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\begin{frame}
\frametitle{Modal Logic}
\bigskip

\begin{exampleblock}{}
Which of the following formulas are valid?
\begin{itemize}
\smallskip
\item $\all p \ifo \neg\some\neg p$
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\item $\some p \wedge \some q \to \some (p\wedge q)$
\smallskip
\item $\all p \to \some p$
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\item $\all p \to p$
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\item $\all (p\to q) \to ( \all p \to \all q)$
\smallskip
\item $\some \some p \to \some p$
\smallskip
\item $\all\,\neg \perp$
\smallskip
\end{itemize}
\end{exampleblock}
\pause
\bigskip

That depends on the interpretation of the modal operators!
\end{frame}