static Lisp nlToCons(Lisp term) {
  if (term.isLeaf() /*|| !term.is("[]")*/)
    ret lisp("[]", "cons", term, "end");
  int n = term.size();
  Lisp x = lisp("end");
  for (int i = n-1; i >= 0; i--)
    x = lisp("[]", "cons", term.get(i), x);
  ret x;
}