static Lisp snlRemoveReferences(Lisp tree) {
  if (tree == null || tree.size() == 0) ret tree;

  Lisp sub = tree.get(tree.size()-1);
  if (snlIsRef(sub))
    if (tree.size() == 1) // it [= x]
      ret lisp(dropSuffix(" *", tree.head));
    else if (tree.size() == 2) // [bla] [= x]
      ret tree.get(0);
    else
      ret tree; // not handled

  // recurse
  Lisp lisp = new Lisp(tree.head);
  for (Lisp child : tree)
    lisp.add(snlRemoveReferences(child));
  ret lisp;
}