# LyX - undefined control sequence but package seems to be added

I am using LyX with MikTeX and I am trying to use the following command \oiiint but I am getting the following error:

 \oiiint

The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., \hobx'), type I' and the correct
spelling (e.g., I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.


I have added \usepackage{mathdesign} to the preamble in:

Document -> Settings -> LaTeX Preamble

Why is this not working?

-
You must add an option to mathdesign for choosing what font family to use; for instance \usepackage[charter]{mathdesign}. Called by itself the package does nothing. –  egreg Oct 10 '13 at 12:50
I tried it using Sublime and it sort of worked, as in it outputted the symbol correctly but I got the following message: C:/Users/Colin/Desktop/first.tex:13: Missing $inserted. [\oiiint] C:/Users/Colin/Desktop/first.tex:14: Missing$ inserted. [] –  Colin747 Oct 10 '13 at 13:44
Do you have a minimal example you can post? –  scottkosty Oct 10 '13 at 16:17
\oiiint has to be placed in math mode, try $\oiiint$. –  Torbjørn T. Oct 10 '13 at 21:29
@TorbjørnT. that worked great, thanks. If you want to put it up as an answer I'll accept. –  Colin747 Oct 11 '13 at 10:14

I know nothing about LyX and how you can eventually accomplish the task with it, but mathdesign needs an option for specifying the main typeface to use, for instance
\usepackage[charter]{mathdesign}

Check in the documentation: texdoc mathdesign on a Unix system or this WEB site.
Note that \oiiint is a math symbol, so you have to input it in math mode (inside $...$ or $$...$$ if inline, inside $...$, equation or one of the amsmath` environments if displayed).