\begin{frame}{Exercise}
  \begin{exampleblock}{}
    Transform the following context-free grammar
    \begin{talign}
      S &\to aSbX \mid a\\
      X &\to Xa \mid aba
    \end{talign}
    into Chomsky normal form.
    \medskip

    The $\lambda$-rules and unit-rules have already been removed.
    \pause\medskip
    
    We continue the transformation:
    \begin{talign}
      S &\to \alt<-6>{\alt<-3>{aSbX}{C_aSC_bX}}{C_aS_2} \mid a & \mpause[5]{S_2 &\to SS_3 & S_3 &\to C_bX}\\
      X &\to \alt<-4>{Xa}{XC_a} \mid \alt<-7>{\alt<-5>{aba}{C_aC_bC_a}}{C_aX_2} & \mpause[6]{X_2 &\to C_bC_a} \\
      \mpause[1]{C_a &\to a} \\
      \mpause[1]{C_b &\to b} \hspace{2.5cm} 
      \mpause{} \mpause{}\mpause{}\mpause{}\mpause{}
    \end{talign}
  \end{exampleblock}
\end{frame}