public Object clone( )
   {  // Clone a Graph object.
      Graph answer;
      
      try
      {
         answer = (Graph) super.clone( );
      }
      catch (CloneNotSupportedException e)
      {  // This would indicate an internal error in the Java runtime system
         // because super.clone always works for an Object.
         throw new InternalError(e.toString( ));
      }
      
      answer.edges = (boolean [ ][ ]) edges.clone( );
      answer.labels = (Object [ ]) labels.clone( );
      
      return answer;
   }