#lang racket

(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 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) set2)))
        (else (intersection-set (cdr set1) set2))))

#|
 union-set and adjoin-set has changed. Rest remain unchanged. 

 Performance while adding a new element is O(1). Same with union. 
 intersection-set remains the same - O(m * n). 
 element-of-set? also remains the same - O (n).

If duplicates are allowed, then Intersection and element-of-set? performance will degrade.

|#