Problem in writing overline

Question

I am trying to write this:

This is what I wrote:

$\pi$'$\cdot$role = $\overline{$\pi$$\cdot$role}$

But I am getting errors:

paper.tex(37): Error: Missing } inserted. paper.tex(37): Error: Missing $ inserted. paper.tex(37): Error: Extra }, or forgotten \endgroup. paper.tex(37): Error: LaTeX Error: Command \end{definition} invalid in math mode. paper.tex(37): Error: LaTeX Error: Something's wrong--perhaps a missing \item. paper.tex(37): Error: LaTeX Error: Something's wrong--perhaps a missing \item. paper.tex(37): Error: Missing $ inserted. paper.tex(50): Overfull \hbox (10.83658pt too

wide) in paragraph at lines 50--51

How can I fix this please?

Answer 1

Try:

    \begin{document}
\begin{preview}
In case of in-line equation you should write $\pi'\cdot\mathit{role} = \overline{\pi\cdot\mathit{role}}$, however in case in displaymath equation as
\[
\pi'\cdot\mathit{role} = \overline{\pi\cdot\mathit{role}}
\]
\end{preview}
    \end{document}

Note: The ...{preview} is used for showing only desired fragment of page:

In document production all had to be removed.

Edit: It is not clear what is "role". Probably it would be better that it will be written as:

$\pi'\cdot\mathrm{role} = \overline{\pi\cdot\mathrm{role}}$

(as indicate David Carlisle in his erased answer)