static Set<S> allNonStaticFields(O o) {
  new TreeSet<S> fields;
  Class _c = _getClass(o);
  do {
    for (Field f : _c.getDeclaredFields())
      if ((f.getModifiers() & Modifier.STATIC) == 0)
        fields.add(f.getName());
    _c = _c.getSuperclass();
  } while (_c != null);
  return fields;
}