Ex2.41.scm

(define (unique-pair-sum n s)
  (define (unique-triplet a) (flatmap (lambda (i)
					(flatmap (lambda (j)
					       (map (lambda (k) (list i j k))
						    (enumerate-interval 1 (- j 1))))
					     (enumerate-interval 1 (- i 1))))
				      (enumerate-interval 1 a)))
  (filter (lambda (x) (= (+ (car x) (cadr x) (caddr x)) s)) (unique-triplet n)))