$($c$)(15$ points$)$ Suppose that $,,$ are well$-$formed formulas generated by some propositions. Now, we know something about the world that $\{{}^{{?}^{?}}\}||==$ holds. Meaning that we don't know exactly about which wffs $(,,)$ are true in our world nor any truth$-$value assignments about the propositions $($model$).$ However, we know that the entailment must hold, $\{{}^{{?}^{?}}\}||==.$

In this case, show that $\{\}||==()$ holds. This may seem hard: but basically, what we're trying to do is show that the first entailment rules out some possible worlds where the entailment doesn't hold. Once we've ruled out those worlds, we can show that the second entailment holds in the worlds that are left. To do this, use a few steps $($show all of these$)$: