more help!! construct an annotated indirect main derivation for the symbolic argument?

Question

1. P -> (Q-> R)
2. ~Q-> ~P
3. ~(S->~P)
4. R

Answer 1

I'm going to use > for → since it uses fewer keystrokes, and - instead of ~.

1. P > (Q > R)
2. -Q > -P
3. -(S > -P)
4. -R ................. assumption for indirect proof
5. -(-S v -P) ....... 4 material implication
6. S & P ............ 5 DeMorgan
7. P ................... 6 simplification
8. Q > R ............ 1,7 modus ponens
9. Q ................... 2,7 modus tollens
10. R ................. 8,9 mp
11. -R & R ......... 4,10 conjunction
12. R ................. 4-11 indirect proof