Ample groupoids that are neither almost finite nor purely infinite
Abstract
We investigate a question posed by Matui concerning the existence of minimal ample groupoids that are neither almost finite nor purely infinite, along with several natural variations of this problem. We begin by noting that there exists minimal, effective, ample transformation groupoids with this property. Moreover, such examples can be chosen to be either principal or amenable. We then construct new examples of essentially principal ample groupoids that are likewise neither almost finite nor purely infinite. These examples rely on the recent twisted topological groupoid construction of Palmer and Wu. In particular, our examples do not arise from transformation groupoids.
Fields of Study & Subjects
Homotopy and Cohomology in Algebraic Topology
Advanced Algebra and Logic
Advanced Operator Algebra Research
Publication details
- Journal / source
- Journal of Topology and Analysis
- Publisher
- World Scientific Pub Co Pte Ltd
- Pages
- 1–23
- Publication date
- 10 April 2026
- Language
- EN