《Algebra》
· 第 135 页 · Chapter III，Section 3，Definition 3.1
A nonzero element $a$ of a commutative ring $R$ is said to divide an element $b\in R$ (notation: $a\mid b$) if there exists $x\in R$ such that $ax=b$. Elements $a,b$ of $R$ are said to be associates if $a\mid b$ and $b\mid a$.
