Published online by Cambridge University Press: 20 November 2018
In this paper we prove the following:
1. Let   $m\ge 2,\,n\ge 1$  be integers and let
$m\ge 2,\,n\ge 1$  be integers and let   $G$  be a group such that
$G$  be a group such that   ${{(XY)}^{n}}\,=\,{{(YX)}^{n}}$  for all subsets
${{(XY)}^{n}}\,=\,{{(YX)}^{n}}$  for all subsets   $X,Y$  of size
$X,Y$  of size   $m$  in
$m$  in   $G$ . Then
$G$ . Then
a)   $G$  is abelian or a
$G$  is abelian or a   $\text{BFC}$ -group of finite exponent bounded by a function of
$\text{BFC}$ -group of finite exponent bounded by a function of   $m$  and
$m$  and   $n$ .
$n$ .
b) If   $m\ge n$  then
$m\ge n$  then   $G$  is abelian or
$G$  is abelian or   $|G|$  is bounded by a function of
$|G|$  is bounded by a function of   $m$  and
$m$  and   $n$ .
$n$ .
2. The only non-abelian group   $G$  such that
$G$  such that   ${{(XY)}^{2}}\,=\,{{(YX)}^{2}}$  for all subsets
${{(XY)}^{2}}\,=\,{{(YX)}^{2}}$  for all subsets   $X,Y$  of size 2 in
$X,Y$  of size 2 in   $G$  is the quaternion group of order 8.
$G$  is the quaternion group of order 8.
3. Let   $m$ ,
$m$ ,   $n$  be positive integers and
$n$  be positive integers and   $G$  a group such that
$G$  a group such that   $${{X}_{1}}\cdot \cdot \cdot \,{{X}_{n}}\,\subseteq \,\bigcup\limits_{\sigma \in {{S}_{n}}\,\backslash \,1}{{{X}_{\sigma (1)}}\cdot \cdot \cdot \,{{X}_{\sigma (n)}}}$$
$${{X}_{1}}\cdot \cdot \cdot \,{{X}_{n}}\,\subseteq \,\bigcup\limits_{\sigma \in {{S}_{n}}\,\backslash \,1}{{{X}_{\sigma (1)}}\cdot \cdot \cdot \,{{X}_{\sigma (n)}}}$$ 
for all subsets   ${{X}_{i}}$  of size
 ${{X}_{i}}$  of size   $m$  in
 $m$  in   $G$ . Then
 $G$ . Then   $G$  is
 $G$  is   $n$ -permutable or
 $n$ -permutable or   $|G|$  is bounded by a function of
 $|G|$  is bounded by a function of   $m$  and
 $m$  and   $n$ .
 $n$ .