anchor.diff:  
   (defun remove-mtoken (sentence start end)
     ;; Removes mtoken with start value equal to `start` and end value equal to `end`
  -  (setf (sentence-mtokens sentence)
  -	(remove-if (lambda (mtk)
  -		     (and
  -		      (equal (mtoken-start mtk) start)
  -		      (equal (mtoken-end mtk) end)))
  -		   sentence-mtokens)))
  +  (let ((mtoken-to-remove
  +	 (find-if (lambda (mtk)
  +		    (and
  +		     (equal (mtoken-start mtk) start)
  +		     (equal (mtoken-end mtk) end)))
  +		  (sentence-mtokens sentence))))
  +    (cond (mtoken-to-remove
  +	   (setf (sentence-mtokens sentence)
  +		 (remove mtoken-to-remove
  +			 (sentence-mtokens sentence)))
  +	   sentence)
  +	  (t
  +	   (format t "There's no ~a-~a mtoken to remove.~%~%" start end)
  +	   sentence))))
     
   (defun mtoken->tokens (sentence mtoken)
     (remove-if-not (lambda (x) (and (>= x (mtoken-start mtoken))
  
positive.code:   ;; Output: removed token with id equal to `id`
    ;; Side-effects: token with id `id` is removed from sentence's token list
    (let ((removed-token (find id (sentence-tokens sentence) :key #'token-id))
  	(in-mtoken
  	 (dolist (interval
  		   (mapcar
  
negative.code: 	      (return nil))
  	     ((>= (cadr interval) id)
  	      (return interval))))))
      (cond ((null removed-token)
  	   (format t "WARNING: There's no token ~a.~%~%" id)
  	   sentence)
  	  (in-mtoken
  	   (format t "WARNING: This token is contained in the multiword token ~{~a-~a~}.~%Not removing.~%Remove the multiword token before removing this token.~%~%" in-mtoken)
  	   sentence)
  	  (is-head
  	   (format t "WARNING: This token is the head of token ~a.~%Not removing.~%Please change its head before removing this token.~%~%" (token-id is-head))
  	   sentence)
  	  (t
  	   (setf (slot-value sentence 'tokens)
  		 (remove removed-token (sentence-tokens sentence)))
  	   (dolist (token (sentence-tokens sentence))
  	     (when (> (token-id token) id)
  	       (setf (slot-value token 'id)
  		     (1- (slot-value token 'id))))
  	     (cond 
  	       ((> (token-head token) id)
  		(setf (slot-value token 'head)
  		      (1- (slot-value token 'head))))
  	       ((= (token-head token) id)
  		;; If a token's head was the removed token, it's new HEAD value is now "_"
  		(setf (slot-value token 'head)
  		      "_"))))
  	   removed-token))))
  