Number of prime numbers in a list, Scheme

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;guile 2.0.11
(define (prime n)
    (letrec
        (
            (notDividable
                (lambda (n m)			                ; n not dividable from m to 2
                    (cond
                        ((= m 1))			        ; m = 1 => not dividable
                        ((zero? (modulo n m)) #f)		; n mod m = 0 => dividable
                        (else (notDividable n (- m 1)))	        ; try with next
                    )			
                )				
            )
        )					                
        (notDividable  n (quotient n 2))		      
    )
)

(define (numOfPrimes l)
     (letrec
         (
             (noDivider
                  (lambda (n divider)
                      (cond
                          ((> divider (quotient n 2)) #t)
                          ((= 0 (modulo n divider)) #f)
                          (else (noDivider n (+ 1 divider)))
                      )
                  )
              )
              (prime
                  (lambda (n)
                       (noDivider n 2)
                  )
              )
         )
         (cond
             ((null? l) 0)
             ((pair? (car l)) (+ (numOfPrimes (car l)) (numOfPrimes (cdr l))))
             ((prime (car l)) (+ 1 (numOfPrimes (cdr l))))
             (else (numOfPrimes (cdr l)))                   
          )
     )
)

(display (numOfPrimes '(1 2 3 4 5 6 7 8 9 10 11 12 13))) ; return num of prime numbers in a list

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