static Lisp simplifySNLTree(Lisp tree) {
  while (tree != null && tree.isA("[]") && tree.size() == 1)
    tree = tree.get(0);
  if (tree == null) ret null;
  Lisp lisp = new Lisp(tree.head);
  for (Lisp child : tree)
    lisp.add(simplifySNLTree(child));
  ret lisp;
}