code: public void updateSequenceElement(int[] sequence, int pos, int oldVal) {
      if(models != null){
        for(int i = 0; i < models.length; i++)
          models[i].updateSequenceElement(sequence, pos, oldVal);
        return; 
      }
      model1.updateSequenceElement(sequence, pos, 0);
      model2.updateSequenceElement(sequence, pos, 0);
    }
docs: Informs this sequence model that the value of the element at position pos has changed.
  This allows this sequence model to update its internal model if desired.