Homomorphisms from infinite semilcyclic $n$-groups to a semiabelian $n$-group
N. A. Shchuchkin Volgograd
State Socio-Pedagogical University (Volgograd)
Abstract:
One of the main problems for semiabelian
$n$-groups is the finding of semiabelian
$n$-groups, which are isomorphic to
$(n)$-groups of homomorphisms from certain
$n$-groups to a semiabelian
$n$-group. Such
$n$-groups are found for infinite semicyclic
$n$-groups.
It is known that the set
$Hom (G, C)$ of all homomorphisms from
$n$-groups
$\langle G, f_1 \rangle$ to a semiabelian (abelian)
$n$-group
$\langle C, f_2 \rangle$ with
$n$-ary operation
$g$ given by the rule
$$g (\varphi_1, \ldots, \varphi_n) (x) = f_2 (\varphi_1 (x), \ldots, \varphi_n (x)), x \in G,$$
forms a semiabelian (abelian)
$n$-group. It is proved that the isomorphisms
$\psi_1$ of
$n$-groups
$\langle G, f_1 \rangle$ and
$\langle G ', f'_1 \rangle$ and
$\ psi_2$ of semiabelian
$n$-groups
$\langle C , f_2 \rangle$ and
$\langle C ', f'_2 \rangle$ induce an isomorphism
$\tau$ of
$n$-groups of homomorphisms
$\langle Hom (G, C), g\rangle$ and
$\langle Hom (G ', C'), g '\rangle$, which acts according to the rule $\tau: \alpha \to \psi_2 \circ \alpha \circ \psi_1 ^ {- 1}$.
On the additive group of integers
$Z$ we construct an abelian
$n$-group
$\langle Z,f_1 \rangle$ with
$n$-ary operation
$f_1 (z_1, \ldots, z_n) = z_1 + \ldots + z_n + l$, where
$l$ is any integer. For a nonidentical automorphism
$ \varphi (z) = - z$ on
$Z$, we can specify semiabelian
$n$-group
$\langle Z, f_2 \rangle$ for
$n = 2k + 1 $,
$ k \in N$, with the
$n$-ary operation $f_2 (z_1, \ldots, z_n) = z_1-z_2 + \ldots + z_ {2k-1} -z_ {2k} + z_ {2k + 1}$. Any infinite semicyclic
$n$-group is isomorphic to either the
$n$-group
$\langle Z, f_1 \rangle$, where
$0 \leq l \leq [\frac {n-1} {2}]$, or the
$n$-group
$\langle Z, f_2 \rangle$ for odd
$n$. In the first case we will say that such
$n$-group has type
$ (\infty, 1, l)$, and in the second case, it has type
$(\infty, -1,0)$.
In studying the
$n$-groups of homomorphisms
$\langle Hom (Z, C), g \rangle$ from an infinite abelian semicyclic
$n$-group
$\langle Z, f_1 \rangle$ (
$0 \leq l \leq \frac {n-1} {2} $) to a semiabelian
$n$-group
$\langle C, f_2 \rangle$ we construct on the
$n$-group
$\langle C, f_2 \rangle$ an abelian group
$C$ with the addition operation $a + b = f_2 (a, \overset {(n-3)} {c}, \bar c, b)$, in which there is an element
$ d_2 = f_2 (\overset {(n)} {c})$ and an automorphism $\varphi_2 (x) = f_2 (c, x, \overset {(n-3)} {c}, \bar c )$. Choose a set
$P_1$ of such ordered pairs
$(a, u)$ of elements from
$C$ that satisfy the equality
$ la = d_2 + \overset {\sim} {\varphi_2} (u)$, where $\overset {\sim} {\varphi_2} (x) = x + \varphi_2 (x) + \ldots + \varphi ^ {n-2} _2 (x), x \in C$ is an endomorphism of the group
$C$, and for the first component of these pairs the equality is true
$\varphi_2 (a) = a$. On this set, we define a
$n$-ary operation
$h_1$ by the rule $h_1 ((a_1, u_1), \ldots, (a_n, u_n)) = (a_1 + \ldots + a_n, f_2 (u_1, \ldots, u_n) )$. It is proved that
$\langle P_1, h_1 \rangle$ is a semiabelian
$n$-group, which is isomorphic to the
$n$-group of homomorphisms from an infinite abelian semicyclic
$n$-group
$\langle Z, f_1 \rangle$ (
$ 0 \leq l \leq \frac {n-1} {2}$) to an
$n$-group
$\langle C, f_2 \rangle$. The consequence of this isomorphism is an isomorphism of
$n$-groups of
$\langle P_1, h_1 \rangle$ and
$n$-groups of homomorphisms from an infinite abelian semicyclic
$n$-group of type
$(\infty, 1, l)$ to a semiabelian
$n$-group
$\langle C, f_2 \rangle$.
When studying the
$n$-group of homomorphisms
$\langle Hom (Z, C), g \rangle$ from the infinite semicyclic
$n$-group
$\langle Z, f'_1 \rangle$ to the semiabelian
$n$-group
$\langle C, f_2 \rangle$ in the abelian group
$C$ choose the subgroup
$H = \{a \in C ~ | ~ \varphi_2 (a) = - a \}$. On
$H$ we define a semiabelian
$n$-group
$\langle H, h \rangle$, where
$h$ acts according to the rule $h (a_1, a_2, \ldots, a_ {n-1}, a_n) = a_1 + \varphi_2 (a_2) + \ldots + \varphi ^ {n-2} _2 (a_ {n-1}) + a_n$. Then in the
$n$-group
$\langle C, f_2 \rangle$ we select the subgroup
$\langle T, f_2 \rangle$ of all idempotents, if
$T \ne \emptyset$. It is proved that for an odd number
$n> 1$ a direct product of semiabelian
$n$-groups $\langle H, h \rangle \times \langle T, f_2 \rangle$ is isomorphic to
$n$-group of homomorphisms from infinite semicyclic
$n$-groups of
$\langle Z, f'_1 \rangle$ to a semiabelian
$n$-group
$\langle C, f_2 \rangle$ with a non empty set of idempotents
$T$. The consequence of this isomorphism is the isomorphism of the
$n$-group $\langle H, h \rangle \times \langle T, f_2 \rangle$ and
$n$-groups of homomorphisms from an infinite semicyclic
$n$-group of type
$(\infty, - 1,0)$ to the semiabelian
$n$-group
$\langle C, f_2 \rangle$.
Similar facts were obtained when studying the
$n$-group of homomorphisms
$\langle Hom (Z, C), g \rangle$ from
$n$-groups
$\langle Z, f_1 \rangle $ and
$\langle Z, f'_1 \rangle$ to an abelian
$n$-group
$\langle C, f_2 \rangle$.
Keywords:
$n$-group, semiabelian $(n,2)$-group, abelian $(n,2)$-group, homomorphism.
UDC:
512.548 Received: 12.11.2020
Accepted: 21.02.2021
DOI:
10.22405/2226-8383-2018-22-1-340-352