(define (moreFrequent l1 l2)
  (cond  ((null? l1) l2)
         ((null? l2) l1)
         ((>= (length l1) (length l2)) l1)
         (else l2)))

(define (mostFrequentList l)
  (if (null? l) '()
    (moreFrequent (filter (lambda (x) (= (car l) x)) l) (mostFrequentList (cdr l)))))

(define (mostFrequentNum l) (car (mostFrequentList l)))

(define (mostFrequent l)
  (let ((mostFrequentInFirst (mostFrequentNum (car l))))
  (if (all? (lambda (x) (= (mostFrequentNum x) mostFrequentInFirst)) (cdr l))
      mostFrequentInFirst
      0)))