(define lat?
  (lambda (l)
    (cond
      ((null? l) #t)
      ((atom? (car l)) (lat? (cdr l)))
      (else #f))))

(becon and eggs)

(define member?
  (lambda (a lat)
    (cond 
      ((null? lat) #f)
      (else (or (eq? a (car lat))
          (member? a (cdr lat)))))))

• Always ask null? as the first question in expressing any function.