static TreeSet<S> toCaseInsensitiveSet(Collection<S> c) {
  // TODO: check if it already is a CI set
  TreeSet<S> set = caseInsensitiveSet();
  if (c != null) set.addAll(c);
  ret set;
}

static TreeSet<S> toCaseInsensitiveSet(S... x) {
  TreeSet<S> set = caseInsensitiveSet();
  addAll(set, x);
  ret set;
}