anchor.diff:  
   (retrieve-by-route '(a b (x (s t u) y z) c) '(2 1 2 1))
   
  -(let ((route (car (find-route '(PUSH I LST) *first-impl*))))
  -  (rdiff *first-impl* (retrieve-by-route *first-impl* (drop (reverse route))) 'ref))
  -
  -(car (find-route '(ref . 11) (rdiff *first-impl* *second-impl* 'ref)))
  -
  -(levenshtein-distance
  -  (mapcar (papply (rdiff *first-impl* _ 'ref))
  -          (retrieve-by-route *first-impl* (drop (nreverse '(2 2 3 0)))))
  -  (retrieve-by-route (rdiff *first-impl* *second-impl* 'ref) (drop (nreverse '(2 2 3 0))))
  -  :test #'equal)
  -
  -(defun longer-length (sec0 sec1)
  -  (length (if (shorter sec0 sec1) sec1 sec0)))
  -
  -(defun similar? (code0 code1)
  -  (< (/ (levenshtein-distance code0 code1 :test #'equal)
  -        (longer-length code0 code1))
  -     0.5))
  -
  -(similar?
  -  (mapcar (papply (rdiff *first-impl* _ 'ref))
  -          (retrieve-by-route *first-impl* (drop (nreverse '(2 2 3 0)))))
  -  (retrieve-by-route (rdiff *first-impl* *second-impl* 'ref) (drop (nreverse '(2 2 3 0)))))
  -
   (defun white (x)
     (format t "<font color=\"#ffffff\">~%<pre> ~a</pre>~%</font>" x))
   
  
positive.code: 
  (find-route '(nreverse lst) *first-impl*)
  (find-route 'lst *first-impl*)
  
  (defun rdiff (base modified refmark)
    (let ((subtrees (collect-effective-refs base)))
      (labels ((rec (code)
                 (aif (find code subtrees :key #'last1 :test #'equal)
                   (cons refmark (car it))
                   (if (atom code) code
                     (mapcar #'rec code)))))
        (rec modified))))
  
  (rdiff *first-impl* *second-impl* 'ref)
  (rdiff *first-impl* *first-impl* 'ref)
  (rdiff '(a (x y z) b c) '(print (a (x y z) b c)) 'ref)
  (rdiff '(a (x y z) b c) '(a (x s z) b c) 'ref)
  
  (defun levenshtein-distance (str0 str1 &key (test #'eql))
    (if (not (shorter-or-equal str0 str1))
  
negative.code:           (if (consp sub)
              (green (third (find (cdr sub) (collect-effective-refs base) :key #'car)))
              (green sub))))))
  
  (defun route-normalize (raw-route)
    (drop (reverse raw-route)))
  