sicp 2.61

sicp_2_61

(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 a '(1 2 4 6))
(define b '(3 4 5 6 7 8))

(element-of-set? 3 a)
(element-of-set? 5 a)

(define (adjoin-set x set)
  (cond ((null? set) (cons x '()))
        ((= x (car set)) set)
        ((< x (car set)) (cons x set))
        ((> x (car set)) (cons (car set)
                               (adjoin-set x (cdr set))))))

(adjoin-set 3 a)