static Set asSet(O[] array) {
  new HashSet set;
  for (O o : array)
    if (o != null)
      set.add(o);
  ret set;
}

static Set<S> asSet(S[] array) {
  new TreeSet<S> set;
  for (S o : array)
    if (o != null)
      set.add(o);
  ret set;
}

static <A> Set<A> asSet(Iterable<A> l) {
  if (l instanceof Set) ret (Set) l;
  new HashSet<A> set;
  for (A o : unnull(l))
    if (o != null)
      set.add(o);
  ret set;
}

ifclass MultiSet
// Note: does not clone the set (keeps multiset alive)
static <A> Set<A> asSet(MultiSet<A> ms) {
  ret ms == null ? null : ms.asSet();
}
endif