Lecture Notes on Bayesian Estimation and Classification
《Lecture Notes on Bayesian Estimation and Classification》 · 第 265 页 · Section 9.2「Sylow Systems and System Normalizers」，小节「Abnormal Subgroups」
A subgroup $H$ of a group $G$ is called abnormal if $g\in\langle H,H^g\rangle$ for all $g$ in $G$. For example, it is simple to show that a nonnormal maximal subgroup is always abnormal.