static <A> Set<A> putSetElementsFirst(Cl<A> cl, Cl<A> elements) {
  Set<A> inputSet = asSet(cl);
  new LinkedHashSet<A> set;
  fOr (A a : elements)
    if (contains(inputSet, a))
      set.add(a);
  addAll(set, cl); // keep order
  ret set;
}

static <A> Set<A> putSetElementsFirst(Cl<A> cl, A... elements) {
  ret putSetElementsFirst(cl, asList(elements));
}