anchor.diff:    "Trie data structure, see package documentation for more info."
     (key "" :read-only t)       ; Generic type -- could be :type char
     (width 0 :type integer)
  -  (branches nil :type list))  ; Could a vector for optimization, but complicates things!
  +  (branches nil :type list))  ; Could a vector, but it complicates things!
   
   (defun test-trie (&optional (lst *banana*))
     "Simple utility function to build a test trie."
  
positive.code:   (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)
  
negative.code:   (find key (trie-branches trie) :test #'equal :key #'trie-key))
  
  (defun sym-interval (trie key)
    "Return interval limits for a symbol matching key.
    Nil if key not found."
    (when (find-key trie key)
      (let* ((node (find-key trie key))
             (low (sym-low trie key))
  