1 (element-of-set? x (adjoin-set x S))
2 (element-of-set? x (union-set S T))
3 (or (element-of-set? x S) (element-of-set? x T))
4 (element-of-set? x '())
5 (define (element-of-set? x set)
6   (cond ((null? set) false)
7 	((equal? x (car set)) true)
8 	(else (element-of-set? x (cdr set)))))
9 (define (adjoin-set x set)
10   (if (element-of-set? x set)
11       set
12       (cons x set)))
13 (define (intersection-set set1 set2)
14   (cond ((or (null? set1) (null? set2)) '())
15 	((element-of-set? (car set1) set2)
16 	 (cons (car set1)
17 	       (intersection-set (cdr set1) set2)))
18 	(else (intersection-set (cdr set1) set2))))
19 
20 (define (union-set