<p>A word <i>w</i> is said to be concise in a class of groups if, for every <i>G</i> in that class such that the set of <i>w</i>-values <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(w\{G\}\)</EquationSource> </InlineEquation> is finite, the verbal subgroup <i>w</i>(<i>G</i>) is also finite. In the context of profinite groups, the notion of strong conciseness imposes a more demanding condition on <i>w</i>, requiring that <i>w</i>(<i>G</i>) is finite whenever <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(|w\{G\}|&lt; 2^{\aleph _0}\)</EquationSource> </InlineEquation>. We investigate the relation between these two properties and the notion of equationally Noetherian groups, by proving that in a profinite group <i>G</i> with a dense equationally Noetherian subgroup, <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(w\{G\}\)</EquationSource> </InlineEquation> is finite whenever <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(|w\{G\}|&lt; 2^{\aleph _0}\)</EquationSource> </InlineEquation>. Consequently, we conclude that every word is strongly concise in the classes of profinite linear groups, pro-<InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\mathcal {C}\)</EquationSource> </InlineEquation> completions of residually <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\mathcal {C}\)</EquationSource> </InlineEquation> linear groups and pro-<InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\mathcal {C}\)</EquationSource> </InlineEquation> completions of virtually abelian-by-polycyclic groups, thereby extending well-known conciseness properties of these classes of groups.</p>

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Strong conciseness and equationally Noetherian groups

  • Iker de las Heras,
  • Andoni Zozaya

摘要

A word w is said to be concise in a class of groups if, for every G in that class such that the set of w-values \(w\{G\}\) is finite, the verbal subgroup w(G) is also finite. In the context of profinite groups, the notion of strong conciseness imposes a more demanding condition on w, requiring that w(G) is finite whenever \(|w\{G\}|< 2^{\aleph _0}\) . We investigate the relation between these two properties and the notion of equationally Noetherian groups, by proving that in a profinite group G with a dense equationally Noetherian subgroup, \(w\{G\}\) is finite whenever \(|w\{G\}|< 2^{\aleph _0}\) . Consequently, we conclude that every word is strongly concise in the classes of profinite linear groups, pro- \(\mathcal {C}\) completions of residually \(\mathcal {C}\) linear groups and pro- \(\mathcal {C}\) completions of virtually abelian-by-polycyclic groups, thereby extending well-known conciseness properties of these classes of groups.