# How to make a new tex command in org-mode-latex?

In a general tex-file, one can easily define a new command, for my case, let me take this as an example:

To put this code in header

\newcommand{\dd}{\,\mathrm{d}}

I can use the shorter command to make the longer command work; it's good to do this, I also can compile org-file into tex if this command is added in header. However the preview C-c-x-l fails to recognize \dd even if this new command have been defined in header.

I think we can add some code in org package to make this work, right? how can I do this? I want to make preview C-c-xl recognize \dd as \mathrm{d}.

## Update

Let me expound my question.

I hope we can amend or add some codes in ~/org path/lisp/org-latex.el to make preview recognize \dd as \,\matherm{d} in every org-file.

The way @pmr posed works in each org-file which added that code by hand. I expect we can make this as default and needn't to add such code every time.

$\dd d$