Abstract:
Let $G$ be a finite group and ${\mathscr L}_{sn}(G)$ be the lattice of
all subnormal subgroups of $G$. Let $A$ and $N$ be subgroups of $G$ and
$1, G\in {\mathscr L}$ be a sublattice of ${\mathscr L}_{sn}(G)$, that is, $A\cap B$, $\langle A, B
\rangle \in {\mathscr L}$ for all $A, B \in {\mathscr L} \subseteq {\mathscr L}_{sn}(G)$.
Then: $A^{{\mathscr L}}$ is the $\mathscr L$-closure of $A$ in $G$, that is,
the intersection of all subgroups in $ {\mathscr L}$ containing
$A$ and $A_{{\mathscr L}}$ is the $\mathscr L$-core of $A$ in $G$, that
is, the subgroup of $A$ generated by all subgroups of $A$ belonging $\mathscr L$.
We say that $A$ is an $N$-${\mathscr L}$-subgroup of $G$ if either
$A\in {\mathscr L}$ or $A_{{\mathscr L}} < A < A^{\mathscr L}$ and $N$ avoids every
composition factor $H/K$ of $G$ between $A_{{\mathscr L}}$ and $ A^{\mathscr L}$, that is,
$N\cap H=N\cap K$.
Using this concept, we give new characterizations of soluble and
supersoluble finite groups.
Some know results are extended.