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Almost locally free groups and the genus question

群论 2009-09-25 v1

摘要

Sacerdote [Sa] has shown that the non-Abelian free groups satisfy precisely the same universal-existential sentences Th(F2_2)\cap \forall \exists in a first-order language Lo_o appropriate for group theory. It is shown that in every model of Th(F2_2)\cap \forall \exists the maximal Abelian subgroups are elementarily equivalent to locally cyclic groups (necessarily nontrivial and torsion free). Two classes of groups are interpolated between the non-Abelian locally free groups and Remeslennikov's \exists -free groups. These classes are the \textbf{almost locally free groups} and the \textbf{quasi-locally free groups}. In particular, the almost locally free% \textbf{\ }groups are the models of Th(F2_2)\cap \forall \exists while the quasi-locally free groups are the \exists -free groups with maximal Abelian subgroups elemenatarily equivalent to locally cyclic groups (necessarily nontrivial and torsion free). Two principal open questions at opposite ends of a spectrum are: (1.) Is every finitely generated almost locally free group free? (2.) Is every quasi-locally free group almost locally free? Examples abound of finitely generated quasi-locally free groups containing nontrivial torsion in their Abelianizations. The question of whether or not almost locally free groups have torsion free Abelianization is related to a bound in a free group on the number of factors needed to express certain elements of the derived group as a product of commutators.

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引用

@article{arxiv.math/9603204,
  title  = {Almost locally free groups and the genus question},
  author = {Anthony Gaglione and Dennis Spellman},
  journal= {arXiv preprint arXiv:math/9603204},
  year   = {2009}
}

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