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: exists x_1: R(x_1) -> U(x_1). forall x_1: S_1(x_1) -> U(x_1). forall x_1: W_4(x_1) or R(x_1). forall x_1: W_4(x_1) <-> S_1(x_1).
forall x_1: W_4(x_1) -> S_1(x_1) can be inferred via the universal biconditional elimination rule. forall x_1: S_1(x_1) -> W_4(x_1) can be inferred via the universal biconditional elimination rule.