The complete scheme code below:

(define (filter-out-er fn) (define (filter-processing x) (if (null? x) '() (if (fn (car x)) (filter-processing (cdr x)) (cons (car x) (filter-processing (cdr x)))) ) ) filter-processing)

Can you explain why need to add " filter-processing" in last line inside the brackets? Otherwise the program will report an error.

Thank you so much.