Translate the following inference to logic notation: If Mary goes running, then Mary is a taxi driver. For all x, if x_8 were a taxi driver, then x_8 is running. For all x, if x_8 goes running, then x_8 is a taxi driver. Therefore Mary is a taxi driver if and only if Mary is running.
P(a) -> Q(a). forall x: Q(x) -> P(x). forall x: P(x) -> Q(x). Therefore Q(a) <-> P(a).