Lecture Notes on Bayesian Estimation and Classification
《Lecture Notes on Bayesian Estimation and Classification》 · 第 121 页 · Section 5.1「Abelian and Central Series」
If $G$ is a soluble group, the length of a shortest abelian series in $G$ is called the derived length of $G$. Thus $G$ has derived length $0$ if and only if it has order $1$. Also the groups with derived length at most $1$ are just the abelian groups.