sets-ordered¶

; Sets as "ordered" lists
(define (element-of-set? x set) 
    (cond ((null? set) false)
          ((= x (car set)) true)
          ((< x (car set)) false)
          (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)))))))