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Ends of graphed equivalence relations,II
Authors:Greg Hjorth  Benjamin D Miller
Institution:(1) Department of Mathematics, University of California, 520 Portola Plaza, Los Angeles, CA 90095-1555, USA
Abstract:Given a graphing MediaObjects/11856_2009_16_Fig1_HTML.gif of a countable Borel equivalence relation on a Polish space, we show that if there is a Borel way of selecting a non-empty closed set of countably many ends from each MediaObjects/11856_2009_16_Fig2_HTML.gif-component, then there is a Borel way of selecting an end or line from each MediaObjects/11856_2009_16_Fig3_HTML.gif-component. Our method yields also Glimm-Effros style dichotomies which characterize the circumstances under which: (1) there is a Borel way of selecting a point or end from each MediaObjects/11856_2009_16_Fig4_HTML.gif-component; and (2) there is a Borel way of selecting a point, end or line from each MediaObjects/11856_2009_16_Fig5_HTML.gif-component. The first author was supported in part by NSF Grant DMS-0140503. The second author was supported in part by NSF VIGRE Grant DMS-0502315.
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