Caption with math gives undefined control sequence [closed]

Question

I'm trying to include a caption for a figure with two subfigures with quite some math. However, I get:

Undefined control sequence

I've tried to replace the the $ with \begin{math} and \end{math} but that only gave the error:

Argument of \@caption has an extra }.

\documentclass{report}
\usepackage[english]{babel}
\usepackage[superscript]{cite}
\usepackage{fixltx2e}
\usepackage{mathtools}
\usepackage{graphicx}
\usepackage{wrapfig}
\usepackage{caption}
\usepackage{subcaption}
\usepackage[export]{adjustbox}
\usepackage{gensymb}
\usepackage{tabulary}
\usepackage{hyphenat}
\usepackage{bbm}

\begin{document}

\begin{figure}[!h]
        \centering
        \begin{subfigure}[t]{0.45\textwidth}
                \centering
                \includegraphics[width=\textwidth,valign=t]{ResultsFlapWinglets}
        \end{subfigure}
        \begin{subfigure}[t]{0.45\textwidth}
                \centering
                \includegraphics[width=\textwidth,valign=t]{ResultsFlapFences}
        \end{subfigure}
\caption{The experiments have been carried out with freestream velocity $u = 30 m/s$, 
angle of attack $\alfa = 10\degree$ and flap deflection $\delta_{f} = 32\degree$.}
\label{fig:FenceResults}
\end{figure}

\end{document}

Answer 1

Probably it is just a simple typo:

Try \alpha instead of \alfa in your caption.