ACL ch1

ch1.lisp

;2.
(cons 'a '(b c))
(cons 'a (cons 'b (cons 'c nil)))
(cons 'a (cons 'b '(c)))

;3.
(defun fourth_number (x)
 (car (cdr (cdr (cdr x)))))

;4.
(defun max_number (x y)
  (if (> x y)
      x
      y))

;5.
(defun enigma (x)
  (and (not (null x))
       (or (null (car x))
           (enigma (cdr x)))))

(defun mystery (x y)
  (if (null y)
      nil
      (if (eql (car y) x)
          0
          (let ((z (mystery x (cdr y))))
            (and z (+ z 1))))))

;6.
(car (car (cdr '(a (b c) d))))
(or 13 (/ 1 0))
(apply #'list 1 nil)

;7.
(defun has_list (x)
  (if (null x)
      nil
      (if (listp (car x))
          T
          (has_list (cdr x)))))