1. ~S -> (~G v ~F) 2. (~F -> ~W) & W / :. S v ~G ---------------------------- 3. ~~S v (~G v ~F) 1 Material Implication 4. S v (~G v ~F) 3 Double Negation 5. (S v ~G) v ~F 4 Association 6. ~F v (S v ~G) 5 Commutation 7. F -> (S v ~G) 6 Material Implication 8. W & (~F -> ~W) 2 Commutation 9. W 8 Simplification 10. ~~W 9 Double Negation 11. ~F -> ~W 2 Simplification 12. ~~F 11,10 Modus Tollens 13. F 12 Double Negation 14. S v ~G 7,13 Modus Ponens