code: public Properties getUnusedProperties()
    {
      Properties p = new Properties();
      for(Map.Entry<Object, Object> entry : properties.entrySet()) {
        if(!usedProperties.contains(entry.getKey())) {
          p.put(entry.getKey(), entry.getValue());
        }
      }
      return p;
    }
docs: Get properties not yet used at the moment this method is executed. A method is considered used if is read at least
  once by {@link #getProperty(String)} or related. This method returns a new properties instance. Changes on returned
  instance does not affect configuration object internal properties.
  
  @return yet unused properties.