anchor.diff:  					  (add (coeff t1) (coeff t2)))
   			       (add-terms (rest-terms l1) (rest-terms l2)))))))))
   
  +(defun minus-terms (l)
  +  (cond ((empty-termlist? l) (the-empty-termlist))
  +	(t
  +	 (let ((term (first-term l)))
  +	   (adjoin-term (make-term (order term)
  +				   (sub 0 (coeff term)))
  +			(minus-terms (rest-terms l)))))))
  +
  +(defun sub-terms (l1 l2)
  +  (add-terms l1 (minus-terms l2)))
  +
   (defun mul-terms (l1 l2)
     (if (empty-termlist? l1)
         (the-empty-termlist)
  
positive.code: 			    (mul-terms (term-list p1)
  				       (term-list p2)))
  		 (error "poly not in same variable -- mul-poly ~A" (list p1 p2))))
  	   (tag (p) (attach-tag 'polynomial p)))
      (my-put 'add '(polynomial polynomial)
  	    #'(lambda (p1 p2) (tag (add-poly p1 p2))))
      (my-put 'mul '(polynomial polynomial)
  	    #'(lambda (p1 p2) (tag (mul-poly p1 p2))))
      ;;2.87 add =zero?
  
negative.code: 
  ;;;;2.87
  
  ;;添加到polynomial的算数包中。
  
  ;;;;2.88
  