(load "2.36.txt") ; for accumulate
(load "1.22.txt") ; for prime?

(define (flatmap proc seq)
  (accumulate append '() (map proc seq)))

(define (enumerate-interval s e)
  (if (> s e)
      '()
      (cons s (enumerate-interval (+ s 1) e))))

(define (unique-pairs n)
  (define (pairs-with i)
    (map (lambda (j) (list i j))
         (enumerate-interval 1 (- i 1))))
  (flatmap pairs-with (enumerate-interval 1 n)))

(define (prime-sum? pair)
  (prime? (+ (car pair) (cadr pair))))

(define (make-pair-sum pair)
  (list (car pair) (cadr pair) (+ (car pair) (cadr pair))))

(define (prime-sum-pairs n)
  (map make-pair-sum (filter prime-sum? (unique-pairs n))))