(cdr '(1))
;=> ()

(null? (cdr '(1)))
;=> #t

pair?
;=> #<Function pair?>

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

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

lat?
;=> #<Closure>

(lat? '(1 2 3))
;=> #t

(lat? '(1 (2) 3))
;=> #f

(null? 3)
;=> #f

(pair? 3)
;=> #f

(pair? '(3))
;=> #t

(define member? 
  (lambda (a l) 
    (cond 
      ((null? l) #f) 
      ((= (car l) a) #t) 
      (else (member? a (cdr l))))))

(member? 1 '(1 2 3))
;=> #t

(member? 4 '(1 2 3))
;=> #f

(member? 4 '(1 2 3 5 4))
;=> #t
   
(define rember 
  (lambda (m l) 
    (cond 
      ((null? l) '()) 
      ((eq? m (car l)) (cdr l)) 
      (else (cons 
        (car l) (rember m (cdr l)))))))

(rember 3 '(1 2))
;=> (1 2)

(rember 3 '(1 2 3 4 5))
;=> (1 2 4 5)