Translate the following inference to logic notation: If Mary plays a game, then Charles is playing squash. If Charles plays squash, then Mary is working. For all x, if x_10 works, then x_10 is playing a game. Therefore Mary is working if and only if Charles is playing squash.
P(a) -> p. p -> Q(a). forall x: Q(x) -> P(x). Therefore Q(a) <-> p.