es12

 data Yunz = Yor | Frunz Int Int Yunz Yunz

 (define Yor ...
 (define (mkYnz n1 n2 Y1 Y2) ....
 (define (is Yor? Y1) ...
 (define (firstNum Y) ...
 (define (secondNum Y) ...
 (define (firstYunz Y) ...
 (define (secondYunz Y) ...


   (define (usableYunz? Y)
        (and (not (isYor? Y))
	     (or (= 276 (firstNum Y))
	         (= 276 (secondNum Y))
		 (usableYunz? (firstYunz Y))
		 (usableYunz? (secondYunz Y))))