Translate the following inference to logic notation: If Jennifer were a taxi driver, then David is playing tennis. For all x, x_9 is a janitor if and only if x_9 is a taxi driver. If David plays tennis, then Jennifer is a taxi driver. Jennifer is not a janitor. Therefore David is not playing tennis.
P(a) -> p. forall x: Q(x) <-> P(x). p -> P(a). ~Q(a). Therefore ~p.