anchor.diff:  
   ;;; Implementations.
   
  +(defun group (x size)
  +  (cond
  +    ((not x) nil)
  +    ((< (length x) size) (list x))
  +    (t (cons (subseq x 0 size)
  +             (group (nthcdr size x) size)))))
  +
  +(defmacro ? (&body body)
  +  (let* ((tests (group body 2))
  +         (end   (car (last tests))))
  +    (unless body
  +      (error "Body is missing."))
  +    `(cond
  +       ,@(if (= 1 (length end))
  +             (append (butlast tests) (list (cons t end)))
  +             tests))))
  +
   (defun %not (&rest x) (every #'not x))
   
   (defun cpr (x) x nil)
  
positive.code: (defun quit (x) x (error "Not implemented."))
  (defun %nconc (&rest x) x (apply #'nconc x))
  (defun string-concat (&rest x) x (apply #'concatenate 'string x))
  
  (defun group (x size)
    (cond
      ((not x) nil)
      ((< (length x) size) (list x))
      (t (cons (subseq x 0 size)
               (group (nthcdr size x) size)))))
  
  (defmacro ? (&body body)
    (let* ((tests (group body 2))
           (end   (car (last tests))))
      (unless body
        (error "Body is missing."))
      `(cond
         ,@(if (= 1 (length end))
               (append (butlast tests) (list (cons t end)))
               tests))))
  
  (defun %string (x)
    (? (numberp x)
  
negative.code: (defun macro? (x) (rassoc x *macros* :test #'eq))
  
  (defun =-aref (v x &rest indexes) v x (apply #'aref x indexes))
  
  (defun %make-hash-table (&key (test #'eql))
    (make-hash-table :test (? (eq test #'==)
                              #'eql
                              test)))
  
  (defun href (x i) (gethash i x))
  (defun =-href (x i) (setf (gethash i x) v))
  