<p>Given two subgroups <i>H</i>,&#xa0;<i>K</i> of a compact group <i>G</i>, the probability that a random element of <i>H</i> commutes with a random element of <i>K</i> is denoted by <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="69" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{Pr} (H,K)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>Pr</mtext> <mo stretchy="false">(</mo> <mi>H</mi> <mo>,</mo> <mi>K</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. We show that if <i>G</i> is a profinite group containing a Sylow 2-subgroup <i>P</i>, a Sylow 3-subgroup <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq2.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(Q_3\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>Q</mi> <mn>3</mn> </msub> </math></EquationSource> </InlineEquation> and a Sylow 5-subgroup <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq3.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(Q_5\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>Q</mi> <mn>5</mn> </msub> </math></EquationSource> </InlineEquation> such that <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{Pr} (P,Q_3)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>Pr</mtext> <mo stretchy="false">(</mo> <mi>P</mi> <mo>,</mo> <msub> <mi>Q</mi> <mn>3</mn> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{Pr} (P,Q_5)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>Pr</mtext> <mo stretchy="false">(</mo> <mi>P</mi> <mo>,</mo> <msub> <mi>Q</mi> <mn>5</mn> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> are both positive, then <i>G</i> is virtually prosoluble (Theorem 1). Furthermore, if <i>G</i> is a prosoluble group in which for every subset <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="71" /> </InlineMediaObject> <EquationSource Format="TEX">\(\pi \subseteq \pi (G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>π</mi> <mo>⊆</mo> <mi>π</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> there is a Hall <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq7.gif" Format="GIF" Height="10" Rendition="HTML" Resolution="72" Type="Linedraw" Width="13" /> </InlineMediaObject> <EquationSource Format="TEX">\(\pi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>π</mi> </math></EquationSource> </InlineEquation>-subgroup <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq8.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(H_\pi \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>H</mi> <mi>π</mi> </msub> </math></EquationSource> </InlineEquation> and a Hall <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq9.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\pi '\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>π</mi> <mo>′</mo> </msup> </math></EquationSource> </InlineEquation>-subgroup <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq10.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="27" /> </InlineMediaObject> <EquationSource Format="TEX">\(H_{\pi '}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>H</mi> <msup> <mi>π</mi> <mo>′</mo> </msup> </msub> </math></EquationSource> </InlineEquation> such that <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3686_Article_IEq11.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="116" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{Pr} (H_\pi ,H_{\pi '})&gt;0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>Pr</mtext> <mo stretchy="false">(</mo> <msub> <mi>H</mi> <mi>π</mi> </msub> <mo>,</mo> <msub> <mi>H</mi> <msup> <mi>π</mi> <mo>′</mo> </msup> </msub> <mo stretchy="false">)</mo> <mo>&gt;</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>, then <i>G</i> is virtually pronilpotent (Theorem&#xa0;2).</p>

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Commuting probability for the Sylow subgroups of a profinite group

  • Eloisa Detomi,
  • Marta Morigi,
  • Pavel Shumyatsky

摘要

Given two subgroups HK of a compact group G, the probability that a random element of H commutes with a random element of K is denoted by \(\textrm{Pr} (H,K)\) Pr ( H , K ) . We show that if G is a profinite group containing a Sylow 2-subgroup P, a Sylow 3-subgroup \(Q_3\) Q 3 and a Sylow 5-subgroup \(Q_5\) Q 5 such that \(\textrm{Pr} (P,Q_3)\) Pr ( P , Q 3 ) and \(\textrm{Pr} (P,Q_5)\) Pr ( P , Q 5 ) are both positive, then G is virtually prosoluble (Theorem 1). Furthermore, if G is a prosoluble group in which for every subset \(\pi \subseteq \pi (G)\) π π ( G ) there is a Hall \(\pi \) π -subgroup \(H_\pi \) H π and a Hall \(\pi '\) π -subgroup \(H_{\pi '}\) H π such that \(\textrm{Pr} (H_\pi ,H_{\pi '})>0\) Pr ( H π , H π ) > 0 , then G is virtually pronilpotent (Theorem 2).