Are $\cap A_n$ and $\cup A_n$ standard notations?

Question

I read several papers using the object: $\cup A_n$.

After thinking for days I fig out that they mean: $\lim_{m\to\infty}\cup_1^m A_n$ or $\cup_1^{\infty} A_n$.

Are those standard notation such that the authors did not even bother to define it?