code: @Beta
    public static ContiguousSet<Long> closed(long lower, long upper) {
      return create(Range.closed(lower, upper), DiscreteDomain.longs());
    }
docs: Returns a nonempty contiguous set containing all {@code long} values from {@code lower}
  (inclusive) to {@code upper} (inclusive). (These are the same values contained in {@code
  Range.closed(lower, upper)}.)
  
  @throws IllegalArgumentException if {@code lower} is greater than {@code upper}
  @since 23.0