static L<OccTree2> findNodes(OccTree2 tree, E e) {
  new L<OccTree2> l;
  findNodes_impl(tree, e, l);
  ret l;
}

static void findNodes_impl(OccTree2 tree, E e, L<OccTree2> l) {
  if (eq(tree.e, e)) l.add(tree);
  for (OccTree2 n : tree.next)
    findNodes_impl(n, e, l);
}