<p>We compare finiteness properties of locally compact groups that generalize the properties of being compactly generated and of being compactly presented. Three such families of properties have been proposed: Abels–Tiemeyer’s type <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="229_2025_1642_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(C_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>C</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation>, coarse <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="229_2025_1642_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="53" /> </InlineMediaObject> <EquationSource Format="TEX">\((n-1)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>-</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-connectedness, and Castellano–Corob-Cook’s type <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="229_2025_1642_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="TEX">\(F_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>F</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation>. The first was defined for locally compact groups, the second can be defined for general topological groups, while the third was defined only for totally disconnected locally compact groups. We prove that all three families lead to the same notion for locally compact groups. This justifies working with these properties despite the fact that it is still unclear in which sense they describe finiteness properties of free classifying spaces for locally compact groups. Various parts of the arguments are well-known to various experts. By putting them together we hope to clarify the literature.</p>

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Pragmatic finiteness properties of locally compact groups

  • Dorian Chanfi,
  • Stefan Witzel

摘要

We compare finiteness properties of locally compact groups that generalize the properties of being compactly generated and of being compactly presented. Three such families of properties have been proposed: Abels–Tiemeyer’s type \(C_n\) C n , coarse \((n-1)\) ( n - 1 ) -connectedness, and Castellano–Corob-Cook’s type \(F_n\) F n . The first was defined for locally compact groups, the second can be defined for general topological groups, while the third was defined only for totally disconnected locally compact groups. We prove that all three families lead to the same notion for locally compact groups. This justifies working with these properties despite the fact that it is still unclear in which sense they describe finiteness properties of free classifying spaces for locally compact groups. Various parts of the arguments are well-known to various experts. By putting them together we hope to clarify the literature.