1. P-> (~Q&R)
2. (Qv~R) ->S
3. ~SvP
Conclusion: ~Q
4. (~~Qv~R) -> S 2,DN (double negation)
5. ~(~Q&R) -> S 4,DM (deMorgan's law)
6. ~S -> ~~(~Q&R) 5,CP (contrapositive)
7. ~S -> (~Q&R) 6,DN (double negation)
8. ~Q&R 7,1,3,CD (constructive dilemma)
9. ~Q 8,simp. (simplification of a conjunction)
Edwin