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_4: U_4(z_4) <-> S(z_4). U_4(f) <-> S(f).
U_4(f) -> S(f) can be inferred via the biconditional elimination rule. S(f) -> U_4(f) can be inferred via the biconditional elimination rule. forall z_4: U_4(z_4) -> S(z_4) can be inferred via the universal biconditional elimination rule. forall z_4: S(z_4) -> U_4(z_4) can be inferred via the universal biconditional elimination rule.