code: public static IntSet or (IntSet... sets)
      {
          checkNotNull(sets);
          IntSet result = create();
          for (IntSet set : sets) {
              result.addAll(set);
          }
          return result;
      }
docs: Create a new IntSet containing the ints that are contained in <b>any</b>
  of the specified sets. The returned set may be further modified per your needs.