Lecture Notes on Bayesian Estimation and Classification
《Lecture Notes on Bayesian Estimation and Classification》 · 第 122 页 · Section 5.1「Abelian and Central Series」
A group $G$ is called nilpotent if it has a central series, that is, a normal series $1=G_0\leq G_1\leq\cdots\leq G_n=G$ such that $G_{i+1}/G_i$ is contained in the center of $G/G_i$ for all $i$.