这道题的代码略长啊。不过我也是因此而知道Edwin上的代码居然可以复制到word上，以前还想当然的以为不能复制的，毕竟在Edwin上粘贴用的Ctrl+Y，而不是Ctrl+V。在这里我就只将书上没有的代码贴出来了。
(define (deriv exp var)
(cond ((number? exp) 0)
((variable? exp)
(if (same-variable? exp var) 1 0))
((sum? exp)
(make-sum (deriv (addend exp) var)
(deriv (augend exp) var)))
((product? exp)
(make-sum (make-product (multiplier exp) (deriv (multiplicand exp) var))
(make-product (deriv (multiplier exp) var) (multiiplicand exp))))
((exponentiation? exp)
(let ((n (exponent exp)) (u (base exp)))
(make-product n (make-product (make-exponentiation u (- u 1)) (deriv u var)))))
(else
(error "unknown expression type -- DERIV" exp))))
(define (make-exponentiation base exponent)
(cond ((= exponent 0)
1)
((= exponent 1)
base)
(else
(list '** base exponent))))
(define (exponentiation? x)
(and (pair? x)
(eq? (car x) '**)))
(define (base exp)
(cadr exp))
(define (exponent exp)
(caddr exp))
