static L flattenIterablesAndArrays(Iterable a) {
  new L l;
  for (O x : a)
    if (x cast Iterable)
      l.addAll(flattenIterablesAndArrays(x));
    else if (x cast Iterator)
      l.addAll(flattenIterablesAndArrays(asList(x));
    else if (x cast O[])
      l.addAll(flattenIterablesAndArrays(asList(x)));
    else
      l.add(x);
  ret l;
}