Inverse systems of groupoids, with applications to groupoid C-algebras

Kyle Austin, Magdalena C. Georgescu

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


We define what it means for a proper continuous morphism between groupoids to be Haar system preserving, and show that such a morphism induces (via pullback) a *-morphism between the corresponding convolution algebras. We proceed to provide a plethora of examples of Haar system preserving morphisms and discuss connections to noncommutative CW-complexes and interval algebras. We prove that an inverse system of groupoids with Haar system preserving bonding maps has a limit, and that we get a corresponding direct system of groupoid C-algebras. An explicit construction of an inverse system of groupoids is used to approximate a σ-compact groupoid G by second countable groupoids; if G is equipped with a Haar system and 2-cocycle then so are the approximation groupoids, and the maps in the inverse system are Haar system preserving. As an application of this construction, we show how to easily extend the Maximal Equivalence Theorem of Jean Renault to σ-compact groupoids.

Original languageEnglish
Pages (from-to)716-750
Number of pages35
JournalJournal of Functional Analysis
Issue number3
StatePublished - 1 Feb 2019


  • Groupoid C-algebras
  • Groupoids
  • Inverse approximation
  • Renault's Equivalence Theorem

ASJC Scopus subject areas

  • Analysis


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