code: public Collection essentialCycles() {
          Collection result = new HashSet();
          //minimize();
  
          for (Object subgraphBase : subgraphBases) {
              SimpleCycleBasis cycleBasis = (SimpleCycleBasis) subgraphBase;
              result.addAll(cycleBasis.essentialCycles());
          }
  
          return result;
      }
docs: Returns the essential cycles of this cycle basis.
  A essential cycle is contained in every minimum cycle basis of a graph.
  
  @return a <Code>Collection</code> of the essential cycles