Over- and Underlining and bracing

The \underline command will place an unbroken line under its argument, and the \overline command will place an unbroken line over its argument. These two commands can also be used in normal paragraphing mode (but be careful: LATEX will not break the line within an under- or overlined phrase, so don't go operating on large phrases).

You can place horizontal braces above or below an expression by making that expression the argument of \overbrace or \underbrace. You can place a label on an overbrace (resp. underbrace) by superscripting (resp. subscripting the group defined by the bracing command.

\begin{mathegs}
\verb@$\overline{a+bi} = a- bi$@ & $\overline{a+bi} = a- bi$\\
...
...\overline{a+bi}} = a+bi$@ & $\overline{\overline{a+bi}} = a+bi$\\
\end{mathegs}

And some examples of horizontal bracing:

0.1

$A^n=\overbrace{A \times A \times \ldots \times A}^{\mbox{$n$ terms}}$

$\forall x \underbrace{\exists y (y \succ x)}_{\mbox{scope of $\forall$}}$
will produce

An = $\displaystyle \overbrace{{A \times A \times \ldots \times A}}^{{\mbox{$n$ terms}}}_{}\,$

and

x$\displaystyle \underbrace{{\exists y (y \succ x)}}_{{\mbox{scope of $\forall$}}}^{}\,$