1 (defun make-exponentiation (base exp)
2   (cond ((=number? exp 0) 1)
3 	((=number? exp 1) base)
4 	((and (numberp base) (numberp exp))
5 	 (expt base exp))
6 	(t (list '** base exp))))
7 
8 (defun exponentiation? (x)
9   (and (consp x) (eql (car x) '**)))
10 (defun base (x)
11   (cadr s))
12 (defun exponent (s)
13   (caddr s))
14 (defun deriv (expr var)
15   (cond ((numberp expr) 0)
16 	((variable? expr)
17 	 (if (same-variable? expr var) 1 0))
18 	((exponentiation? expr)
19 	 (make-product
20 	  (make-product
21 	   (exponent expr)
22 	   (make-exponentiation
23 	    (base expr)
24 	    (1- (exponent expr))))
25 	  (deriv (base expr) var)))
26 	((sum? expr)
27 	 (make-sum (deriv (addend expr) var)
28 		   (deriv (augend expr) var)))
29 	((product? expr)
30 	 (make-sum
31 	  (make-product (multiplier expr)
32 			(deriv (multiplicand expr) var))
33 	  (make-product (deriv (multiplier expr) var)
34 			(multiplicand expr))))
35 	(t (error "unknown expression type -- DERIV ~A" expr))))
36