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\begin{frame}{Operations on Words (2)}
  \begin{block}<+->{Power}
    The power \alert{$v^k$} consists of $k$ concatenations of $v$'s:
    \begin{talign}
      v^0 &= \lambda  \\
      v^{k+1} &= v^k v
    \end{talign}
  \end{block}
  \bigskip
  
  \begin{block}<+->{Reverse}
    The reverse of $a_1 \cdots a_n$ is 
    \begin{talign}
      \alert{(a_1 \cdots a_n)^R}=a_n \cdots a_1
    \end{talign}
    The reverse can be inductively defined
    \begin{talign}
      \lambda^R &= \lambda \\
      (va)^R &= a(v^R)
    \end{talign}
  \end{block}
\end{frame}