1. ~N > (~R > C) 2. R > N 3. ~C // N ------------------------------------------------------- 4. (~N & ~R) > C 1 Exportation 5. (~N & ~R) > ~(~C) 4 Double Negation 6. ~(~N & ~R) 5,3 Modus Tollens 7. ~(~N) v ~(~R) 6 De Morgan's Law 8. ~(~N) v R 7 Double Negation 9. ~N > R 8 Material Implication 10. ~N > N 9,2 Hypothetical Syllogism 11. ~(~N) v N 10 Material Implication 12. N v N 11 Double Negation 13. N 12 Tautology