code: public Iterator<Tuple> getUsed()
      {
      if( usedChanged_)
        {
        // Order to prefer reuse of larger tuples first. By preferring "intact" tuples over post-reduction singletons,
        // we hope to minimize reoccurrence of once-only tuples.
        Collections.sort( used_, tupleSizeDescending_);
        usedChanged_ = false;
        }
      
      return used_.iterator();
      }
docs: Returns input tuples already used in a test case.