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\begin{frame}
  \frametitle{Propositional Logic: Syntax}

  \begin{block}{Syntax of Propositional Logic}
    \begin{itemize}
    \pause
      \item propositional variables
        \begin{talign}
          p,\; q,\; r,\;\ldots \quad p_0,\;p_1,\;\ldots
        \end{talign}%
      \item \pause propositional connectives
        \begin{talign}
          \neg,\; \wedge,\; \vee,\; \to
        \end{talign}%
      \item \pause propositional formulas
        \begin{talign}
          \begin{gathered}
          p \\
          \neg p \\
          (\neg p \wedge q) \to r 
          \end{gathered}
          && 
          \begin{gathered}
          p \wedge q\\
          p \vee \neg q
          \end{gathered}
        \end{talign}
    \end{itemize}
  \end{block}
  \pause
  
  We use Greek letters for formulas: 
  \begin{align*}
    \phi &\quad \text{phi} &
    \psi &\quad \text{psi} &
    \xi &\quad \text{xi} \\
    \alpha &\quad \text{alpha} &
    \beta &\quad \text{beta} &
    &\ldots
  \end{align*}
\end{frame}