\item \self For the formula below,  find one
    model that satisfies the formula, and one model that does not
    satisfy the formula.
    Explain your answer by drawing a \textbf{syntax tree} and evaluate the model $\mathcal{M}$ with the help of this syntax tree.

 $$\exists x (P(x) \land Q(f(x))) \lor (\neg P(x) \land \neg Q(f(x))$$