code: private static String changeIdForRNA(MonomerNotation monomerNotation) {
  		if (monomerNotation instanceof MonomerNotationUnitRNA) {
  			StringBuilder changeid = new StringBuilder();
  
  			for (MonomerNotation not : ((MonomerNotationUnitRNA) monomerNotation).getContents()) {
  				Monomer monomer = nucleotidesNaturalAnalog.get(not.getUnit().replace("[", "").replace("]", ""));
  				String id = monomer.getNaturalAnalog();
  				if (monomer.getMonomerType().equals(Monomer.BRANCH_MOMONER_TYPE)) {
  					id = "(" + id + ")";
  				}
  				changeid.append(id);
  			}
  			return changeid.toString();
  		} else {
  			Monomer monomer = nucleotidesNaturalAnalog.get(monomerNotation.getUnit().replace("[", "").replace("]", ""));
  			String id = monomer.getNaturalAnalog();
  			if (monomer.getMonomerType().equals(Monomer.BRANCH_MOMONER_TYPE)) {
  				id = "(" + id + ")";
  			}
  			return id;
  		}
  	}
docs: method to get the natural analogue sequence of a MonomerNotation
  
  @param monomerNotation
  MonomerNotation
  @return natural analogue sequence of MonomerNotation