Problem with math text and decorations [tikz]

Question

I want to write some math text arround a circle, it works fine for math formulas but when I tried to write \varSigma and \varPi from amsmath package, it doesn't work. How can I fix this?

code

\documentclass{article}
\usepackage{tikz,amsmath}
\usetikzlibrary{decorations.text} 
\begin{document}
\begin{tikzpicture}[decoration={text along path, text={$\varSigma \varPi MAX$}}]
\path [decorate]
(0,0) .. controls (0,6) and (9,6) .. (9,0);
\end{tikzpicture}
\end{document}

Answer 1

Each math symbol needs to be a in a separated couple of brackets:

\documentclass{article}
\usepackage{tikz,amsmath}
\usetikzlibrary{decorations.text} 
\begin{document}
\begin{tikzpicture}[decoration={text along path, text={{$\varSigma$} {$\varPi$} {$MAX$}}}]
\path [decorate]
(0,0) .. controls (0,6) and (9,6) .. (9,0);
\end{tikzpicture}
\end{document}

Alternatively, you need to put something (like a {})after the couple of brackets where the math env is: {$\varSigma \varPi MAX$}{}