static Lisp listToSNLTree(L<S> list) {
  if (empty(list)) ret lisp("emptylist");
  Lisp tree = lisp(quote(last(list)));
  for (int i = l(list)-2; i >= 0; i--)
    tree = lisp("<", lisp(quote(list.get(i))), tree);
  ret tree;
}