(import srfi-1)
(require-extension srfi-1)

(define (is-prime? n)
  (cond
    ((<= n 3) (>= n 2))
    ((or (= (modulo n 2) 0) (= (modulo n 3) 0)) #f)
    (else (do ((i 5 (+ i 6))) ((> i (+ (sqrt n) 1)))
        (if (or (= (modulo n i) 0) (= (modulo n (+ i 2)) 0))
          #f)) #t)))

(define (prime-gap n g)
  (if (and (is-prime? n) (is-prime? (- n g)))
    (list (- n g) n)
    #f))

(define proc (lambda vars
  (length vars)))

(define (argcheck args default)
  (define len (length args))
  (cond
    ((= len 2) (string->number (list-ref args 1)))
    ((= len 4) (string->number (list-ref args 3)))
    (else default)))

(define (main args)
    (define gap (argcheck (args) 6))
    (display (remove (lambda (x) (not x)) (map (lambda (x) (prime-gap x gap)) (iota (* 1 1000) 1))))
    (newline)
    (exit))

(if (not (equal? (program-name) "csi"))
  (main argv))