What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: forall x: Q_4(x) -> P(x). forall x: ~P(x). forall x: Q_4(x) <-> Q_2(x). exists x: P(x) -> Q_4(x).
forall x: ~Q_4(x) can be inferred via the universal modus tollens rule. exists x: P(x) <-> Q_4(x) can be inferred via the existential biconditional introduction rule. exists x: Q_4(x) <-> P(x) can be inferred via the existential biconditional introduction rule. forall x: Q_4(x) -> Q_2(x) can be inferred via the universal biconditional elimination rule. forall x: Q_2(x) -> Q_4(x) can be inferred via the universal biconditional elimination rule.