<p>In [<CitationRef CitationID="CR11">11</CitationRef>] Sklinos proved that any uncountable free group is not <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="153_2025_982_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\aleph _1\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ℵ</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation>-homogeneous. This was later generalized by Belegradek in [<CitationRef CitationID="CR1">1</CitationRef>] to torsion-free residually finite relatively free groups, leaving open whether the assumption of residual finiteness was necessary. In this paper we use methods arising from the classical analysis of relatively free groups in infinitary logic to answer Belegradek’s question in the negative. Our methods are general and they also apply to varieties with torsion, for example we show that if <i>V</i> contains a finite non-nilpotent group, then any uncountable <i>V</i>-free group is not <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="153_2025_982_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\aleph _1\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ℵ</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation>-homogeneous.</p>

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The construction principle and non homogeneity of uncountable relatively free groups

  • Davide Carolillo,
  • Gianluca Paolini

摘要

In [11] Sklinos proved that any uncountable free group is not \(\aleph _1\) 1 -homogeneous. This was later generalized by Belegradek in [1] to torsion-free residually finite relatively free groups, leaving open whether the assumption of residual finiteness was necessary. In this paper we use methods arising from the classical analysis of relatively free groups in infinitary logic to answer Belegradek’s question in the negative. Our methods are general and they also apply to varieties with torsion, for example we show that if V contains a finite non-nilpotent group, then any uncountable V-free group is not \(\aleph _1\) 1 -homogeneous.