty$-dimensional vector space over a finite field, the automorphism group of the countable atomless Boolean algebra,etc. So we have here a reversal in the traditional relationship between topological dynamics and Ramsey theory, the Ramsey-theoretic results are used in proving theorems of topological dynamics rather than vice versa.

Keywords: group actions, universal minimal flows, Fra\"{i}sse theory, structural Ramsey theory

Classification (MSC2000): 05D10, 05C55, 22A10, 22A05, 22F05, 37B05, 37F20, 54H20

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Electronic fulltext finalized on: 17 Sep 2003. This page was last modified: 20 Jun 2011.

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