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_4. u_3. ~u.
u_3 and ~u can be inferred via the conjunction rule. ~u and u_3 can be inferred via the conjunction rule. u -> u_4 can be inferred via the biconditional elimination rule. u_4 -> u can be inferred via the biconditional elimination rule. ~u_4 can be inferred via the biconditional elimination rule.