Translate the following inference to logic notation: For all x, x_13 will drink water if and only if x_13 is a janitor. Patricia is writing a letter if and only if Elisabeth is a janitor. Patricia is writing a letter or Elisabeth is drinking water. Therefore Elisabeth is a janitor.
forall x: P(x) <-> Q(x). p <-> Q(a). p or P(a). Therefore Q(a).