SICP Practice

(define (element-of-set? x set)
  (cond ((null? set) '())
        ((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 set2))
    
(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-element-set (car set1) set2))))
     (else (intersection-set (cdr set1) set2))))
          
(define (remove-element-set x set)
  (cond ((null? set) '())
    ((equal? x (car set)) (cdr set))
    (else (cons (car set) (remove-element-set x (cdr set))))))
          
(define (remove-element-set x set)
  (define (remove-element-set-iter acc origin)
    (cond ((null? origin) acc)
      ((equal? (car origin) x) (append acc (cdr origin)))
      (else (remove-element-set-iter (cons (car origin) acc) (cdr origin)))))
  (remove-element-set-iter '() set))