# Math Help - Contrapositive proof

1. ## Contrapositive proof

Having a contrapositive proof in which negation was done by DeMorgan's law, .
Would it be correct to say that in some proofs just one of the cases, ~P or ~Q is true? If so, would it be enough to stop proving when one of the cases was shown to be true?

Thanking you in anticipation

2. ## Re: Contrapositive proof

Do I understand correctly that you need to prove $\neg(P\land Q)$ and you want to prove $\neg P\lor\neg Q$ instead? Then yes, to prove a disjunction, it is sufficient to prove one of the disjuncts.