Lecture Notes on Bayesian Estimation and Classification
《Lecture Notes on Bayesian Estimation and Classification》 · 第 364 页 · Section 12.2「Some Special Types of Locally Nilpotent Groups」，小节「Hypercentral Groups」
An ascending series $1=G_0\triangleleft G_1\triangleleft\cdots G_\beta=G$ in a group $G$ is said to be central if $G_\alpha\triangleleft G$ and $G_{\alpha+1}/G_\alpha$ lies in the center of $G/G_\alpha$ for every $\alpha<\beta$. A group which possesses a central ascending series is called hypercentral.