Notation for the area outside of an area?

Question

Given how one can denote the intersection of areas as $A_1 \cap A_2$, it would make sense if one could use other set-theoretic notation in regards to geometric objects.

So I wonder, is the area outside of an area $A_1$ denotable as $A_1^C$? And if so, I assume one could call it "the complement of $A_1$?" If this notation/terminology is not conventionally used, then what is?

Answer 1

The complement of any set A contained in $\Omega$ would be $A^c$ or $A'$ where $A'=\left\{x \in \Omega \mid x \notin A\right\}$.