anchor.diff:  
   (defun trie-prob (root suffix)
     "Returns probability of suffix on given trie."
  -  (let ((node (find-seq root suffix)))
  +  (let ((node (obtain-seq root suffix)))
       (when node
         (/ (trie-width node) (trie-width root)))))
   
  
positive.code: 
  ;;; Retrieval
  
  (defun find-seq (trie seq)
    "Find a sequence from trie"
    (when (zerop (length seq))
      (return-from find-seq trie))
    (let ((symbol (find-key trie (elt seq 0))))
      (when symbol
        (find-seq symbol (subseq seq 1)))))
  
  (defun find-key (trie key)
    "Return a symbol matching key from trie's branches."
    (find key (trie-branches trie) :test #'equal :key #'trie-key))
  
  (defun sym-interval (trie key)
  
negative.code: 
  ; (defun remove-seq (trie seq &optional (count 1))
  ;   "### Remove a sequence from trie"
  ;   (unless (obtain-seq trie seq)
  ;     (return-from remove-seq nil))
  ;   (decf (trie-width trie) (max count 1))
  ;   (when (zerop (length seq))
  