(define (sorted? lon) (or (null? lon) (null? (cdr lon)) (and (<= (car lon) (cadr lon)) (sorted? (cdr lon))))) ; A shorter way: (define (sorted? lon) (or (null? lon) (apply <= lon))) (sorted? '()) (sorted? '(3)) (sorted? '(2 4 5 3 6)) (sorted? '(2 3 4 5 6))