+ $\intersectthree{A}{B}{C}$. 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*}
+
+ Finally, we have the four standard types of intervals in $\Rn[1]$,
+ %
+ \begin{align*}
+ \intervaloo{a}{b} &= \setc{ x \in \Rn[1]}{ a < x < b },\\
+ \intervaloc{a}{b} &= \setc{ x \in \Rn[1]}{ a < x \le b },\\
+ \intervalco{a}{b} &= \setc{ x \in \Rn[1]}{ a \le x < b }, \text{ and }\\
+ \intervalcc{a}{b} &= \setc{ x \in \Rn[1]}{ a \le x \le b }.
+ \end{align*}
+ \end{section}
+
+ \begin{section}{Complex}
+ We sometimes want to conjugate complex numbers like
+ $\compconj{a+bi} = a - bi$.