Instead of using `\left(`

and `\right)`

to auto-size the outermost set of parentheses, you could use `\biggl(`

and `\biggr)`

:

(Aside: See the postings Why the control sequences \bigl, \biggl, \bigr or \biggr, as I can always use \big or \bigg? and Difference between \big[ and \bigl[ for a discussion of the differences between `\Bigg(`

and `\Biggl(`

.)

I would recommend, actually, using `\Biggl[`

(while adding `\,`

immediately afterwards) and `\Biggr]`

to provide a bit more -- but not too much... -- visual prominence as well as variety to the outer fences:

The default LaTeX/amsmath style for underbraces frankly looks quite boring to me. If you have access to the mtpro2 package, you could use its macro `\undercbrace`

to generate a curly underbrace. Cautions: (i) The font used by this package is Times Roman, which may or may not be to your liking. (ii) The `mtpro2`

package isn't free of charge; however, its "lite" subset, which is all that's needed to use the `\undercbrace`

macro, *can* be obtained without (financial) charge.

```
\documentclass[preview,border=12pt,varwidth]{standalone}
\usepackage{amsmath}
\usepackage[lite]{mtpro2}
\begin{document}
\[
12\Biggl[\,\undercbrace{y^2 +2y\left(-\frac{2}{3}\right) +\left(-\frac{2}{3}\right)^2}_{\left[y+\left(-\frac{2}{3}\right)\right]^2}{} -\left(-\frac{2}{3}\right)^2 +\frac{4}{5}\Biggr] = 0
\]
\end{document}
```

*Addendum*: The immediately preceding example is intended mainly to demonstrate the shape of the "curly" underbrace. Thus, the only changes, relative to the code used in the second example, were in loading the `mtpro2`

package and using `\undercbrace`

instead of `\underbrace`

.

If you're serious about using the `mtpro2`

package, I would recommend making a few additional changes to the code. Chief among them are these: (i) load the `mleftright`

package and execute `\mleftright`

in the preamble to eliminate the extra horizontal whitespace that's otherwise inserted by `\left`

and `\right`

; (ii) don't insert a thinspace after `\Biggl[`

; and (iii) insert a negative thinspace (`\!`

) after the undercbrace material.

```
\documentclass[preview,border=12pt,varwidth]{standalone}
\usepackage{amsmath}
\usepackage{mleftright}\mleftright
\usepackage[lite]{mtpro2}
\begin{document}
\[
12\Biggl[ \undercbrace{y^2 +2y\left(-\frac{2}{3}\right)
+\left(-\frac{2}{3}\right)^2}_{
\left[y+\left(-\frac{2}{3}\right)\right]^2} \! {}
-\left(-\frac{2}{3}\right)^2 +\frac{4}{5}\Biggr] = 0
\]
\end{document}
```

How about this?

```
\documentclass{article}
\newcommand\mydots{\hbox to 1em{.\hss.\hss.}}
\begin{document}
Hello\dots
Hello again\mydots
\end{document}
```

Or if you prefer to keep it all "clean" LaTeX commands:

```
\newcommand\mydots{\makebox[1em][c]{.\hfil.\hfil.}}
```

A further consideration would be whether you care about maths mode or not. The standard `\dots`

command carefully checks whether we are in maths or not and does the right thing. If you want to worry about this, then you would need this:

```
\newcommand\mydots{\ifmmode\ldots\else\makebox[1em][c]{.\hfil.\hfil.}\fi}
```

In order to change the spacing of the dots with this solution, you change the overall width of the ellipsis. In the above examples I've made it `1em`

wide, and the the `\hss`

or the `\hfil`

commands expand as needed to make the dots evenly spaced.

If your ellipsis is ever followed by more text, then there is another consideration: whether you want any built-in space after the ellipsis (as pointed out in the comments). The original `\dots`

command has a small amount of space after it, but my suggested replacement above does not. For example

To fix this you can either add a thin space after it by hand or amend the definition to:

```
\newcommand\mydots{\ifmmode\ldots\else\makebox[1em][c]{.\hfil.\hfil.}\thinspace\fi}
```

## Best Answer

You could use the package

`MnSymbol`

, which allows for smaller braces. In addition you could use`\smash`

so that the smaller brace is closer to the eta symbol. Finally, you could use the package`mathtools`

and`\clap`

to avoid too much space after the minus sign.Here you have the code/pictures showing the 3 successive improvements I described:

You can even use a second smash to lift the larger brace:

where you can play with the "6mm" value.