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_21: ~R_21(x_21). forall x_3: S_4(x_3) <-> T(x_3). S_4(a_16) <-> R_21(c). w_3.
S_4(a_16) -> R_21(c) can be inferred via the biconditional elimination rule. R_21(c) -> S_4(a_16) can be inferred via the biconditional elimination rule. forall x_3: S_4(x_3) -> T(x_3) can be inferred via the universal biconditional elimination rule. forall x_3: T(x_3) -> S_4(x_3) can be inferred via the universal biconditional elimination rule.