# making new symbol from two symbols

I would like to make a new math symbol from overlapping two symbols, such as $\nabla\kern-7.5pt\nabla$. The problem is that the symbol spacing is altered depending on the line, often to the point where the overlap is not recognisable. From looking at other replies I understand that fixing this is likely to do with adding box commands, but there are so many of these that I am not sure where to start! Any help appreciated (I am obviously not an expert ...)

• Are you using the new symbol in math formulas? What should it denote? – egreg Oct 30 '16 at 15:14
• Yes, it is an operator, a variant of nabla for a derivative – Edwin Beggs Oct 30 '16 at 15:16

I would use \mkern instead of \kern, because it uses unit mu, which follows the math style:

\documentclass{article}
\newcommand*{\doublenabla}{%
{\nabla\mkern-12mu\nabla}% subformula acts as \mathord
}
\begin{document}
$\doublenabla_{\doublenabla_{\doublenabla}}$
\end{document}


Another possibility using mathtools to specify the offset from the left rather than from the right produces slightly different spacing:
\documentclass{article}
$\nnabla_{\nnabla_{\nnabla}}$