static O[] flattenArray_recursive(O... a) {
  new L l;
  if (a != null) for (O x : a)
    if (x cast O[])
      l.addAll(flattenList2(asList(x)));
    else if (x cast Collection)
      l.addAll(flattenList2(x));
    else
      l.add(x);
  ret asObjectArray(l);
}