code: public void addKeywords(String[] keywords) {
          for (String keyword : keywords) {
              if (taxonomy.concepts.containsKey(keyword)) {
                  throw new IllegalArgumentException(String.format("Concept %s already exists.", keyword));
              }
          }
  
          for (String keyword : keywords) {
              taxonomy.concepts.put(keyword, this);
          }
  
          if (synset == null) {
              synset = new TreeSet<>();
          }
  
          for (String keyword : keywords) {
              synset.add(keyword);
          }
      }
docs: Add a list of synomym to the concept synset.