Here is an alternative to your current situation - using an optional argument to specify the derivative order. This way you don't have to define a macro for "each" derivative:

```
\deriv[<order>]{<func>}{<var>}
```

Here's a minimal example:

```
\documentclass{article}
\newcommand{\deriv}[3][]{% \deriv[<order>]{<func>}{<var>}
\ensuremath{\frac{\partial^{#1} {#2}}{\partial {#3}^{#1}}}}
\begin{document}
In text mode there is~\deriv{y}{x} and~\deriv[2]{y}{x}. In display mode there is
\[
\deriv{y}{x}\ \textrm{and}\ \deriv[2]{y}{x}\rlap{.}
\]
\end{document}
```

The default `<order>`

is empty, implying the first order partial derivative. If you want the default to be `2`

, modify the definition to read

```
\newcommand{\deriv}[3][2]{...}
```

Technically it is possible to use a macro with numbers in them, but the usage is much less intuitive than adding something like an optional argument (as given above). Here's an implementation that now allows you to use `\nameuse{deriv2}{y}{x}`

:

```
\expandafter\def\csname deriv2\endcsname#1#2{%
\ensuremath{\frac{\partial^2 {#1}}{\partial {#2}^2}}}
\makeatletter
\newcommand{\nameuse}[1]{\@nameuse{#1}}%
\makeatother
```

The optional argument beats this hands down.

Perhaps you meant something like the following, note that `dcases`

*must* be in `mathmode`

, and ideally in `displayed mathmode`

such as

`\[...\]`

`\begin{equation}...\end{equation}`

`\begin{equation*}...\end{equation*}`

Here's a complete MWE:

```
% arara: pdflatex
\documentclass{article}
\usepackage{mathtools}
\begin{document}
Let $g: N \rightarrow N$ be given by
\[
n=
\begin{dcases*}
1 & if $n=1$ \\
n-1 & if $n \ne 1$
\end{dcases*}
\]
\end{document}
```

For future reference, you can view pages 17 and 18 of `the documentation`

which describe that

`dcases`

puts every column in `mathmode`

`dcases*`

puts only the *first* column in `mathmode`

, and the second column in the normal roman font of the document (hence the need to step back into `mathmode`

in the second column)

## Best Answer

Before you load the offending package, put

and then you can say

`Erd\Horig{o}s`