what is the error occured? how can i put if the statement true of false? the question that i want to do is to know weather the input value of year month and date is correct or not

Untitled 2 - DrRacket* File Edit View Language Racket Isert Tabs Help Untitled 2 (define... #lang racket (define year "") (define month "") (define day "") (define (check-available) (display "Please enter year ") (define yr (read-line)) (newline) (display "Please enter month: ") (define mon (read-line)) (newline) (display "Please enter day: ") (define da (read-line)) (newline) (check-year)) (define (check-year) (cond (and(> year 999) (