Lecture Notes on Bayesian Estimation and Classification
《Lecture Notes on Bayesian Estimation and Classification》 · 第 379 页 · Section 12.4「Classes of Groups Defined by General Series」
An important subclass of $SI$ is the class of groups which have an ascending normal series with abelian factors; these are called hyperabelian groups. Being much closer to soluble groups this is a relatively tractable class.