\item \ifassignmentsheet \points{3} \fi  For the formula below, state one
    model that satisfies the formula, and one model that does not
    satisfy the formula.
    Explain your answer by drawing a syntax tree and evaluate your models with the help of this syntax tree.

 $$\forall x \exists y (P(f(x),y) \land \neg P(x,f(y)))$$
