@Override
    public Node prepend(Node node) {
      if(node.myAnchor == null) return this;
      if(PsiTreeUtil.isAncestor(myHead.myAnchor, node.myAnchor, false)) {
        Node newHead = myHead.prepend(node);
        return new Cons(newHead, myTail);
      }
      return new Cons(node, this);
    }
@Override
    public Node prepend(Node node)