Alessio Russo

ON GROUPS WHICH CONTAIN NO HNN-EXTENSIONS

A group is called HNN-free if it has no subgroups that are nontrivial HNN-extensions. We prove that finitely generated HNN-free implies virtually polycyclic for a large class of groups. We also consider finitely generated groups with no free subsemigroups of rank 2 and show that in many situations such groups are virtually nilpotent. Finally, as an application of our results, we determine the structure of locally graded groups in which every subgroup is pronormal, thus generalizing a theorem of Kuzennyi and Subbotin.

GROUPS WHOSE PROPER SUBGROUPS ARE GENERALIZED FC-GROUPS

Let 𝔛 be a class of groups. A group G is said to be minimal non-𝔛 if all proper subgroups of G are 𝔛-groups but G itself is not. The aim of this paper is to study the class of minimal non-FCn-groups, where FCn (n is a positive integer) is a class of generalized FC-groups introduced in [F. de Giovanni, A. Russo and G. Vincenzi, Groups with restricted conjugacy classes, Serdica Math. J.28 (2002) 241–254].

Groups without proper abnormal subgroups

Abstract A subgroup H of a group G is said to be abnormal in G if g ∈ for each element g ∈ G. It is well known that every locally nilpotent group has no proper abnormal subgroups, but it is an open question whether the converse holds. In this article we prove this conjecture for some classes of infinite groups. In particular, it is proved that an FC-nilpotent group without proper abnormal subgroups is hypercentral. Also groups with finitely many abnormal subgroups are considered.

Groups whose all subgroups are ascendant or self-normalizing

This paper studies groups G whose all subgroups are either ascendant or self-normalizing. We characterize the structure of such G in case they are locally finite. If G is a hyperabelian group and has the property, we show that every subgroup of G is in fact ascendant provided G is locally nilpotent or non-periodic. We also restrict our study replacing ascendant subgroups by permutable subgroups, which of course are ascendant [Stonehewer S.E., Permutable subgroups of infinite groups, Math. Z., 1972, 125(1), 1–16].

On Groups in Which Normality Is a Transitive Relation

A subgroup H of a group G is said to be weakly normal if H g = H whenever g is an element of G such that H g ≤ N G (H). There is a strictly relation between weak normality and groups in which normality is a transitive relation ( T-groups). In [Ballester-Bolinches, A., Esteban-Romero, R. (2003). On finite T-groups. J. Aust. Math. Soc. 75:181–191] it is proved that a finite group G is a soluble T-group if and only if every subgroup of G is weakly normal. In this article, we extend the above result to infinite groups having no infinite simple sections. Moreover, it will be shown that every locally graded non-periodic group, all of whose subgroups are weakly normal, is abelian.

Groups with Finitely Many Homomorphic Images of Finite Rank

A group is called a Cernikov group if it is abelian-by-finite and satisfies the minimal condition on subgroups. A new characterization of Cernikov groups is given here, by proving that in a suitable large class of generalised soluble groups they coincide with the groups having only finitely many homomorphic images of finite rank (up to isomorphisms) and admitting an ascending normal series whose factors have finite rank.

ON A CLASS OF NORMAL ENDOMORPHISMS OF GROUPS

It is proved that if θ is an endomorphism of a group G such that 〈x, xθ〉 is cyclic for all elements x of G, then θ is a normal endomorphism of G, i.e. it commutes with all inner automorphisms of G.