#| BEGIN (Write your solution here) |#

(define (element-of-set? x set)
(cond ((null? set) #f)
((= x (car set)) #t)
((< x (car set)) #f)
(else (element-of-set? x (cdr set)))))

(define (intersection-set set1 set2)
(if (or (null? set1) (null? set2))
'()
(let ((x1 (car set1)) (x2 (car set2)))
(cond ((= x1 x2)
(cons x1 (intersection-set (cdr set1)
(cdr set2))))
((< x1 x2)
(intersection-set (cdr set1) set2))
((< x2 x1)
(intersection-set set1 (cdr set2)))))))

(define (union-set set1 set2)
    (cond ((null? set1) set2)
          ((null? set2) set1)
        (else
            (let ((x1 (car set1)) (x2 (car set2)))
                (cond ((= x1 x2) (cons x1 (union-set (cdr set1) (cdr set2))))
                      ((< x1 x2) (cons x1 (union-set (cdr set1) set2)))
                      ((> x1 x2) (cons x2 (union-set set1 (cdr set2)))
                ))
            )
        )
    )

)
#| END |#