code: private int[] getParentIDs(){
  
  		if(parentsVariables == null) {
  			return null;
  		}
  
  		int[] parentIDs = new int[parentsVariables.size()];
  
  		for(int i = 0; i < parentsVariables.size(); i++){
  			parentIDs[i] = parentsVariables.get(i).getVariableID();
  		}
  
  		/*DO NOT sort this array! This deletes the information for divisions (de-/nominator)*/
  
  		return parentIDs;
  	}
docs: /*---------------------------------------------------------------------------------------------------------------------------------