anchor.diff:      (when (zerop (length seq))
           (return-from find-seq trie))
       (let ((symbol (find-key trie (elt seq 0))))
  -        (if (null symbol)
  -            (return-from find-seq nil)
  +        (when symbol
               (find-seq symbol (subseq seq 1)))))
   
   (defun find-key (trie key)
  
positive.code: ;;; Insertion
  
  (defun add-seqs (trie seqs)
      (mapcar #'(lambda (seq) (add-seq trie seq))
          seqs))
  
  (defun add-seq (trie seq &optional (count 1))
      "Add a branch to the trie count times. If branch already exists, increase it’s width.
      A count below one is changed to one. Modifies trie in-place."
      (when (< count 0) (error (format nil "Negative count ~A." count)))
      (incf (trie-width trie) count)
      (when (zerop (length seq))
          (add-key trie t count)
          (return-from add-seq trie))
      (let ((symbol (add-key trie (elt seq 0) 0)))
          ; (add-key trie (elt seq 0) count)
          (add-seq symbol (subseq seq 1) count)))
  
  (defun add-key (trie key &optional (count 1))
      "Add a node to trie. If node exists, increases it’s width."
      (when (< count 0) (error (format nil "Negative count ~A." count)))
      (let ((node (find-key trie key)))
          (if node
              (incf (trie-width node) count)
  
negative.code: ;;;     Peter Hillerström
  ;;; Version:
  ;;;     0.1
  ;;; Initial Common Lisp version:
  ;;;     2010-08-01
  ;;; 
  ;;; Features:
  