Question concerning an error occurring only one time in two similar examples (tables/array and I cannot find the mistake)

Question

I'd like to create a table, but I get the strange error "Missing $ inserted \end{frame}". Here is the code. See below for a similar example, where it worked.

Unfortunately, I cannot find my mistake.

Thank you very much for the help.

The non-working example:

\documentclass{beamer}
\usepackage{graphicx}
\title{MyTitle}
\author{Bibabutzemann}
\date{August 2023}
\begin{document}
\maketitle
\section{Introduction}
\begin{frame}

\begin{definition} 
    The blahblah is given by:
    \begin{center}
        \begin{tabular}{@{}l@{}l@{}l@{}l@{}l@{}l@{}}
            \hline
            (\begin{array}{|c|ccccc|}
            & a & \cdots & m & \cdots & p\ \hline
            [W_{1}] & & & & & \
            \vdots & & & \vdots & & \
            [W_{i}] & \cdots & \cdots & \psi(x,y) & \cdots & \cdots \
            \vdots & & & \vdots & & \
            [W_{k}] & & & \vdots & & \
            \hline
            \end{array})\
        \end{tabular}
    \end{center}
\end{definition}
\end{frame}
\end{document}

The working example:

\documentclass{beamer}
\usepackage{graphicx}
\title{MyTitle}
\author{Bibabutzemann}
\date{August 2023}
\begin{document}
\maketitle
\section{Introduction}
\begin{frame}

        \begin{center}
            \begin{tabular}{@{}l@{}l@{}l@{}}
                \hline
                (\begin{array}{|l|ccc|}
                & u & v & w \ \hline
                X & 1 & 1 & 1\
                Y & 1 & 1 & 1\
                Z & 1 & 1 & 1\
                \hline
                \end{array})\
            \end{tabular}
        \end{center}
\end{frame}
\end{document}