\begin{frame}
  \frametitle{Precise Definition of Limits - Example}
  
  \begin{alertblock}{}
    \mpause[1]{If}\hphantom{then}the next exam will be insanely hard,\\
    \mpause[1]{then}\hphantom{if}many students will fail.
  \end{alertblock}
  \pause\pause\bigskip
  
  The words \alert{if} and \alert{then} are hugely important!
  \pause\bigskip
  
  \begin{exampleblock}{}
    In exams many students write:
    \begin{itemize}
      \item[] $0<|x-3| <\frac{\epsilon}{4}$
      \item[] $|(4x-5) - 7|  < \epsilon$
    \end{itemize}
    which is wrong.
    \pause\bigskip
    
    Correct is:
    \begin{itemize}
      \item[] \alert{If }$0<|x-3| <\frac{\epsilon}{4}$
      \item[] \alert{then }$|(4x-5) - 7|  < \epsilon$
    \end{itemize}
  \end{exampleblock}
\end{frame}