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: U_2(z) <-> S(z). u_2. ~S(a_11).
u_2 and ~S(a_11) can be inferred via the conjunction rule. ~S(a_11) and u_2 can be inferred via the conjunction rule. forall z: U_2(z) -> S(z) can be inferred via the universal biconditional elimination rule. forall z: S(z) -> U_2(z) can be inferred via the universal biconditional elimination rule.