LaTeX provides commands for putting lines, braces, and arrows over or under math material.

`\underline{`

¶`math`}Underline

`math`. For example:`\underline{x+y}`

. The line is always completely below the text, taking account of descenders, so in`\(\underline{y}\)`

the line is lower than in`\(\underline{x}\)`

. As of approximately 2019, this command and others in this section are robust; before that, they were fragile (see`\protect`

).The package

`ulem`

(https://ctan.org/pkg/uelem) does text mode underlining and allows line breaking as well as a number of other features. See also`\hrulefill`

&`\dotfill`

for producing a line for such things as a signature or placeholder.`\overline{`

¶`math`}Put a horizontal line over

`math`. For example:`\overline{x+y}`

. This differs from the accent command`\bar`

(see Math accents).`\underbrace{`

¶`math`}Put a brace under

`math`. For example:`(1-\underbrace{1/2)+(1/2}-1/3)`

.You can attach text to the brace as a subscript (

`_`

) or superscript (`^`

) as here:\begin{displaymath} 1+1/2+\underbrace{1/3+1/4}_{>1/2}+ \underbrace{1/5+1/6+1/7+1/8}_{>1/2}+\cdots \end{displaymath}

The superscript appears on top of the expression, and so can look unconnected to the underbrace.

`\overbrace{`

¶`math`}Put a brace over

`math`. For example:

`\overbrace{x+x+\cdots+x}^{\mbox{\(k\) times}}`

.`\overrightarrow{`

¶`math`}Put a right arrow over

`math`. For example:`\overrightarrow{x+y}`

.`\overleftarrow{`

¶`math`}Put a left arrow over

`math`. For example:`\overleftarrow{a+b}`

.

The package `mathtools`

(https://ctan.org/pkg/mathtools)
adds an over- and underbracket, as well as some improvements on the
braces.