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 -> r_1. r_1 -> u. ~r_1. q or ~u.
~q can be inferred via the modus tollens rule. q -> u can be inferred via the transitivity rule. u -> q can be inferred via the rewriting rule.