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: 	      (return nil))
  	     ((>= (cadr interval) id)
  	      (return interval))))))
      (if in-mtoken
  	(progn (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)
  	(progn (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))))
  
negative.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))
  	(is-head (find-if
  		  (lambda (x) (equal id (token-head x)))
  		  (sentence-tokens sentence)))
  	(in-mtoken
  	 (dolist (interval
  		   (mapcar
  