You can use the `\substack`

command from the `amsmath`

package, like this:

```
\begin{equation}
d(\vec{x},\vec{y}) =
\sum_{\substack{Z_{xy}\in\vec{Z}_{xy}\\
\forall x\in\vec{x}\\
\forall y\in\vec{y}}}
f(Z_{xy})
\end{equation}
```

However, the result still doesn’t look good, because of the extra spacing around the sum symbol:

To fix this, you can use the `\mathclap`

command from the `mathtools`

package, like this:

```
\begin{equation}
d(\vec{x},\vec{y}) =
\sum_{\mathclap{\substack{Z_{xy}\in\vec{Z}_{xy}\\
\forall x\in\vec{x}\\
\forall y\in\vec{y}}}}
f(Z_{xy})
\end{equation}
```

But perhaps you might be happy using **only** `\mathclap`

, and not `\substack`

. The result looks good as long as the subscript is not too wide.

```
\begin{equation}
d(\vec{x},\vec{y}) =
\sum_{\mathclap{{Z_{xy}\in\vec{Z}_{xy},
\forall x\in\vec{x},
\forall y\in\vec{y}}}} f(Z_{xy})
\end{equation}
```

The `mathtools`

package also have several other useful commands for typesetting mathematics, including more commands for improving the display of subscripts and superscripts. I very much recommend taking a look at its documentation.

The typography as displayed by `LaTeX`

is the correct one. A comma needs to be placed at the baseline.

If you need to make any adjustments rather place the fraction within brackets. Agreed that the comma can be mistaken as a prime, but remember that mathematics is read in context, i.e., if no primes are used on the variables it is highly unlikely that a mathematically inclined reader will mix it up.

I have checked the above with a couple of books and always the comma is as shown by LaTeX.

```
\documentclass{article}
\usepackage{amsmath}
\usepackage{mathpazo} % To get Palatino
\linespread{1.05} % See question 31064
\usepackage[small, euler-digits]{eulervm} % and now Euler
\begin{document}
If the number of independent variable is~$n$, we must have
\[
p = - \frac{n-2}{2}, \quad \text{or} \quad -\left(\frac{n-2}{2} + 1\right), \quad -\left(\frac{n-2}{2} + 2\right),\quad \left(\frac{n-2}{2+a}\right), \quad \dots.
\]
\end{document}
```

Your suggestion of raising the comma can lead to other problems such as `$(a,b)\frac{a}{b},`

resulting in the commas not lining up.

## Best Answer

If you're using the comma as decimal separator, then you should consider using the semi-colon for the interval separator, it will be more readable:

(Instead of typing

`1{,}5`

, you can also use the`icomma`

package as suggested by egreg or`\num`

as suggested by Werner.)