(define (first-replaced item sent)
	 (sentence item (butfirst sent)) )

(define (paired-sent sent1 sent2)
	 (sentence 
		  (word (first sent1) (first sent2))
		  (word (second sent1) (second sent2))
		  (word (third sent1) (third sent2)) ))

(define (square-then-attach num sent)
	 (sentence (* num num) sent) )

(define (sub-from-all sent num)
	(sentence 
		(- (first sent) num)
		(- (second sent) num)
		(- (third sent) num) ) )

(define (combined e1 e2 e3)
	(sentence e1 (word e2 e3)) )

(define (all-firsts sent1 sent2 sent3)
	(sentence 
		(first sent1) (first sent2) (first sent3) ) )

(define (mystery a b)
  (if (odd? a)
      (if (odd? b) #f #t)
      (if (odd? b) #t #f) ) )

(define (second sent)
        (first (butfirst sent)) )

(define (third sent)
        (second (butfirst sent)) )