Lecture Notes on Bayesian Estimation and Classification
《Lecture Notes on Bayesian Estimation and Classification》 · 第 106 页 · Section 4.3「Pure Subgroups and p-Groups」
A subgroup $H$ of an abelian group $G$ is called pure if $nG\cap H=nH$ for all integers $n>0$; in words, $H$ is pure if every element of $H$ that is divisible by $n$ in $G$ is divisible by $n$ in $H$.