(indexed) union and intersections of things, like
$\unionmany{k=1}{\infty}{A_{k}}$ or
$\intersectmany{k=1}{\infty}{B_{k}}$. The best part about those
- are that they do the right thing in a display equation:
+ is that they do the right thing in a display equation:
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\begin{equation*}
\unionmany{k=1}{\infty}{A_{k}} = \intersectmany{k=1}{\infty}{B_{k}}