Published online by Cambridge University Press: 20 November 2018
Let $G$ be any group, and
$H$ be a normal subgroup of
$G$. Then M. Hartl identified the subgroup
$G\,\cap \,(1+\,{{\Delta }^{3}}\,(G)\,+\,\Delta (G)\Delta (H))$ of
$G$. In this note we give an independent proof of the result of Hartl, and we identify two subgroups
$G\,\cap \,(1\,+\,\Delta (H)\Delta (G)\Delta (H)\,+\,\Delta (\left[ H,\,G \right]\Delta (H)),\,G\,\cap \,(1\,+\,{{\Delta }^{2}}\,(G)\Delta (H)\,+\,\Delta (K)\Delta (H))$ of
$G$ for some subgroup
$K$ of
$G$ containing
$[H,G]$.