static HashSet mapToHashSet(O f, Iterable l) {
  HashSet x = l cast Cl ? : new(l.size()) : new HashSet;
  if (l != null) for (O o : l)
    x.add(callF(f, o));
  ret x;
}

static <A, B> HashSet<B> lambdaMapLike mapToHashSet(IF1<A, B> f, Iterable<A> l) {
  HashSet<A> x = l cast Cl ? : new(l.size()) : new HashSet;
  if (l != null) for (O o : l)
    x.add(f.get(o));
  ret x;
}