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(z) -> Q(z). u_2 -> U(a_20). s <-> Q(a_20). s -> u_2.
s -> U(a_20) can be inferred via the transitivity rule. s -> Q(a_20) can be inferred via the biconditional elimination rule. Q(a_20) -> s can be inferred via the biconditional elimination rule.