How to deal with the following contradiction in notation?
$\bigcup a$ may mean both:
- the union of a collection of sets $a$;
- $\bigcup_{i\in \operatorname{dom}a} a_i$ for an indexed family $a$ of sets.
I deal with mathematics long time, but discovered this contradictory notation only a few minutes ago.
What is the right way to deal with this?