\begin{frame} \frametitle{Modal Logic} \bigskip \begin{exampleblock}{} Which of the following formulas are valid? \begin{itemize} \smallskip \item $\all p \ifo \neg\some\neg p$ \smallskip \item $\some p \wedge \some q \to \some (p\wedge q)$ \smallskip \item $\all p \to \some p$ \smallskip \item $\all p \to p$ \smallskip \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}