anchor.diff:  		    (apply #'apply-generic (cons op new-args)))
   		  (error "not these type methods--apply-generic ~A" (list op type-tags new-type-tags)))))))))
   		  
  +;;;;2.86
  +
  +;;更改complex的算术运算函数，将里面的 +-*/换成add,sub,mul,div
  +;;在scheme-number和rational中加入对应的sine cosine函数。
  +;;这里就不写了，直接改在上面吧。
  +
  +;;;;2.87
  +
  
positive.code: (defun square (x)
    (* x x))
  ;;;;2.1
  
negative.code:     (let ((proc (my-get op type-tags)))
        (if proc
  	  (let ((res (apply proc (mapcar #'contents args))))
  	    (if (or (eq op 'add) (eq op 'sub) (eq op 'mul) (eq op 'div))
  		(drop res)
  		res))
  
  