\begin{frame}{Decidability of Equivalence}
  \begin{goal}{Theorem}
    It is decidable if two regular languages $L_1$ and $L_2$ are equal.
  \end{goal}
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  \begin{proof}
    We have 
    \begin{talign}
      L_1 = L_2 \quad\iff\quad \mpause[1]{ (L_1 \subseteq L_2) \wedge (L_2 \subseteq L_1) }
    \end{talign}
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    Both problems on the right are decidable. 
  \end{proof}
\end{frame}