static <A> Collection<S> subMapWithKeysStartingWithIC(S prefix, Map<S, A> map) {
  if (empty(prefix)) ret keys(map);
  if (map instanceof NavigableMap && isCIMap(map)) {
    ret ((NavigableMap) map).subMap(prefix, true, lexicographicallyNextString(prefix), false);
  }
  ret filterKeys(swic(prefix), map);
}