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(x_2) -> U_1(x_2). forall x_2: ~U_1(x_2). exists x_2: U_1(x_2) -> U(x_2). forall x_2: U(x_2) or W_2(x_2).
forall x_2: ~U(x_2) can be inferred via the universal modus tollens rule. exists x_2: U_1(x_2) <-> U(x_2) can be inferred via the existential biconditional introduction rule. exists x_2: U(x_2) <-> U_1(x_2) can be inferred via the existential biconditional introduction rule.