#lang sicp

(define (element-of-set? x set)
  (cond ((null? set) false)
	((equal? x (car set)) true)
	(else (element-of-set? x (cdr set)))))

; we will simply adjoin elements of set1 to set2 if they are not there
; and drop them if they are there
(define (union-set set1 set2)
  (cond ((null? set1) set2)
	((null? set2) set1)
	((element-of-set? (car set1) set2)
	 (union-set (cdr set1) set2))
	(else (union-set (cdr set1) (cons (car set1) set2)))))