(defun adj* ()
  (if (= (random 2) 0)
      nil
    (append (adj) (adj*))))

(defun pp* ()
  (if (random-elt '(t nil))
      (append (pp) (pp*))
    nil))

(defun noun-phrase ()
  (append (article) (adj*) (noun) (pp*)))

(defun pp ()
  (append (prep) (noun-phrase)))

(defun adj ()
  (one-of '(big little blue green long)))

(defun prep () 
  (one-of '(to in by with on)))