<p>A subgroup <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11202_2025_1579_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">$ H $</EquationSource> </InlineEquation> of a group <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11202_2025_1579_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">$ G $</EquationSource> </InlineEquation> is said to be pronormal if, for every element <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11202_2025_1579_Article_IEq3.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="49" /> </InlineMediaObject> <EquationSource Format="TEX">$ g\in G $</EquationSource> </InlineEquation>, the subgroups <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11202_2025_1579_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">$ H $</EquationSource> </InlineEquation> and <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11202_2025_1579_Article_IEq5.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">$ H^{g} $</EquationSource> </InlineEquation> are conjugate in the subgroup <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11202_2025_1579_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="63" /> </InlineMediaObject> <EquationSource Format="TEX">$ \langle{}H,H^{g}\rangle{} $</EquationSource> </InlineEquation>.It is known that a substantial portion of finite simple groups possesses property&#xa0;<InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11202_2025_1579_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="23" /> </InlineMediaObject> <EquationSource Format="TEX">$ (*) $</EquationSource> </InlineEquation>: every subgroup of odd index is pronormal in the group.To date, finite simple groups with property&#xa0;<InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11202_2025_1579_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="23" /> </InlineMediaObject> <EquationSource Format="TEX">$ (*) $</EquationSource> </InlineEquation> have been classified, except for finite simple linear and unitary groups subject to certain restrictions on their natural arithmetic parameters.In 2024, a&#xa0;classification was initiated for finite simple linear and unitary groups in which all subgroups of odd index are pronormal.The plan is to identify all possible sources of nonpronormal subgroups of odd index and then prove that there are no other such examples.In 2024, series of examples of nonpronormal subgroups of&#xa0;odd index were found in finite simple linear and unitary groups over fields of odd characteristic.In&#xa0;the present paper, we construct a new series of examples of nonpronormal subgroups of odd index in finite simple linear and unitary groups over a field of odd characteristic.</p>

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New Examples of Nonpronormal Subgroups of Odd Index in Finite Simple Linear and Unitary Groups

  • J. Guo,
  • W. Guo,
  • N. V. Maslova,
  • D. O. Revin

摘要

A subgroup $ H $ of a group $ G $ is said to be pronormal if, for every element $ g\in G $ , the subgroups $ H $ and $ H^{g} $ are conjugate in the subgroup $ \langle{}H,H^{g}\rangle{} $ .It is known that a substantial portion of finite simple groups possesses property  $ (*) $ : every subgroup of odd index is pronormal in the group.To date, finite simple groups with property  $ (*) $ have been classified, except for finite simple linear and unitary groups subject to certain restrictions on their natural arithmetic parameters.In 2024, a classification was initiated for finite simple linear and unitary groups in which all subgroups of odd index are pronormal.The plan is to identify all possible sources of nonpronormal subgroups of odd index and then prove that there are no other such examples.In 2024, series of examples of nonpronormal subgroups of odd index were found in finite simple linear and unitary groups over fields of odd characteristic.In the present paper, we construct a new series of examples of nonpronormal subgroups of odd index in finite simple linear and unitary groups over a field of odd characteristic.