 Solution

A two-element model of $\varphi$ would be a finite model with even size, contrary to the defining property established in part (b). Every model of $\varphi$ therefore has size other than two, and the preceding interpretation of $\psi$ gives $\boxed{\{\varphi \}\models \psi }$. This includes infinite models, since the antecedent of $\psi$ is false there.