Translate the following inference to logic notation: For all x, x is a police officer if and only if x will write a letter. For all x, x will write a letter if and only if x is a police officer. Therefore for all x, x is a police officer if and only if x will write a letter.
forall x: P(x) <-> Q(x). forall x: Q(x) <-> P(x). Therefore forall x: P(x) <-> Q(x).