9. Bonus: In the lecture, we talked about how to convert certain questions about how formulas relate to each other into questions about individual formulas. For example, we discussed the fact that two formulas p and q are logically equivalent if and only if the formula pHq is a tautology. Because these conversions are so simple, computer scientists rarely work on trying to find algorithms that determine the equivalence of formulas, the consistency of sets of formulas, or the validity of arguments. (E.g., if you want to know whether the set {P1, P2, ... , Pn} is consistent, you can instead ask whether p Ap2A... APn is satisfiable.) Instead, the focus is on algorithms that answer questions about single formulas. In fact, the focus is almost entirely on methods to determine whether a formula of propositional logic is satisfiable. This is because there's an easy way to convert the question of whether a formula is a tautology or not into a question about satisfiability. Fill in the blanks in the following fact: Fact. The formula p is a tautology if and only if the formula is