static class Synonyms {
  Map<S, L<S>> synMap = new TreeMap<S, L<S>>();
  
  void addSynonym(S a, S b) {
    L<S> la = synMap.get(a), lb = synMap.get(b);
    if (la == null && lb == null) {
      L<S> l = litlist(a, b);
      synMap.put(a, l);
      synMap.put(b, l);
    } else if (la == lb) {
      // nothing to do, they're already synonyms
    } else if (lb == null) {
      la.add(b);
      synMap.put(b, la);
    } else if (la == null) {
      lb.add(a);
      synMap.put(a, lb);
    } else
      mergeLists(la, lb);
  }
  
  void mergeLists(L<S> la, L<S> lb) {
    for (S b : lb) {
      la.add(b);
      synMap.put(b, la);
    }
  }
  
  // returns null or a list
  L<S> getSynonyms(S x) {
    ret synMap.get(x);
  }
}

Began life as a copy of #1001511