code: public void put(String string,Object value)
      {
          if (frozen) throw new IllegalStateException("can't add new values to a frozen dictionary");
          Set valset = (Set)valueMap.get(string);
          if (valset==null) valueMap.put(string, (valset=new HashSet()));
          valset.add( value );
      }
docs: Insert a string into the dictionary, and associate it with the
  given value.