On the existence of complements in a group to some abelian normal subgroups

Abstract

A complement to a proper normal subgroup \(H\) of a group \(G\) is a subgroup \(K\) such that \(G=HK\) and \(H\cap K=\langle1\rangle\). Equivalently it is said that \(G \) splits over \(H\). In this paper we develop a theory that we call hierarchy of centralizers to obtain sufficient conditions for a group to split over a certain abelian subgroup. We apply these results to obtain an entire group-theoretical wide extension of an important result due to D. J. S. Robinson formerly shown by cohomological methods.