(define num-sixes      ; number of 6's in
       (lambda (n)          ; decimal representation of n
         (cond ((< n 0) (num-sixes (- n)))
               ((= n 0) 0)
               ((= (remainder n 10) 6) (+ 1 (num-sixes (quotient n 10))))
               (else (num-sixes (quotient n 10))))))
     
     (define num-odds     ; number of odd digits
       (lambda (n)        ; in decimal representation of n
         (cond ((< n 0) (num-odds (- n)))
               ((= n 0) 0)
               ((odd? (remainder n 10)) (+ 1 (num-odds (quotient n 10))))
               (else (num-odds (quotient n 10))))))