anchor.diff:  
   ;;;;基于类型的分派
   (defun attach-tag (type-tag contents)
  -  (cons type-tag contens))
  +  (cons type-tag contents))
   (defun type-tag (datum)
     (if (consp datum)
         (car datum)
  
positive.code: (defun my-get (sym1 sym2)
    (labels ((lookup (sym lst)
  	     (cond ((null lst) nil)
  		   ((eq sym (get-sym (car lst)))
  		    (get-val (car lst)))
  		   (t (lookup sym (cdr lst))))))
      (lookup sym2 (lookup sym1 *datum*))))
  
  
  (defun install-rectangular-package ()
  
negative.code: (defun my-put (sym1 sym2 item)
    (labels ((lookup (sym lst)
  	     (cond ((null lst) nil)
  		   ((equal sym (get-sym (car lst)))
  		    (get-val (car lst)))
  		   (t (lookup sym (cdr lst)))))
  	   (put (lst)
  