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: q_8 <-> u. u <-> q_8.
q_8 -> u can be inferred via the biconditional elimination rule. u -> q_8 can be inferred via the biconditional elimination rule. u -> q_8 can be inferred via the biconditional elimination rule. q_8 -> u can be inferred via the biconditional elimination rule.