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_18: P(x_18) -> U_1(x_18). forall x_18: U_1(x_18) -> P(x_18). exists x_18: T(x_18) -> W(x_18). forall x_18: T_2(x_18) or T(x_18). forall x_18: P(x_18) -> ~W(x_18). forall x_18: T_2(x_18) -> W(x_18).
exists x_18: W(x_18) can be inferred via the existential disjunction elimination rule. forall x_18: P(x_18) <-> U_1(x_18) can be inferred via the universal biconditional introduction rule. forall x_18: U_1(x_18) <-> P(x_18) can be inferred via the universal biconditional introduction rule.