static <A> Collection<A> filterByField_smart(Collection<A> l, S field, O value) {
  if (l == null) null;
  for (A n : l)
    if (!eq(getOpt(n, field), value)) {
      Iterator<A> it = iterator(l);
      A node;
      new L<A> x;
      while ((node = it.next()) != n)
        x.add(node);
      while (it.hasNext()) {
        node = it.next();
        if (eq(getOpt(node, field), value))
          x.add(node);
      }
      ret x;
    }
  ret l;
}