code: func (list *LinkedList) Sorti() (err error) {
  	list.key.Lock()
  	defer list.key.Unlock()
  
  	list.first, err = mergeSort(list.first, func(a, b interface{}) (int, error) {
  		castA, ok := a.(int)
  		if !ok {
  			return 0, ErrUnexpectedType
  		}
  		castB, ok := b.(int)
  		if !ok {
  			return 0, ErrUnexpectedType
  		}
  
  		return castA - castB, nil
  	})
  	if err != nil {
  		return
  	}
  	list.last = findLast(list.first)
  	return
  }
docs: // Sorti rearranges the position of integer entries in this list so that they
  // are ascending.