<p>In this second part we prove that, if <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1363_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>G</mi> </math></EquationSource> <EquationSource Format="TEX">$G$</EquationSource> </InlineEquation> is one of the groups <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1363_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="58" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="normal">PSL</mi> <mn>2</mn> </msub> <mo stretchy="false">(</mo> <mi>q</mi> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$\mathrm{PSL}_{2}(q)$</EquationSource> </InlineEquation> with <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1363_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="41" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>q</mi> <mo>&gt;</mo> <mn>5</mn> </math></EquationSource> <EquationSource Format="TEX">$q&gt;5$</EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1363_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="111" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>q</mi> <mo>≡</mo> <mn>5</mn> <mspace width="0.25em" /> <mo stretchy="false">(</mo> <mi mathvariant="normal">mod</mi> <mspace width="0.25em" /> <mn>24</mn> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$q\equiv 5\ (\mathrm{mod}\ 24)$</EquationSource> </InlineEquation> or <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1363_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="119" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>q</mi> <mo>≡</mo> <mn>13</mn> <mspace width="0.25em" /> <mo stretchy="false">(</mo> <mi mathvariant="normal">mod</mi> <mspace width="0.25em" /> <mn>24</mn> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$q\equiv 13 \ (\mathrm{mod}\ 24)$</EquationSource> </InlineEquation>, then the fundamental group of every acyclic 2-dimensional, fixed point free and finite <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1363_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>G</mi> </math></EquationSource> <EquationSource Format="TEX">$G$</EquationSource> </InlineEquation>-complex admits a nontrivial representation in a unitary group <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1363_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="44" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi mathvariant="bold">U</mi> <mo stretchy="false">(</mo> <mi>m</mi> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$\mathbf{U}(m)$</EquationSource> </InlineEquation>. This completes the proof of the following result: every action of a finite group on a finite and contractible 2-complex has a fixed point.</p>

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Group actions on contractible 2-complexes II

  • Kevin Iván Piterman,
  • Iván Sadofschi Costa

摘要

In this second part we prove that, if G $G$ is one of the groups PSL 2 ( q ) $\mathrm{PSL}_{2}(q)$ with q > 5 $q>5$ and q 5 ( mod 24 ) $q\equiv 5\ (\mathrm{mod}\ 24)$ or q 13 ( mod 24 ) $q\equiv 13 \ (\mathrm{mod}\ 24)$ , then the fundamental group of every acyclic 2-dimensional, fixed point free and finite G $G$ -complex admits a nontrivial representation in a unitary group U ( m ) $\mathbf{U}(m)$ . This completes the proof of the following result: every action of a finite group on a finite and contractible 2-complex has a fixed point.