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On the commutator subgroups of finite $2$-groups generated by involutions
B. M. Veretennikov Ural Federal University, Yekaterinburg,
620002 Russia
Abstract:
For a finite group
$G$ we denote by
$d(G)$ the minimum number of its generators and by
$G'$ the commutator group of
$G$. In 1975 Ustyuzhaninov published without proof the list of finite
$2$-groups generated by three involutions with elementary abelian commutator subgroup. In particular,
$d(G') \leq 5$ for such a group
$G$. Continuing this research, we pose the problem of classifying all finite
$2$-groups generated by
$n$ involutions (for any
$n\geq 2$) with elementary abelian commutator subgroup. For a finite
$2$-group
$G$ generated by
$n$ involutions with
$d(G)=n$, we prove that
$$d(G') \leq \left(
\begin{array}[c]{c}n\\2 \end{array}
\right) + 2 \left(
\begin{array}[c]{c}n\\3 \end{array}
\right) + \dots + (n-1) \left(
\begin{array}[c]{c}n\\n \end{array}
\right)$$
for any
$n \geq 2$ and that the upper bound is attainable. In addition, we construct for any
$n \geq 2$ a finite
$2$-group generated by
$n$ involutions with elementary abelian commutator subgroup of rank $\left(
\begin{array}[c]{c}n\\2 \end{array}
\right) + 2 \left(
\begin{array}[c]{c}n\\3 \end{array}
\right) + \dots + (n-1) \left(
\begin{array}[c]{c}n\\n \end{array}
\right)$. The method of constructing this group is similar to the method used by the author in a number of papers for the construction of Alperin's finite groups. We obtain
$G$ as the consecutive semidirect product of groups of order
$2$. We also give an example of an infinite
$2$-group generated by involutions with infinite elementary abelian commutator subgroup; the example is obtained from the constructed finite
$2$-groups.
Keywords:
$2$-group, generation by involutions, commutator subgroup.
UDC:
512.54
MSC: 20D15 Received: 10.04.2017
DOI:
10.21538/0134-4889-2017-23-4-77-84