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_3. t -> u_3. u -> q_3. ~q_3.
~u can be inferred via the modus tollens rule. u -> u_3 can be inferred via the biconditional elimination rule. u_3 -> u can be inferred via the biconditional elimination rule.