# How to define a fixed spacing between characters independent of font-size?

As it can be seen in the following two equations, the spacing between the first two A's depends on the font size and changes if the new AA symbol is used in a fraction.

- ${A\hspace{-.7ex}A}{AA}$
- $\frac{A\hspace{-.7ex}A}{AA}$


I have tried em, mm, and pt with no success. How can one define a negative spacing that functions the same way everywhere, independent of the font size?

Or similarly, how can I define a new composit symbol (e.g. AA) that looks the same everywhere?

Set it up to account for the math style.

\documentclass{article}
\newcommand\dblA{\mathchoice
{A\hspace{-.7ex}A}
{A\hspace{-.7ex}A}
{A\hspace{-.58ex}A}
{A\hspace{-.55ex}A}%
}
\begin{document}
$\dblA AA$

$\scriptstyle\dblA AA$

$\scriptscriptstyle\dblA AA$
\end{document}


Use mathematical kerns, that automatically adapt to the style.

\documentclass{article}

\DeclareRobustCommand{\AAA}{A\mkern-5mu A}

\begin{document}

$\AAA\frac{\AAA}{AA}\textstyle\frac{\AAA}{AA}\scriptstyle\frac{\AAA}{AA}$

\end{document}