1 (define (test-case actual expected)
2   (newline)
3   (display "Actual:   ")
4   (display actual)
5   (newline)
6   (display "Expected: ")
7   (display expected)
8   (newline))
9 
10 (define (memq item x)
11   (cond ((null? x) false)
12 	((eq? item (car x)) x)
13 	(else (memq item (cdr x)))))
14 
15 (define (equal? a b)
16   (cond ((and (null? a)
17 	      (null? b)) 
18 	 #t)
19 	((and (not (pair? a))
20 	      (not (pair? b))
21 	      (eq? a b)) 
22 	 #t)
23 	((and (pair? a)
24 	      (pair? b))
25 	 (and (equal? (car a) (car b))
26 	      (equal? (cdr a) (cdr b))))
27 	(else #f)))
28 
29 (test-case (equal? 4 4) #t)
30 (test-case (equal? 4 0) #f)
31 (test-case (equal? 4 '()) #f)
32 (test-case (equal? '() 4) #f)
33 (test-case (equal? '() '()) #t)
34 (test-case (equal? '(4) '()) #f)
35 (test-case (equal? '((4) (3)) '((4 3))) #f)
36 (test-case (equal? '((4) (3)) '((4) (3))) #t)
37 (test-case (equal? '((4) (3)) '((4) (2))) #f)
38 (test-case (equal? '(4 3 2) '(4 3 2 5)) #f)