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: P(f) <-> s_4. forall x_9: P(x_9) <-> Q_9(x_9). forall x_9: ~Q_9(x_9).
P(f) -> s_4 can be inferred via the biconditional elimination rule. s_4 -> P(f) can be inferred via the biconditional elimination rule. forall x_9: P(x_9) -> Q_9(x_9) can be inferred via the universal biconditional elimination rule. forall x_9: Q_9(x_9) -> P(x_9) can be inferred via the universal biconditional elimination rule. forall x_9: ~P(x_9) can be inferred via the universal biconditional elimination rule.