We also have a few basic set operations, for example the union of
two or three sets: $\union{A}{B}$, $\unionthree{A}{B}{C}$. And of
course with union comes intersection: $\intersect{A}{B}$,
- $\intersectthree{A}{B}{C}$.
+ $\intersectthree{A}{B}{C}$. We can also take an arbitrary
+ (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
+ is that they do the right thing in a display equation:
+ %
+ \begin{equation*}
+ \unionmany{k=1}{\infty}{A_{k}} = \intersectmany{k=1}{\infty}{B_{k}}
+ \end{equation*}
+ %
\end{section}
\begin{section}{Cone}