Question 1029122
1. Y ⊃ ( N • U)  ----------Hypothesis
2. ~Y v ( N • U) ----------Material Implication
3. (~Y v N) • (~Y v U)-----Distributivity
4. ~Y v N -----------------Simplification
5. Y ⊃ N -----------------Material Implication
5.  S ⊃ (~ N • U)----------Hypothesis
6. ~S v ( ~N • U) ---------Material Implication
7.  (~S v ~N) • (~S v U)-----Distributivity
8.  ~S v ~N -----------------simplification
9. ~N v ~S -----------------Commutativity
10. N ⊃ ~S ----------------Material Implication
11. Y ⊃ ~S ----------------#5 and #10 and Hypothetical syllogism