LaTeX.org

I would like to some straight text inside a theorem environment (which is slanted)
Example:

\begin{theorem} (straight text)
It holds that $a^2+b^2 = c^2$.
\end{theorem}


I've tried \text \mbox \textrm,... nothing seems to work.

Also, I do not want the result as

\begin{theorem}[straight text ...