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Products and joins of locally normal Fitting classes
A. V. Martsinkevich,
N. T. Vorob'ev Vitebsk State University named after P. M. Masherov
Abstract:
Let
$\pi$ be a nonempty set of primes. A nontrivial Fitting class
$\mathfrak{F}$ is said to be normal in the class
$\mathfrak{S}_\pi$ of all finite soluble
$\pi$-groups or
$\pi$-normal (we write
$\mathfrak{F\trianglelefteq S}_\pi$) if
$\mathfrak{F\subseteq S}_\pi$ and the
$\mathfrak{F}$-radical of every
$\pi$-group
$G$ is a
$\mathfrak{F}$-maximal subgroup of
$G$. If
$\pi$ is the set of all primes, then
$\mathfrak{F}$ is called normal. The product
$\mathfrak{FH}$ of Fitting classes
$\mathfrak{F}$ and
$\mathfrak{H}$ is called
$\pi$-normal if
$\mathfrak{FH}$ is a
$\pi$-normal Fitting class. We prove the existence of
$\pi$-normal products of Fitting classes factorizable by non-
$\pi$-normal factors. Assume that
$\mathbb{P}$ is the set of all primes,
$\varnothing\neq\pi\subseteq\mathbb{P}$,
$\mathfrak{F}$ is some Fitting class of
$\pi$-groups, and
$\omega=\sigma(\mathfrak{F})$ is the set of all prime divisors of all groups from
$\mathfrak{F}$. It is proved that if
$\mathfrak{F^2=F}$ and
$\mathfrak{H}$ is the class of all
$\pi$-groups with central
$\omega$-socle, then the product
$\mathfrak{FH}$ is
$\pi$-normal although each of the factors
$\mathfrak{F}$ and
$\mathfrak{H}$ is not
$\pi$-normal. The lattice join
$\mathfrak{F\vee H}$ of Fitting classes
$\mathfrak{F}$ and
$\mathfrak{H}$ is the Fitting class generated by
$\mathfrak{F\cup H}$. If
$\mathfrak{F\vee H}$ is a
$\pi$-normal Fitting class, then
$\mathfrak{F\vee H}$ is called
$\pi$-normal. Let
$\mathfrak{F}$ and
$\mathfrak{H}$ be Fitting classes of
$\pi$-groups. We prove that the lattice join
$\mathfrak{F\vee H}$ is a
$\pi$-normal Fitting class if and only if
$\mathfrak{F}$ or
$\mathfrak{H}$ is a
$\pi$-normal Fitting class.
Keywords:
$\mathfrak{F}$-radical, Fitting class, $\pi$-normal Fitting class, join of Fitting classes.
UDC:
512.542
MSC: 20D10,
20D15 Received: 16.11.2017
DOI:
10.21538/0134-4889-2018-24-2-152-157