Above and Below

It is useful to be able to draw horizontal lines and braces above and below parts of a formula. We can combine the \overline, \overbrace, \underline, and \underbrace commands to our heart's content.

$$
\left(
\begin{array}{c}
m+n\\
m
\end{array}
\right)
= \frac{(m+n)!}{m!n!}
= \frac
	{\overbrace{(m+n)(m+n-1)\cdots(n+1)}^\mbox{$m$ factors}
	{\underbrace{m(m-1)\cdots 1}_\mbox{$m$ factors}}
$$

produces

$$\left( \begin{array}{c} m+n\\ m \end{array}\right) = \frac ... ... } { \underbrace {m(m-1)\cdots 1} _{\mbox{$m$ factors}} }$$

while

$\overline{x+\overline{y}} = \overline{x}+y$

produces

$\overline{x+\overline{y}} = \overline{x}+y$

Practice: Construct an equation using all four of these commands.