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