code: final boolean link(Index<K,V> succ, Index<K,V> newSucc) {
              Node<K,V> n = node;
              newSucc.right = succ;
              return n.value != null && casRight(succ, newSucc);
          }
docs: Tries to CAS newSucc as successor.  To minimize races with
  unlink that may lose this index node, if the node being
  indexed is known to be deleted, it doesn't try to link in.
  @param succ the expected current successor
  @param newSucc the new successor
  @return true if successful