Question 928647
<pre> 
 1. A->(QvR)
 2. (R&Q)->B	
 3. A&~B
 Conclusion: R<->~Q

 4. ~B               3,simp.
 5. ~B->~(R&Q)       2,CP
 6. ~(R&Q)           5,4,MP
 7. ~Rv~Q            6,DM
 8. ~~R->~Q          7,writing a disjunction as a conditional  
 9. R->~Q            8,DN
10. A                3,simp
11. QvR              1,10,MP
12. ~~QvR            11,DN
13. ~Q->R            10,writing a disjunction as a conditional
14. (R->~Q)&(~Q->R)  9,13,conjunction
15. R<->~Q           14, definition of biconditional   

Edwin</pre>