\begin{frame}
  \frametitle{Example: ATM Transaction}

  \begin{exampleblock}{Concurrent ATM Transaction}
    \begin{tcenter}
    \begin{tabular}{|l|l|c|}
    \hline
    \emph{Transaction 1} & \emph{Transaction 2} & \emph{DB state} \\
    \hline
    & & \\[-1ex]
    \textcolor{dgreen}{$\fun{slock}(\var{account})$} &  & 1200 \\
    $\fun{read}(\var{account})$ &  & \\
    \textcolor{dgreen}{$\fun{unlock}(\var{account})$} &  & \\
    & \textcolor{dgreen}{$\fun{slock}(\var{account})$} & \\
    & $\fun{read}(\var{account})$ & \\
    & \textcolor{dgreen}{$\fun{unlock}(\var{account})$} &  \\
    \textcolor{dgreen}{$\fun{xlock}(\var{account})$} \error &  &\\
    $\fun{write}(\var{account})$ &  & 1100 \\
    \textcolor{dgreen}{$\fun{unlock}(\var{account})$} &  & \\
    & \textcolor{dgreen}{$\fun{xlock}(\var{account})$} \error & \\
    & $\fun{write}(\var{account})$ & 1000 \\
    & \textcolor{dgreen}{$\fun{unlock}(\var{account})$} &  \\
    \hline
    \end{tabular}
    \end{tcenter}
    \error Once a lock has been released, no new lock can be acquired.
  \end{exampleblock}
\end{frame}