Ends, tangles and critical vertex sets

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Erscheinungsjahr:
2019
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Text
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  • Article
  • Article
Beschreibung:
  • We show that an arbitrary infinite graph G can be compactified by its ends plus its critical vertex sets, where a finite set X of vertices of an infinite graph is critical if its deletion leaves some infinitely many components each with neighbourhood precisely equal to X. We further provide a concrete separation system whose aleph(0)-tangles are precisely the ends plus critical vertex sets. Our tangle compactification |G|Gamma is a quotient of Diestel's (denoted by |G|Theta), and both use tangles to compactify a graph in much the same way as the ends of a locally finite and connected graph compactify it in its Freudenthal compactification. Finally, generalising both Diestel's construction of |G|Theta and our construction of |G|Gamma, we show that G can be compactified by every inverse limit of compactifications of the sets of components obtained by deleting a finite set of vertices. Diestel's |G|Theta is the finest such compactification, and our |G|Gamma is the coarsest one. Both coincide if and only if all tangles are ends. This answers two questions of Diestel.
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  • info:eu-repo/semantics/restrictedAccess
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Forschungsinformationssystem der UHH

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oai:www.edit.fis.uni-hamburg.de:publications/567429e6-5466-469a-a27d-4a0b3e5e5d8a