(define atom?
  (lambda (x)
    (and (not (pair? x))
         (not (null? x)))))

(define o?
  (lambda (l)
    (cond
      ((null? l) #f)
      (else (and (atom? (car l))
                 (e? (cdr l)))))))

(define e?
  (lambda (l)
    (cond
      ((null? l) #t)
      (else (and (atom? (car l))
                 (o? (cdr l)))))))