(define (sent-max sent)
  (if (empty? sent) 0
      (max (first sent)
	    (sent-max (butfirst sent)))))


(define (sent-sum sent)
  (if (empty? sent) 0
      (+ (first sent)
	  (sent-sum (butfirst sent)))))


(define (word-ify sent)
  (if (empty? sent) ""
      (word (first sent)
	     (word-ify (butfirst sent)))))


(define (collapse bi-fn base sent)
  (if (empty? sent) base
      (bi-fn (first sent)
             (collapse bi-fn base (butfirst sent)))))


(define (member? wd sent)
  (collapse (lambda (new-wd bool)
	        (or (equal? new-wd wd) bool))
	    #f
	    sent))