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_2 -> ~q_1. s <-> u. s <-> q_2. q_1.
~q_2 can be inferred via the modus tollens rule. s -> u can be inferred via the biconditional elimination rule. s -> q_2 can be inferred via the biconditional elimination rule. u -> s can be inferred via the biconditional elimination rule. q_2 -> s can be inferred via the biconditional elimination rule.