 involving perceived distances between 
      pairs of 11 chain letters.
      <ul>
        <li>
          <a href = "chain_letter_distance.txt">chain_letter_distance.txt</a>,
          the distance table for the chain letters.
        </li>
        <li>
          <a href = "chain_letter_distance.png">chain_letter_distance.png</a>,
          a plot of the estimated positions of the chain letters.
        </li>
        <li>
          <a href = "chain_letter_distance.coord.txt">chain_letter_distance.coord.txt