Introduction to Commutative Algebra
《Introduction to Commutative Algebra》 · 第 8 页 · Chapter 1「Rings and Ideals」
If $\mathfrak a,\mathfrak b$ are ideals in a ring $A$, their ideal quotient is $(\mathfrak a:\mathfrak b)=\{x\in A:x\mathfrak b\subseteq\mathfrak a\}$, which is an ideal.