\begin{frame}{Exercise} \begin{exampleblock}{} Consider the following grammar \begin{talign} S &\to ABaC & A &\to BC & B &\to b \mid \lambda & D &\to d \\ &&&& C &\to D \mid \lambda \end{talign} \pause What variables are erasable? \begin{itemize} \pause \item $A$, $B$ and $C$ \end{itemize} \pause\medskip Construct the resulting grammar after removing all $\lambda$-rules: \pause \begin{talign} S &\to ABaC \mpause[1]{\mid BaC} \mpause{\mid AaC} \mpause{\mid ABa} \mpause{\mid aC} \mpause{\mid Ba} \mpause{\mid Aa} \mpause{\mid a} \\ A &\to BC \mpause{\mid C} \mpause{\mid B} \mpause{\onslide<-15>{\mid \lambda}} \\ B &\to b \onslide<-15>{\mid \lambda} \hspace{2cm} C \to D \onslide<-15>{\mid \lambda} \hspace{2cm} D \to d\mpause{} \end{talign} \end{exampleblock} \end{frame}