\begin{frame}
  \frametitle{Covers}

  \begin{exampleblock}{}
  Consider the following set $\mathcal{F}$ of FDs:
  \begin{enumerate}
    \item $\sql{isbn}           \to \sql{title}, \sql{publisher}$
    \item $\sql{isbn}, \sql{no} \to \sql{author}$
    \item $\sql{publisher}      \to \sql{publisherURL}$ 
  \end{enumerate}
  Compute the cover $\{\sql{isbn}\}_{\mathcal{F}}^+$:
  \begin{itemize}
  \pause
  \item We start with $x = \{\sql{\,isbn\,}\}$.
  \pause
  \item FD $1$ is applicable since $\{\sql{\,isbn\,}\} \subseteq x$.\\[.5ex]
    \pause
    We get $x = \{\, \sql{isbn}, \sql{title}, \sql{publisher} \,\}$.
  \pause
  \item FD $3$ is applicable since $\{\sql{\,publisher\,}\} \subseteq x$.\\[.5ex]
    \pause
    We get $x = \{\, \sql{isbn}, \sql{title}, \sql{publisher}, \sql{publisherURL} \,\}$.
  \pause
  \end{itemize}
  No further way to extend set $x$, thus
    \begin{talign}
      \{\sql{isbn}\}_{\mathcal{F}}^+ \;=\; \{\, \sql{isbn}, \sql{title}, \sql{publisher}, \sql{publisherURL} \,\}
    \end{talign}
  \pause 
  We may now conclude, e.g., $\sql{isbn} \to \sql{publisherURL}$.
  \end{exampleblock}
\end{frame}