;; RETURNS POWERSET OF SET s

(define (powerset s)
  (if (null? s)
      (list nil)
      (let ((rest (powerset (cdr s))))
             (append rest (map (lambda (x) (cons (car s) x)) rest)))))


;; ITER RETURNS SUBSETS OF SIZE n

(define (iter s n new)
     (if (null? s)
         new
         (if (= (length (car s)) n)
             (iter (cdr s) n (cons (car s) new))
             (iter (cdr s) n new))))