code: func (l *list) MoveToBack(e *element) {
  	if e.list != l || l.root.prev == e {
  		return
  	}
  	// see comment in List.Remove about initialization of l
  	l.insert(l.remove(e), l.root.prev)
  }
docs: // MoveToBack moves element e to the back of list l.
  // If e is not an element of l, the list is not modified.