static ItIt<Pair<S, Int>> returnCodesOfMultipleServers(S... servers) {
  ret returnCodesOfMultipleServers(asList(servers));
}

static ItIt<Pair<S, Int>> returnCodesOfMultipleServers_iterator(Iterable<S> servers) {
  ret map_iterator_asPair(returnCodeHttpHEAD, servers);
}