(define (argue sent)
  (if (empty? sent) '()
      (se (replace (first sent))
	  (argue (bf sent)))))

(define (replace wd)
  (cond ((equal? wd 'love) 'hate)
	((equal? wd 'good) 'bad)
	((equal? wd 'happy) 'sad)
	((equal? wd 'joy) 'gloom)
	((equal? wd 'berkeley) 'stanford)
	(else wd)))