\begin{frame}
  \frametitle{Finding a Minimal Key}
  
  \begin{exampleblock}{}
    \begin{center}
    {\ttfamily\footnotesize
      \colorbox{rellight}{%
        \begin{tabular}{|r|r|r|r|}
          \multicolumn{4}{c}{Results}
          \\
          \hline
          \hd{sid} & \hd{exercise} & \hd{points} & \hd{maxPoints}
          \\
          \hline
          100 & 1 & 9  & 10 \\
          101 & 1 & 8  & 10 \\
          101 & 2 & 11 & 12 \\
          \hline
        \end{tabular}%
      }}\\[1ex]
      $
      \mathcal{F} = \left\{
      \begin{array}{rcl}
        \sql{sid}, \sql{exercise} & \to & \sql{points} \\
        \sql{exercise} & \to & \sql{maxPoints}
      \end{array} \right\}
      $
    \end{center}
    \pause
    
    We determine a minimal key for the relation $\sql{Results}$:
    \begin{enumerate}
    \pause
      \item $x = \{\;\sql{sid},\; \sql{exercise},\; \sql{points},\; \sql{maxPoints}\;\}$
    \pause
      \item We remove \sql{points} since $\{\;\sql{sid},\; \sql{exercise}\;\} \subseteq x$: \\
            $x = \{\;\sql{sid},\; \sql{exercise},\; \sql{maxPoints}\;\}$
    \pause
      \item We remove \sql{maxPoints} since $\{\;\sql{exercise}\;\} \subseteq x$: \\
            $x = \{\;\sql{sid},\; \sql{exercise} \;\}$
    \pause
    \end{enumerate}
    Nothing else can be removed. We have a minimal key:
    \begin{malign}
      \{\;\sql{sid},\; \sql{exercise}\;\}
    \end{malign}
  \end{exampleblock}
\end{frame}