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_2: U_4(x_2). forall x_2: P_2(x_2) -> S_1(x_2). forall x_2: P_2(x_2) -> ~U_4(x_2). forall x_2: S_1(x_2) -> P_2(x_2).
forall x_2: ~P_2(x_2) can be inferred via the universal modus tollens rule. forall x_2: P_2(x_2) <-> S_1(x_2) can be inferred via the universal biconditional introduction rule. forall x_2: S_1(x_2) <-> P_2(x_2) can be inferred via the universal biconditional introduction rule.