h1>
  <pre>
disjoint_sets&lt;Rank, Parent, FindCompress&gt;
</pre>

  <p>This is class that provides disjoint sets operations with <i>union by
  rank</i> and <i>path compression</i>. A disjoint-sets data structure
  maintains a collection <i>S = {S<sub>1</sub>, S<sub>2</sub>, ...,
  S<sub>k</sub>}</i> of disjoint sets. Each set is identified by a
  <i>representative</i> which is some member of of the set. Sets are
  represented by rooted trees which are encoded in the <tt>Parent</tt>
  property map. Two heu