set? with no helper function

isset.rkt

#lang racket

(define set?
  (lambda (lat)
    (cond
      [(null? lat) #t]
      [(null? (cdr lat)) #t]
      [(eq? (car lat) (car (cdr lat))) #f]
      [else (and (set? (cons (car lat) (cdr (cdr lat))))
                 (set? (cdr lat)))])))

(set? '()) ;; #t
(set? '(a)) ;; #t
(set? '(a b)) ;; #t
(set? '(a a)) ;; #f
(set? '(a b c d e)) ;; #t
(set? '(a b c b a)) ;; #f