(define num-digits-in-satisfying
(lambda (n test?)
(cond ((< n 0) (num-digits-in-satisfying (- n) test?))
((< n 10) (if (test? n) 1 0))
((test? (remainder n 10)) (+ (num-digits-in-satisfying
(quotient n 10) test?)
1))
(else _____________________))))