(defun compress (alist)
  (if (null alist)
    nil
    (append
      (if (equalp
            (car alist)
            (car (cdr alist)))
        nil
        (list (car alist)))
      (compress (cdr alist)))))

(defun my-flatten (alist)
  (if (null alist)
    nil
    (append
      (if (listp (car alist))
        (my-flatten (car alist))
        (list (car alist)))
      (my-flatten (cdr alist)))))

(defun my-reverse (alist)
  (if (null alist)
    nil
    (append
      (my-reverse (cdr alist))
      (list (car alist)))))

(defun my-palindromep (alist)
  (equalp alist (my-reverse alist)))

(defun my-reverse (alist)
  (if (null alist)
    nil
    (append
      (my-reverse (cdr alist))
      (list (car alist)))))

(defun my-len (alist)
  (if (null alist)
    0
    (1+ (my-len (cdr alist)))))