anchor.diff:  
   (defun numbered-letter (n)
     (case n
  -    ( 1 "a") ( 2 "b") ( 3 "c") ( 4 "d") ( 5 "e") ( 6 "f") ( 7 "g") ( 8 "h") ( 9 "i") (10 "j")
  -    (11 "k") (12 "l") (13 "m") (14 "n") (15 "o") (16 "p") (17 "q") (18 "r") (19 "s") (20 "t")
  +    ( 1 "a") ( 2 "b") ( 3 "c") ( 4 "d") ( 5 "e")
  +    ( 6 "f") ( 7 "g") ( 8 "h") ( 9 "i") (10 "j")
  +    (11 "k") (12 "l") (13 "m") (14 "n") (15 "o")
  +    (16 "p") (17 "q") (18 "r") (19 "s") (20 "t")
       (21 "u") (22 "v") (23 "w") (24 "x") (25 "y") (26 "z")))
  -+
   
   (defun chang&lee-examples nil
     (print 'chang&lee-examples)
  
positive.code:     (setq value (query/0 0 #'query-success))
      (setq stop-time (get-internal-run-time))
      (when (> *ncalls* 0)
        (setq time (/ (max 1 (- stop-time start-time *trace-search-time* *print-proof-time*))
  		    (float internal-time-units-per-second)))
        (format t "~2&Execution time: ~:D inferences in ~,3F seconds (~,2F K lips)~%" *ncalls* time (/ *ncalls* time 1000)))
      value))
  
  ;; INPUT EXPRESSION CANONICALIZATION
  
  (defun make-functor (name arity)
    (let ((l (get name 'functors)))
      (or (cdr (assoc arity l))
  	(let ((w (intern (concatenate 'string (symbol-name name) "/" (princ-to-string arity)) 'pttpp)))
  	  (setf (get name 'functors) (cons (cons arity w) l))
  	  (setf (get w 'arity) arity)
  	  (setf (get w 'name) name)
  
negative.code:     (setq start-time (get-internal-run-time))
      (setq wffs (canonicalize-functors-in-terms wffs))
      (setq stop-time (get-internal-run-time))
      
      (when print-clauses
        (setq wff-number 0)
        (setq clause-numbers nil)
  