Having problems with iguanatex

Question

I'm trying to type an equation and this is what I have input,

\documentclass{article}
\usepackage{amsmath}
\pagestyle{empty}
\begin{document}

$\frac{\partial f}{\partial t} + \dot \textbf{w}. \nabla_6 f = 0$

\end{document}

However it is not working and I am unsure on the causes.

Answer 1

Like this?

Observe that I wrote \nabla_{\!6} -- this "snugs up" the digit 6 to the \nabla symbol.

\documentclass{article}
\pagestyle{empty}
\begin{document}
$\frac{\partial f}{\partial t} + \dot{\mathbf{w}}\cdot \nabla_{\!6} f = 0$
\end{document}