anchor.diff:  		  (unless (equalp (third res-fact) res)
   		    (when res-fact (delete! book res-fact))
   		    (insert! book (list cell-id :result res)))))))
  -      (write-delta! book))))
  +      (write! book))))
   
   (defmethod empty-expression? ((contents string))
     (when (cl-ppcre:scan "^[ \n\t\r]*$" contents) t))
  
positive.code:   (awhen (lookup book :b :cell-order)
      (delete! book (car it)))
    (insert-new! book :cell-order cell-order)
    (write-delta! book)
    (publish! :cl-notebook-updates (update :book (notebook-name book) :action 'reorder-cells :new-order cell-order))
    :ok)
  
  (define-json-handler (cl-notebook/notebook/kill-cell) ((book :notebook) (cell-id :integer))
    (loop for f in (lookup book :a cell-id) do (delete! book f))
    (write-delta! book)
    (publish! :cl-notebook-updates (update :book (notebook-name book) :cell cell-id :action 'kill-cell))
    :ok)
  
  
negative.code: (define-json-handler (cl-notebook/notebook/rename) ((book :notebook) (new-name :string))
    (let* ((old-name (notebook-name book))
  	 (book (rename-notebook! book new-name)))
      (write! book)
      (publish! :cl-notebook-updates (update :book old-name :action 'rename-book :new-name new-name)))
    :ok)
  
  