// f must return a collection of strings
static Set<S> mapLike concatMapToCISet(O f, Iterable l) {
  Set<S> set = ciSet();
  if (l != null) for (O o : l)
    addAll(set, (Collection<S>) callF(f, o));
  ret set;
}

static <A> Set<S> mapLike concatMapToCISet(Iterable<A> l, IF1<A, Cl<S>> f) {
  ret concatMapToCISet(f, l);
}