exercise2-62.lisp

(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)))))))
(define (adjoin-set x set)
  (cond ((null? set) '())
        ((= x (car set)) set)
        ((> x (car set)) (cons (car set) (adjoin-set x (cdr set))))
        (else (cons x set))))
(define (union-set set1 set2)
  (cond ((null? set1) set2)
        ((null? set2) set1)
        (else
          (if (or (null? set1) (null? set2))
            '()
            (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)))
                    ((< x2 x1)
                     (cons x2
                           (union-set set1
                                      (cdr set2))))))))))
(union-set '(1 2 3 4 5) '(3 4 5 6 7))