anchor.diff:        (defun rewind-book (index)
   	(post/json "/cl-notebook/notebook/rewind" (create :book (notebook-id *notebook*) :index index)
   		   #'notebook!))
  +
  +      (defvar debounced-rewind (debounce #'rewind-book 50))
   
         (defun fork-book (callback)
   	(post/json "/cl-notebook/notebook/fork-at" (create :book (notebook-id *notebook*) :index (@ (by-selector "#book-history-slider") value))
  
positive.code: 	clone))
  
      (defun prevent (ev) (chain ev (prevent-default)))
  
      (defun scroll-to-elem (elem)
        (let ((x (@ elem offset-left))
  
negative.code: 
       (:body
        (:div :class "main-controls"
  	    (:input :id "book-history-slider" :onchange "rewindBook(this.value)" :oninput "debouncedRewind(this.value)" :type "range" :min 0 :max 500 :value 500)
  	    (:input :id "book-history-text" :onchange "rewindBook(this.value)")
  	    (:button :onclick "newCell()" "+ New Cell")
  	    (:button :onclick "newBook()" "+ New Book")
  