\begin{frame}{Post Correspondence Problem (1946)}
  \begin{minipage}{.7\textwidth}
    \begin{block}{Post Correspondence Problem (PCP)}
      Given $n$ pairs of words:
      \begin{talign}
        (w_1,v_1),\;\ldots,\;(w_n,v_n)
      \end{talign}
      Are there indices $i_1,i_2\ldots,i_k$ ($k \ge 1$) s.t.
      \begin{talign}
        w_{i_1} w_{i_2} \cdots w_{i_k} ~~ = ~~ v_{i_1} v_{i_2} \cdots v_{i_k} ~~ ?
      \end{talign}
    \end{block}
    \bigskip\bigskip
  \end{minipage}
  \begin{minipage}{.29\textwidth}
    \begin{center}
      \includegraphics[height=30mm]{images/emil-post.jpeg}\\
      \footnotesize{Emil Post\\ (1897-1954)}
    \end{center}
  \end{minipage}
  \pause

  \begin{exampleblock}{Exercise}
    Find a solution for
    \begin{talign}
      (w_1,v_1) &= (01,100) \\
      (w_2,v_2) &= (1,011) \\
      (w_3,v_3) &= (110,1)
    \end{talign}
  \end{exampleblock}  
  %% Oplossing w_3 w_3 w_2 w_2 = v_3 v_3 v_2 v_2
\end{frame}