<Dd> (A → B) → (¬ B → ¬ A) (\ displaystyle (A \ to B) \ to (\ neg B \ to \ neg A)) </Dd> <P> We can apply the same process the other way round: </P> <Dl> <Dd> (¬ B → ¬ A) ∧ A (\ displaystyle (\ neg B \ to \ neg A) \ land A) </Dd> </Dl> <Dd> (¬ B → ¬ A) ∧ A (\ displaystyle (\ neg B \ to \ neg A) \ land A) </Dd>

The double negation of a statement is equivalent to the​ statement's negation