Group actions on treelike compact spaces

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12 Scopus citations


We show that group actions on many treelike compact spaces are not too complicated dynamically. We first observe that an old argument of Seidler (1990) implies that every action of a topological group G on a regular continuum is null and therefore also tame. As every local dendron is regular, one concludes that every action of G on a local dendron is null. We then use a more direct method to show that every continuous group action of G on a dendron is Rosenthal representable, hence also tame. Similar results are obtained for median pretrees. As a related result, we show that Helly’s selection principle can be extended to bounded monotone sequences defined on median pretrees (for example, dendrons or linearly ordered sets). Finally, we point out some applications of these results to continuous group actions on dendrites.

Original languageEnglish
Pages (from-to)2447-2462
Number of pages16
JournalScience China Mathematics
Issue number12
StatePublished - 1 Dec 2019

Bibliographical note

Publisher Copyright:
© 2019, Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature.


  • Primary 54H20
  • Rosenthal Banach space
  • amenable group
  • dendrite
  • dendron
  • fragmentability
  • median pretree
  • proximal action
  • secondary 54H15, 22A25
  • tame dynamical system


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