Ex2_60.scm

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

(define (adjoin-set x set)
  (cons x set))

(define (union-set set1 set2)
  (append set1 set3))

(define (remove-set-element x set)
  (define (remove-set-element-iter acc rest)
    (cond ((null? rest) acc)
	  ((equal? x (car rest)) (append acc (cdr rest)))
	  (else (remove-set-element-iter (adjoin-set (car rest acc)
						     (cdr rest))))))
  (remove-set-element-iter '() set))

(define (intersection-set set1 set2)
  (cond ((or (null? set1) (null? set2)) '())
	((element-of-set? (car set1) set2)
	 (cons (car set1)
	       (intersection-set (cdr set1) (remove-set-element (car set1)
								set2))))
	(else (intersection-set (cdr set1) set2))))