Question

Anyone care to explain this proof in Logic?

Answer 1

Problem: Show that the set {∧,∨} of connectives is not universal.

Solution: It is easy to see that any connective f(x1,...,xn), defined in terms of
∧ and ∨, satisfies f(1,...,1)=1. Thus it follows that negation cannot be defined in
terms of ∧ and ∨.