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 z: S_4(z) <-> S_3(z). exists z: S_4(z) <-> U(z).
forall z: S_4(z) -> S_3(z) can be inferred via the universal biconditional elimination rule. exists z: S_4(z) -> U(z) can be inferred via the existential biconditional elimination rule. forall z: S_3(z) -> S_4(z) can be inferred via the universal biconditional elimination rule. exists z: U(z) -> S_4(z) can be inferred via the existential biconditional elimination rule.