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: u. U_1(b_3) <-> s. forall x: ~U_1(x).
U_1(b_3) -> s can be inferred via the biconditional elimination rule. s -> U_1(b_3) can be inferred via the biconditional elimination rule.