static <A> L<A> filterByType(Collection c, Class<A> type) {
  new L<A> l;
  for (O x : c)
    if (isInstanceX(type, x))
      l.add((A) x);
  ret l;
}

static <A> L<A> filterByType(A[] c, Class<A> type) {
  ret filterByType(asList(c), type);
}