What does I\(a) notation mean for ideals?

Question

I do know the notation R/I where R is a ring and I is an ideal. But recently saw the following notation I \ (a) where I is an ideal and (a) is a principal ideal. In this specific scenario (a) is a proper subset of I, however, I also saw a version where it was not the case

Answer 1

It is silly to rob answerers of the context by saying "in a paper I saw" without referencing the paper, so that others can confirm the context.

Here's the best I can do without information:

When $A, B$ are ideals, $B\subseteq A$,

1. The notation $A\setminus B$ means $\{x\in A\mid x\notin B\}$
2. The notation $A/B$ means the equivalence classes of $A$ modulo the subgroup $B$.