(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
(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