Lecture Notes on Bayesian Estimation and Classification
《Lecture Notes on Bayesian Estimation and Classification》 · 第 393 页 · Section 13.2「Permutability and Subnormality」
Recall that subgroup $H$ is said to be permutable in a group $G$ if $HK=KH$ whenever $K\le G$. We shall sometimes write $H\ \mathrm{per}\ G$ to denote this relation.