static void printOccTree2(OccTree2 t) {
  printOccTree2_sub(t, "");
}

static void printOccTree2_sub(OccTree2 t, S indent) {
  print(indent + "[" + t.count + "]" + (t.e == null ? "" : " " + t.e));
  for (OccTree2 t2 : t.next)
    printOccTree2_sub(t2, indent + "  ");
}