#| BEGIN (Write your solution here) |#
; Code from the book
(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 (intersection-set set1 set2) (cond ((or (null? set1) (null? set2)) '()) ((element-of-set? (car set1) set2) (cons (car set1) (intersection-set (cdr set1) set2))) (else (intersection-set (cdr set1) set2))))

; My set
(define (union-set s1 s2)
    (if (null? s2)
        s1
        (union-set (adjoin-set (car s2) s1) (cdr s2))
    )
)
#| END |#