When do we say that two FOL formulas are logically equivalent? - How would you determine if two formulas are logically equivalent? - Compare the laws (logical equivalences) given for propositional logic and those given for first-order logic. How similar/different are they? - How can we prove the laws given for first-order logic? - How different is the Hilbert system defined for propositional logic compared to the one defined for first-order logic?