#| BEGIN (Write your solution here) |#
; Code from the book
(define (variable? x) (symbol? x))
(define (same-variable? v1 v2) (and (variable? v1) (variable? v2) (eq? v1 v2)))
(define (sum? x) (and (pair? x) (eq? (car x) '+)))
(define (addend s) (cadr s))
(define (augend s) (caddr s))
(define (product? x) (and (pair? x) (eq? (car x) '*)))
(define (multiplier p) (cadr p))
(define (multiplicand p) (caddr p))
(define (make-sum a1 a2) (cond ((=number? a1 0) a2) ((=number? a2 0) a1) ((and (number? a1) (number? a2)) (+ a1 a2))
(else (list '+ a1 a2))))
(define (=number? exp num) (and (number? exp) (= exp num)))
(define (make-product m1 m2) (cond ((or (=number? m1 0) (=number? m2 0)) 0) ((=number? m1 1) m2) ((=number? m2 1) m1) ((and (number? m1) (number? m2)) (* m1 m2)) (else (list '* m1 m2))))

; My code
(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? e) (and (pair? e) (eq? (car e) '**)))
(define (base e) (cadr e))
(define (exponent e) (caddr e))
(define (make-exponentiation base exponent)
    (cond
        ((=number? exponent 0) 1)
        ((=number? exponent 1) base)
        (else (list '** base exponent))
    )
)
#| END |#