#| BEGIN (Write your solution here) |#
(define (element-of-set? x set)
(cond ((null? set) #f)
((equal? x (car set)) #t)
(else (element-of-set? x (cdr set)))))

(define (adjoin-set x set)
(if (element-of-set? x set)
set
(cons x set)))

(define (union-set set1 set2)
    (if (null? set2) set1
        (union-set (adjoin-set (car set2) set1) (cdr set2))
    )
)
#| END |#