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\begin{frame}
  \frametitle{Properties of Formulas}

  \begin{block}{Contingency\mpause[1]{ = sometimes true and sometimes false}}
    \mpause{
    \begin{tgather}
      p \wedge q \wedge \neg r
    \end{tgather}}\vspace{-1.5ex}
  \end{block}  

  \begin{block}{Tautology\mpause{ = always true}}
    \mpause{
    \begin{tgather}
      p \vee \neg p\\
      p \to p\\
      ((p \to q) \to p) \to p
    \end{tgather}}\vspace{-1.5ex}
  \end{block}  

  \begin{block}{Contradiction\mpause{ = always false}}
    \mpause{
    \begin{tgather}
      p \wedge \neg p\\
      ((p \to q) \to p) \wedge \neg p
    \end{tgather}}\vspace{-1.5ex}
  \end{block}  
\end{frame}