1.Prove that the set {|}—the set containing just the Sheffer stroke, that is, nand—is universal. 2.Prove that the singleton set {↓} is universal. 3.Prove that the set {∧,∨} is not universal. (Hint:...

1.Prove that the set {|}—the set containing just the Sheffer stroke, that is, nand—is universal.

2.Prove that the singleton set {↓} is universal.

3.Prove that the set {∧,∨} is not universal. (Hint: what happens under the all-true truth assignment?)