i> by element <tt>x</tt> and
      <tt>y</tt>.</td>
    </tr>

    <tr>
      <td><tt>template &lt;class Element&gt;<br>
      void union_set(Element x, Element y)</tt></td>

      <td>Union the two sets that <i>contain</i> elements <tt>x</tt> and
      <tt>y</tt>. This is equivalent to
      <tt>link(find_set(x),find_set(y))</tt>.</td>
    </tr>

    <tr>
      <td><tt>template &lt;class Element&gt;<br>
      Element find_set(Element x)</tt></td>

      <td>Return the representative for the set containing 