(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 (adjoin-set x set)
(define (iter x items product)
(cond ((null? items) (append product (list x)))
((= x (car items)) set)
((< x (car items)) (append product (cons x items)))
(else (iter x (cdr items)
(append product (list (car items)))))))
(iter x set '()))
(adjoin-set 3 (adjoin-set 5 '(1 2 4 6)))
