(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)
(multiplicand exp))))
((exponentiation? exp)
(make-product
(make-product (exponent exp)
(make-exponentiation (base exp)
(- (exponent exp) 1)))
(deriv (base exp) var)))
(else
(error "unknown expression type -- DERIV" exp))))
(define (exponentiation? x)
(and (pair? x) (eq? (car x) '**)))
(define (base x)
(cadr x))
(define (exponent x)
(caddr x))
(define (make-exponentiation b e)
(cond ((=number? e 0) 1)
((=number? e 1) b)
((and (number? b) (number? e)) (expt b e))
(else (list '** b e))))
