code: func (list *LinkedList) Sort(comparator Comparator) error {
  	list.key.Lock()
  	defer list.key.Unlock()
  	var err error
  	list.first, err = mergeSort(list.first, comparator)
  	if err != nil {
  		return err
  	}
  	list.last = findLast(list.first)
  	return err
  }
docs: // Sort rearranges the positions of the entries in this list so that they are
  // ascending.