code: public void expand(Configuration configuration) {
          OperationIterator it = this.problem.getOperationIterator(configuration);
          while (it.hasNext()) {
              Configuration c = it.next().execute(configuration);
              if (!this.queue.testPresence(c)) this.queue.add(c);
          }
      }
docs: Expands one element.
  <p/>
  Adds new elements to queue (if they fail testPresence, eg. was not yet parsed).
  
  @param configuration attributes to expand