Question

Which of the following is De-Morgan’s law?

(a) P ∧ (Q v R) Ξ (P ∧ Q) v (P ∧ R)

(b) ~(P ∧ R) Ξ ~P v ~R, ~(P v R) Ξ ~P ∧ ~R

(c) P v ~P Ξ True, P ∧ ~P Ξ False

(d) None of the mentioned

I have been asked this question during an interview.

My doubt stems from Logics and Proofs in division The Foundation: Logics and Proofs of Discrete Mathematics

Answer 1

Correct option is (b) ~(P ∧ R) Ξ ~P v ~R, ~(P v R) Ξ ~P ∧ ~R

For explanation I would say: Definition of De–Morgan’s Law.