A digraph is associated with a finite group by utilizing the power map $f:G\to G$ defined by $f\left(x\right)=x^k$ for all $x\in G$, where $k$ is a fixed natural number. It is denoted by ${\gamma }_G(n,k)$. In this paper, the generalized quaternion and $2$-groups are studied. The height structure is discussed for the generalized quaternion. The necessary and sufficient conditions on a power digraph of a $2$-group are determined for a $2$-group to be a generalized quaternion group. Further, the classification of two generated $2$-groups as abelian or non-abelian...

General concepts and strategies are developed for identifying the isomorphism type of the second $p$-class group $G=\mathrm{Gal}\left({\mathrm{F}}_p^2\left(K\right)\right|K)$, that is the Galois group of the second Hilbert $p$-class field ${\mathrm{F}}_p^2\left(K\right)$, of a number field $K$, for a prime $p$. The isomorphism type determines the position of $G$ on one of the coclass graphs $𝒢(p,r)$, $r\ge 0$, in the sense of Eick, Leedham-Green, and Newman. It is shown that, for special types of the base field $K$ and of its $p$-class group ${\mathrm{Cl}}_p\left(K\right)$, the position of $G$ is restricted to certain admissible branches of coclass...

Let $G$ be a group and $p$ a prime. The subgroup generated by the elements of order different from $p$ is called the Hughes subgroup for exponent $p$. Hughes [3] made the following conjecture: if $H_p\left(G\right)$ is non-trivial, its index in $G$ is at most $p$. There are many articles that treat this problem. In the present Note we examine those of Strauss and Szekeres [9], which treats the case $p=3$ and $G$ arbitrary, and that of Hogan and Kappe [2] concerning the case when $G$ is metabelian, and $p$ arbitrary. A common proof is...

Let $p$ be a prime number. This paper introduces the Roquette category ${ℛ}_p$ of finite $p$-groups, which is an additive tensor category containing all finite $p$-groups among its objects. In ${ℛ}_p$, every finite $p$-group $P$ admits a canonical direct summand $\partial P$, called the edge of $P$. Moreover $P$ splits uniquely as a direct sum of edges of Roquette $p$-groups, and the tensor structure of ${ℛ}_p$ can be described in terms of such edges. The main motivation for considering this category is that the additive functors from ${ℛ}_p$ to...