2. For the following proposition, describe (i) a model on which it is true (and explain why it is true on this model), and (ii) a model on which it is false (and explain why it is false on this model). If there is no model of one of these types, explain why. \forall x \forall y(R x y \rightarrow(x=y \wedge P x \wedge Q y)) \wedge \neg \exists x(P x \wedge Q x)