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 
11 (define (element-of-set? x set)
12   (cond ((null? set) false)
13 	((equal? x (car set)) true)
14 	(else (element-of-set? x (cdr set)))))
15 (define (adjoin-set x set)
16   (if (element-of-set? x set)
17       set
18       (cons x set)))
19 (define (intersection-set set1 set2)
20   (cond ((or (null? set1) (null? set2)) '())
21 	((element-of-set? (car set1) set2)
22 	 (cons (car set1)
23 	       (intersection-set (cdr set1) set2)))
24 	(else (intersection-set (cdr set1) set2))))
25 (define (union-set set1 set2)
26   (cond ((null? set1) set2)
27 	((null? set2) set1)
28 	((element-of-set? (car set1) set2) (union-set (cdr set1) set2))
29 	(else (cons (car set1) (union-set (cdr set1) set2)))))
30 
31 (test-case (union-set '(1 2 3 4 5) '(1 3 4)) '(2 5 1 3 4))
32 
33