Abstract:
A subgroup $H$ of a group $G$ is called modular in $G$ if $H$ is a modular element (in sense of Kurosh) of the lattice $L(G)$ of all subgroups of $G$. The subgroup of $H$ generated by all modular subgroups of $G$ contained in $H$ is called the modular core of $H$ and denoted by $H_{mG}$. In the paper, we introduce the following concepts. A subgroup $H$ of a group $G$ is called $m$-supplemented ($m$-subnormal) in $G$ if there exists a subgroup (a subnormal subgroup respectively) $K$ of $G$ such that $G = HK$ and $H \cap K \le H_{mG}$. We proved the following theorems. Theorem A.A group$G$is soluble if and only if each Sylow subgroup of$G$is$m$-supplemented in$G$. Theorem B.A group$G$is soluble if and only if every its maximal subgroup is$m$-subnormal in$G$.