<p>In terms of the existence of a single clopen set and two related nets, we characterize when the full Boolean algebra <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\mathfrak {B}}(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="fraktur">B</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> of clopen subsets of a topological group <i>G</i> is left introverted. We employ this characterization to show that when <i>G</i> is a first countable, <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\sigma \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>σ</mi> </math></EquationSource> </InlineEquation>-compact, totally disconnected locally compact group, <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({\mathfrak {B}}(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="fraktur">B</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is left introverted if and only if <i>G</i> is compact or discrete, thus providing a strong positive answer to a question posed in Stephens and Stokke (Q J Math 74:301–326 2023). Examples of clopen sets and nets witnessing our non-introversion theorem are presented. Some hereditary properties of left introversion of <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({\mathfrak {B}}(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="fraktur">B</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> are proved and then employed to extend our main result to other classes of topological groups.</p>

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Totally disconnected semigroup compactifications: non-introversion of the full Boolean algebra of clopen sets

  • Joshua Basman Monterrubio,
  • Thomas Czyzowicz,
  • Ross Stokke,
  • Emily Thevenot

摘要

In terms of the existence of a single clopen set and two related nets, we characterize when the full Boolean algebra \({\mathfrak {B}}(G)\) B ( G ) of clopen subsets of a topological group G is left introverted. We employ this characterization to show that when G is a first countable, \(\sigma \) σ -compact, totally disconnected locally compact group, \({\mathfrak {B}}(G)\) B ( G ) is left introverted if and only if G is compact or discrete, thus providing a strong positive answer to a question posed in Stephens and Stokke (Q J Math 74:301–326 2023). Examples of clopen sets and nets witnessing our non-introversion theorem are presented. Some hereditary properties of left introversion of \({\mathfrak {B}}(G)\) B ( G ) are proved and then employed to extend our main result to other classes of topological groups.