Translate the following inference to logic notation: For all x, x_20 will write a letter if and only if x_20 is a janitor. If Susan were a police officer, then Linda is writing a letter. Linda is not a janitor. Therefore Susan is not a police officer or it is overcast.
forall x: P(x) <-> Q(x). p -> P(a). ~Q(a). Therefore ~p or q.