tequilasunset

(define (flatten lst)
  (if (null? lst)
      '()
      (let ((a (car lst)) (d (cdr lst)))
        (if (pair? a)
            (append (flatten a) (flatten d))
            (cons a (flatten d))))))
(define fringe flatten)

tequilasunset

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