\begin{frame}
  \frametitle{Truth Values}
  
  \begin{goal}{}
    In propositional logic,
    the \emph{truth value} of a formula  is
    determined by a \emph{truth assignment} of the variables in the formula.
  \end{goal}
  \pause\smallskip
  
  \begin{exampleblock}{}
    For example, assigning  
    \begin{itemize}
      \item to $p$ and $q$ the truth value $\T$, and
      \item to $r$ the truth value $\F$,
    \end{itemize}
    determines the truth value of the formula $p \vee \neg q \to r$.
  \end{exampleblock}  
  \pause\bigskip
  
  The truth value of a formula can, for example, 
  be computed via:
  \begin{itemize}
    \item the \emph{parse tree}, or
    \item by making a \emph{truth table}.
  \end{itemize} 
\end{frame}